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Dystrophies musculaires (DM) : Du Duchenne (DMD) au Becker (DMB)

  • Principles of multidisciplinary management of Duchenne muscular dystrophy

    B. Chabrola,*, M. Mayerb

    aCentre de référence des maladies neuromusculaires de l’enfant, Hôpital d’Enfants, CHU Timone, 13385 Marseille cedex 5
    bCentre de référence des maladies neuromusculaires de l’EST parisien, Hôpital Armand Trousseau, 26 avenue du Dr Arnold Netter, 75571 Paris cedex 12

    Summary

    Given the gradual progression observed in Duchenne muscular dystrophy (DMD), the organization of care in the form of multidisciplinary consultations is essential for optimal management of the different aspects of the disease. Drawing up a care plan is always preceded by a specific consultation for the announcement of the diagnosis to the parents, without overlooking the child. Explaining to the child, in simple terms, the origin of his problems, telling him that we understand why he has experienced a particular symptom, is a fundamental step. The child needs to receive the information at different times in the course of his disease in line with the stages of the disease, and with appropriate lead times. With the progress achieved in managing this disease, more than 90% of DMD children now live into adulthood. The switch from pediatric consultations to adult consultations, marking the transition from childhood management to adulthood management, is a major challenge in the organization of care.

    While death now occurs most often in adulthood, some patients die in childhood. For most teams who care for children, whatever the initial disease may be, the concept of continuity of care and support from the announcement of the disease to the terminal phase is essential.

    Increasing numbers of therapeutic trials including children with DMD have been set up in recent years. However, the trials must not distract from overall patient care and the best support possible.

    © 2017 Elsevier Masson SAS. All rights reserved.

    Résumé

    Du fait de l’atteinte progressive observée au cours de la dystrophie musculaire de Duchenne, l’organisation des soins est essentielle permettant de mieux appréhender les différents aspects de la maladie au cours de consultations pluridisciplinaires.

    La mise en place des soins est toujours précédée d’une consultation spécifique d’annonce du diagnostic auprès des parents, sans oublier l’enfant. Le fait de lui expliquer avec des mots simples l’origine de ses difficultés, lui dire que l’on a compris pourquoi il ressentait tel ou tel symptôme est une étape fondamentale. L’enfant a besoin de recevoir l’information à différents moments de sa maladie aux rythmes des étapes, avec un délai approprié d’anticipation.

    Avec les progrès de la prise en charge, plus de 90 % de ces enfants vivent désormais jusqu’à l’âge adulte. Le passage des consultations « enfants » aux consultations « adultes » marquant la transition de la prise en charge de l’enfance à l’âge adulte, représente un défi majeur dans l’organisation des soins.

    Si le décès survient actuellement le plus souvent à l’âge adulte, certains enfants décèdent à l’âge pédiatrique. Pour la majorité des équipes qui prennent en charge des enfants, quelle que soit la pathologie initiale, la notion de continuité des soins et d’accompagnement depuis l’annonce du diagnostic jusqu’à la phase terminale est essentielle Mis en place ces dernières années, des essais thérapeutiques de plus en plus nombreux vont se développer destinés aux enfants porteurs de DMD. Ils ne doivent cependant pas faire oublier la prise en charge globale de ces patients, en assurant le meilleur accompagnement possible.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction: organization of care for children with Duchenne muscular dystrophy

    Given the gradual progression observed in Duchenne muscular dystrophy (DMD), the organization of care in the form of multidisciplinary consultations is essential for optimal management of the different aspects of the disease. Management is to address not only the functional, orthopedic, cardiac, respiratory and nutritional aspects but also the psychological, cognitive and other aspects [1].

    At the end of the diagnostic period, of variable brevity, care organization is always preceded by a specific consultation during which the diagnosis is announced. The consultation thus becomes the platform for organizing the indispensable multidisciplinary support.

    2. The announcement consultation

    Announcing a diagnosis is fundamentally an ethical act requiring truthfulness and the pediatrician’s commitment to the child suffering from a myopathy and his family [2]. The announcement of the diagnosis is an integral component of the care system and is only meaningful if accompanied by ongoing support.

    3. “Good announcement practices” have been defined

    The announcement is to be made in the course of a dedicated conversation in a peaceful setting. The physician is to set aside the necessary time and ensure his availability. Both parents together or with a trusted family friend are to be present. The announcement is to be made as soon as possible so as to minimize the period of uncertainty. The language used is to be simple and accessible so as to prevent an impression of selective filtering and the “doorstep syndrome” (everything seems to have been covered and understood but just before leaving the parents ask a question that reveals that they have not really understood what they have just been told). Fridays and holiday periods are to be avoided. Subsequent conversations are to be scheduled rapidly. Provisions for management and support are to be made as of the announcement. In all cases, the physician is to demonstrate the greatest availability.

    The information resources available online to patients and physicians are not to compromise the good announcement practices. On the contrary, online resource may enable the child’s and family’s concerns and problems to be addressed more thoroughly.

    4. Impact of the announcement

    4.1. On the parents

    Numerous studies of the impact of the announcement on the parents have been published in the literature. The concept of psychological trauma is undoubtedly the most pertinent to the parents’ feelings of teetering on the verge, of being overwhelmed, by the announcement.

    4.2. On the child

    Few studies have addressed the information given to the child. The latter is generally aware of his limitations, his discomfort, his pain, his difference. The caregiver team has now put a name to the disease and informed the child about it. Explaining to the child, in simple terms, the cause of his difficulties and telling him that the team knows why he experiences this or that symptom constitute a fundamental stage. The child must be given the opportunity to express what he is experiencing. Parents and caregivers may have real difficulty in continuing to talk to the child. They say they are “scared of communicating their anxiety” or “scared of making him suffer and of the suffering being to much for him”. Nonetheless, telling the child too much and projecting him into a reality that is not currently his own may be psychologically overwhelming and compromise the child’s development. The child needs to receive information at different times in his disease, in line with the stages and with appropriate lead times. Thus, certain stages, such as the loss of the ability to walk, force the child’s attention back to his disease, and the caregiver team needs to be particularly supportive at those times. As the disease progresses, the emergence of new signs and their consequences must be further addressed with the child who has now entered adolescence [3]. This is known as the “deferred announcement of the diagnosis”. The pediatrician also needs to be attentive to the impact of the announcement on the child’s siblings who are still all t often overlooked when it comes to sharing information.

    5. Multidisciplinary consultations

    Duchenne muscular dystrophy (DMD) progresses gradually, involving not only the skeletal muscles but also respiratory function and cardiac muscle. In addition cognitive disorders are frequent. In recent years, it has become increasingly obvious that a multidisciplinary approach is necessary. In consequence, dedicated specific consultations are set up. The Association Française contre les Myopathies [4] was highly instrumental in initiating such consultations more than 25 years ago (1988). The consultations are to embody a number of basic principles: unity of place, unity of time, consistency of the specialists’ information, time to review, facility accessibility, result reporting to the family, appointment of a coordinator, etc. Thus, over a time ranging from a half-day to two days, the child will consult the various specialists and undergo the necessary follow-up investigations, in compliance with the schedule previously compiled by the coordinating physician. The follow-up frequency is once or twice per year, and depends on the child, his disease, and the stage of progression. Consultations are also to address all the specificities related to the child’s situation: schooling with set-up of specific aids; social and financial assistance; referral to a handicapped persons’ organizations (MDPH). Hospital emergency department or other department reception, which is not always suitable, may require adaptation, with preparation of the more intensive techniques sometimes necessary in light of the seriousness of the handicap and the potential life threat (deglutition disorders, undernutrition, chronic respiratory insufficiency, life threat). Hence the importance of the pediatrician as coordinator, and a reference team ensuring continuously updated knowledge sharing. The consultations also provide the opportunity for evaluating whether inclusion in a clinical trial should be proposed to the child and his family.

    6. The child – adult transition

    As a result of the progress in DMD management, over 90% of the children now survive into adulthood. The switch from “child” consultations to “adult” consultations, reflecting the transition from childhood to adulthood, constitutes a major challenge for healthcare institutions. Hudsmith and Thorne [5] define the transition as “a planned, deliberate process that responds to the medical, psychosocial, educational and professional needs of the adolescents or young adults suffering from chronic physical and medical diseases when they transition from pediatric medicine to the adult healthcare system”. This process of transition remains difficult and too often takes the form of an abrupt transfer of young people who are insufficiently prepared. The transition constitutes a real challenge due to the complexity of myopathy management at a time of life characterized by multiple physical, psychological and social changes.

    7. Support toward the end of life

    While death now most frequently occurs in adulthood some patients die in childhood.

    For most teams who care for children, whatever the initial disease may be, the concept of continuity of care and support from the announcement of the disease to the terminal phase is essential. 

    Pierre Canoui has clearly said that “the triangular relationship that exists between the pediatrician (and his team), the child and the child’s family is the base on which the therapeutic relationship is founded, making the child and his family fully fledged interlocutors; this necessitates a multidisciplinary approach as of the initial diagnosis to which contribute the pediatric specialty teams and/or the pediatric palliative care teams and/or the ethical committees and families. This attitude enables support throughout the care trajectory with set-up of real supportive care and joint ethical decision making toward the end of life, with the constant objective of ensuring quality of life and beneficence, and thus ensuring that the child always remains at the center of the project”.

    8. Rare diseases

    Rare disease plan No. 1 (PNMR 1: 2004-2008) [6] accredited 13 Reference Centers and 4 Skill Centers in the field of neuromuscular diseases in France. A Reference Center is defined as a set of hospital multidisciplinary skills organized around highly specialized medical teams with ministerial accreditation on the basis of defined specifications. A Center provides expertise and recourse with respect to a rare disease or group of rare diseases including beyond its medical catchment area. A center is entrusted with several missions:

    • ensuring overall and consistent disease management for the patient and his family;
    • enhancing proximity management in liaison with healthcare establishments and professionals;
    • contributing to enhancing professional knowledge and practices;
    • developing tools for the coordination of the various structures and players;
    • providing the authorities with essential knowledge in the field of rare diseases and interfacing with patient associations.

    Rare disease plan No. 2 (PNMR 2: 2011-2014) [7] followed on from plan No. 1 and recommended, in particular, the creation of a rare disease network. The 13 Reference Centers and 4 Skill Centers in the field of neuromuscular diseases formed a network known as Filnemus consisting of several commissions enabling homogeneous and collaborative work in areas such as databases, diagnostic and treatment protocol compilation (PNDS), research, teaching, and clinical trial organization.

    9. Overall

    Increasing numbers of therapeutic trials including children with DMD have been set up in recent years. However, the trials must not distract from overall patient care and the best support possible. at the level of both the Reference Centers and Skill Centers, and in opencare settings. The existence of the open-care – hospital network is of fundamental importance in that it enables implementation of integrated care trajectories for patients with DMD and in which the skills of all players (hospital and open-care pediatricians) are necessary. Similarly, regular contact with the healthcare providers (SESSAD, CAMSP, CMP, etc.) and schools attended by the children is indispensable for optimal practical implementation of prescriptions, but also for the collection of information on everyday life experiences. In addition, patient follow-up in compliance with identified, harmonized and shared protocols enables enhanced evaluation of the various indications for new therapies. Only prospective cohort studies will generate answers to unresolved questions relating to the precise indications of new treatments, and their choice and pursuit, without overlooking the ethical dimension, which must always remain present.

    Statement of interests

    Over the last 5 years, Brigitte Chabrol has contributed to clinical trials in the capacity of principal investigator, coordinator or principal experimenter (PTC 124), and in the capacity of co-investigator, non-principal experimenter, and study team member (Biomarin); she has contributed to expert reports (PTC Board, Biomarin Board, Shire Board), and has contributed to conferences in the capacity of auditor (Biomarin, Genzyme, Shire).

    M. Mayer has not communicated a statement of interests.

    References

    [1] Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis and pharmacological and psychosocial management. Lancet Neurol 2010;9:77-94.

    [2] Chabrol B. Le pédiatre et l’enfant handicapé: réflexions éthiques Arch Pediatr 2005;12:776-7.

    [3] Alvin P. L’annonce du handicap à l’adolescence. Collection Espace éthique. Vuibert 2005.

    [4] AFM: www.afm-telethon.fr.

    [5] Hudsmith LE, Thorne SA. Transition of care from paediatric to adult services in cardiology. Arch Dis Child 2007 ; 92: 927-30.

    [6] Plan maladies rares n °1 : http://www.sante.gouv.fr/IMG/pdf/ Maladies_rares_plan_sante_publique_2005_2008.pdf.

    [7] Plan maladies rares n °2: http://www.sante.gouv.fr/2eme-plannational-maladies-rares-pnmr-2011-2014.html.

  • The basic concepts of therapeutic approaches for DMD

    H. Amthor

    Université de Versailles Saint-Quentin-en-Yvelines, CHU Raymond Poincaré, Service de Pédiatrie, 92380 Garches, et UMR S 1179 INSERM, 78180 Montigny-le-Bretonneux

    Summary

    Duchenne muscular dystrophy (DMD) is the most frequent hereditary neuromuscular disorder in childhood. Over the past 30 years, increasingly better standards of care have considerably improved the quality of life as well as the life expectancy of DMD patients. Despite such progress in disease management, DMD remains a devastating disorder with continuous decline of motor and cardiac function. Only corticosteroid therapy moderately slows clinical progression. However, new therapeutic approaches are currently being developed. This review discusses the rationales and underlying molecular mechanisms of the new strategies and the progress made in recent clinical trials. The new therapeutic strategies have the potential to profoundly modify the future of patients with DMD.

    © 2017 Elsevier Masson SAS. All rights reserved.

    Résumé

    La dystrophie musculaire de Duchenne de Boulogne (DMD) est la maladie héréditaire du système neuromusculaire la plus fréquente chez l’enfant. L’amélioration de sa prise en charge depuis une trentaine d’années a fortement amélioré la qualité et l’espérance de vie des patients. Néanmoins, cette myopathie reste dévastatrice au niveau moteur et cardiaque. Seul le traitement par corticoïdes ralentit modestement la progression clinique, mais de nouvelles approches thérapeutiques sont en cours de développement. Nous présentons ici les rationnels et mécanismes moléculaires sous-jacents ainsi que l’état d’avancement des essais cliniques. Ces nouvelles stratégies thérapeutiques portent le potentiel de profondément changer l’avenir des patients DMD. © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    Retrospective studies have demonstrated that management of patients with Duchenne muscular dystrophy (DMD) using the following combination: i) vertebral arthrodesis to correct the scoliosis; ii) respiratory physiotherapy with intermittent positive pressure ventilation; iii) non-invasive ventilatory assistance to treat the respiratory insufficiency; and iv) cardiac protective treatment with angiotensin converting enzyme inhibitors enables an increase in the average life expectancy of the patients, who may now live 30-40 years [1,2] while life expectancy without that management was only 17-18 years. Nonetheless, the rapid loss of motor function remains unchanged and patients live longer in an increasingly critical condition, requiring increasing assistance.

    2. Use of corticosteroids

    To date, corticosteroids are the only drugs to have procured a benefit with respect to motor function in DMD. Their use is now widely recommended although the underlying molecular mechanisms giving rise to the therapeutic benefit remain poorly understood. The first studies of the effects of corticosteroids on DMD, conducted in a purely empirical manner at Johns-Hopkins hospital, date back to the 1970s [3]: 13 of the 14 boys included in the study clearly showed an improvement in motor function, particularly walking. The interpretation of the data was nonetheless difficult and controversial. The authors were confronted with: i) the impossibility of a double-blind design because of the patent adverse reactions; ii) the difficulty of distinguishing between the therapeutic effect and the natural motor development of the young; iii) the question of a psychological effect related to enthusiastic participation in a study; iv) and above all a very modest therapeutic effect that was difficult to measure and thus contestable. Demonstrating therapeutic pertinence remains an issue for the clinical trials on biotherapeutic strategies, which are becoming increasingly sophisticated and onerous without, however, demonstrating any major impact on the course of the disease. Despite the countless clinical studies on the positive effects of corticosteroids that have been conducted since the initial findings [4], it has taken almost 40 years for the soundness of long-term corticosteroid therapy in DMD to be fully elucidated. This was made possible, in particular, by retrospective comparisons of the results of numerous studies of the natural histories of large cohorts of treated and untreated patients. It has been shown that:

    • the mean age at which the ability to walk is lost is 14.5 years on continuous corticosteroid therapy, 12 years on intermittent therapy, and 10 years for the historical untreated cohorts [5];
    • cardiomyopathy is deferred with onset at age of 15.2 years on treatment vs. 13.1 years without treatment [6];
    • Only 20% of patients on corticosteroid therapy develop scoliosis necessitating vertebral arthrodesis vs. 92% of untreated patients [7];
    • corticosteroids improve respiratory function [8];
    • a marked reduction in mortality in patients on corticosteroid therapy vs. untreated patients [9].

    All of the foregoing led to recommendations being formulated by an international multidisciplinary consortium of 84 specialists in compliance with the RAND Corporation-University of California Los Angeles Appropriateness Method [10,11].

    In France, today, the majority of ambulatory patients are treated with corticosteroids while the majority of non-ambulatory patients have never been treated. However, no data on the therapeutic efficacy of corticosteroid therapy initiated before the ability to walk is lost are available. Nonetheless, a benefit is highly probable even after late treatment institution, as is suggested by a number of isolated clinical case reports.

    3. New therapeutic approaches

    In recent years, new therapeutic strategies have been developed for DMD with the aims of correcting the primary genetic defect, compensating for the pathological secondary impacts on cell metabolism and stimulating skeletal muscle growth in order to overcome muscle wasting. Herein, we will discuss five new strategies that have already been tested in DMD patients: i) exon skipping; ii) read through of the nonsense codons (stop codon read through) generated by point mutations; iii) overexpression of a microdystrophin by a gene therapy approach; iv) treatment of oxidative metabolism with idebenone; and v) blockade of the myostatin signaling pathway.

    3.1. Exon skipping

    The first of the new strategies is based on approaches aimed at modulating messenger RNA splicing, commonly referred to as exon skipping. The strategy reflects the fact that the clinical course is much less severe in patients whose DMD gene mutations do not modify the reading frame as is the case in Becker muscular dystrophy (BMD): the ability to walk is often retained throughout life and life expectancy is almost normal [12]. Thus, large intra-gene deletions of up to 35 exons out of 79 give rise to a relatively benign BMD phenotype if the reading frame of the final mRNA is maintained [13,14], while smaller mutations, such as point mutations or deletion of a single exon may result in serious DMD when the mRNA reading frame is affected, completely abolishing dystrophin production [15-17]. The new drugs under development for exon skipping deploy their therapeutic potential at the level of maturation of pre-messenger RNA (pmRNA) into mature messenger RNA (mRNA) of the dystrophin gene, enabling transformation of out of phase DMD mRNA into in phase mRNA. In other words, the drugs transform the original mRNA inducing a Duchenne phenotype into an mRNA inducing a Becker phenotype [18]. Mechanistically, the process is based on the targeted inhibition of reading certain exons during the DMD pmRNA splicing reaction. The inhibition is implemented using small synthetic oligonucleotide sequences known as anti-sense oligonucleotides (AON), able to hybridize and mask the consensual motifs defining the targeted exons at the limits of the mutation. The system is designed to selectively exclude one or several exons in order to restore an operational reading frame in the final mRNA, enabling the synthesis of a dystrophin that, while truncated, remains functional [19]. Analysis of genetic databases has clearly shown that a large variety of DMD mutations may, theoretically, be converted into mutations whose reading frame is usable. The best known example, since it has already been clinically trialed, is skipping exon 51, which enables operational reading frame restoration for a set of DMD mutations accounting for almost 13% of patients according to the Leiden DMD database [15,20]. The set covers deletions of exon 50, exon 52, exons 49 and 50, exons 48 to 50, exons 47 to 50, and exons 45 to 50. Theoretically, 80 % of DMD mutations could be treated by this type of approach and the concept has already been applied to a large number of mutations using patient muscle cell cultures [20]. Various chemical approaches for the synthesis of AON are available. To date, only drugs from the 2’-O-methyl-phosphorothioate (2OMePS) and phosphorodiamidate morpholino (PMO) series have been tested in DMD patients, in particular to target mutations that can be corrected by skipping exon 51. The pioneering clinical trials in that context have generated very promising results: the levels of dystrophin restoration in muscles biopsied after only a few weeks of systemic administration by the subcutaneous or intravenous route were of the order of 15% and 18%, respectively [21,22]. The results of a more recent double-blind placebo-controlled phase IIb study using AON of the PMO series (Etiplersen) suggest clinical stabilization of disease progression in a sub-group of patients during a 24 week open-label extension study, but not during the initial 24 week double-blind phase [23]. This finding suggest that almost a year is required to detect measurable clinical effects at the dosage used in the study. However, another recent phase III study using 2OMePS AON (Drisapersen) unfortunately failed to demonstrate patent efficacy on ambulation as measured by the 6 minute walk test (6MWT) (press release, GlaxoSmithKline, published on 20 September 2013 in London, UK, and Leiden, the Netherlands). Surprisingly, a phase II study using 2OMePS AON (Drisapersen) at the same dosage, conducted concomitantly in some of the centers involved, evidenced a slight but statistically significant clinical effect as measured by the 6 minute walk test (6MWT) after 24 weeks, but not after 48 weeks [24].

    These mixed results do not invalidate the underlying therapeutic rationale of exon skipping for DMD, but indicate that the AON generations currently available are still insufficiently effective [25,26]. Currently, several clinical trials using 2OMePS and morpholino AON are ongoing or nearing completion. The trials, which included ambulatory and non-ambulatory DMD patients, target skipping exons 44 (drug: PRO044), 45 (drug: PRO045), 51 (drugs: Drisapersen and Etiplersen) and 53 (drug: PRO053) (https://clinicaltrials.gov).

    None of the studies cited above has yet resulted in a patent clinical improvement in DMD patients. Moreover, the AON compounds currently being trialed showed little or no action on cardiac muscle or the central nervous system during pre-clinical evaluation using animal models of DMD. Development of new drugs with greater efficacy is therefore indispensable in order to achieve a life changing therapy. Recent preclinical studies conducted by our team on mdx mice have shown that the chemistry of tricyclo-DNA, a new class of DNA analog, may enable achievement of that objective: tricyclo-DNA significantly improves motor, ambulatory, respiratory and cardiac function, and certain cognitive parameters following systemic treatment inducing a restoration of dystrophin in skeletal and cardiac muscles, and in the CNS that is markedly superior to that induced by the compounds currently being trialed on DMD patients [27].

    3.2. Stop codon read through

    Another therapeutic strategy aims to overcome nonsense mutations, also known as stop mutations, that are present in about 10% of DMD patients. These mutations consist in a change of nucleotide in any codon transforming it into a premature stop codon (UAA, UAG or UGA) in the middle of a coding sequence. Thus, translation of the mRNA is prematurely terminated, preventing dystrophin production. There is now a drug, PTC124, that decreases the number of those stop codons taken into account. The stop codons are inappropriate and not consolidated by the environment of the true stop codons located at the end of the coding sequences. Skipping those codons is termed stop codon read through [28]. Treatment thus theoretically enables synthesis of a protein of normal size but which may contain an amino acid resulting from reading a nonsense (stop) codon as a missense codon. Although the treatment proved promising in the murine model (mdx) of Duchenne myopathy, a phase IIa study in DMD patients, which included 174 patients, failed to evidence clinical efficacy [29]. However, further analysis evidenced clinical stabilization (slowing of the walking distance loss, in meters, as measured by the 6 minute walk test) after 48 weeks of treatment in a sub-group of patients receiving a dosage of 40 mg/kg/d, but not in the higher dosage group receiving 80 mg/kg/d. These ambiguous results necessitated a new phase III trial, currently ongoing, to determine whether the drug was indeed effective at a dosage of 40 mg/kg/d (http://clinicaltrials.gov/show/ NCT01826487). In the meantime, the European Medicines Agency (EMA) has authorized marketing the drug under certain conditions (approval date: 31/07/2014).

    3.3. Overexpression of a micro-dystrophin by a gene therapy approach

    The therapeutic strategies addressed above, exon skipping and stop codon read through, are only applicable to sub-groups of DMD patients presenting with the ad hoc mutation. A wider therapeutic approach would consist in supplying an artificial compensatory DMD gene congruent for all patients independently of mutation nature or site. The proof of principle of the approach was obtained 11 years ago by the intramuscular injection of a plasmid coding for the entire DMD gene into DMD patients. Dystrophin expression was restored locally [31]. Since then, transgene and vector design have evolved considerably toward a veritable gene therapy on the whole body scale. The DMD gene has been reduced and amputated in silico and by genetic engineering to a size sufficiently small to enable it to be packaged in a viral vector (adeno-associated virus (AAV)). The gene produces a functional truncated dystrophin protein, known as micro-dystrophin [32,33]. Several pre-clinical studies have demonstrated the feasibility of the approach in animal models of DMD [34]. Currently, a phase 1 clinical trial is ongoing and another has been completed but the results have not yet been released. The objective was to test two versions of AAV-micro-dystrophin with different promoters administered by intramuscular injection (ClinicalTrials.gov NCT02376816 and NCT00428935). However, numerous clinical and pre-clinical studies have shown very strong immune responses, cell-mediated and humoral, both to viral capsids and transgene product (in this case micro-dystrophin) resulting in the absence or loss of expression of the transgene [34]. The immune response could, however, be controlled or contained by concomitant immunosuppression, resulting in successful treatment as suggested by the results in animal models [35,36].

    3.4. Treatment of oxidative metabolism with idebenone

    The absence of dystrophin decreases the oxidative metabolism of striated muscle by indirect mechanisms that have yet to be fully elucidated [37]. Idebenone is a synthetic analog of coenzyme Q10. It was first shown to have a positive effect on cardiac function and exercise capability in a murine model of DMD [38]. Particularly interestingly, a clinical trial in DMD patients showed that idebenone only improved respiratory function in the group not on concomitant glucocorticoid therapy. Idebenone did not exert any additional or synergistic effect in the group on corticosteroid therapy [8,39]. A  phase III trial (DELOS) recently confirmed the protective effect with regard to respiratory function in patients not on corticosteroid therapy [40]. For 52 weeks the authors treated 33 patients with placebo and 31 patients with idebenone (ages eligible for inclusion: 10-18 years). The principal endpoint, peak expiratory flow as percentage predicted (PEF %p), changed by -8.84%p in the placebo group (95% CI: -12.73-4.95) vs -2.57%p (-6.68 to 1.54) in the idebenone group, i.e. a difference of 6.27 %p (0.61 to 11.93). Despite those encouraging results, reflection is called for. What does the reduction in PEF %p really mean in light of the progression of the disease, particularly, with regard to the other respiratory parameters, which did not change during the study? While statistically valid, a moderate difference in only a few respiratory function values does not necessarily imply a real clinical benefit. It has therefore not yet been conclusively demonstrated that idebenone could be a veritable alternative to corticosteroid therapy. However, the duration of the study was 52 weeks. It cannot be ruled out that long term treatment may be more effective by procuring a series of small benefits that, taken together, may impact the general condition of patients.

    3.5. Blockade of the myostatin signaling pathway

    Lastly, several experimental strategies have been developed with a view to preventing muscle wasting in DMD patients. Various approaches have been tested in various animal models. Among those approaches, myostatin blockade has proved to be particularly promising. Myostatin is a growth factor of the TGF-β series. Blockade of its receptor, activin receptor IIB (ActRIIB), spectacularly stimulates muscle growth in various animal models [41]. This finding provided the rationale for a clinical trial conducted in 2010 (ClinicalTrials. gov NCT01099761]. The aim of the study was to test soluble activin receptor IIB (sActRIIB-Fc or ACE-031] by the systemic route although the exact function of myostatin in the regulation of skeletal muscle and the role of its receptor in the regulation of multiple tissues and organs was not yet fully understood. The trial was, in fact, very rapidly suspended in light of potentially dangerous vascular adverse reactions: the patients treated rapidly presented with bleeding from the nasal mucosa and gums, and, more generally, cutaneous vessel dilatation (TREAT-NMD Newsletter no. 99. 21st April, 2011). In addition, recently published studies have shown that the myostatin signaling pathway plays a key role in oxidative metabolism [42]. Thus, inhibition of the pathway by sActRIIB-Fc induces severe secondary mitochondrial myopathy in the murine model of DMD [43]. Other drugs that interfere with myostatin signaling are under evaluation in the context of Duchenne myopathy (e.g.: ClinicalTrials.gov NCT02515669, NCT02354781). Given the multiple adverse reactions already observed in numerous clinical and preclinical studies, it would nonetheless appear that the therapeutic rationale for myostatin pathway blockade in the context of DMD should be reconsidered.

    4. Conclusion

    The main lesson to be drawn from the clinical trials conducted in recent years is that the candidate drugs, at best, exert a protective effect or slow disease progression. None of the approaches developed to date ensures a curative effect, particularly in patients with a long history of the disease or handicapped by it.

    Most of the studies were conducted over a short period of less than one year. Under those conditions, the potentially protective effect of a drug is difficult to measure, particularly since the clinical progression of DMD is slow. Secondly, the inclusion of patients at about the age they lose their ability to walk complicates ascertaining the potential effect of a drug substance whose action is not immediate. Those specificities have necessitated changes in the design and conduct of DMD studies. More recent studies are conducted over almost 2 years and the age at inclusion has fallen to 4-6 years (ClinicalTrials.gov NCT02420379, NCT02255552). It will thus indubitably be necessary to pursue treatment over several years before formulating a conclusion as to the efficacy of a given drug. We should bear in mind that several decades were required to conclude that long-term corticosteroid therapy was sound.

    Statement of interests

    H. Amthor states that he has been a member of the AFM scientific board.

    References

    [1] Ishikawa Y, Miura T, Aoyagi T, et al. Duchenne muscular dystrophy: survival by cardio-respiratory interventions. Neuromuscul Disord 2011;21:47-51.

    [2] Eagle M, Bourke J, Bullock R, et al. [2007]. Managing Duchenne muscular dystrophy--the additive effect of spinal surgery and home nocturnal ventilation in improving survival. Neuromuscul Disord 2007;17:470-5.

    [3] Drachman DB, Toyka KV, Myer E . Prednisone in Duchenne muscular dystrophy. Lancet 1974;2:1409-12.

    [4] Manzur AY, Kuntzer T, Pike M et al. Glucocorticoid corticosteroids for Duchenne muscular dystrophy. Cochrane Database Syst Rev 2008;CD003725.

    [5] Ricotti V, Ridout DA, Scott E, et al. Long-term benefits and adverse effects of intermittent versus daily glucocorticoids in boys with Duchenne muscular dystrophy. J Neurol Neurosurg Psychiatr 2013;84:698-705.

    [6] Barber BJ, Andrews JG, Lu Z, et al. Oral corticosteroids and onset of cardiomyopathy in Duchenne muscular dystrophy. J Pediatr 2013;163:1080-4.e1.

    [7] Lebel DE, Corston JA, McAdam LC, et al. Glucocorticoid treatment for the prevention of scoliosis in children with Duchenne muscular dystrophy: long-term follow-up. J Bone Joint Surg Am 2013;95:1057-61.

    [8] Buyse, GM, Goemans, N, van den Hauwe, M et al. Effects of glucocorticoids and idebenone on respiratory function in patients with duchenne muscular dystrophy. Pediatr Pulmonol 2013;48:912-920.

    [9] Schram G, Fournier A, Leduc H, et al. All-cause mortality and cardiovascular outcomes with prophylactic steroid therapy in Duchenne muscular dystrophy. J. Am. Coll. Cardiol 2013;61:948-54.

    [10] Bushby, K, Finkel, R, Birnkrant, DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care. Lancet Neurol 2010;9:177-189.

    [11] Bushby K, Finkel R, Birnkrant DJ et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol 2010;9:77-93.

    [12] Bushby KM, Gardner-Medwin D, Nicholson LV, et al. The clinical, genetic and dystrophin characteristics of Becker muscular dystrophy. II. Correlation of phenotype with genetic and protein abnormalities. J Neurol 1993;240:105-12.

    [13] England SB, Nicholson LV, Johnson MA, et al. Very mild muscular dystrophy associated with the deletion of 46 % of dystrophin. Nature 1990;343:180-2.

    [14] Mirabella M, Galluzzi G, Manfredi G, et al. Giant dystrophin deletion associated with congenital cataract and mild muscular dystrophy. Neurology 1998;51:592-5.

    [15] Aartsma-Rus A, Van Deutekom JC, Fokkema IF, et al. Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule. Muscle Nerve 2006;34:135-44.

    [16] Deburgrave N, Daoud F, Llense S, et al. Protein-and mRNA-based phenotype-genotype correlations in DMD/BMD with point mutations and molecular basis for BMD with nonsense and frameshift mutations in the DMD gene. Hum Mutat 2007;28:183-95.

    [17] Monaco AP, Bertelson CJ, Liechti-Gallati S, et al. An explanation for the phenotypic differences between patients bearing partial deletions of the DMD locus. Genomics 1988;2:90-5.

    [18] Benchaouir R, Goyenvalle A. Splicing modulation mediated by small nuclear RNAs as therapeutic approaches for muscular dystrophies. Curr Gene Ther 2012;12:179-91.

    [19] Aartsma-Rus A. Antisense-mediated modulation of splicing: therapeutic implications for Duchenne muscular dystrophy. RNA Biol 2010;7:453-61.

    [20] Aartsma-Rus A, Fokkema I, Verschuuren J, et al. Theoretic applicability of antisense-mediated exon skipping for Duchenne muscular dystrophy mutations. Hum Mutat 2009;30:293-9.

    [21] Cirak S, Arechavala-Gomeza V, Guglieri M, et al. Exon skipping and dystrophin restoration in patients with Duchenne muscular dystrophy after systemic phosphorodiamidate morpholino oligomer treatment: an open-label, phase 2, dose-escalation study. Lancet 2011;378:595-605.

    [22] Goemans NM, Tulinius M, van den Akker JT, et al. Systemic administration of PRO051 in Duchenne’s muscular dystrophy. N Engl J Med 2011;364:1513-22.

    [23] Mendell JR, Rodino-Klapac LR, Sahenk Z, et al. Eteplirsen for the Treatment of Duchenne Muscular Dystrophy. Ann. Neurol 2013;74:637-47.

    [24] Voit T, Topaloglu H, Straub, V, et al. Safety and efficacy of drisapersen for the treatment of Duchenne muscular dystrophy (DEMAND II): an exploratory, randomised, placebo-controlled phase 2 study. Lancet Neurol 2014;13:987-96.

    [25] Goyenvalle A, Babbs A, Avril A, et al. Tricyclo-DNA: A promising chemistry for the synthesis of antisense molecules for spliceswitching approaches in DMD. Neuromuscul Disord 2012;22:907.

    [26] Moulton HM, Moulton JD. Morpholinos and their peptide conjugates: therapeutic promise and challenge for Duchenne muscular dystrophy. Biochim Biophys Acta 2010;1798:2296-303.

    [27] Goyenvalle A, Griffith G, Babbs A, et al. Functional correction in mouse models of muscular dystrophy using exon-skipping tricyclo-DNA oligomers. Nat Med 2015;21:270-5.

    [28] Welch EM, Barton ER, Zhuo J, et al. PTC124 targets genetic disorders caused by nonsense mutations. Nature 2007;447:87-91.

    [29] Bushby K, Finkel R, Wong B, et al. Ataluren treatment of patients with nonsense mutation dystrophinopathy. Muscle Nerve 2014;50:477-87.

    [30] Kerem E, Konstan MW, De Boeck K, et al. Ataluren for the treatment of nonsense-mutation cystic fibrosis: a randomised, double-blind, placebo-controlled phase 3 trial. Lancet Respir Med 2014;2:539-547.

    [31] Romero NB, Braun S, Benveniste O, et al. Phase I study of dystrophin plasmid-based gene therapy in Duchenne/Becker muscular dystrophy. Hum Gene Ther 2004;15:1065-76.

    [32] Athanasopoulos T, Graham IR, Foster H et al. Recombinant adenoassociated viral (rAAV) vectors as therapeutic tools for Duchenne muscular dystrophy (DMD). Gene Ther 2004;11 Suppl 1:S109-21.

    [33] Jørgensen LH, Larochelle N, Orlopp K, et al. Efficient and fast functional screening of microdystrophin constructs in vivo and in vitro for therapy of duchenne muscular dystrophy. Hum Gene Ther 2009;20:641-50.

    [34] Okada T, Takeda S. Current Challenges and Future Directions in Recombinant AAV-Mediated Gene Therapy of Duchenne Muscular Dystrophy. Pharmaceuticals 2013;6:813-36.

    [35] Wang Z, Storb R, Halbert CL, et al. Successful regional delivery and long-term expression of a dystrophin gene in canine muscular dystrophy: a preclinical model for human therapies. Mol Ther J Am Soc Gene Ther. 2012;20:1501-7.

    [36] Chicoine LG, Montgomery CL, Bremer WG, et al. Plasmapheresis eliminates the negative impact of AAV antibodies on microdystrophin gene expression following vascular delivery. Mol Ther J Am Soc Gene Ther 2014;22:338-47.

    [37] Jongpiputvanich S, Sueblinvong T, Norapucsunton, T. Mitochondrial respiratory chain dysfunction in various neuromuscular diseases. J Clin Neurosci 2005;12:426-8.

    [38] Buyse GM, Van der Mieren G, Erb M, et al. Long-term blinded placebo-controlled study of SNT-MC17/idebenone in the dystrophin deficient mdx mouse: cardiac protection and improved exercise performance. Eur. Heart J. 2009;30:116-24.

    [39] Buyse GM, Goemans N, van den Hauwe M, et al. Idebenone as a novel, therapeutic approach for Duchenne muscular dystrophy: results from a 12 month, double-blind, randomized placebo-controlled trial. Neuromuscul Disord 2011;21:396- 405.

    [40] Buyse GM, Voit T, Schara U, et al. Efficacy of idebenone on respiratory function in patients with Duchenne muscular dystrophy not using glucocorticoids (DELOS): a doubleblind randomised placebo-controlled phase 3 trial. Lancet. 2015;385:1748-57.

    [41] Amthor H, Hoogaars WM. Interference with myostatin/ActRIIB signaling as a therapeutic strategy for Duchenne muscular dystrophy. Curr Gene Ther 2012;12:245-59.

    [42] Mouisel E, Relizani K, Mille-Hamard L, et al. Myostatin is a key mediator between energy metabolism and endurance capacity of skeletal muscle. Am. J.  Physiol. Regul. Integr. Comp. Physiol 2014;307:R444-54.

    [43] Relizani K, Mouisel E, Giannesini B, et al. Blockade of ActRIIB signaling triggers muscle fatigability and metabolic myopathy. Mol Ther J Am Soc Gene Ther 2014;22:1423-33.

  • Central manifestations of dystrophinopathies

    J.-M. Cuisseta, F. Rivierb,c, *

    aService de Neuropédiatrie, Centre de Référence des Maladies Neuromusculaires, CHRU, 59307 Lille cedex, France
    bCHRU de Montpellier, Neuropédiatrie & Centre de Référence des Maladies Neuromusculaires, Montpellier, France
    cU1046 INSERM, UMR9214 CNRS, Université de Montpellier, France

    Summary

    The dystrophin gene involved in Duchenne and Becker muscular dystrophies is expressed in three main tissues where it gives rise to clinical manifestations: the skeletal muscle, heart and central nervous system. The 6 different dystrophins in the brain have been reported to play a role in the maturation and plasticity of neuronal synapses, in particular through their functions with regard to the clustering and stabilization of various receptors on the post-synaptic membrane.

    The possibility of an intellectual deficiency in Duchenne muscular dystrophy has been known since the original description by Duchenne himself. Current data are in line with a constant cognitive impairment with the normal distribution curve for intellectual quotients (IQ) down shifted by 1 standard deviation from the standard population curve, and with an average IQ of about 80. Clinical manifestations reflecting central nervous system involvement may be present in all classic dystrophinopathies with muscle impairment, and may also be present in isolation without myopathic signs. The phenotypic spectrum appears broader and more subtle than the intellectual deficiency. The isolated or combined involvement of specific cognitive functions is possible (memory functions, executive functions, attention) with or without intellectual deficiency. Autistic spectrum disorders may also be observed.

    In clinical practice, plasma creatine kinase (CK) is to be determined in the various settings, bearing in mind that pure central forms of dystrophinopathy with normal plasma CK level have recently been reported.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    Le gène dystrophine impliqué dans les dystrophies musculaires de Duchenne et de Becker est exprimé dans 3 principaux tissus à l’origine des manifestations cliniques: le muscle strié squelettique, le cœur et le système nerveux central.

    Les 6 dystrophines différentes présentes au niveau du cerveau joueraient un rôle dans la maturation et la plasticité des synapses des neurones en particulier par leur fonction au niveau de l’agrégation et de la stabilisation de différents récepteurs de la membrane post synaptique.

    La possibilité d’une déficience intellectuelle dans la dystrophie musculaire de Duchenne est connue depuis la description princeps par Duchenne lui-même. Les données actuelles vont dans le sens d’une atteinte cognitive constante avec une courbe de Gauss des quotients intellectuels (QI) décalée de -1 écart-type par rapport à la population standard, et un QI moyen autour de 80. Les manifestations témoignant d’une atteinte du système nerveux central peuvent concerner l’ensemble des dystrophinopathies classiques avec atteinte musculaire, et se présenter isolément, sans signe myopathique. Le spectre phénotypique apparaît plus large et subtil que la déficience intellectuelle. L’atteinte isolée ou combinée de fonctions cognitives spécifiques (fonctions mnésiques, fonctions exécutives, attention) est possible, associée ou non à une déficience intellectuelle. Les troubles du spectre de l’autisme font également partie des manifestations rencontrées.

    En pratique clinique, il faut penser à réaliser un dosage des CPK plasmatiques dans ces différentes situations, en sachant qu’il a été rapporté très récemment des formes centrales pures de dystrophinopathies à CPK plasmatiques normales.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    The dystrophinopathies constitute a set of diseases related to mutation of the dystrophin gene at Xp21. Dystrophin is mainly expressed in skeletal striated muscle and the heart, but it is also expressed in a marked and complex manner in the central nervous system [1,2]. The latter location explains the frequency and diversity of the cognitive disorders observed in dystrophinopathies. The disorders were clearly reported in Duchenne’s initial description with respect to his own patients whose intelligence he considered to often be « obtuse, sometimes to the point of idiocy » [3]. Since then, the intellectual impairment in Duchenne muscular dystrophy (DMD) has come to be considered, in itself, a clinical manifestation of the disease, like the muscle impairment [4,5]. The findings of more recent studies are in favor of constant impairment of cognitive function in general, with a broad phenotypic spectrum. The clinical presentations range from intellectual deficiency of variable severity to particular neuropsychological profiles involving memory functions, executive functions and the attention processes, and including autistic spectrum disorders and social skill disorders.

    2. Molecular pathophysiology of central nervous system involvement in dystrophinopathies

    The dystrophin gene is the largest gene known and has a length of 2.3 Mb and codes for 7 dystrophin proteins of different sizes under the control of specific promoters. In the central nervous system, there are 6 different dystrophins: Dp427b, Dp427m, Dp427p, Dp260 (retina), Dp140 and Dp71, which are mainly located in structures involved in cognitive and behavioral processes (cerebellum, hippocampus, prefrontal cortex, motor association cortex) [1,2]. The «  cerebral  » dystrophins are incorporated in dystrophin associated protein and glycoprotein complexes, which are involved in the aggregation and anchoring of ion channels and membrane receptors at neuron and astrocyte level. Dystrophins thus play a role in the molecular organization of post-synaptic membranes. The dystrophins have different functions. Dp427, is reported to be involved, via GABA A post-synaptic receptor aggregation, in the GABAergic function of the synapses of pyramidal neurons and in the synaptic plasticity of the adult brain. Dp71, via interactions with aquaporin channel 4 (AQP4) and potassium channel Kir4.1, is reported to play a role at the gliovascular interface on water homeostasis and vascular permeability. It is also reported to exert a role in the maturation and plasticity of glutamatergic synapses [2,6].

    In a population of 81 patients with Duchenne or Becker phenotype dystrophinopathies, Daoud et al. compared those whose mutation was distal to exon 62 and affected all dystrophin products including Dp71, and those whose mutation was proximal to exon 62 and affected all dystrophin products except Dp71. In the group of 54 patients who did not express Dp71, the mean IQ was about 50. In the other group of 27 patients, in whom Dp71 expression was maintained, the mean IQ was about 73. In both groups, IQ seemed to have a normal distribution and the percentage of patients presenting with intellectual deficiency, particularly severe deficiency, was significantly higher in the group not expressing Dp71 [7]. These findings show, first, that the absence of Dp71 does not appear indispensable for intellectual impairment, and, second, that Dp71 deficiency may contribute to the severity of intellectual deficiency [7].

    3. Phenotypic spectrum of central nervous system impairment in dystrophinopathies

    3.1. Reality of the intellectual impairment

    The intellectual quotients (IQ) of children with DMD have a normal distribution similar to that of the standard population. Overall, the values are lower with a mean IQ for DMD patients of about 80 [8]. A meta-analysis of 32 studies, which included 1231 patients (1224 DMD patients, 7 patients with Becker muscular dystrophy (BMD)) over some forty years, showed an overall mean IQ of 80.2 (verbal IQ: 80.4; performance IQ: 85.4). The mean IQ was one standard deviation lower than that of the standard population, with a normal distribution left shifted by about twenty points. More than 20% of the meta-analysis population had an overall IQ of less than 70 [9].

    3.2. Neuropsychological profile of dystrophinopathies

    Since intellectual impairment was known to occur in DMD, beginning in the 1990 several authors studied the neuropsychological characteristics of DMD patients, with a view to investigating for a particular neuropsychological profile. Billard et al. studied DMD patients aged between 12 and 16 years in comparison with patients presenting with typical spinal amyotrophy: the DMD patients had more learning disorders, a verbal IQ lower than the performance IQ, reading difficulties with more specific difficulties in reading non-words, and short term memory disorders [10]. Bresolin et al. studied 50 DMD patients and detected non-specific verbal expression disorders and short term memory disorders [11]. Hinton et al. studied 80 DMD patients, of whom 41 were compared with their healthy siblings: all presented with a reduced verbal span, recall and verbal comprehension difficulties, and working verbal memory deficiency. Their scholastic performance was inferior to that of their siblings [12-14]. Wicksell et al. stressed the impairment of the executive functions, which are used in all the strategies for elaboration of tasks appropriate to achieving an end (planning, impulse inhibition and control, process of actively searching the memory, flexibility of thought and action). The authors also stressed the preservation of visual-spatial and auditory-verbal functions [15]. Donders and Taneja, compared 22 DMD patients aged from 6 to 16 years with their siblings and showed that the memory deficiencies were marked when there was a time lapse between verbal information acquisition and recall. The authors postulated that the dysfunction was related to a brain circuit involving the cerebellum, hippocampus and neo-association cortex, areas in which the cerebral transcripts of dystrophin are strongly expressed [16]. All of the above studies of the neuropsychological characteristics of DMD patients concur with respect to the following findings: the cognitive impairment is real and of early onset; the memory disorders are probably present, to a variable degree, in all DMD patients and particularly relate to verbal immediate memory; there is impairment of executive and attention functions.

    The study of the neuropsychological profile was broadened to include BMD patients and female carriers of dystrophinopathies. Young et al. have reported that patients with a Becker phenotype, have an overall mean IQ of 95.6, i.e. a normal value [17]. However, they experience scholastic difficulties that are significantly greater than those experienced by the general population, and learning difficulties particularly with regard to reading, writing and arithmetic. Two thirds of BMD patients present with behavioral disorders, of which 8.1% with autistic spectrum disorders [17]. With regard to female dystrophinopathy carriers, Mercier et al. studied 26 symptomatic female patients: 7 (27%) presented with cognitive impairment and in 6 the mutation involved the distal part of the dystrophin gene, beyond exon 44 (thus involving the expression of Dp140) or beyond exon 62 (thus involving the expression of Dp71) [18].

    3.3. Other “central” manifestations in dystrophinopathies

    Hendriksen and Vles used the results of a parental questionnaire to study the psychological and behavioral comorbidities of 351 DMD patients: 11.7% had an attention deficit with hyperactivity; 3.1% an autistic spectrum disorder; and 4.8% an obsessive compulsive disorder [19].

    Pane et al. studied the frequency of attention deficit with or without hyperactivity disorder (ADHD) in 103 male DMD patients aged between 4 and 17 years. An attention deficit was detected in 33 cases (31%), and was associated with hyperactivity in 17 cases (16.5%), and isolated in 15 cases (14.6%). Intellectual deficiency was identified in 27 of the 103 patients (24.6%). Sixty-two of the 103 patients were free from intellectual deficiency and ADHD, 9 had intellectual deficiency without ADHD, 14 had ADHD without intellectual deficiency and 18 had both intellectual deficiency and ADHD. ADHD was found to be more frequently correlated with dystrophin gene mutations affecting transcript Dp140 (exons 45 to 55) or mutations affecting all dystrophin transcripts of which transcript Dp71.

    An association between autism and DMD was first reported by Komoto et al. in 1984. The case consisted in a boy aged of 11 years, diagnosed with myopathy at age of 2 years [21]. More recently, Wu et al. determined the prevalence of autism in 158 male DMD patients in the state of Massachusetts. The prevalence was 4% versus 0.16% in the general population [22]. Several hypotheses have been proposed to explain the comorbidity, which does not seem to be the fruit of chance: mutation of the distal part of the gene affecting the cerebral dystrophin transcripts; contiguous gene syndrome in which impairment of the dystrophin gene is associated with impairment of neighboring genes at Xp21, some of which are involved in mental retardation [22].

    3.4. Pure central forms of dystrophinopathies

    North et al. reported on 4 male patients aged between 15 and 42  years who presented with intellectual deficiency (IQ between 60 and 68), psychiatric disorders, no muscle deficiency, and creatine kinase (CK) elevation. In all the cases, muscle biopsy showed a dystrophic formula and qualitative and quantitative dystrophin expression abnormalities as evidenced by immunohistochemistry and Western blot, leading to diagnosis of BMD. For 2 cases, deletion of the dystrophin gene was evidenced. The authors therefore concluded that there may be dystrophinopathies of the Becker type with predominantly neuropsychiatric expression [23]. Srour et al. reported the case of a child with developmental retardation, without motor impairment. The case progressed toward intellectual deficiency without any muscle deficit. A DNA chip used in the etiologic investigation of the mental retardation showed deletion of the dystrophin gene, confirmed by PCR, from exons 3 to 9 of the gene, affecting expression of Dp427, the longest isoform of dystrophin [24]. In a study of a family presenting with X-linked non-specific intellectual deficiency, De Brouwer et al. sequenced the exons of 86 genes involved in X-linked intellectual deficiency and evidenced, in 4 adult male patients, deletion of 3 base pairs of the dystrophin gene, only affecting expression of protein Dp71. One of the patients had slightly elevated serum CK values: 279 IU/L (normal range: 30-200 IU/L). None of the patients presented with signs of muscle impairment. The authors concluded that they had identified the first mutation of the dystrophin gene affecting expression of Dp71, responsible for intellectual deficiency without any muscular dystrophy [25]. Using high throughput sequencing of 217 genes from 106 patients who presented with intellectual deficiency or an autistic spectrum disorder of indeterminate etiology, Redin et al. identified 26 causal mutations of which 1 deletion of the DMD gene in two brothers. The latter presented with intellectual deficiency and behavioral disorders with no sign of muscle involvement. In particular, their plasma CK values were below the upper limit of the normal range [26].

    The above cases point to the existence of dystrophinopathies with an isolated or clinically prominent intellectual deficiency associated with cognitive or behavioral disorders, and in which muscular expression is minimal or absent.

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    4. Conclusion

    Central nervous system impairment is an integral component of the symptoms of dystrophinopathies, particularly DMD. The diversity and complexity of the products of the dystrophin gene that are expressed at central nervous system level constitute the molecular bases of the manifestations but the underlying pathological mechanisms have yet to be fully elucidated.

    In clinical practice, plasma CK is to be determined in any patient, child or adult, irrespective of gender (male cases are more common) who presents with, or has presented with, psychomotor retardation, language acquisition disorders, autistic spectrum disorders, scholastic difficulties, intellectual deficiency, social or behavioral disorders, or ADHD (Table I). In the light of recent publications reporting cases of dystrophinopathies whose expression is purely central, it would appear essential to include study of the dystrophin gene in the molecular genetics workup for X-linked intellectual deficiency even if plasma CK is normal, in particular when the new techniques for multiple and concomitant sequencing of a panel of genes are used.

    Statement of interests

    Over the last 5 years, François Rivier and Jean-Marie Cuisset have received financing from the pharmaceutical company, PTC Therapeutics, for participation in and oral communications at symposiums during congresses, and for participation in expert groups.

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    [15] Wicksell RK, Kihlgran M, Melin L, et al. Specific cognitive deficits are common in children with Duchenne muscular dystrophy. Dev Med Child Neurol 2004;46:154-9.

    [16] Donders J, Taneja C. Neurobehavioural characteristics of children with Duchenne muscular dystrophy. Child Neuropsychol 2009;15:295-304.

    [17] Young HK, Barton BA, Waisbren S, et al. Cognitive and psychological profile of males with Becker muscular dystrophy. J Child Neurol 2008;23:155-62.

    [18] Mercier S, Toutain A, Toussaint A, et al. Genetic and clinical specificity of 26 symptomatic carriers for dystrophinopathies at pediatric age. Eur J Hum Genet 2013;21:855-63.

    [19] Hendriksen JG, Vles JS. Neuropsychiatric disorders in males with Duchenne muscular dystrophy: frequency rate of attentiondeficit hyperactivity disorder (ADHD), autism spectrum disorder and obsessive compulsive disorder. J Child Neurol 2008;23:477- 81.

    [20] Pane M, Lombardo ME, Alfieri P, et al. Attention deficit hyperactivity disorder and cognitive function in Duchenne Muscular dystrophy: Phenotype-Genotype Correlation. J Pediatr 2012;161:705-9.

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  • Respiratory and intensive care aspects of muscular dystrophies

    X. Ambrosia, L. Lamothea, N. Heminga, D. Orlikowskia,b,*

    aService de réanimation, unité de ventilation à domicile, hôpital Raymond Poincaré, 104 boulevard Raymond Poincaré, 92380 APHP, Garches, France
    bCentre d’investigation clinique Inserm 1429, hôpital Raymond Poincaré, 104 boulevard Raymond Poincaré, 92380 APHP, Garches, France

    Summary

    Among the various myopathies, Duchenne muscular dystrophy (DMD) constitutes the myopathy with the most stereotypical respiratory course. The progressive respiratory failure develops in parallel with the motor deficit, leading to mechanical ventilation at the end of the patient’s second decade. In the absence of curative therapies, respiratory management and the prevention of respiratory complications, in a systematic and organized manner, have enabled a marked reduction in patient morbidity and mortality. Life expectancy in excess of forty years is no longer exceptional. In addition to spinal stabilization, cough and swallowing disorder management is to be associated with mechanical ventilation set-up and management. Invasive ventilation techniques such as tracheotomy remain pertinent although alternative techniques enabling non-invasive daytime ventilation have been developed in recent years.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    Parmi les différentes myopathies, la dystrophie musculaire de Duchenne représente la myopathie dont l’évolution respiratoire est la plus stéréotypée. Cette atteinte respiratoire progressive va se développer de façon parallèle à celle du déficit moteur conduisant les patients à la ventilation mécanique à la fin de leur seconde décade. En l’absence de thérapeutique curative, la prise en charge ventilatoire et la prévention des complications respiratoires, de façon systématique et organisée, a permis de diminuer de façon importante la morbidité et la mortalité de ces patients. Il n’est plus exceptionnel de rencontrer des patients dont l’espérance de vie dépasse la quarantaine. Outre la stabilisation rachidienne, la prise en charge de la toux, la gestion des troubles de déglutition doivent être associées à la prise en charge et la mise en place de la ventilation mécanique. Les techniques de ventilation invasive comme la trachéotomie gardent leur place dans cette pathologie même si des techniques alternatives permettant une ventilation diurne non invasive se sont développées ces dernières années.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    Duchenne muscular dystrophy (DMD) is a progressive muscular dystrophy that is particular in that it homogeneously affects both the limb muscles and the respiratory muscles.

    While the respiratory impairment does not predominate early in the disease, it emerges over time and leads to mechanical ventilation initially at night and then day and night, culminating in total ventilator dependence [1]. The introduction of mechanical ventilation, now used universally, has transformed patient prognosis [2]. Life expectancy has increased from 25 to 40 years in a few decades [3]. Continuous mechanical ventilation also enables quality of life maintenance including for highly dependent patients. However, the question of tracheotomy will ultimately arise, with the associated medical and social impact. Current treatment resources often enable tracheotomy to be avoided. Tracheotomy is thus to be organized and decided on with the patient and his family; emergency decision making is to be avoided.

    2. Course of the respiratory impairment

    With regard to respiration, the natural history of DMD is characterized by an initial rising phase over the first 10 years of life during which respiratory function develops normally. With the emergence of muscle weakness, a plateau occurs followed by gradual deterioration of respiratory function with, on average, a forced vital capacity of 20% of the theoretical capacity at age of 21 years [4]. The respiratory insufficiency generally necessitates mechanical ventilation at the end of puberty [5]. Cardiac impairment is almost always associated [6,7]. The mean age at which vital capacity (VC) falls below 1 liter is 18.1  years [8]. The annual rate of respiratory function decline has been reported for patient cohorts and ranges from 4 to 8.6% of the theory [9,10] with acceleration of the rate of decline at the end of the patient’s second decade.

    Follow-up of a cohort of 58 patients, showed that the factors predictive of survival were the maximum value of the forced vital capacity and its rate of decline [11]. In the absence of treatment by mechanical ventilation, a vital capacity of less than 1  L was a predictive factor for mortality with a median survival of 3.1 years and a 5-year survival of 8% [12]. A vital capacity (VC) of less than 30% of the theoretical has been reported to be a predictive factor for a greater number of post-operative complications following-spinal surgery and the need for post-operative ventilation [13].

    A decrease in FEV1 to less than 40% of the theory, an increase in capnia to above 45 mm Hg and a base excess greater than 4 mmol/L have been reported to be predictive of alveolar hypoventilation [14]. VC < 680 mL and a peak inspiratory pressure (PIP) < 22 cm H2O are highly predictive of hypoventilation in DMD [15].

    3. Evaluation of the respiratory impairment

    3.1. Pathophysiology of the respiratory impairment

    DMD is characterized by a very stereotypical clinical presentation and constantly-present respiratory impairment related to the loss of muscle strength.

    Respiratory muscle impairment thus affects both the inspiratory and expiratory muscles in a relatively homogeneous manner. A  decrease in inspiratory muscle strength induces a decrease in the pressures generated [16]. The impairment of inspiratory muscle strength induces a limitation of rib cage expansion, reducing static lung volumes and giving rise to a restrictive syndrome with a decrease in total lung capacity (TLC) and VC.

    The decrease in expiratory muscle strength induces a decrease in the expiratory pressures generated with, as main consequence, a less effective cough, and, sometimes, speech impairment. The cough is less effective due to: i) expiratory muscle impairment; ii) inspiratory impairment; and sometimes iii) glottal function impairment.

    Sleep disorders are common in DMD patients [14] and influence the prognosis [12]. Episodes of hypopnea and desaturation may occur during sleep, particularly during rapid eye movement (REM) sleep [17], and are probably related to a physiological reduction in the activity of the accessory respiratory muscles. In addition, there is a decrease in the efficacy of diaphragmatic contraction in the prone position [18]. Episodes of obstructive apnea may also occur due to a decrease in the activity of the pharyngeal musculature or ENT anomalies [19]. Lastly, physical discomfort and pain (nighttime positions) may interfere with the quality of sleep.

    Sleep disorders probably emerge well before dyspnea and blood gas abnormalities [14]. With the progression of the respiratory impairment all stages of sleep are affected by frequent episodes of nighttime hypoventilation and desaturation, resulting in marked fragmentation of sleep. Symptoms related to the sleep disorders will then emerge [20].

    Deglutition disorders are common in neuromuscular diseases (NMD) but rarely prominent in DMD [21,22]. They often emerge late (long meals, difficulty eating rather than choking) and constitute aggravating or decompensating factors. They may induce aspiration, pneumonia and atelectasis in patients whose coughing function is already impaired [23]. Investigation for and treatment of deglutition disorders thus constitute an important aspect of management. Deglutition disorders may influence the modalities of mechanical ventilation such as tracheotomy [22].

    3.2. Clinical aspect of the respiratory impairment

    Various clinical signs orient diagnosis of severe respiratory impairment in a patient with DMD. The patient interview is an essential component of the examination. Dyspnea or signs of diaphragmatic dysfunction such as orthopnea are rarely observed outside of episodes of acute decompensation [24]. Paradoxical respiration, use of the accessory respiratory muscles with supra-sternal, supra-clavicular or inter-costal hollowing may emerge late. The signs of hypercapnia are headaches in the morning or some time after ventilation, mood, concentration and character disorders, and asthenia. Signs suggesting poor quality of sleep, such as nighttime awakenings, nightmares and a feeling of non-restorative sleep may also be observed. Daytime drowsiness also suggests sleep disorders and my sometimes be prominent [20].

    3.3. Components of respiratory function monitoring

    In addition to the clinical aspect, the monitoring of respiratory impairment is to be based on regular determination (e.g.: during the multidisciplinary consultations) of vital capacity (VC) in the sitting and lying position, and peak inspiratory pressure (PIP) and peak expiratory pressure (PEP). Blood gases are also to be determined with the patient breathing freely and on ventilation if mechanical ventilation has already been instituted [6,16]. Blood gas determination is to be conducted during the initial assessment and is to be repeated in the event of significant abnormalities of the other respiratory function parameters (spirometry and/or muscle tests). Nighttime oximetry is sometimes of value. A normal result is reassuring. In contrast, in the event of the existence of episodes of nighttime desaturation, the underlying mechanism is to be elucidated by means of polygraphy or polysomnography. In a recent consensus conference on the respiratory management of DMD, simple nighttime oximetry was considered to be an alternative to polysomnography when the latter was not available [6]. Nighttime oximetry is much more accessible and can easily be repeated as often as necessary during monitoring.

    Daytime hypercapnia (> 45 mmHg) is preceded by nighttime hypercapnia with episodes of marked desaturation particularly during REM sleep [25-27]. Nighttime transcutaneous PCO2 (PtcCO2) monitoring is thus more sensitive than daytime gas monitoring, but the technique is more complex to implement and is only just becoming available for use at home. While the correlation between PaCO2 and PtcCO2 is relatively good, a reference blood gas determination is nonetheless required [28]. The emergence of nighttime hypercapnia is strongly predictive of the need for non-invasive ventilation (NIV) within the year [29]. In DMD, determination of bicarbonate and base excess on a specimen obtained on patient awakening is also of value since those parameters are correlated with nighttime hypoventilation [14].

    In DMD, according to the ATS consensus, blood gas determination is not indispensable and may be replaced by annual capnography. This is, however, an expert opinion and the recommendation also relates to children, who are less at risk of presenting with hypercapnia before adolescence. Bicarbonate determination is also recommended [6]. A recent study has shown a high risk of daytime hypercapnia in patients with VC < 680 mL or PIP < 22 cm H2O [15].

    3.4. Investigation of the cough

    The overall efficacy of coughing may be very simply evaluated in routine clinical practice by determination of the cough peak expiratory flow (CPEF). The advantage of the method is that it takes into account glottal function, which is essential for effective coughing since the initial glottal closure enables pressure build up in the airways. Rapid opening then enables a high expiratory flow rate. Depending on the study, a peak expiratory flow rate of 160-270  L/min is considered necessary for effective bronchial drainage and weaning from tracheotomy [30,31]. Coughing assistance is to be prescribed when the flow rate is less than 180 L/min [32]. CPEF is currently the most pertinent indicator for the evaluation of the risk of bronchial congestion in NMD patients [33,34].

    4. Ventilation: indication, set-up and follow-up

    4.1. Indications of ventilation

    Recourse to mechanical ventilation is an important stage in the life of a patient with NMD. Home ventilation requires the active cooperation of the patient and his family and its institution is associated with both practical and psychological problems. Mechanical ventilation means that a further stage in disease progression has been reached and the patient and his family are to be informed of the need for mechanical ventilation before any episode of acute decompensation [35].

    Usually, scheduled institution of home ventilation is instituted for a patient who has been informed and is followed-up. Non-invasive ventilation is then instituted. The recognized criteria for indication of home mechanical ventilation are as follows [36]:

    • a. The existence of clinical signs (dyspnea, orthopnea, headache, asthenia, daytime drowsiness, etc.) associated with at least one of the following physiological criteria;
    • b. Hypercapnia with PCO2> 45 mm Hg;
    • c. Nighttime desaturation < 88 % de SaO2 for more than 5 consecutive minutes;
    • d. VC < 50% of the theory or PIP < 60 cm H2O.

    These indications are to be modulated in the light of the disease and clinical presentation. Thus, in DMD, institution of excessively early mechanical ventilation (VC between 20 and 50% of the theory) was associated with reduced survival [5]. Thus, in the absence of clinical signs, hypercapnia or sleep disorders, we consider it legitimate to indicate mechanical ventilation when VC falls to less than 30% of the theory in the absence of clinical symptoms [37].

    4.2. Practical modalities

    The aims of ventilation are to correct the alveolar hypoventilation, correct the sleep disorders and alleviate the symptoms. The first two aims are rapidly achieved while the last is frequently delayed for a few weeks.

    The initiation of home ventilation takes time in order to determine the optimum interface, determine the optimum mode of ventilation, adjust the settings, check the efficacy of ventilation, teach the patient and his family how to use the equipment, and synchronize discharge with the organization managing home ventilation. There can be no question of simply expediting the choice of mask and system, and then sending the patient home. The patient is to be hospitalized for several days or to return on several consecutive days if the patient is ambulatory. The main difficulty consists in the patient becoming used to ventilation at night. Almost complete nighttime compliance is only achieved after several days of adaptation and acclimatization.

    The AFM/HAS consensus conference recommended that long term NIV should be instituted in an facility (usually a hospital) appropriate to the patient’s age and disease. The first line mode of ventilation is to be that with which the medical and paramedical team is familiar. Hospital personnel training of the patient and his family is also recommended. Training by vicinity healthcare professionals and ventilation suppliers is to be pursued at home [32].

    In practice, the nasal interface remains the first line particularly since its tolerability seems superior to that of facial interfaces [38]. In DMD patients with a major motor deficit, face masks may be dangerous in that there is a risk that the patient may be unable to call out or remove the mask in the event of bronchial congestion, a deglutition disorder or a ventilator failure or shutdown. The choice of an interface with or without leakage will depend on the mode of ventilation, system, and the patient’s facial morphology and tolerance.

    An error to be avoided consists in using a hermetic mask with a circuit and ventilator not fitted with an expiratory valve (e.g. BiPap). The choice of type of ventilation and ventilator is to take into account not only the severity of the respiratory insufficiency and the patient’s comfort, but also the foreseeable duration of ventilation and whether or not an alarm and battery are necessary. There is currently no difference between the barometric and volumetric modes. The setting modalities are indicated in the HAS/AFM document and are not specific to DMD. The choice of ventilator and interface may be reviewed in light of disease progression but, in DMD, it seems legitimate to propose, from the outset, a polyvalent ventilator fitted with a battery. The HAS/AFM consensus conference recommended that the ventilator selected should be one with which the medical and paramedical team is familiar and competent and one that is suitable for the conditions under which it will be used (fixed, wheelchair, mobile). It was also recommended that a second ventilator fitted with alarms, and incorporating a battery and/or additional battery should be prescribed for patients ventilated for more than 16 hours per day. Similarly, a second ventilator is also to be available for patients ventilated at different locations (e.g.: home and school) [32].

    Follow-up after one month and then at least annually will enable verification of ventilation efficacy and tolerability, adjustment of settings and provision of assistance.

    5. Management of cough and decongestion

    Maintenance of an effective cough is essential in DMD in order to prevent complications such as atelectasis or pneumonia. Bronchial congestion may give rise respiratory distress and premature death [39]. It has been shown that early use of decongestion techniques enabled a reduction in the number of emergency hospitalizations and cases of pneumonia [40].

    The techniques that may be used are designed to increase the maximum insufflation capacity either manually (glossopharyngeal respiration or air stacking) or assisted by application of positive pressure by an insufflation balloon pressure valve or ventilator. The pressure may be applied via a mask, mouth piece or tracheotomy cannula [40].

    The techniques most widely used currently are based on concomitant use of positive pressure followed by a negative pressure (in-exsufflator). These techniques seem superior in terms of cough flow rate to the manual techniques and hyper-insufflations alone. The techniques are well tolerated and may be used by non-qualified caregivers and family members who have received training once the adjustments have been made. They have enabled a reduction in the number of hospitalizations and tracheotomies in DMD patients with a cough flow rate > 160 L/min [31].

    6. Emergencies and DMD

    The emergency issues mainly consist in episodes of respiratory or cardiac decompensation. Patients may be exposed to the risk of acute respiratory decompensation even in the event of a benign cold or rhinopharyngitis [39].

    It is always necessary to investigate for and eradicate any promoting factors, in particular digestive, potentially promoted by the metabolic disorders [41].

    The respiratory insufficiency is exacerbated by the difficulty of coughing, particularly in the event of associated deglutition disorders. Management essentially consists in non-invasive ventilation combined with bronchial decongestion. In emergency settings, patients are exposed to the risk of invasive ventilation, difficult intubation, and thus complications in patients with marked orthopedic deformations, restricted oral opening or macroglossia [42].

    The signs of a respiratory alert may be discrete and consist in:

    • dyspnea;
    • orthopnea;
    • inspiratory retraction;
    • paradoxical respiration;
    • bronchial congestion;
    • desaturation in ambient air or need for oxygen therapy;
    • patient already ventilated and ventilation time increased;
    • patient with tracheotomy: intra-tracheal aspiration impossible or profuse bleeding.

    The alerting signs of poor hemodynamic tolerance are as follows:

    • hypotension (to be interpreted in light of previous blood pressure figures, which are often low);
    • low cardiac output, mental confusion, cardiac liver.

    Arterial blood gas determination (sometimes capillary blood gas if blood sampling difficult) to enable initial investigation for alveolar hypoventilation (with or without respiratory acidosis), in practice: PaCO2 > 45 mm Hg. Testing for hypoxemia is also conducted.

    Chest X-ray enables investigation for a parenchymal etiology (pneumonia, atelectasis, pulmonary edema, etc.) or pleural etiology (pneumothorax, pleural effusion, etc.). In the event of respiratory insufficiency, DMD patients are to be referred to an intensive care or respiratory intensive care department familiar with the disease and transported by ambulance because the patient is at high risk (venous access, intubation risk). The mortality rate in the ICU is low, fully justifying admission [43]. The patient’s position must be respected (do not lay an orthopneic patient down because of the risk of respiratory failure). Great caution is required when moving the patient (risk of fractures).

    Ventilation is to be initiated by the non-invasive route so as to avoid recourse to endotracheal intubation [44,45]. Moreover, intubation is sometimes hazardous or even impossible, due to the combination of a limited respiratory reserve, orthopedic and/or oral and facial deformations and the potential risk associated with anesthetics and muscle relaxants [46]. Sedatives and neuromuscular blocking agents (particularly depolarizing agents) are to be avoided. Hypnotics such as propofol combined with short acting opioids have been proposed. Intubation under endoscopic guidance is to be preferred [47].

    Oxygen therapy is to be administered with caution and is necessary in the event of patent hypoxemia, possibly in combination with NIV [48]. Diuretics may be of value in the event of concomitant pulmonary edema. Bronchial mucolytics are strictly contra-indicated due to the risk of exacerbating the congestion.

    While non-invasive management of acute respiratory insufficiency is to be preferred, recourse to endotracheal intubation and invasive ventilation may nonetheless be necessary. Clearly, consciousness disorders, a state of shock and respiratory and cardiac arrest are formal indications, as are failure and intolerance of NIV, provided that intubation and invasive ventilation are conducted optimally and combined with bronchial decongestion.

    7. Role of tracheotomy

    Tracheotomy continues to be used for 24/7 ventilation of DMD patients but the emergence of mouthpiece ventilation [49] and the widespread use of decongestion techniques [50] have reduced its indications. Tracheotomy is no longer a first line procedure but used in the event of NIV failure or intolerance, deglutition disorders or insurmountable congestion [6].

    In emergency settings, tracheotomy is often the only alternative that enables patient discharge from intensive care following an acute episode. While tracheotomy is of considerable medical utility, it should be borne in mind that it exacerbates the patient’s dependence and limits his subsequent choices and possibilities [35].

    8. Conclusion

    Duchenne myopathy is a myopathy in which systematic and organized respiratory management has enabled survival to be increased to to several decades. Management is to be initiated in childhood and pursued through adulthood, and is not restricted to institution of mechanical ventilation. Management of the defective cough and deglutition disorders is also a major component to be taken into account. A diagnosis of DMD is not a justification for not treating the patient in intensive care, given the low mortality in the ICU. Despite the development of alternative methods for daytime ventilation, ventilation via tracheotomy remains a technique that must still be available for patients and proposed to their families.

    Statement of interests

    Over the last 5 years, David Orlikowski has received fees and financing for participation in congresses, training operations, research studies, expert groups and consulting from the pharmaceutical companies: BRESAS, RESMED, PHILLIPS RESPIRONICS and AFM. He has also been an investigator or principal investigator in clinical trials sponsored by AFM, RESPIRONICS and RESMED.

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  • Functional and orthopedic aspects of dystrophinopathies

    C. Boulaya,b,*, G. Finidoric

    aService de neurologie pédiatrique, Centre de Référence des maladies neuromusculaires de l’enfant, CHU Timone Enfants, 13385 Marseille cedex5
    bService de chirurgie orthopédique pédiatrique, CHU Timone Enfants, 13385 Marseille cedex5
    cService de chirurgie orthopédique pédiatrique, CHU Necker-enfants malades, 75015 Paris

    Summary

    Although the clinical presentation and natural progression of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) differ, borderline forms exist. Conventional orthopedic treatment is based on self-rehabilitation (by the parents and patient), physiotherapy, posture alignment with orthoses, and ergotherapy to set up technical aids, notably positioning in an electric wheelchair to ensure more satisfactory autonomy. The functional aspect thus predominates over pure orthopedics. Although surgical indications have evolved for the lower limbs, pelvic-spinal arthrodesis for treatment of scoliosis remains the reference treatment, but the modalities have changed with the advent of corticosteroid therapy for DMD. Corticosteroid therapy slows the progression of motor deficits; the age at which the ability to walk is lost is delayed (shifting from 10 years to 13–14 years depending on the study); scoliosis progresses later; respiratory insufficiency is better controlled; and thus survival is prolonged (between 20 and 40 years). However, while the functional aspect seems to respond better to the progress in overall management, it also results from a multidisciplinary approach to the disease. Nevertheless, there is a corollary: assessment is required, not at a time t as in the scales currently in use, but during daily activities by qualitative and quantitative monitoring designed to model nyctohemeral functional motor skills. The principle is to characterize the type of activity (sitting, standing, lying down, walking), its duration, intensity (walking speed), frequency (number of activity changes, number of walking episodes), and their sequence (temporal sequence, organization of activity variation). The goal is to identify the variety of functional motor skills and their occurrence over time to determine whether treatment contributes a functional benefit and whether this benefit is put into practice daily.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    Au sein des dystrophies musculaires de Duchenne (DMD) au Becker (DMB), si les tableaux cliniques et l’évolution naturelle de la maladie diffèrent, il existe des formes «  borderline  ». La prise en charge classique sur le plan orthopédique est basée sur l’autorééducation (par les parents et par le patient), la kinésithérapie, les orthèses de posture, l’ergothérapie pour la mise en place des aides techniques notamment le positionnement global dans le fauteuil roulant électrique afin d’assurer une autonomie la plus satisfaisante. Ainsi l’aspect fonctionnel a une part prédominante sur l’orthopédie pure. Si les indications chirurgicales ont évolué pour les membres inférieurs, l’arthrodèse pelvi-rachidienne pour le traitement de la scoliose reste le traitement de référence mais selon des modalités différentes depuis l’avènement de la corticothérapie dans la DMD. La corticothérapie ralentit la progression des déficits moteurs, l’âge de la perte de la marche se fait plus tardivement (décalage de 10 ans à 13-14 ans selon les études), l’évolution de la scoliose se fait plus tardivement, l’insuffisance respiratoire est mieux contrôlée et, ainsi, la survie est prolongée (entre 20 et 40 ans). Cependant si cet aspect fonctionnel semble mieux répondre à l’évolution de la prise en charge globale c’est grâce, aussi, à l’approche pluridisciplinaire. Néanmoins il existe son corollaire : la nécessité d’une évaluation, non pas à un instant t comme le font les échelles, mais au cours des activités quotidiennes comme le propose un monitoring qualitatif et quantitatif afin de modéliser la motricité fonctionnelle au cours du nycthémère. Le principe est de caractériser le type d’activité (station assise, debout, couchée, la marche), sa durée, son intensité (vitesse de marche), sa fréquence (nombre de changements d’activités, nombre d’épisodes de marche), leur séquence (séquence temporelle, l’organisation de la variation des activités). Le but est d’identifier la variété de la motricité fonctionnelle et de leur occurrence dans le temps afin de savoir si le traitement apporte un bénéfice fonctionnel et si ce dernier est exploité au quotidien.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    The functional and orthopedic (surgical and non-surgical) aspects are indissociable. We will not address the natural course, described previously, which differs markedly between Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). However, there is a common rationale: evaluation of the various items of the International Classification of Functioning, Disability and Health (CIF) [1]. First, the impairment of organic functions (anatomical, histological and pathophysiological impairments). The growing child presents with muscle deficiency and its consequences, namely muscle and tendon retractions and then joint retractions fixing the deformations in a non-reducible state.

    Subsequently, the functional impairment determines a level of function which deteriorates with the natural history of the disease. The limitations and capacities determine the degree of independence of the child, adolescent and finally adult.

    The impact on the activities of everyday life will give rise to situations of handicap (restrictions on social participation), a veritable interface between the remaining capacities and the environment in which the child and then adolescent develops, with impact on daily life at home (washing, dressing, undressing, eating, transfers, falls, fatigability), getting around (walking maintained, limited, at risk of falls and then loss of the ability to walk, manual wheelchair with or without propulsion, electrically powered wheelchair with or without the scope for independent driving), emotional life, life at school (independence, dependence on a school assistant) and then university or professional life, leisure (sports, music, singing, which are excellent means of rehabilitation and re-adaptation, particularly if they are chosen by the child).

    Lastly, environmental factors (family life style) and personal factors (child, parents, siblings) intervene at all the levels previously described and condition the degree of subjectivity with which the child thinks about his muscle disease, functional limitations and situations of handicap, which evolve as the child ages.

    For example the orthopedic therapeutic strategy is to be adapted for a child with DMD on the basis of whether or not he presents with cognitive impairment (cf. specific article): it is not a question of managing DMD but of managing a child with DMD.

    In addition, while the physicians (orthopedic surgeons and/or physical medicine and rehabilitation (MPR) physicians) assess the various impairments (deficiencies, degree of independence, and situations of handicap) the subjective experience is assessed by the child and his parents.

    The contribution of Magalhaes and Hamonet [2-4] to this holistic approach is major. While the four dimensions are clearly separate (the changes in the body, the universal functional capacities of human beings and the situations of life), the subjective experience is isolated as a separate dimension in its own right: the person’s point of view conditions the way in which he reacts to his bodily, functional and situational state. In pediatrics, this aspect conditions orthopedic management (surgery or no surgery) and the patient’s compliance and tolerance especially with regard to rehabilitation and re-adaptation: orthoses, physiotherapy, and installation in a sitting position in a wheelchair.

    Orthopedic management involves explanation, determination and acceptance of objectives that will change with the natural history of the disease in parallel with the remaining respiratory and cardiac capabilities. Evaluation of the therapeutic objectives is also a component of the child’s overall management and follow-up. In that context, the assistance available from AFM-Téléthon through its health trajectory referring physicians in liaison with the departmental house for handicapped persons (MDPH) is of fundamental importance.

    2. Functional assessment

    2.1. Why?

    The motor deficit is assessed by manual testing [5-7] but its reliability (intra- and extra-observer reproducibility) is impeded, in pediatrics, particularly in very young children by cooperation problems (particularly in the event of cognitive disorders, which are common in DMD).

    Thus the clinician has an evaluation of little sensitivity particularly in the event of a reduction in functional capabilities reported by the parents, which may not necessarily be confirmed by manual testing. The latter has been shown to be of limited utility in clinical trials, particularly multicenter trials. Another method of quantified testing uses an instrument of the dynamometer type, which may or may not be isokinetic [4,8,9]. However, the correlation between the motor deficit assessment and functional performance is not clear [10].

    2.2. Functional assessments

    Thus, it is indeed the assessment of functional impairment which is fundamental because it quantifies the handicaps or limitations of activities relative to the CIF [1].

    2.2.1. Timed tests

    Brooke et al. [6,7] were the first to use standardized procedures in which assessment was based on the time taken to accomplish tasks and address their statistical reliability with a view to potential future use in clinical trials.

    Another approach consists in measuring the distance covered in a fixed duration: the 12-minute walk test, and above all, the 6-minute walk test [11-18]. The child is required to walk as best he can for 6 minutes and the distance covered is measured. The test has given rise to numerous publications and was used in DMD (with a stop codon) in clinical trial PTC124 [12,18].

    2.2.2. Motor function measurement test

    Bérard et al. [19,20] reported on the importance of evaluating motor function in neuromuscular diseases, of which DMD and BMD, in particular with regard to disease management, progression follow-up, clinical trial research, and informing the patient’s family with a view to anticipating and minimizing situations of handicap. The team developed the motor function measurement (MFM) scale in 1998. The scale is applicable to all patients with neuromuscular disease irrespective of whether they are ambulatory or not. The scale consists of 32 items (MFM-32) or 20 items for children aged less than 7 years (MFM-20) in 3 dimensions: D1, standing position and transfers; D2, axial and proximal mobility; and D3, distal mobility. A score by dimension, expressed as a percentage of normal motor function, is thus calculated together with a total score. The user’s manual in several languages is available from the website www.mfm-nmd.org. The MFM scale has been validated by Bérard et al. and is in widespread international use [19,20]. According to the authors, the scale measures motor function (and not the deficiencies), is easy to use, is reproducible across centers, enables the child’s course to be monitored irrespective of whether the child is ambulatory or not, and is precise, reliable and sensitive to change.

    2.3. Contribution of Quantified Analysis of Movement: the future

    The current trend in Quantified Analysis of Movement (QAM) is to use portable equipment in order to leave the gait analysis laboratory behind and conduct qualitative and quantitative monitoring of functional mobility in the activities of everyday life (AEL). The objective is to identify, in the context of the AEL, the varieties of functional mobility and their occurrence over time in children suffering from various diseases. Color barcodes are assigned to physical activities (PA). Hence the interest of QAM in that scope is vast with respect to elucidation of the natural course of the disease, assessing treatments (pre- versus post-treatment; monitoring progression on treatment: efficacy, stability or degradation of the AEL; functional AEL benefits of treatment). Aminian et al. developed and then validated miniaturized portable systems for the qualitative and quantitative monitoring of motor functions in the AEL [21]. The autonomous systems contain inertial sensors and gyroscopes. The systems have been validated against conventional systems for quantified analysis of gait in a variety of diseases (DMD, elderly subjects, young subjects, Parkinson’s disease, children with cerebral palsy, osteoarthritis, evaluation of chronic pain). The principle consists in quantifying and characterizing the type of activity (sitting, standing, lying, walking), its duration, intensity (walking speed), frequency (number of activity changes, number of episodes of walking), sequence of activities (temporal sequence, organization of the variation of activities). The aim is to identify the variety of motor functions and their occurrence over time. Thus, the motor functions are modeled (quantitatively and qualitatively) in the form of a color barcode as per the methodology reported by Aminian et al. [21]. During the AEL, 3 sensors (55 × 40 × 18 mm; 50  g) are affixed to the skin (potential conformation: sternum, ipsilateral thigh and leg) in order to acquire the vertical and frontal accelerations together with the sagittal angular velocities of the anatomical segments relative to each other. Recording may be conducted on 5 consecutive days per week for 8 diurnal hours daily. Since the child is at home, the parents position the sensors. The recently developed color barcode for physical activity is particularly indicated for neuromuscular diseases and thus may be legitimately used for children suffering from DMD or BMD. Moreover, the measurement can be used in the event of cognitive disorders, which is not always the case for motor function assessment scales. In addition the system may be used irrespective of whether or not the child is ambulatory. Studies focusing on the upper limbs may also be conducted. This type of assessment has a promising future in that it reflects the reality of the AEL rather than constituting a snapshot. Lastly, the system is not particularly onerous.

    3. Duchenne muscular dystrophy

    Corticosteroid treatment of DMD is known to be beneficial for children and to modify the natural course of the disease. The benefits (evidence level between I and IV) relate to motor performance, slowing of the progression of the motor deficits, scoliosis and respiratory insufficiency, and prolongation of survival (between 20 and 40 years) [22-24]. The details of corticosteroid therapy initiation will not be addressed. However, it has been reported [22,23] that treatment beyond the loss of the ability to walk slows the emergence of scoliosis and respiratory insufficiency; that treatment is to be initiated during the motor performance plateau stage between age of 4 and 8 years, but that failing early instauration, later instauration is still justified with a view to maintaining the functions of the upper limbs and ventilatory muscles. The age at which the ability to walk is lost is delayed (from 10 years to 13-14 years, depending on the study) when corticosteroid therapy is administered, preferably with early initiation. However, the adverse effects are undeniable [24,25].

    3.1. Lower limbs

    3.1.1. Position of orthopedic treatment

    3.1.1.1. Ambulatory child

    While the child remains ambulatory, ambulation is to be maintained and all the activities that appeal to the child are to be promoted. The child alone sets the limits of his physical activity. The gait is defective and characteristic: hyperlordosis, pelvic anteversion, waddling, hip flexion abduction, talipes equinovarus. But the gait is functional and that is what matters. The function is the harmonious resultant of the deficiencies and losses of length of the aponeuroses, muscles and tendons, and a biomechanical economy (muscles, joints and energy).

    At analytical level, the deformations result from the fibrous transformation of the aponeurosis, muscle and tendon complex and the disequilibrium between agonists (predominant deficiencies) and antagonists (lesser deficiencies). The classic presentation is hip flexion abduction in lateral rotation with knee flexion and equinovarus.

    In order to prevent, insofar as possible, and avoid the (ineluctable) exacerbation of the deformations, the physical activities of children with DMD must not be restricted. Then, during the consultation, the parents should be taught to conduct muscle stretching and instructed to carry it out daily in the evening at bedtime or after the bath. This is self-rehabilitation carried out by the parents. The latter are very willing and readily agree (especially the dads); another relationship with the child needs to be developed. This is no substitute for physiotherapy, which is not to be instituted too early in order not to overload the child or his parents, but we are aware of its importance as the child grows older and then becomes an adolescent. The physiotherapist also needs to guide the parents with regard to implementing stretching correctly, as is done in North America. The muscles to be stretched are the iliopsoas, rectus femoris, sartorius, tensor fascia lata, gluteus medius, hamstring, sural triceps (soleus and gastrocnemius medialis-lateralis) and posterior tibialis: in open chains (contract –  relax technique) and closed chains. Self-stretching teaching by the physiotherapist is a good way of ensuring the child’s compliance with his treatment. The other physiotherapeutic resources are passive mobilization and assisted active work (analytical and overall interest of Kabat diagonals) for optimal maintenance of the most deficient muscles: the extensors of the hips; knee extension, ankle dorsal flexion and toe extensors. The number of physiotherapy sessions per week is difficult to determine and is the fruit of a compromise between all the constraints to which the child and his family are subject. Acceptance of long-term treatment is the primary objective. Just as the parents have a right to vacation time children must be given time off physiotherapy. It’s good for everyone.

    Orthoses constitute another means of preventing exacerbation of the deformations. In 2001, a consensus conference [3] recommended 2 types of orthosis.

    First, postural orthoses: the ankle-foot orthosis against equinovarus (frequently fitted as of 0° of dorsal flexion of the ankle, knee stiff, which is well tolerated with good compliance and relative efficacy), the crural-sural orthosis against genu flexum (little used, well tolerated but poor compliance) or the crural-pedal orthosis against the above two deformations (acceptance more difficult). A compromise consists in making detachable orthoses: a suralpedal part which may be fitted to the crural-sural prosthesis, enabling them to be worn independently, enhancing compliance. For enhanced compliance and tolerability, we add a Tamarack® prestress system to the orthoses so that the child can always mobilize his segments but with a passive return to the correction (fig. 1).

    The child’s acceptance is markedly better and the parents can check on correct use of the orthosis more easily. The same type of orthosis may be used to combat genu flexum but we use an Ultraflex® joint. With regard to acceptance and duration of correction, this type of orthosis is best worn at night. However, compromises are essential: alternation of left and right every other day, staggering during the week, orthosis use during the day when resting.

    The posture against hip abduction and rotation is achieved with a cushion and not an orthosis (tolerability and compliance). Verticalization in a posture apparatus of a walking child is difficult to accept given the natural course of the disease.

    The consensus conference [26] recommended functional orthoses with a view to facilitating walking. However, as described above, walking in a child with DMD is a compromise between the deficiencies associated with retractions and compensatory mechanisms. The latter are of value. Walking equinovarus is not synonymous with sural triceps retraction and fitting a sural-pedal orthosis. The compensatory mechanisms are to be respected. We do not prescribe walking orthoses for DMD children given the extent of the orthosis (pelvic, crural, sural and pedal), its poor acceptance, the absence of benefit and the risk of falls. This is accepted by all the teams working in France [27].

    [[{"fid":"80","view_mode":"full","fields":{"format":"full","field_file_title[fr][0][value]":"","field_els_file_description[fr][0][value]":"","field_els_file_description[fr][0][format]":"els_basic","field_file_copyright_note[fr][0][value]":"","field_file_image_alt_text[fr][0][value]":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction.","field_file_image_title_text[fr][0][value]":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction."},"type":"media","field_deltas":{"1":{"format":"full","field_file_title[fr][0][value]":"","field_els_file_description[fr][0][value]":"","field_els_file_description[fr][0][format]":"els_basic","field_file_copyright_note[fr][0][value]":"","field_file_image_alt_text[fr][0][value]":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction.","field_file_image_title_text[fr][0][value]":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction."}},"link_text":false,"attributes":{"alt":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction.","title":"Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correction.","height":"1115","width":"1414","style":"width: 634px; height: 500px;","class":"media-element file-full","data-delta":"1"}}]]

    Figure 1. Sural-pedal postural orthosis with a Tamarack® prestress joint enabling the child to freely mobilize his ankle but with a passive return to equinovarus correctio​n.

    3.1.1.2. The transition toward loss of walking

    The child still has the ability to walk, but the function is reduced, the deformations are intensifying and the risk of falls is growing. The acceptance of the transition to a manual wheelchair (MWC) first and then to an electric scooter and/or electric wheelchair (EWC) will naturally emerge: there are more risks (traumatic falls, fractures) associated with walking than there are functional benefits. When this is explained to the parents, the increase in independence procured by the MWC, electric scooter or EWC is appreciated by the child and his family. The means and principles of physiotherapeutic management remain the same. At this stage the aid of a reinforced twill corset is quite effective, particularly for walking at home and transfers.

    3.1.1.3. Non-walking child

    The main aim is to attempt to combat the exacerbation of the pelvic and spinal postural disorders and their functional consequences, and to ensure the comfort of the sitting position on the electric scooter or, more often, EWC. The interactions between the subpelvic, pelvic and supra-pelvic levels make an overall vision of the deformation and hence the patient’s installation obligatory. The equinovarus may be contained with orthoses at night and in the EWC (fig. 1). Normal shoe wearing should be pursued as long as possible. Orthopedic shoes are rarely prescribed except in the event of major deformations when conventional shoes have become impossible or uncomfortable and/or in the event of skin lesions. Despite the deformations, it is important for the child and his family for him to wear shoes like other children’s’.

    According to Ragot-Mandry et al. [27], the stand-up lift (lift on molding, standing table, lift incorporated in the EWC) is proposed even after walking has stopped. But there are many limitations: height, weight, motivation, orthopedic deformations, pain, and constraints for the parents. For DMD children the optimum compromise appears to be a lift incorporated in the EWC Experience has shown that if the parents want the child to stand, the child and then (especially) the adolescent does not do so. However, we can relate an exception; a family who requested surgical equinovarus therapy to enable continued use of the EWC lift. Another exception consisted in a young adult with DMD (with no scoliosis, which is of capital importance), aged 20 years who wished to continue assuming an upright posture in an EWC on a daily basis because for him it is “very useful and indispensable” and stated that was “very moved to be able to stand up to other people”. It is therefore important to be attentive and not adopt a systematic approach.

    3.1.2. Role of surgery

    The multi-level tenotomies of the legs recommended twenty years ago have gradually lost their indication. They do not enable walking to be prolonged. They may be indicated in the event of severe varus deformations of the feet preventing standing or putting on shoes, or in the event of fascia lata tensors and hip flexors with an oblique pelvis compromising pelvic equilibrium and thus arthrodesis of the spine subsequently. Per-operative care is to be of high quality with respect to pain management and orthosis fitting. The initial immobilization and rapid passive mobilization post-operatively are to be conducted in a center experienced in that type of care and for at least six weeks in order for the patient to experience benefit from the procedure.

    3.2. Spine

    3.2.1. Role of orthopedic treatment

    3.2.1.1. Walking child

    The self-rehabilitation conducted by the parents and the physiotherapy are to have the aim of preventing exacerbation of the deformations:

    • not only in the sagittal plain (flexum of the hips, pelvic anteversion; thoracolumbar hyperlordosis is an equilibration compensation) by stretching the flexors of the hips;
    • but also in the frontal plane (the scoliosis is initiated before the loss of walking) by stretching the quadratus lumborum in the concavity and the proprioceptive work of the spinal muscles by rendering the iliocostal angles symmetrical;
    • and lastly in the horizontal plane (twisting of the pelvic vertebra initiated by 3-D asymmetrical sub-pelvic retractions combining flexion of the hip, pelvic anteversion, abduction and lateral rotation of the hip) by stretching the abductor, median rotator and flexor muscles and active work on the extensors of the hip.
    3.2.1.2. Non-walking child

    Boulay et al. [28] have addressed the potential role of orthopedic treatment (Garchois corset) of scoliosis in DMD children. They stressed that scoliosis remained a major orthopedic problem, of early onset, progressive, and correlated with the proximal and spinal deficiencies and loss of the ability to walk. In that context, corticosteroid therapy retards the loss of walking, and scoliosis has a later onset and is less severe. However, corticosteroid therapy does not modify the progressive potential or natural history of the scoliosis, but it is retarded. Nonetheless, experience and published data on progression in adulthood are not available. For that reason, arthrodesis remains the reference treatment, which needs to be redefined over time in order to determine when to operate because of the joint cardiac and respiratory impairment. Currently, orthopedic treatment of DMD scoliosis (Garchois corset) is not standard practice and our experience of Garchois corsets in DMD is limited to cases in which the family refused surgery and/or surgery was contra-indicated. The corsets were well tolerated and compliance was good.

    While pelvic and spinal arthrodesis reduces the pelvic and spinal deformations and their progression, it also enables compensation for the deviation of the occipital and spinal axis and comfortable installation in a sitting position. Gélis et al. [28] have described the main complaints: pain, discomfort, loss of independent activities (eating, transfers, EWC driving), loss of leisure activities. Assessment of positioning is based on the patient’s expectations, his type of sitting postural equilibrium (Bourgès score, which has not been validated for DMD), his sitting posture (Measurement of Postural Control in the Sitting Position of Adults (MCP2A)) [28]. The technical postural aids reflect the assessment and the EWC chosen together with the position of the cervical spine and head (motor deficit and not included in the pelvic and spinal arthrodesis), and the upper limbs. Frequently, tailor made adjunctions are made by the ortho-prosthetists with the aid of the ergotherapists, who have a fundamental role to play in the therapeutic education of the patient and his caregivers. Once again compromises need to be made between the patient’s medical and functional needs in order to achieve optimum tolerability and acceptance. It is to be noted that scoliosis is absent in certain DMD children and adolescents. Mild scoliosis which is not progressive even at Tanner 5 and Risser 5 may be present. Those DMD adolescents do not have an oblique pelvis or collapse of the trunk.

    3.2.2. Role of surgery

    Following loss of the ability to walk, boys gradually experience kypho- or lordoscoliosis and about 90% require surgery. In general, for patients who have lost the ability to walk, a cumbersome spinal orthosis is not fitted since it is not very effective with regard to the deformation, which will shortly require surgery. Instead, good installation in the sitting position is addressed. Rehabilitation as of an early age is very important, particularly in order to maintain satisfactory suppleness of the cervical spine and prevent emergence of tipping of the pelvis, which may contribute to disequilibrium and exacerbation of the underlying spinal deformations [29]. Cardiac function is to be very attentively and regularly monitored. In addition to the conventional examinations (echocardiography, Holter recording), a myocardial scintigraphy study is to be conducted together with ejection fraction determination and dobutamine testing pre-operatively. In practice, the patients are to undergo surgery before structural deformation emerges right at the start of vertebral rotation and/or constitution of a disequilibrium in the sagittal plane [30].

    The current techniques used for pelvic and sacral fixation based on pedicular screws and sub-laminar sutures or links enable, solid synthesis even with porotic bone. Usually, posterior vertebral arthrodesis extends from the thoracic spine to the sacrum. This rule applies to all serious forms of muscle impairment in non-ambulatory patients. Galvestone’s pelvic fixation technique [31], which we widely used in the past, now seems to have been superseded. Pelvic fixation by iliosacral screws enhances performance and is not associated with a risk of painful phenomena related to displacement of the rods in the pelvis, particularly in subjects with marked retractions and hip deformations. The procedures are certainly difficult, long (four hours and sometimes more, not including the time for patient installation in and removal from the operating room), and potentially dangerous. It is necessary to try to operate once only using procedures that minimize the risk of repeat surgery. Spinal fixation should not aim for optimal correction, which would be difficult to achieve and may be dangerous in patients with marked deformations. The primary objective is satisfactory spinal and pelvic equilibrium in both the sagittal and frontal planes, which is one of the essential conditions for patient comfort and the sitting position [32].

    3.2.3. Peri-operative risks

    Regular practice of and experience with the procedures have reduced the post-operative complications. The patients undergo surgery under medullary monitoring (motor and somatosensory evoked potentials). Neurological complications are exceptional. The risks of per-operative bleeding are now greatly reduced by the spinal access techniques and anesthesia quality. However, blood transfusions are frequently necessary.

    The principal risk is that of infection during the post-operative period, which, in the most severe cases, may occur in 10% of patients in our experience. Post-operative infections must be treated rapidly in order to control the infection, retain the osteosynthesis material and transplants, and not lose the benefit of the procedure. The osteosyntheses and arthrodeses are solid and yield stable results. Losses of correction over time are minimal and mainly affect patients who undergo surgery early before the bone has matured. Arthrodesis does not resolve all the problems and an orthosis is sometimes necessary, in particular in order to maintain the cervical spine in patients with severe muscle impairment. The morphological changes following correction are great. Height has changed; the distance between table and mouth is much greater. During transfers, the mobility of the spine can no longer be used. The new situation has to be evaluated. Once again the assistance of physiotherapists and ergotherapists is particularly important. Lastly, the spinal fixations are a source of comfort for patients in that they prevent progressive deterioration of the spinal column over time, which is incapacitating, painful and life threatening.

    Given the current patient life expectancy, simple fixation without any transplant, as was previously the case, is no longer sufficient. On the contrary, a good quality transplant is required. We usually use a tibial transplant even though it prolongs the procedure somewhat. In the event of heavy bleeding, one can make do with rapid bone refreshment and transplant placement in order to ensure arthrodesis quality

    Post-operatively, the major risk is transient aggravation of respiratory function (30% reduction in vital capacity) if the patients are not managed correctly. Patients are thus to be ventilated until recovery of a respiratory function status the same as or similar to the pre-operative status. The benefits of the surgery have been clearly demonstrated in several studies addressing quality of life, respiratory function and long-term survival [31-33].

    3.3. Upper limbs

    3.3.1. Role of orthopedic treatment

    The upper limbs stiffen mainly in flexion, adduction and median rotation of the shoulder, flexion and pronation of the elbow, and flexion and ulnar inclination of the wrist. Digital involvement is less standardized, although there is closure of the first commissura and flexion of the fingers and thumbs. Physiotherapy tends to be based on passive and active mobilization aided by postures to manage muscle stretching times in order to combat the deformations. Postural apparatus is accepted for the wrists and fingers but compliance is problematic. The children acquire skills (to be respected) that enable them to perform functions (writing, IT self-sufficiency, EWC driving.

    4. Becker muscular dystrophy and role of orthopedic treatment

    Scoliosis in the context of BMD is infrequent and, classically, is not associated with any orthopedic problems since disease onset (average age: 12 years) is gradual and later, with the deficit predominating in the pelvic and scapular girdles (and not the trunk). Furthermore, the course of the disease is variable. In particular, the loss of the ability to walk only occurs before age of 40 years in 50% of cases. Thus, in order to maintain walking despite the proximal motor deficits, the spinal deformation tends to be sagittal with marked hyperlordosis and thoracolumbar equilibration in a context of pelvic anteversion and flexum of the hips. This attitude of compensation for the motor deficits may become decompensated if the biomechanical principle of articular, muscular and energetic economy is overcome, in particular over time in adults. The sagittal deformation of the spine thus forms at the end of growth in young adults with exposure to the natural course of adult spinal deformation [34] in a context of proximal deficiency.

    The objective of management is to combat reduced extensibility of the flexors of the hips (iliopsoas, rectus femoris) and to work actively (open and closed chains) on the deficient muscles (gluteus medius and maximus). Self-rehabilitation and physiotherapy are to contribute, together with games. Orthoses are not indicated. The upper limbs retain satisfactory function because of the scapular involvement: numerous compensations ensure function. Overall, functional capability is maintained for a long time. If status deteriorates, technical assistance (MWC, electric scooter, EWC) are to be provided as is the case for DMD but with fewer constraints and dependencies.

    5. Conclusion

    Thus, in both DMD and BMD, the functional aspects take precedence over the orthopedic aspect, as shown by the change in surgical indications. The functional aspects have become predominant because of the multidisciplinary management in which each dimension is evaluated. For instance, pelvic and spinal arthrodesis is decided on the basis of that principle. Thus, orthopedic or surgical treatment is to be evaluated on the basis of the child’s and family’s subjective experience in light of remaining function. Compliance with treatment depends on this. This obliges the caregivers not only to determine the functional objectives but also to evaluate the everyday life of the child, adolescent or adult with DMD or BMD. For that reason, the functional evaluation of everyday life involves quantitative and qualitative function monitoring. This is all the more pertinent with the new therapeutic approaches in order to respond to the question: what functional benefit, on an everyday basis, does the treatment procure?

    Statement of interests

    The authors state that they have no interests related to this article.

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    [4] Magalhaes T, Hamonet C.Handicap assessment: setting the grounds for an effective intervention in the community. Med Law 2001;20:153-66.

    [5] Bendixen RM, Lott DJ, Senesac C, et al. Participation in daily life activities and its relationship to strength and functional measures in boys with Duchenne muscular dystrophy. Disabil Rehabil 2014;36:1918-23.

    [6] Brooke MH, Griggs RC, Mendell JR, et al. The natural history of Duchenne muscular dystrophy: a caveat for therapeutic trials. Trans Am Neurol Assoc 1981;106:195-9.

    [7] Brooke MH, Griggs RC, Mendell JR, et al. Clinical trial in Duchenne dystrophy. I.  The design of the protocol. Muscle Nerve 1981;4:186-97.

    [8] Lerario A,Bonfiglio S,Sormani M,et al.Quantitative muscle strength assessment in Duchenne muscular dystrophy: longitudinal study and correlation with functional measures. BMC Neurol 2012;12:91.

    [9] Stuberg WA, Metcalf WK. Reliability of quantitative muscle testing in healthy children and in children with Duchenne muscular dystrophy using a hand-held dynamometer. Phys Ther 1988;68:977-82.

    [10] de Lattre C, Payan C, Vuillerot C, et al. Motor function measure: validation of a short form for young children with neuromuscular diseases. Arch Phys Med Rehabil 2013;94:2218-26.

    [11] Henricson E, Abresch R, Han JJ, et al. The 6-minute walk test and person-reported outcomes in boys with duchenne muscular dystrophy and typically developing controls: longitudinal comparisons and clinically-meaningful changes over one year. PLOS Currents Muscular Dystrophy 2013. Edition 1.

    [12] Henricson E, Abresch R, Han JJ, et al. Percent-predicted 6-minute walk distance in duchenne muscular dystrophy to account for maturational influences. PLoS Curr 2012;4:RRN1297.

    [13] Henricson EK, Abresch RT, Cnaan A, et al. The cooperative international neuromuscular research group Duchenne natural history study: glucocorticoid treatment preserves clinically meaningful functional milestones and reduces rate of disease progression as measured by manual muscle testing and other commonly used clinical trial outcome measures. Muscle Nerve 2013;48:55-67.

    [14] McDonald CM, Henricson EK, Abresch RT, et al. The 6-minute walk test and other clinical endpoints in Duchenne muscular dystrophy: reliability, concurrent validity, and minimal clinically important differences from a multicenter study. Muscle Nerve 2013;48:357-68.

    [15] McDonald CM, Henricson EK, Abresch RT, et al. The 6-minute walk test and other endpoints in Duchenne muscular dystrophy: longitudinal natural history observations over 48 weeks from a multicenter study. Muscle Nerve 2013;48:343-56.

    [16] McDonald CM, Henricson EK, Abresch RT et al. The cooperative international neuromuscular research group Duchenne natural history study--a longitudinal investigation in the era of glucocorticoid therapy: design of protocol and the methods used. Muscle Nerve 2013;48:32-54.

    [17] McDonald CM, Henricson EK, Han JJ, et al. The 6-minute walk test in Duchenne/Becker muscular dystrophy: longitudinal observations. Muscle Nerve 2010;42:966-74.

    [18] McDonald CM, Henricson EK, Han JJ, et al. The 6-minute walk test as a new outcome measure in Duchenne muscular dystrophy. Muscle Nerve 2010;41:500-10.

    [19] Vuillerot C, Braillon P, Fontaine-Carbonnel S, et al. Influence of a two-year steroid treatment on body composition as measured by dual X-ray absorptiometry in boys with Duchenne muscular dystrophy. Neuromuscul Disord 2014;24:467-73.

    [20] Vuillerot C, Girardot F, Payan C, et al. Monitoring changes and predicting loss of ambulation in Duchenne muscular dystrophy with the Motor Function Measure. Dev Med Child Neurol 2010;52:60-5.

    [21] Jeannet PY, Aminian K, Bloetzer C, et al. Continuous monitoring and quantification of multiple parameters of daily physical activity in ambulatory Duchenne muscular dystrophy patients. Eur J Paediatr Neurol 2011;15:40-7.

    [22] Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol 2010;9:77-93.

    [23] Bushby K, Finkel R, Birnkrant DJ, et al. Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care. Lancet Neurol 2010;9:177-89.

    [24] Ricotti V, Ridout DA, Scott E, et al. Long-term benefits and adverse effects of intermittent versus daily glucocorticoids in boys with Duchenne muscular dystrophy. J Neurol Neurosurg Psychiatry 2013;84:698-705.

    [25] Ricotti V, Ridout DA, Pane M, et al. The North Star Ambulatory Assessment in Duchenne muscular dystrophy: considerations for the design of clinical trials. J Neurol Neurosurg Psychiatr 2015.

    [26] Beltramo F. L’appareillage des membres inférieurs. Ann Readaptation Med Phys 2001;44:225-8.

    [27] Humbertclaude V, Hamroun D, Bezzou K, et al. Motor and respiratory heterogeneity in Duchenne patients: implication for clinical trials. Eur J Paediatr Neurol 2012;16:149-60.

    [28] Porte M, Patte K, Pélissier J, et al. Dystrophinopathies de l’enfant à l’adulte, coll Problèmes en médecine de rééducation. Elsevier Masson SAS. 2010.

    [29] Shapiro F, Zurakowski D, Bui T, et al. Progression of spinal deformity in wheelchair-dependent patients with Duchenne muscular dystrophy who are not treated with steroids: coronal plane (scoliosis) and sagittal plane (kyphosis, lordosis) deformity. Bone Joint J 2014;96-B:100-5.

    [30] Alexander WM, Smith M, Freeman BJ, et al. The effect of posterior spinal fusion on respiratory function in Duchenne muscular dystrophy. Eur Spine J 2013;22:411-620.

    [31] Van Opstal N, Verlinden C, Myncke J, et al. The effect of LuqueGalveston fusion on curve, respiratory function and quality of life in Duchenne muscular dystrophy. Acta Orthop Belg 2011;77:659-65.

    [32] Takaso M, Nakazawa T, Imura T, et al. Surgical management of severe scoliosis with high risk pulmonary dysfunction in Duchenne muscular dystrophy: patient function, quality of life and satisfaction. Int Orthop 2010;34:695-702.

    [33] Eagle M, Bourke J, Bullock R, et al. Managing Duchenne muscular dystrophy--the additive effect of spinal surgery and home nocturnal ventilation in improving survival. Neuromuscul Disord 2007;17:470-5.

    [34] Marty-Poumarat C, Scattin, L, Marpeau M, et al. Natural history of progressive adult scoliosis. Spine 2007;32:1227-34.

  • Cardiac involvement in dystrophinopathies

    K. Wahbi

    AP-HP, Cochin Hospital, Department of Cardiology, Paris, France Paris Descartes University, Paris, France

    Summary

    Dystrophinopathies may be associated with dilated cardiomyopathy, characterized by an impairment of left ventricular ejection fraction and potentially complicated by heart failure. Conduction disorders and arrhythmia may also be present. The risk of developing cardiomyopathy is extremely high in Duchenne muscular dystrophy, intermediate in Becker dystrophy, and lower in female carriers. Cardiac follow-up is indicated, more frequently the greater the risk, for all cases, and based, in the first line, on electrocardiogram and echocardiograph monitoring. The objective of systematic cardiac follow-up enables diagnosis, as early as possible, of cardiomyopathy and prompt treatment. The first-line treatments continue to be angiotensin converting enzyme inhibitors and other heart failure treatments, which are to be systematically and prophylactically initiated by age of 10 years in Duchenne muscular dystrophy and at the slightest premonitory sign in other dystrophinopathies.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    Toutes les dystrophinopathies peuvent être associées à des cardiomyopathies dilatées, caractérisées par des altérations de la fraction d’éjection ventriculaire gauche et potentiellement compliquées d’insuffisance cardiaque, parfois avec des troubles conductifs et des troubles du rythme. Le risque pour les patients de développer une cardiomyopathie est très élevé dans la myopathie de Duchenne, intermédiaire dans les dystrophies de Becker et plus faible chez les conductrices. Dans tous les cas, un suivi est indiqué, d’autant plus rapproché que le risque est élevé et basé en première intention sur l’électrocardiogramme et l’échographie cardiaque. Ce suivi systématique a pour objectif un diagnostic le plus précoce possible des cardiomyopathies pour traiter rapidement d’éventuelles anomalies. Les traitements de première ligne restent les inhibiteurs de l’enzyme de conversion et les autres thérapeutiques de l’insuffisance cardiaque, à débuter systématiquement à titre préventif dans la myopathie de Duchenne au plus tard à l’âge de 10 ans, et au moindre signe d’alerte dans les autres dystrophinopathies.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    Cardiac involvement in dystrophinopathies constitutes a vast subject. I have therefore decided to focus this article on the information enabling clinicians to orient daily management. While considerable pertinent literature is available, comprehensive responses to numerous crucial questions have yet to be formulated, largely due to methodological considerations (inadequate populations, nonpertinent cardiological assessment endpoints, poorly implemented statistical analyses).

    2. The continuum of dystrinopathyassociated cardiomyopathies

    There is a common cardiological pattern in all dystrophinopathies, despite the differences in prevalence, penetrance, age of onset and severity. The impairment of contractile function predominates with a gradual reduction in cardiac systolic function with a decrease in left ventricle ejection fraction (LVEF) and emergence of myocardial fibrosis. Usually the phenomena predominate at the level of the inferior and lateral walls of the left ventricle. The systolic dysfunction may be accompanied by heart failure, which usually occurs at a late stage as in Duchenne myopathy, with rapid progression toward end stage heart failure, which constitutes one of the principal causes of death. Cardiac electrical impairment, characterized by conduction disorders and, sometimes, rhythm disorders, which are usually ventricular, also coexists relatively frequently but has less clinical impact.

    3. Genotype – phenotype correlations

    3.1. Duchenne vs. the other dystrophinopathies

    Mutations with a reading frame shift are associated with a cardiac phenotype that is, overall, more severe than that of the mutations with no frame shift. However, that statement is only valid on a population scale since some Becker patients with very moderate muscle impairment may experience more severe and earlier onset cardiomyopathy than some Duchenne patients.

    3.2. Mutations with harmful cardiac effects vs. supposed protectors

    The issue of cardiac genotype –  phenotype (G-P) correlations has yet to be fully elucidated. Table I shows the absence of homogeneity of the G-P studies and even their contradictory results [1-7]. In addition to the influence of the genetic background and environmental factors that may predominate over the mutation itself, the discordances may simply be explained by the absence of a study which is sufficiently robust, includes a sufficiently large population, and provides for reliable cardiac phenotype characterization, pertinent cardiac endpoints (LVEF, cardiac death), a pertinent classification of the mutations, and inclusion of other factors liable to influence the comparisons (age, medications). At present it is not justified to orient the cardiac treatment strategy in the context of dystrophinopathies on the basis of the type of mutation.

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    3.3. X linked cardiomyopathies

    This special case is most frequently related to mutations of the DMD gene, with no other muscle manifestation than CK elevation, and usually involving the 5’ extremity of the gene, mainly exon 1, with compensatory expression of other isoforms (brain, Purkinje) only in skeletal muscle [8].

    4. Duchenne myopathy

    4.1. Natural history

    The history is relatively stereotyped and characterized by an increasing incidence of cardiomyopathies from age of 10 years with a gradual reduction in LVEF. Before age of 10 years dysfunctions are present in less than 5% of cases; after age of 18 years they are present in over 70% of cases. Before emergence of systolic dysfunction, the majority of patients present with ECG anomalies: inferior and lateral Q waves; large right precordial R waves; sometimes a short PR interval; and in most cases sinus tachycardia (fig.  1). End stage heart failure and respiratory insufficiency are the main causes of death (20 to 40%). The degradation of cardiac function is usually progressive but subacute progression is not rare, raising the issue of the influence of environmental factors, particularly viral infection.

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    Figure 1. Electrocardiogram of a patient with Duchenne myopathy: short PR interval, large right precordial R waves and inferior and lateral Q waves

    4.2. Diagnosis and follow-up strategy

    The most useful examinations in the context of standard care are ECG and echocardiography, which enable rapid and reliable identification of systolic function abnormalities, in particular by determination of LVEF, which constitutes the most powerful prognostic factor. The examinations are recommended at least every two years before age of 10 years and annually after that age. Holter ECG recording is also recommended in the event of palpitations, anomalies of systolic function or conduction disorders evidenced by ECG. Currently ventricular hyperexcitability is probably greatly underestimated although it may have a harmful effect in certain patients if it is marked. Thus, our team systematically records a Holter ECG every 2 years after age of 10 years.

    Further investigations are prescribed with a view to refining the characterization of the cardiac involvement or for patients who become sonolucent. Other ultrasound methods (Speckle tracking echocardiography, tissue Doppler ultrasound) enable detection of impairment of myocardial contractility while the LVEF is still normal. Cardiac MRI enables enhanced evaluation of myocardial contractility and investigation for myocardial fibrosis, which is of potential independent diagnostic value. Study of the contractile reserve obtained by determining LVEF (echocardiography or gamma-angiography) during dobutamine infusion enables diagnosis of early anomalies of contractile function associated with emergence of patent dysfunction in the medium term.

    Practically speaking, in the context of standard care, the combination of ECG and echocardiography with or without Holter ECG recording appears to be optimal. Other instruments will no doubt find a role in coming years with a view to elucidating the cardiac effects of certain treatments, as interim assessment criteria, and as therapeutic tools interfaced with the current diagnostic platform.

    4.3. Treatment

    There are two prescription contexts: preventive indications in patients whose left ventricular function is still maintained and curative indications in the event of potentially symptomatic LVEF impairment. In the first case, the aim is to maintain, for as long as possible, cardiac function, which is destined to decline, almost inexorably. In the second case, the aim is to deploy strategies that have been validated in cardiology and are not specific to dystrophinopathies. Herein, we will only address the preventive treatments, whose prescription is considered on a daily basis, without considering the numerous other treatments under study or having generated positive or negative preliminary results (idebenone, exon skipping, etc.).

    4.3.1. Angiotensin converting enzyme (ACE) inhibitors

    ACE inhibitor therapy is the only treatment whose efficacy has been validated in a randomized clinical trial. ACE inhibitor therapy in patients aged about 10 years with maintained cardiac function (LVEF > 55%) was associated with a lower risk of developing dilated cardiomyopathy in 5 years and an improvement in vital prognosis at 10 years, with prevention of severe heart failure [9,10]. ACE inhibitor treatment is systematically recommended from age of 10 years and many centers initiate therapy earlier. The optimum age for initiation is not known.

    4.3.2. Other treatments for heart failure

    A possible beneficial effect of eplerenone (anti-mineralocorticoid) in primary prevention was suggested in a recently published study [11], with many limitations, but based on a strong rationale and interesting preliminary data from animal studies. The treatment will very probably become a first line treatment if the beneficial effect is confirmed in other studies and providing that the safety data (hyperkalemia) are reassuring. Two studies of beta-blockers (BB) are currently being conducted (the NEBIDYS study, ACE inhibitor + BB combination vs. ACE inhibitor + placebo, inclusions ongoing) in France and Germany. Prescription, which remains empirical, may be proposed for patients with palpitations in a context of sinus tachycardia or in the event of ventricular extrasystoles.

    4.3.3. Corticosteroids

    The cardiological protective effect of corticosteroids remains controversial. The results of the various retrospective studies conducted by a number of teams are relatively concordant and show a significant association between steroids and enhanced cardiac function during follow-up and/or lower long term cardiac morbidity and mortality [12]. However, the results are to be interpreted with caution in light of the often weak methodologies of the clinical trials and a certain number of animal studies, particularly in the mdx mouse that suggest more severe cardiac involvement on steroids, with increased myocardial fibrosis.

    5. Becker myopathy

    5.1. Natural history

    In Becker myopathy, the issues are substantially different to those in Duchenne myopathy because cardiac involvement is less prevalent and often of later onset even though it constitutes the leading cause of disease related premature death. The prevalence of dilated cardiomyopathy is between 30 and 40%. Penetrance is age related (15% before 20 years, 54% after 40 years) [13]. Less than 5% of patients develop severe conduction disorders requiring pacemaker implantation.

    5.2. Diagnosis and follow-up strategy

    ECG and echocardiography are necessary at the time of diagnosis. The frequency of follow-up examinations depends on patient age, the results of the initial assessment, and the time since the initial diagnosis: at least every 2 years.

    5.3. Treatment

    The management of patients with dilated cardiomyopathy (LVEF<45%) is the same as that for any other patient at risk of heart failure. In the event of LVEF > 50-55%, institution of systematic preventive treatment is not indicated. When LVEF is between 45 and 50-55 %, the question of treatment arises. While treatment is not usually validated by the cardiological community, it is nonetheless to be considered given that many Becker patients will ultimately die of heart failure and that ACE inhibitors have a good safety profile.

    6. Situation of carrier females

    Dilated cardiomyopathy is present in 5 to 10% of women carrying a dystrophin gene mutation [14,15]. From a public health perspective, a Scottish study has shown that the life expectancy of female carriers is not significantly different from that of the overall population [16]. However, a small number of patients develop very severe cardiac dysfunction and heart failure, which may necessitate heart transplant. The usual recommendation is diagnostic ECG and echocardiography followed by repetition of those examinations every 5 years. Our team employs that schedule but it is difficult to apply in practice since the majority of carriers are lost from followup after the initial assessment.

    7. Conclusion

    Cardiomyopathy may be associated with all the types of dystrophinopathy and, like muscle impairment, constitutes an integral component of those diseases. In all cases, close monitoring is indicated to enable diagnosis as early as possible in order to rapidly initiate or intensify effective treatment; The first line treatments are those for heart failure, which are to be systematically initiated as prophylaxis in Duchenne muscular dystrophy and in the event of the slightest alert in more benign forms.

    Statement of interests

    Over the last 5 years, Karim Wahbi has received fees and financing from PTC Therapeutics for participation in congresses and communications and participation in expert groups.

    References

    [1] Ashwath ML, Jacobs IB, Crowe CA, et al. Left ventricular dysfunction in duchenne muscular dystrophy and genotype. Am J Cardiol 2014;114:284-9.

    [2] Saito M, Kawai H, Akaike M, et al. Cardiac dysfunction with Becker muscular dystrophy. Am Heart J 1996;132:642-7.

    [3] Magri F, Govoni A, D’Angelo MG, et al. Genotype and phenotype characterization in a large dystrophinopathic cohort with extended follow-up. J Neurol 2011;258:1610-23.

    4] Nigro G, Politano L, Nigro V, et al. Mutation of dystrophin gene and cardiomyopathy. Neuromuscul Disord. 1994;4:371-9.

    [5] Melacini P, Fanin M, Danieli GA, et al. Cardiac involvement in Becker muscular dystrophy. J Am Coll Cardiol 1993;22:1927-34.

    [6] Jefferies JL, Eidem BW, Belmont JW, et al. Genetic predictors and remodeling of dilated cardiomyopathy in muscular dystrophy. Circulation 2005;112:2799-804.

    [7] Kaspar RW, Allen HD, Ray WC, et al. Analysis of dystrophin deletion mutations predicts age of cardiomyopathy onset in becker muscular dystrophy. Circ Cardiovasc Genet 2009;2:544-51.

    [8] Muntoni F, Torelli S, Ferlini A. Dystrophin and mutations: one gene, several proteins, multiple phenotypes. Lancet Neurol 2003;2:731-40.

    [9] Duboc D, Meune C, Pierre B, et al. Perindopril preventive treatment on mortality in Duchenne muscular dystrophy: 10 years’follow-up. Am Heart J 2007;154:596-602.

    [10] Duboc D, Meune C, Lerebours G, et al. Effect of perindopril on the onset and progression of left ventricular dysfunction in Duchenne muscular dystrophy. J Am Coll Cardiol 2005;45:855-7.

    [11] Raman SV, Hor KN, Mazur W, et al. Eplerenone for early cardiomyopathy in Duchenne muscular dystrophy: a randomised, doubleblind, placebo-controlled trial. Lancet Neurol 2015;14:153-61.

    [12] Schram G, Fournier A, Leduc H, et al. All-cause mortality and cardiovascular outcomes with prophylactic steroid therapy in Duchenne muscular dystrophy. J Am Coll Cardiol 2013;61:948-54.

    [13] Nigro G, Comi LI, Politano L, et al. Evaluation of the cardiomyopathy in Becker muscular dystrophy. Muscle Nerve 1995;18:283- 91.

    [14] Hoogerwaard EM, Bakker E, Ippel PF, et al. Signs and symptoms of Duchenne muscular dystrophy and Becker muscular dystrophy among carriers in The Netherlands: a cohort study. Lancet 1999;353:2116-9.

    [15] Politano L, Nigro V, Nigro G, et al. Development of cardiomyopathy in female carriers of Duchenne and Becker muscular dystrophies. JAMA 1996;275:1335-8.

    [16] Holloway SM, Wilcox DE, Wilcox A, et al. Life expectancy and death from cardiomyopathy amongst carriers of Duchenne and Becker muscular dystrophy in Scotland. Heart 2008;94:633-6.

  • Specific features of Becker Muscular Dystrophy patients and female carriers

    A. Magot*, S. Mercier, Y. Péréon

    Centre de Référence des Maladies Neuromusculaires Nantes-Angers, Hôtel-Dieu, Nantes

    Summary

    Becker muscular dystrophy (BMD) was first described in 1955 and linked to the dystrophin gene in 1987. In contrast to Duchenne muscular dystrophy (DMD), the clinical onset of BMD usually occurs after the age of 12 years and a wheelchair is required after the age of 16 years. In males BMD is characterized by generalized weakness first affecting the limb girdle muscles, hypertrophy of the calves and cardiomyopathy. Some patients have only mild symptoms throughout their lives such as cramps or isolated elevated serum creatine kinase (CK). CK levels are usually greatly increased. Muscle biopsy shows a dystrophic pattern with abnormal dystrophin immunolabeling. Diagnosis is confirmed by DMD gene sequencing. Deletions or duplications of one or several exons are identified in the majority of cases. Care is multidisciplinary, combining neurology, physical medicine and rehabilitation, respiratory medicine and cardiology, with a particular focus on cardiomyopathy, which is responsible for death in the majority of cases but responds to appropriate treatment. Like BMD, isolated X-linked cardiomyopathies are also related to DMD gene mutations. Some female carriers of dystrinopathies (DMD or BMD) may develop, in an inconsistent manner, muscle involvement, which is generally markedly milder and of later onset than in males. Cardiomyopathy is nonetheless the most frequent impairment and should be closely monitored. Genetic counseling should be systematically proposed.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    La dystrophie musculaire de Becker (DMB) a été décrite pour la première fois en 1955 et sa liaison au gène de la dystrophine date de 1987. Elle se différencie de la dystrophie musculaire de Duchenne (DMD) par une atteinte clinique débutant après l’âge de 12 ans et une dépendance au fauteuil après l’âge de 16 ans. Chez un sujet masculin, elle associe typiquement un déficit des ceintures, une hypertrophie des mollets et une cardiomyopathie. Certains patients peuvent rester pauci-symptomatiques tout au long de leur vie, présentant seulement des crampes ou une augmentation isolée de la créatine kinase (CK). Le taux de CK est généralement très augmenté. La biopsie musculaire montre un aspect dystrophique avec un immunomarquage anormal de la dystrophine. L’étude moléculaire du gène DMD confirme le diagnostic et identifie le plus souvent une délétion ou une duplication d’un ou plusieurs exons. La prise en charge de la maladie est multidisciplinaire, neurologique, par la MPR (médecine physique et de réadaptation), respiratoire et cardiologique avec une attitude attentive vis-à-vis de la cardiomyopathie, responsable du décès dans la majorité des cas mais qui peut bénéficier d’un traitement adapté. On rapproche des DMB, les cardiomyopathies isolées liées à l’X qui sont dues également à des mutations dans le gène DMD.

    Les femmes conductrices d’une dystrophinopathie (DMD ou DMB) peuvent développer de manière inconstante une atteinte musculaire, généralement beaucoup plus modérée et plus tardive que chez l’homme. L’atteinte la plus fréquente demeure néanmoins la cardiomyopathie qu’il faudra là aussi surveiller. Un conseil génétique doit être systématiquement proposé.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Becker muscular dystrophy

    1.1. Background

    In 1955, Becker and Keiner [1] reported a new X chromosome linked muscular dystrophy. The cases occurred in two German families and presented as muscle impairment similar to Duchenne muscular dystrophy but with a slower course. The clinical similarities between the two diseases led the authors two suggest a common genetic etiology. This was confirmed in 1987 with the discovery of the DMD gene that gives rise to Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) [2] and identification of the protein involved, dystrophin [3].

    1.2. Epidemiology

    Becker muscular dystrophy (BMD) is a rare disease. Accurate prevalence data are not available. The incidence reported in the north of England was 1/18,450 live male births [4]. The occurrence of mild and even asymptomatic forms may in part explain the difference in incidence, which is seven times lower than that of DMD. Fifty percent of BMD cases are familial (vs. 38.5% for DMD).

    1.3. Clinical characteristics

    Dystrophinopathies constitute a broad spectrum of muscle diseases ranging from mild to severe. The mildest phenotypes consist in asymptomatic forms with CK elevation, muscle cramps and myoglobinuria. The most severe forms consist in DMD and BMD, in which skeletal muscle is affected, and DMD gene linked cardiomyopathy in which the heart is primarily affected. DMD and BMD may be distinguished by the age of onset of wheelchair dependence: before 13 years for DMD and after 16 years for BMD with an intermediate group between 13 and 16 years. It is now known that certain BMD patients with disease onset after age of 30 years may remain ambulatory up to age of 60 years [5]. There are also BMD cases who only present with mild symptoms: CK elevation; myalgia; hypertrophy of the calves; cramps; with no patent motor deficit [6]. There is generally no cardiac involvement at the early stage of the disease but sinus tachycardia and ECG abnormalities may be detected. Ninety percent of patients present with clinical or subclinical cardiac involvement. The classic presentation is dilated cardiomyopathy (DCM) with early right ventricle involvement, and subsequently left ventricle involvement. DCM is the principal complication in patients with few symptoms or minor form BMD: myocardial involvement may emerge in such patients in the event of excessive exertion in a context of an unhealthy heart and induce mechanical stress that is toxic for dystrophin deficient cells [7]. Cardiac involvement is responsible for 50% of the mortality of BMD patients [8]. The heart transplant rate is high in the first five years following DCM diagnosis [9]. The mean age of death is 45 years.

    1.4. Particular cases of X-linked cardiomyopathy

    A variant of BMD, for which a link with the DMD gene has been demonstrated, has been reported for males who presented with DCM in their 2nd or 3rd decade, with rapid progression and ventricular rhythm disorders, and for females in their 4th decade, with a slower course. The only abnormality observed was CK elevation [10]. Subsequent studies have shown that in subjects with the most severe cardiological phenotype, skeletal muscle produced detectable dystrophin [11,12].

    1.5. Clinical diagnosis

    Familial history may be suggestive: transmission is X-linked and recessive. Muscle involvement in BMD has a similar distribution to that in DMD but the progression is slower and the course less severe. Disease onset is usually at about age of 12 years but may occur much later in life. There is progressive loss of the strength of the muscles of the limbs and trunk. Initially, only the leg muscles are affected, in a symmetrical manner, and walking becomes tiring. Then, in a variable timeframe, motor difficulties emerge inducing difficulty standing up from a squat or walking uphill. The gait may be digitigrade and waddling gradually emerges. Finally, the ability to walk independently is lost. During progression, flexor tendon retraction may be observed. Hypertrophy of the calves is common and appears to be related to muscle hypertrophy rather than fat infiltration [13]. Attention has recently been drawn to the predominance of the quadriceps, hip flexors and biceps, while hypertrophy of the wrist extensors may also develop [14]. Cramps are frequent, particularly after physical exertion. The underlying mechanism in BMD patients has yet to be elucidated. The cramps are thought to be related to physical exercise: patients with a lesser degree of muscle involvement experience more cramps due to maintenance of greater physical activity than that of patients with severe BMD. Some female carriers may present with muscle weakness or hypertrophy of the calves associated with chronic CK elevation. Isolated dilated myocardiopathy occurs in about 7% of cases [15].

    Pseudometabolic presentations have occasionally been reported: severe cramps, exercise intolerance, recurrent myoglobinuria and even fatal rhabdomyolysis during general anesthesia may be the only manifestations of BMD [16,17].

    As is the case for DMD, a certain degree of cognitive impairment may be present and is most often related to a genetic abnormality pertaining to isoforms Dp140 and Dp71 [18], expressed in the central nervous system. In addition to learning difficulties, some patients may present with autistic spectrum disorders or an attention deficit hyperactivity disorder.

    1.6. Differential diagnosis

    The group of limb girdle muscular dystrophies (LGMD) comprises over 30 diseases whose presentation may be similar to that of the dystrophinopathies, but which occur in both genders with a dominant or recessive inheritance mode. LGMD generally result from a deficiency in one of the proteins of the dystrophin associated complex. Screening for LGMD is to be conducted for patients whose biopsy specimens do not show dystrophin deficiency. Among such patients, those carrying mutations of the FKRP gene may present with hypertrophy of the calves and macroglossia [19].

    1.7. Paraclinical investigations

    CK is generally greatly elevated to over 1000 IU/L but some patients with benign forms may have lower values [20]. Needle electrode electromyography (EMG) is typically myogenic during contraction and activity such as fibrillation and slow denervation potentials may even persist at rest. Muscle MRI evidences predominant impairment of the teres major, long head of the triceps, biceps of the arm, greatest and middle gluteus, vastus, long and great abductor, semitendinous, semimembranous and femoral biceps muscle [21]. Muscle biopsy remains of value for BDM diagnosis and is conducted in the event of a negative result for the molecular study of the DMD gene. Biopsy evidences non-specific dystrophic abnormalities including variations in fiber size, necrosis – regeneration phenomena, hyalinization, and, later, fat and connective tissue infiltration. Immunolabeling of dystrophin is generally reduced, but may be normal. Diagnosis is then to be confirmed or ruled out by Western Blot which may evidence dystrophin bands whose quantity is abnormal or whose size is decreased [20].

    1.8. Molecular biology

    BMD is related to abnormalities of the DMD gene, which result in partial deficiency of the protein dystrophin or production of dystrophin of abnormal size. The DMD gene is the only gene known to be responsible for DMD, BMD and X-linked dilated cardiomyopathy. Penetrance is complete in males. The daughters of BMD fathers are obligatorily disease carriers. They are to receive appropriate medical follow-up and genetic counseling on the risk of transmission to their offspring: 50% risk of having a son with BMD; 50% risk of having a BMD carrying daughter. Prenatal or preimplantation diagnosis is to be considered as a function of disease severity and the family’s experience.

    BMD patients more frequently have deletions of one or several exons [81% versus 61% for DMD patients); exon duplications are present in 6% of cases; point mutations (deletion, duplication or insertion of a few nucleotide base pairs) are present in 13% of cases [22]. Generally, the deletions or duplications comply with the gene reading frame and are said to be in phase. The point mutations are not truncating. In consequence, dystrophin synthesis is possible even though the quantity and/or size of the protein are abnormal. Only 7% of BMD patients have out of phase duplications or nonsense (frame shift) mutations giving rise to a shift of the reading frame. In some patients, there is a phenomenon of correction of the genetic abnormality by physiological exon skipping [22].

    In a male with a compatible phenotype, and CK elevation to >1000 IU/L, it is appropriate, initially, to conduct a molecular study of the DMD gene to confirm the diagnosis. Currently, a Multiple Ligationdependent Probe Amplification (MLPA) study is conducted to investigate for an exon deletion or duplication. If the result is negative, muscle biopsy, immunohistochemistry and Western blot study of dystrophin are recommended. High throughput sequencing enables study of the entire DMD gene. Investigation for remodeling (deletions or duplications) and point mutations is conducted on leukocyte DNA. The development of these technologies (particularly the study of panels of the genes involved in muscular dystrophies, or, more broadly, myopathies) may obviate the need for diagnostic muscle biopsy.

    1.9. Genotype – phenotype correlations

    When a dystrophinopathy has been diagnosed using molecular biology it may sometimes be difficult to distinguish between DMD and BMD. In dystrophinopathies, the best correlation with the phenotype is with the degree of dystrophin expression, which is largely determined by the compliance or non-compliance with the reading frame [23]. This rule holds true for about 96% of DMD patients and 93% of BMD patients [24]. It is therefore essential to warn the patient that the rule does not always hold true. Deletions in the N terminal domain and in the proximal part, at exon 45, of the central rod domain of dystrophin are associated with earlier disease onset [25]. Deletions of exons 3 to 7 have also been reported with BMD and DMD phenotypes [26]. The most benign forms of BMD have been reported for deletions of only the first part of the rod domain. In general, the degree of dystrophin expression is positively correlated with clinical benignity [27]. The role of variations in the expression of the other associated proteins remains a matter of debate [28]. Study of the structure of the dystrophin deriving from different deletions of the DMD gene is instructive with regard to explaining the clinical heterogeneity observed in patients. Thus, certain mutations (deletions 45-48 and 45-51] are associated with later loss of walking or emergence of dilated cardiomyopathy than others (deletions 45-47 and 45-49] [29].

    1.10. Surveillance and management of complications

    The disease is chronic and progressive, necessitating regular, ideally multidisciplinary, follow-up throughout the patient’s life. Follow-up enables enhanced quality of life and longer survival [30-32]. The physical medicine, rehabilitation and respiratory follow-up are not specific and are similar to those recommended for DMD patients [33,34]. Cognitive assessment is of value in the event of difficulties at school with a view to scholastic adaptation if necessary. The cardiomyopathy is to be evaluated by electrocardiogram and echocardiography [32,34] as of diagnosis and then at least every two years. Cardiac MRI may be prescribed for earlier detection of dilated cardiomyopathy. Cardiac and pulmonary evaluation is to be conducted before any surgical procedure [33].

    1.11. Therapy

    The principal treatment to be considered is that for the cardiomyopathy. It is not specific and based on angiotensin converting enzyme (ACE) inhibitors and beta blockers, which are conventionally instituted when the LVEF is less than 55%. In the event of terminal heart failure, heart transplant is to be considered for patients with little or no muscle impairment: myopathy does not obligatorily contra-indicate transplant. Unlike DMD, in BMD there is insufficient evidence for the prescription of corticosteroids [35]. Recent phase 1 and 2 studies on a myostatin antagonist have generated encouraging results [36]. However, a double blind controlled study of sildenafil failed to show efficacy with regard to cardiac function in BMD patients and the phase 3 study was discontinued [37].

    Although avoidance of succinylcholine analgesia and halogen anesthetics is recommended, an extensive literature search did not evidence an increased risk of malignant hyperthermia relative to the general population. Lastly, botulinum toxin injections are to be avoided.

    2. Special features of female DMD carriers

    According to the studies, up to 19% of female DMD carriers regularly present with myalgia and cramps, without muscle weakness; 17% report a minimal to moderate deficit; 8% present with dilated cardiomyopathy with a mean age of onset of 33 years [38]. In rare cases, female carriers may have a classic DMD phenotype [39-40]. CK elevation is constant in symptomatic female characters [41,42]. In females, penetrance is thus variable and the principal hypothesis to explain this is preferential inactivation of the X  chromosome not carrying the mutation [41]. Certain studies have not, however, shown any clear correlations between leukocyte X  chromosome inactivation profile and CK level, clinical signs or the number of dystrophin negative fibers evidenced by muscle biopsy [42]. However, over 90% of heterozygous females with X  inactivation bias develop a mild, moderate or severe phenotype of muscular dystrophy [43]. In the three largest series of female carriers, the proportion of symptomatic women was between 5 and 22% [38,42,44]. The cases of childhood onset are rare. In a study of childhood onset cases [39], muscle weakness was present in 88%. Exercise intolerance was often the first sign (27%) and sometimes remained isolated. The course could also be negative, toward authentic DMD with loss of the ability to walk during adolescence, or toward BMD, with, in addition, cardiac involvement after age of 30 years in a quarter of the patients. Significant cognitive impairment was present in 27% of the cases, and almost always associated with a genetic abnormality involving Dp140 or Dp71.

    Muscle biopsy seems indispensable in pseudometabolic forms with exercise intolerance. In general female carriers present with mosaic expression of dystrophin as evidenced by immunohistochemistry. The mosaic probably reflects the formation of polynuclear muscle fibers from mononuclear myoblasts with varying dystrophin expressions resulting from different X inactivations. According to studies, the proportion of immunohistochemical abnormalities ranges from 10 to 100% depending on whether or not the patients are symptomatic [38,39]. Western blotting also contributes to diagnosis in patients whose immunohistochemistry is less suggestive.

    With regard to genetics, symptomatic women carry the same genetic abnormalities as DMD patients, namely a majority of deletions or duplications [39,40]. Investigation for X inactivation bias has been conducted in various studies, but the results vary between publications. Most of the studies were conducted on cohorts of symptomatic carriers but who were mainly asymptomatic [45]. In the symptomatic carrier cohorts, X inactivation bias was observed with preferential expression of the mutant allele of the DMD gene rather than the healthy allele [35,60,63]. The phenotype is particularly severe in female carriers with complete inactivation bias. Other modifying factors are probably involved [42].

    The US recommendations [32] call for warning female carriers of the risk of developing cardiomyopathy; cardiological follow-up is to begin as of the end of adolescence and be pursued every five years. Treatment is the same as for DMD or BDM patients. Specific cardiological evaluation before becoming pregnant is recommended. The prevalence of dilated cardiomyopathy in carrier females increases with age: from 15% before age of 16 years to 45% after age of 16  years [45,46]. Sports may reveal left systolic dysfunction. The seriousness of the cardiomyopathy may necessitate heart transplant for certain patients [47]. Appropriate management and special needs education may be offered in the event of learning difficulties.

    Statement of interests

    Over the last 5 years, Armelle Magot has been an investigator in clinical trials sponsored by the pharmaceutical companies: PTC Therapeutics, Lilly and GSK; Sandra Mercier has been a co-investigator in clinical trials sponsored by the pharmaceutical companies: PTC Therapeutics, Lilly, GSK and Généthon; Yann Péréon has received fees for participation in expert groups from PTC Therapeutics and has been an investigator in clinical trials sponsored by the pharmaceutical companies: PTC Therapeutics, Lilly and GSK.

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    [16] Bush A, Dubowitz V. Fatal rhabdomyolysis complicating general anaesthesia in a child with Becker muscular dystrophy. Neuromuscul Disord 1991;1:201-4.

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    [18] Daoud F, Angeard N, Demerre B, et al. Analysis of Dp71 contribution in the severity of mental retardation through comparison of Duchenne and Becker patients differing by mutation consequences on Dp71 expression. Hum Mol Genet 2009;18:3779-94.

    [19] Schwartz M, Hertz JM, Sveen ml, et al. LGMD2I presenting with a characteristic Duchenne or Becker muscular dystrophy phenotype. Neurology 2005;64:1635-7.

    [20] SJ, Kim WJ, Kim SM, et al. Clinical, immunohistochemical, Western blot, and genetic analysis in dystrophinopathy. J Clin Neurosci 2013;20:1099-105.

    [21] Tasca G, Iannaccone E, Monforte M, et al. Muscle MRI in Becker muscular dystrophy. Neuromuscul Disord 2012;22:100-6.

    [22] Juan-Mateu J, Gonzalez-Quereda L, Rodriguez MJ, et al. DMD Mutations in 576 Dystrophinopathy families: a step forward in genotype-phenotype correlations. PLoS One 2015;10:e0135189.

    [23] Koenig M, Beggs AH, Moyer M, et al. The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion. Am J Hum Genet 1989;45:498-506.

    [24] Tuffery-Giraud S, Béroud C, Leturcq F, et al. Genotype-phenotype analysis in 2,405 patients with a dystrophinopathy using the UMD-DMD database: a model of nationwide knowledgebase. Hum Mutat 2009;30:934-45.

    [25] Magri F, Govoni A, D’Angelo mg, et al. Genotype and phenotype characterization in a large dystrophinopathic cohort with extended follow-up. J Neurol 2011;258:1610-23.

    [26] Aartsma-Rus A, Van Deutekom JCT, Fokkema IFet al. Entries in the Leiden Duchenne muscular dystrophy mutation database: An overview of mutation types and paradoxical cases that confirm the reading-frame rule. Muscle and Nerve 2006;34:135-44.

    [27] Anthony K, Cirak S, Torelli S, et al. Dystrophin quantification and clinical correlations in Becker muscular dystrophy: implications for clinical trials. Brain 2011;134:3547-59.

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    [29] Nicolas A, Raguénès-Nicol C, Ben Yaou R, et al. Becker muscular dystrophy severity is linked to the structure of dystrophin. Hum Mol Genet 2015;1:1267-79.

    [30] Jefferies JL. Genetic Predictors and Remodeling of Dilated Cardiomyopathy in Muscular Dystrophy. Circulation 2005;112:2799- 804.

    [31] Viollet L,Thrush PT, Flanigan KM, et al. Effects of angiotensinconverting enzyme inhibitors and/or beta blockers on the cardiomyopathy in Duchenne muscular dystrophy. Am J Cardio 2012;110:98-102.

    [32] American Academy of Pediatrics Section on Cardiology and Cardiac Surgery. Cardiovascular health supervision for individuals affected by Duchenne or Becker muscular dystrophy. Pediatrics 2005;116:1569-73.

    [33] Finder JD. A 2009 perspective on the 2004 American Thoracic Society statement, “respiratory care of the patient with Duchenne muscular dystrophy”. Pediatrics 2009;123:S239-41.

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    [35] Rahbek J, Steffensen BF, Bushby K, et al. 206th ENMC International Workshop: Care for a novel group of patients – adults with Duchenne muscular dystrophy Naarden, The Netherlands, 23-25 May 2014. Neuromuscul Disord 2015;25:727-38.

    [36] Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy. Mol Ther 2015;23:192-201.

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    [39] Mercier S, Toutain A, Toussaint A, et al. Genetic and clinical specificity of 26 symptomatic carriers for dystrophinopathies at pediatric age. Eur J Hum Genet 2013;21:855-63.

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  • Diagnosis and natural history of Duchenne muscular dystrophy

    I. Desguerrea, *, V. Laugelb

    aCentre de référence Maladies neuromusculaires GNMH, Filière FILNEMUS, Hôpital Necker Enfants Malades, 149 rue de Sèvres, 75015 Paris, France 
    bUnité de neuropédiatrie, CHU Strasbourg, France

    Summary

    Duchenne myopathy is currently the most frequently encountered progressive muscular dystrophy in children, with an inexorable, progressive course to death in the third decade. The improvement in survival is related to the improvement in orthopedic management, and early screening for cardiac and respiratory complications, but no curative therapy is available today outside of recent pharmacogenetic advances. The diagnosis is to be considered in the event of evidence of proximal muscular deficiency after an interval free from symptoms lasting from one to several years. The mechanism of muscular dystrophy is suggested by a significant increase in creatine kinase (CK) and confirmed by muscle biopsy. The motor and cognitive clinical heterogeneity of the disease and its natural history need to be elucidated because that heterogeneity will condition future clinical trials. Identification of outcome measures such as the 6-minute walking test, MFM score, manual muscle testing, and biomarkers are indispensable for patient follow-up and collaborative studies.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    La myopathie de Duchenne est à ce jour la dystrophie musculaire progressive la plus fréquente chez l’enfant avec une évolution inexorable, progressive conduisant au décès dans la troisième décennie. L’amélioration de la survie est liée à l’amélioration de la prise en charge orthopédique, au dépistage précoce des complications cardiaques et respiratoires mais aucune thérapeutique curative n’est applicable à ce jour en dehors des pistes pharmacogénétiques récentes. Ce diagnostic est évoqué devant un déficit musculaire progressif proximal débutant après un intervalle libre de une à plusieurs années. Le mécanisme de dystrophie musculaire est évoqué devant une augmentation significative des CK (créatine kinase) et confirmé par la biopsie musculaire. L’hétérogénéité clinique motrice et cognitive de cette pathologie et son histoire naturelle nécessite d’être bien connue car elle conditionne les essais thérapeutiques à venir. L’identification d’« outcome measures » comme le score de 6 min de marche, le score MFM, le testing musculaire manuel ou de biomarqueurs est indispensable pour le suivi des patients et les études collaboratives.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction: Duchenne myopathy

    Duchenne myopathy is currently the most common progressive muscle dystrophy in children, with an inexorable progressive course culminating in death in the third decade [1]. The improvement in survival is related to enhanced orthopedic management and early screening for cardiac and respiratory complications; but no curative therapy is currently available. In the Lancet, in 1851, Edward Meryon reported on the cases of 9 boys from three different families who presented with progressive muscle weakness. In 1868, in the Archives Générales de Médecine, Duchenne described a new form of muscle disease on the basis of a personal series of 13 boys who developed progressive muscle weakness during childhood, initially with a pseudo hypertrophic presentation and died due to respiratory failure at the age of about 15 years. For a century, the description remained clinical, with the discovery of elevation of serum creatine kinase, confirmation of X-linked transmission and a more accurate description of the pathological neurological lesions by Bell [2] (figs. 1 and 2). The location and discovery of the gene, and then the protein dystrophin and its structure, and then the glycocosarcolemmic complex, of which dystrophin is a component, were to enable partial elucidation of the molecular and cellular mechanisms underlying the muscular dystrophy and formulation of therapeutic strategies The incidence of Duchenne muscular dystrophy was estimated to be 1/3500 male births in Wales [1]. Those data are supported by the Leyden database, which shows a prevalence of 23.7/100,000 male births (1/4213) [3]. The incidence of dystrophin gene mutations is of the order of 1/10,000. The prevalence of female dystrophinopathy carriers (Becker and Duchenne) is estimated to be 40/100,000.

    The descriptions of clinical progression in a few large series of cases confirms the broad clinical characteristics of DMD. The neonatal vital signs are normal, as is initial growth (weight and height), although a small number of DMD patients are small for their age as of 2 years. The initial symptoms reported by the parents are psychomotor retardation, difficulty running and climbing stairs, and frequent falls. In a series of 283 DMD cases followed up for 2 to 10 years clinical heterogeneity was undeniable in terms of muscle strength, but also in terms of cardiac and respiratory function [3]. Overall, the children in the series lost the ability to walk after age of 8 years, with something of a plateau between 3 and 6 years, but a degree of heterogeneity in disease progression was confirmed. It is to be noted that the studies were conducted before discovery of the gene and protein, and that the diagnoses were clinical and probably included patients with a little residual dystrophin and thus with an intermediate form of the disease.

    The Leyden database series included 473 cases of DMD born between 1961 and 1982. The patients were divided into 2 groups, G1 (1961-1974) for which the diagnosis was clinical only, and G2 (1975-1982) for which the diagnosis was genetic. Diagnosis was earlier for children with overall psychomotor retardation, reflecting cognitive impairment (4.6 vs. 5.8 years). The principal symptoms leading to diagnosis were motor retardation (31.7%), frequent falls (8.7 %), late acquisition of walking (6.8%), psychomotor retardation (5.7 %), difficulty climbing stairs (3.4%), muscle weakness (2.6%), hypotonia (2.3%), elevated CK in a suggestive familial context (1.5 %) and fortuitous discovery (1.2%) [6]. The 3 principal causes of death were heart failure (30%), respiratory failure (25%) and pulmonary infection (18.6%) [3].

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    Figure 1. Deltoid muscle. Gomori trichrome staining. Muscular dystrophy: blue endomysial and perimysial fibrosis; fuchsinophilic highly contracted muscle fiber; irregular muscle fiber caliber and necrosis (I. Desguerre, Prof. Gherardi’s histology laboratory, Hôpital Henri Mondor).

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    Figure 2. Western blot analysis of the muscle proteins of the glycosarcolemmic complex (Dr. F. Leturcq, Laboratoire biochimie génétique, Hôpital Cochin).

    2. The diagnostic strategy in the event of suspected muscular dystrophy is clearly defined

    The diagnosis is to considered in the event of proximal progressive muscular deficiency emerging after a free interval of one to several years. The mechanism of muscular dystrophy is suggested by significant creatine kinase (CK) elevation A myogenic EMG tracing is not particularly pertinent; Muscle biopsy, usually open biopsy of the quadriceps or deltoid, necessitates adequate sampling conditions with fixation of a fragment in isopentane and immediate freezing for cryostat sectioning, and a frozen fragment for Western Blot analysis. Complete analysis confirms, using conventional histology, muscular dystrophy with a phenomenon of necrosis and regeneration associated with progressive endomysial fibrosis and later adiposis (fig. 1). Immunohistochemical analysis of the various membrane proteins of the glycosarcolemmic complex enables identification of the deficient protein. Subsequent Western blotting enables quantification of the proteins of the dystrophin associated glycoprotein (DAG) complex: dystrophin, sarcoglycans (α, β, χ, δ), dysferlin, calpain, caveolin, and α-dystroglycan (fig. 2), and confirms the absence of dystrophin (< 5%).

    A 10-mL whole blood sample on EDTA for analysis of the dystrophin gene confirms the diagnosis by identifying a deletion, duplication or point mutation (the genetic aspects are addressed in another chapter).

    3. The natural history of DMD

    We studied the course over 10 years of 75 Duchenne patients characterized in genetic terms by the complete absence of muscle dystrophin as evidenced by Western blot and immunohistochemistry and not on corticosteroid therapy [4]. The cohort was followed up by the same medical team. Multiple parameter analysis of the functional muscle, cardiac, respiratory and cognitive data enabled four sub-groups of DMD patients to be distinguished. Group A (20%) presented with marked intellectual impairment with psychomotor retardation, which is the diagnostic symptom, from the outset, late walking (age >18 months), muscle impairment (loss of the ability to walk at age of 8 years), cardiac impairment (72% presented with cardiomyopathy before age of 12 years) and severe respiratory impairment (pulmonary growth arrested before age of 10 years and vital capacity (VC): 60% at 10 years). Group B (28%) presented with a classic form of DMD with borderline or moderately impaired cognitive function and median motor course (loss of walking at age of 9.8 years). Group C (22%) did not present with intellectual impairment and, above all, had a good motor prognosis with an age at loss of walking greater than 11 years, with a later onset of respiratory impairment and scoliosis (p <0.01). Group D (30%) showed the best intellectual performance but had a poor motor prognosis very different from that of group C [4]. A genotype – phenotype correlation was only evidenced for cognitive impairment: the patients with severe cognitive impairment had mutations in the N terminal part of the gene, involving transcripts DP 71 and DP140 as has been reported in several publications [4]. In contrast, the severity of the motor impairment could not be correlated with the patients’ genetic status and required investigation for epigenetic factors by muscle biopsy specimen analysis [5].

    Collation of the results of precise morphometric and stereologic analysis of the patients’ initial biopsy specimens (muscle necrosis/ regeneration, highly contracted muscle fibers, adipocytes, interstitial edema, endomysial and perimysial fibrosis) and simple motor clinical data (age of walking, age of loss of walking, age of scoliosis onset, overall muscle score (Manual Muscle Testing (MMT) score) and quadriceps score at 10 years) enabled, by multiple parameter statistical analysis, clear identification of endomysial fibrosis as an early marker for a poor motor prognosis (early loss of walking) (p<0.002). Endomysial fibrosis is independent of perimysial fibrosis, the other necrosis –  regeneration parameters and number of muscle fibers [5]. Endomysial fibrosis maintains a vicious circle promoting the pro-fibrotic role of muscle macrophages, limiting the muscle regeneration induced by satellite cells, and promoting ischemic distress by increasing the distance between myocytes and capillaries (tableau I) [5].

    [[{"fid":"77","view_mode":"full","fields":{"format":"full","field_file_title[fr][0][value]":"","field_els_file_description[fr][0][value]":"","field_els_file_description[fr][0][format]":"els_basic","field_file_copyright_note[fr][0][value]":"","field_file_image_alt_text[fr][0][value]":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson.","field_file_image_title_text[fr][0][value]":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson."},"type":"media","field_deltas":{"4":{"format":"full","field_file_title[fr][0][value]":"","field_els_file_description[fr][0][value]":"","field_els_file_description[fr][0][format]":"els_basic","field_file_copyright_note[fr][0][value]":"","field_file_image_alt_text[fr][0][value]":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson.","field_file_image_title_text[fr][0][value]":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson."}},"link_text":false,"attributes":{"alt":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson.","title":"Tableau I. Correlation between residual dystrophin quantity and clinical phenotype after Nicholson.","height":"398","width":"844","class":"media-element file-full","data-delta":"4"}}]]

    4. Patient motor and orthopedic course

    Walking is usually acquired below the upper limit of the normal age range even though, in general, 50% of the children affected are never able to run smoothly. At age of 3 to 6 years, the gait is waddling and associated with hyperlordosis, and Gowers’ sign emerges, reflecting pelvic muscle deficiency

    Between ages of 6 and 11 years girdle muscle strength declines almost linearly [6] in a symmetrical manner but predominating in certain muscles, leading to imbalances and asymmetrical tendon retractions: flexor tendons of the nape < extensors tendons of the nape, biceps and triceps < deltoid, extensors of the hips (gluteus medius and gluteus maximus) < flexors of the hips (TFL), quadriceps < iliotibial tract, anterior and peroneal tibialis < posterior tibialis and soleus. The facial and oculomotor muscles are spared for a long time, except for the sternocleidomastoids. In 50% of cases, the deep tendon reflexes disappear after age of 10 years. Retractions of the flexors of the hips and Achilles tendons emerge sometimes before the age of 6 years, and, if not, always between the ages of 6 and 11 years. The loss of muscle strength is not linearly correlated with loss of function, such as climbing stairs with or without assistance, walking distance, and standing up from a sitting position [7]. The Vignos score (from 1 to 9) was used to evaluate the loss of function over 2-3 years [7]. The regression of the abdominal and para-spinal muscles leads to kyphotic collapse after age of 10 years. The Brooke score was used to test upper limb function and investigate the heterogeneity of progression in a series of 114 DMD patients. The score for overall muscle strength fell by 0.4 units per year on a scale from 0 to 10 [7]. Use of the manual muscle testing (MMT) score by various teams with a view to future clinical trials showed not only its power but also its limitations.

    The variability of disease progression and the patients’ understanding and cooperation, depending on age and cognitive impairment, together with the variability of the method, depending on the investigator, call for prudence in the use of MMT in clinical trials [8]. The management of lower limb tendon retractions remains difficult and certain points remain controversial. The use of nighttime calf, plantar and cruropedal orthoses is recommended by some teams as of onset of stiffening of the Achilles tendon. For other teams orthoses are only indicated during the day, in order to enable assisted walking when muscle strength declines. Use of a series of reducing plasters in the event of moderate retraction has also been recommended. Lower limb tenotomy in the event of retraction of the Achilles tendons, hip flexors, and fascia lata tensors do not enable walking to be resumed once the ability has been lost, but are proposed by some teams to prevent an oblique pelvis and pursue passive resumption of a vertical position [9]. Scoliosis is an almost constant development. In a series of 123 DMD cases, 1/3 of which were on corticosteroid therapy, 77% of the patients had scoliosis at an angle greater than 30° at a mean age of 12 years. Only 50% had undergone arthrodesis. Scoliosis onset was correlated with age at loss of walking. Surgical treatment indubitably improved the patients’ duration and quality of life. Surgery also improved respiratory function, if implemented at the right time before excessive orthopedic deformation and with maintained respiratory function (Vital capacity (VC) > 1 liter) and cardiac function (left ventricle ejection fraction (LVEF) >50%) [10].

    5. Respiratory muscle impairment

    The respiratory muscle impairment noted very early by Duchenne is the main cause of death in the absence of management. Impairment of the respiratory muscles only becomes clinically patent late, after age of 12 years on average, but close analysis of the physiology and ability of the respiratory muscled to perform work shows onset to be early. The residual functional capacity remains normal up to age of 12-14 years reflecting an initially normal lung volume and maintained pulmonary growth. From age of 6 years, the work capacity of the respiratory muscles declines although the results of conventional respiratory function tests (RFT) (Vital capacity (VC) and residual volume (RV)) remain normal. The work capacity of the respiratory muscles is reduced by 50% but VC remains normal. The secondary increase in residual volume relative to the theoretical value reflects the predominant impairment of the expiratory muscles. The reduction in VC from age of 10 years, on average by 200 mL/year, is regular and results in a patent restrictive syndrome at age of 15 years. Sniff nasal pressure testing constitutes a noninvasive means of determining maximum inspiratory pressure and is a better marker of inspiratory muscle work capability than VC. Excellent correlations have been evidenced in patients presenting with neuromuscular disease. Respiratory monitoring and management are fairly standardized [11]. RFT (VC, RV and sniff test if possible) are to be conducted annually until age of 12 years, and then every 6 months. Nighttime oximetry monitoring is to be conducted when VC falls below 1.25 L, or if the patient is older than 15 years or presents with signs of alveolar hypoventilation. A VC less than 680  mL is associated with a high risk of nighttime hypercapnia and thus necessitates nighttime ventilatory support [12]. The use of non-invasive ventilation (NIV) for DMD patients has markedly improved patient survival (about 10 years and even more if the patient has undergone arthrodesis [12]. Anglo-Saxon teams, particularly Bach’s team, are, however, very hostile toward ventilatory support with tracheotomy proposed for DMD patients in France when the patient’s ventilatory autonomy is less than 6 hours out of 26.

    6. Cardiac impairment

    Cardiac impairment in Duchenne myopathy is well known and often asymptomatic until age of 15 years. The data have been confirmed in a recent US review of 128 cases [13] for whom the mean age of cardiomyopathy diagnosis was 14.6 years. However, in France, experience has shown that abnormalities may be evidenced earlier, by echocardiography, with respect to left ventricle kinetics, and by myocardial scintigraphy, even before age of 10 years in 20% of cases [14]. Preventive treatment with an angiotensin converting enzyme (ACE) inhibitor is recommended as of age of 10 years for DMD patients in the light of two studies conducted by the French cardiology group. In 2005, a double-blind placebo-controlled study showed retardation of the emergence of cardiomyopathy in asymptomatic patients who received ACE inhibitor therapy between ages of 9.5 and 13 years. Ten-year cohort follow-up showed significantly greater survival in the early treatment group [15]. Subsequent symptomatic treatment of heart failure is conventional and combines β-blockers, ACE inhibitors and diuretics. Cardiac rhythm disorders are often reported but rarely related to early mortality. The disorders mainly consist in supraventricular arrhythmia.

    The nutrition of DMD patients raises two types of question. First, it is necessary to refer to the specific curves for DMD children. Forty percent of DMD patients develop obesity while not on corticosteroids, before age of 12 years, and loss of the ability to walk that the weight gain precipitates [16,17]. No physiological or hormonal explanation has been advanced to date. In addition, after age of 18  years, 44% of DMD cases present with undernutrition even when muscle wasting is taken into account in body mass index calculation. Chewing and swallowing difficulties are preponderant and require treatment.

    7. Cognitive impairment

    Cognitive impairment is a classic feature of DMD and may reveal the myopathy in 10% of cases. The absence or reduction of dystrophin transcripts in the central nervous system, mainly in the dendrites of the pyramidal cells of the cortex and hippocampus, and in the Purkinje cells of the cerebellum, leads to variety of cognitive deficiencies (18,19]. Since Duchenne’s initial description in 1868, a cognitive deficiency has been evidenced in patients, with a mean IQ of 85; 30% of patients have an IQ of less than 70. There is a dissociation of verbal and performance IQ in favor of performance, despite what might be expected (differential of 5 to 8 points). There is a higher prevalence of invasive developmental disorders in DMD patients: 4/100 vs. 1.6/1000 in the general. In a recent study, there were 18% autistic spectrum disorders (ASD) [20].

    8. Pluridisciplinary management

    The pluridisciplinary management of DMD patients may thus be considered indispensable and this is recognized by all the teams in the field. International recommendations were formulated in 2010 [21]. Such management and, in particular, orthopedic, cardiac and respiratory follow-up, has improved patient survival and quality of life. French teams have been implementing coordinated pluridisciplinary management for 15-20 years and have thus accumulated experience in DMD patient management ensuring enhanced long-term survival in an orthopedic, respiratory, cardiac and nutritional condition that is more satisfactory than that of the old Anglo-Saxon series or that reported in recent publications focusing on the benefits of short and medium term corticosteroid therapy.

    9. Biomarkers and measurement instruments

    The difficulty associated with evidencing a therapeutic benefit of innovative therapies in a context of a monogenic disease with a mutation dependent targeted therapy has confirmed the heterogeneity of the disease and the need to further elucidate its natural history despite the fact that it was considered well known [3,4,22].

    9.1. Six minute walk test

    The 6 minute walk test, the primary endpoint in all the studies, has been shown to be robust and simple (measurement of the number of meters covered over a defined course in 6 minutes) [23]. The time course of the walking distance does not vary linearly with age. Three periods may be distinguished: an early period between age of 3 and 6 years during which the walking score may improve; a period of stability between one and two years; and then a period of degradation culminating in definitive loss of the ability to walk. A 6-min score less than 100 m would appear to predict loss of the ability to walk within a year. It is therefore indispensable to stratify the patients on inclusion in clinical trials on the basis of their baseline walking score, which is predictive of the natural future disease exacerbation [23]. The test has been validated in healthy children as a function of age and is in use in other pediatric and adult diseases. Test results correlate with other motor functions in the context of DMD: time score for a 10-m walk; climbing stairs; muscle strength measured by MMT; Northern Star score. Various publications have documented the time course on or off steroids [24]. Upper limb scoring systems for gait-deprived DMD patients are under evaluation.

    9.2. Predictive and progressive biomarkers

    The quest for predictive and progressive blood biomarkers is continuing with serum miRNA assays [25], assays of extracellular matrix markers such as fibronectin and mmP9, and determination of integrin expression by circulating T cells [26].

    9.3. MRI muscle analysis

    MRI analysis of the various muscle groups, a non-invasive method, appears promising and shows the distribution of their involution over time. T2 MRI also enables quantification of fat and water infiltration while diffusion tensor imaging (DTI) enables change quantification [27]. Quantification of muscle fibrosis remains a challenge. Comparative analysis of Pi/ATP metabolic indicators reveals marked differences between ambulatory and non-ambulatory DMD patients while T2 MRI reveals differences in the indicators of muscle inflammation [28].

    Statement of interests

    Over the last 5 years, Prof. Isabelle Desguerre has received fees or financing for participation in congresses, training courses and expert groups from the pharmaceutical companies, PTC Therapeutics Inc, GSK and Servier. Isabelle Desguerre has also been principal investigator in clinical trials sponsored by PTC Inc and GSK V. Laugel has not forwarded a statement of interests.

    References

    [1] Darin N, Tulinius M. Neuromuscular disorders in childhood: a descriptive epidemiological study from western Sweden. Neuromuscular Disorders 2000;10:1-9.

    [2] Brooke MH, Fenichel GM, Griggs RC, et al. Clinical investigation in Duchenne Dystrophy: Determination of the power of therapeutic trials based on natural history. Muscle Nerve 1983;6:91- 103.

    [3] Van Essen AJ, Verheij JBGM, Reefhuis J, et al. The natural history of Duchenne muscular dystrophy: analysis of data from a Dutch survey and review of age-related events. Leyden Muscular Dystrophy 2004.

    [4] Desguerre I, Christov C, Mayer M et al. Phenotypic heterogeneity of Duchenne muscular dystrophy assessed by long-term follow-up: identification of indicators predicting future oucome. PlosOne 2009;4:e437.

    [5] Desguerre I, Mayer M, Leturcq F et al. Endomysial fibrosis in Duchenne muscular dystrophy (DMD): a marker of poor outcome associated with macrophage alternative activation. J Neuropathol Exp Neurol 2009;68:762-73.

    [6] Allsop KG, Ziter FA. Loss of strength and functional decline in Duchenne’s dystrophy. Arch Neurol 1981;38:406-11.

    [7] Brooke MH, Fenichel GM, Griggs RC, et al. Duchenne muscular dystrophy: patterns of clinical progression and effects of supportive therapy. Neurology 1989;39:475-81.

    [8] Bakker JP, de Groot IJ, Beckerman H, et al. The effects of kneeankle-foot orthoses in the treatment of Duchenne muscular dystrophy: review of the literature. Clin Rehabil 2000;14:343-59.

    [9] Eagle M, Bourke J, Bullock R et al. Managing Duchenne muscular dystrophy. The additive effect of spinal surgery and home nocturnal ventilation in improving survival. Neuromuscul Disord 2007;17:470-5.

    [10] Kinali M, Main M, Eliahoo J, et al. Predictive factors for the development of scoliosis in Duchenne muscular dystrophy. Eur J Paediatr Neurol 2007;11:160-6.

    [11] Stefanutti D, Benoist MR, Scheinmann P, et al. Usefulness of sniff nasal pressure in patients with neuromuscular or skeletal disorders. Am J Respir Crit Care Med 2000;162:1507-11.

    [12] Jeppesen J, Green A, Steffensen BF, et al. The Duchenne muscular dystrophy population in Denmark, 1977–2001: prevalence, incidence and survival in relation to the introduction of ventilator use. Neuromuscul Disord 2003;13:804-12.

    [13] Connuck DM, Sleeper LA, Colan SD, et al; Study Group. Characteristics and outcomes of cardiomyopathy in children with Duchenne or. Becker muscular dystrophy: a comparative study from the Pediatric Cardiomyopathy Registry. Am Heart J 2008;155:998-1005.

    [14] Duboc D, Meune C, Lerebours G, et al. Effect of perindopril on the onset and progression of left ventricular dysfunction in Duchenne muscular dystrophy. J Am Coll Cardiol 2005;45:855-67.

    [15] Duboc D, Meune C, Pierre B, et al. Perindopril preventive treatment on mortality in Duchenne muscular dystrophy: 10 years’ follow-up. Am Heart J 2007;154:596-602.

    [16] Willig TN, Carlier L, Legrand M, et al. Nutritional assessment in Duchenne muscular dystrophy. Dev Med Child Neurol 1993;35:1074-82.

    [17] Mok E, Béghin L, Gachon P, et al. Estimating body composition in children with Duchenne muscular dystrophy: comparison of bioelectrical impedance analysis and skinfold-thickness measurement. Am J Clin Nutr 2006;83:65-9.

    [18] Muntoni F, Torelli S, Ferlini A. Dystrophin and mutations: one gene, several proteins, multiple phenotypes. Lancet Neurol 2003;2:731-40.

    [19] Mehler MF. Brain dystrophin, neurogenetics and mental retardation. Brain Res Brain Res Rev 2000;32:277-307.

    [20] Ricotti V, Mandy WP, Scoto M et al. Neurodevelopmental, emotional, and behavioural problems in Duchenne muscular dystrophy in relation to underlying dystrophin gene mutations. Dev Med Child Neurol 2016 Jan;58(1):77-84.

    [21] Bushby K, Finkel R, Birnkrant DJ et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol 2010;9:77-93.

    [22] Hoffman EP, Dressman D. Molecular pathophysiology and targeted therapeutics for muscular dystrophy. Trends Pharmacol Sci 2001;22:465-70.

    [23] Henricson E, Abresch R, Han JJ, et al.The 6-minute walk test and person-reported outcomes in boys with Duchenne muscular dystrophy and typically developing controls: longitudinal comparisons and clinically-meaningful changes over one year. PLoS Curr 2013;8:5.

    [24] McDonald CM, Henricson EK, Abresch RT, et al. The 6-minute walk test and other endpoints in Duchenne muscular dystrophy: longitudinal natural history observations over 48 weeks from a multicenter study. Muscle Nerve 2013;48:343-56.

    [25] Hu J, Kong M, Ye Y, et al. Serum miR-206 and other musclespecific microRNAs as non-invasive biomarkers for Duchenne muscular dystrophy.J Neurochem 2014;129:877-83.

    [26] Cynthia Martin F, Hiller M, Spitali P, et al. Fibronectin is a serum biomarker for Duchenne muscular dystrophy. Proteomics Clin Appl 2014;8:269-78.

    [27] Hooijmans MT, Damon BM, Froeling M, et al. Evaluation of skeletal muscle DTI in patients with duchenne muscular dystrophy.

    [28] NMR Biomed 2015;28:1589-97

    [29] Wary C, Azzabou N, Giraudeau C, et al. Quantitative NMRI and NMRS identify augmented disease progression after loss of ambulation in forearms of boys with Duchenne muscular dystrophy. NMR Biomed 2015;28:1150-62.

  • Duchenne muscular dystrophy: pathophysiology

    Y. Péréon*, S. Mercier, A. Magot

    Centre de Référence des Maladies Neuromusculaires Nantes-Angers, Hôtel-Dieu, 44093 Nantes cedex, France

    Summary

    Dystrophin is one of the largest proteins in the body and is located on the internal surface of skeletal muscle fiber where it ensures a structural link between the cytoskeleton and sarcolemma via a set of proteins known as the dystrophin-associated glycoprotein complex (DGC). Dystrophin is also involved in many cell signaling cascades, either directly, by regulating membrane proteins such as calcium channels, or indirectly via calcium or nitric oxide (NO) signaling pathways. In Duchenne muscular dystrophy (DMD), not only is dystrophin lacking but the expression of the proteins constituting DGC is markedly reduced. The excessive fragility of the membrane under mechanical stress, increase in membrane permeability, dysregulation of calcium homeostasis, disturbances in NO synthase and oxidative stress, all of which result from the lack of dystrophin, underlie the muscle necrosis followed by initially successful regeneration. Over time, the regenerative capacity of muscles is exhausted, endomysial inflammation and fibrosis emerge, and muscle fibers are gradually replaced by fibrousadipose tissue with loss of muscle function.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    La dystrophine est une des protéines les plus grandes de l’organisme, localisée à la face interne de la fibre musculaire squelettique, où elle assure un lien structurel entre le cytosquelette et le sarcolemme, via un ensemble de protéines appelé « complexe des protéines associées à la dystrophine  » (CPAD). Elle est de plus impliquée dans des cascades de signalisation cellulaire soit directement en régulant des protéines membranaires telles que les canaux calciques, soit indirectement par l’intermédiaire des voies de signalisation calciques ou de l’oxyde nitrique (NO). Au cours de la dystrophie musculaire de Duchenne (DMD), non seulement la dystrophine fait défaut, mais l’expression des protéines constitutives du CPAD est également très réduite. La fragilité excessive de la membrane vis-à-vis d’un stress mécanique et l’augmentation de sa perméabilité, la dysrégulation de l’homéostasie calcique, les perturbations de la NO synthase, le stress oxydatif qui tous résultent de la perte de la dystrophine sont à l’origine de la nécrose musculaire, suivie d’une régénération initialement efficace. Avec le temps, celle-ci s’épuise, inflammation et fibrose endomysiale s’installent, avec le remplacement progressif des fibres musculaires par du tissu fibro-adipeux et la perte de la fonction musculaire.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction: dystrophin: structure and, function [1]

    Dystrophin is one of the largest proteins in the body to have been identified. There are five isoforms; the complete form is mainly expressed in skeletal and cardiac striated muscle. It is located on the internal surface of the skeletal muscle fiber, where it ensures a structural link between the cytoskeleton, particularly actin filaments, and the sarcolemma, via a set of proteins known as the dystrophin-associated glycoprotein complex (DGC) (fig. 1) [2].

    Dystrophin has four structural domains: an N-terminal extremity, with homologies with α-actin binding domains; a central domain constituted of the repetition of 24 repeat segments similar to spectrin and containing four hinge regions [3]; a cysteine rich domain itself consisting of an aWW domain, two EE-hand-like domains and a ZZ domain, linking to the DGC via β-dystroglycan; and lastly, a C-terminal extremity, in the form of a helix, which interacts with syntrophins [4,5]. Even though the repetitive segments of the central domain are somewhat redundant in terms of the mechanical role of dystrophin, they contain an additional actin binding domain and interact with membrane phospholipids, nNO synthase and other cytoskeletal proteins such as plectin, intermediate filaments and microtubules [6].

    The primary role of dystrophin is to contribute to the structural integrity of muscle fiber through its interactions with the cytoskeleton and DGC. It enables the sarcolemma and neighboring tissues, via the extracellular matrix, to withstand the mechanical stress of myofibril contraction. Simplistically, dystrophin acts like a spring stretched between the membrane and myofibrils.

    The DGP, with which dystrophin is closely associated, includes intra-cytoplasmic proteins (α1 – and β1-syntrophins, α-dystrobrevin, neuronal NO synthase), trans-membrane proteins (β-dystroglycan, α-, β –, γ- and δ-sarcoglycans, sarcospan) and extracellular proteins (α-dystroglycan, laminin 2). The DGC plays a fundamental role in contraction through its links with the extracellular matrix [7]. With dystrophin, DGC is a component of the costamere and enables maintenance of the alignment of the sarcolemma and contractile structures while protecting it from lesions induced by contraction. Lastly, DGC transmits a fraction of the contraction forces laterally toward the extracellular matrix.

    The second function of dystrophin at skeletal muscle level is to contribute to the regulation of several metabolic functions. These include excitation-contraction coupling, calcium homeostasis, mitochondrial functions, interactions with motor proteins, and the expression of certain genes. Dystrophin is thus involved in cell signaling cascades either directly by regulating membrane proteins such as calcium channels or indirectly via calcium or NO signaling pathways

    For example, the correct function of the motor plate acetylcholine receptor, that of muscle sodium channels Nav1.4 and Nav1.5, skeletal and cardiac, respectively, that of type L calcium channels, that of aquaporin, and that of stretch activated ion channels are all closely dependent on their association with DGC and thus with dystrophin.

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    F​igure 1. Dystrophin and associated proteins.
    DG: dystroglycan; SGC: sarcoglycan complex; SS: sarcospan.

    2. Pathophysiology

    While the genetic etiology of the dystrophinopathies has been clearly elucidated the exact mechanisms giving rise to the process of muscle necrosis, inflammation, and fibrosis observed throughout the disease remain partially unexplained. In the course of Duchenne muscular dystrophy (DMD), not only is dystrophin lacking but the expression of the proteins constituting DGC is markedly reduced while, in contrast, the expression of certain other associated proteins is increased. It is of interest to note that the absence of other DGC proteins is responsible for the emergence of muscular dystrophy with variable phenotypic expression in terms of the selectivity of muscle involvement, age of onset and presence of cardiomyopathy. In the absence of dystrophin, the membrane becomes fragile and permeable: the increase in intracellular calcium concentrations, one of the first biomarkers to be identified, triggers a typical process of necrosis and fibrosis in the various types of muscle. The deregulation of calcium homeostasis is an early pathophysiological event and relatively common in muscular dystrophies. Several principal mechanisms have been advanced to explain muscle degeneration in the context of DMD, in man and in animal models (fig. 2) [8].

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    Figure 2. Principal pathophysiological mechanisms.

    2.1. Membrane fragility under mechanical stress

    The mechanical action of muscle fiber contraction generates microscopic lesions of the sarcolemma in the absence of the link between the muscle fiber membrane and myofibrils constituted by dystrophin and DGC [9,10]. Skeletal muscle fiber is rendered markedly fragile by the absence of those proteins since the costamere no longer fulfills its role. A fundamental biomarker of the disease, present at birth and well before symptom onset, is marked elevation of creatine kinase (CK). Elevation strongly suggests an increased permeability of the muscle membrane allowing soluble enzymes to exit the cell freely. The first electron microscopy studies of skeletal muscle in DMD showed local breaks in the membrane surface associated with contractures of the neighboring myofibrils. This led to formulation of the hypothesis that the membrane damage is an early characteristic of the disease and that calcium enters the cell via those breaks. The increased permeability has been repeatedly confirmed experimentally using markers such as albumin and Evans blue [11].

    2.2. Deregulation of calcium homeostasis

    Cytosolic calcium, including resting cytosolic calcium, is increased [12]. The elevation of intracellular calcium concentrations induces critical activation of several signaling pathways including calpain, a calcium dependent proteinase, which degrades proteins and contributes to cell death mediated by the mitochondria [13].

    Intracellular calcium elevation has several associated underlying mechanisms [14]: the four main calcium entry routes are as follows:

    • the leakage channels naturally present on the surface of the sarcolemma, the opening of which is enhanced in DMD;
    • the focal tears in the sarcolemma (vide supra);

    The stretch activated cation channels of the sarcolemma. The channels, which are sensitive to mechanical stimuli, are members of the vast transient receptor potential (TRP) series [15,16]. Channels TRPC1 and TRPC4 are expressed on the sarcolemma of skeletal muscle fibers and normally contribute to calcium and magnesium regulation. They are associated with the DGC via α-syntrophin 1, whose expression is decreased in DMD. Their activity is increased in DMD, perhaps due to excessive stretching of the plasma membrane, which is no longer correctly attached to the myofibrils by the costamere. Other channels, such as TRPC3 and TRPV2 may also be involved.

    The store operated calcium entry (SOCE) channels of the transverse tubular system, which manages the calcium storage level in the sarcoplasmic reticulum (SR). This mechanism, which was elucidated relatively recently, plays an important role in calcium homeostasis during excitation-contraction coupling, particularly during muscle development or remodeling. The SOCE system enables resupply of the SR with calcium during repeated contractions. The system is based on the coupling of two structures: Orai1, a highly selective calcium channel located in the transverse tubular system, and STIM1, a trans-membrane protein of the sarcoplasmic reticulum. Both are members of the TRP channel series. STIM1 acts as a calcium detector and controls Orai1 opening. They are very highly expressed (threefold increase) in the mdx mouse, with a stronger SOCE activity that may contribute to intracellular calcium elevation [17].

    Other proteins whose expression is reduced in DMD are involved in calcium deregulation: calsequestrin, suggesting reduced calcium sequestration capability in the SR; sarcalumenin, which regulates recapture of calcium for the SR via the SERCA calcium ATPase pump; and calpastatin, a calpain specific endogenous inhibitor [8].

    3. Disturbances of NO synthase

    Three isoforms of NO synthase are normally present in skeletal muscle: the neuronal isoform (nNOS), which is the most abundant, the endothelial isoform (eNOS), and the inducible isoform (iNOS), in very small quantities. The absence of dystrophin induces a reduction in the activity of nNOS, linked to syntrophin. Lack of NO synthesis induces deregulation of several NO-dependent pathways, including the regulation of contraction, mitochondrial metabolism, and glucose homeostasis, and deregulation of metabolic, immune and vascular responses. In particular, the diffusion of NO outside of skeletal muscle fibers is necessary for the vasodilatation occurring during contraction with the aim of promoting muscle oxygenation. Reduced NO production by nNOS may induce vasoconstriction due to reduced cyclic GMP production in arteriolar smooth muscle cells promoting exertional ischemia and impaired performance [18].

    4. Oxidative stress

    Excessive production of free radicals or reactive oxygen species (ROS) is also observed in DMD and animal models [19], in both skeletal and cardiac muscle.

    Production increases further during exercise; following increased membrane NOX2 NADPH oxidase activity, but also due to the mitochondrial consequences of intracellular calcium elevation. The excessive ROS contribute to activation of inflammatory mechanisms via, successively, nuclear factor kβ (NF-kβ) and TNFα. The ROS also contribute to activation of calpain, promoting cell necrosis, and, in an authentic vicious circle, by increasing intracellular calcium concentrations by sensitizing the ryanodin receptors of the sarcoplasmic reticulum (with, in consequence an increase in intracytoplasmic calcium release) and by activating membrane stretch sensitive TRP channels.

    5. Inflammatory process

    Skeletal muscle is unusual in that it has relatively little ability to generate local immune responses; it contains few dendritic cells, mast cells or other pro-inflammatory cells. In DMD shortly after birth, part of the immune system is activated, including, before emergence of the first functional signs, impairment of signaling via toll like receptors TLR4 and TLR7 and NF-kβ, and expression of class I major histocompatibility complex (MHC) molecules [20]. The leakage toward the extracellular medium via the tears in the sarcolemma related to the absence of dystrophin constitutes a factor triggering innate immune responses, including the binding of molecules such as heat shock proteins and nucleic acids to the TLR, with initiation of an inflammatory process [21]. Pro-inflammatory cytokines induce expression of class I and II MHC in muscle fibers, the recruitment of T- and B-cells, and the generation of an adaptive immune response in muscle. The pro-inflammatory micro-environment is superimposed on the neutrophil and macrophage infiltration in response to the successive cycles of muscle degeneration and regeneration [22].

    All the above mechanisms are, of course, inter-dependent and the cellular phenotype of DMD results from their action. Other pathophysiological mechanisms are also involved [23]. Examples include the metalloproteases of the extracellular matrix, whose expression is increased in dystrophinopathies, which very probably contributes to the phenomena of muscle fiber inflammation, necrosis and fibrosis [24]. Cardiac and central nervous system involvement are addressed in other articles in this number.

    6. Conclusions: consequences over time

    Skeletal muscle is a dynamic tissue regularly subjected to mechanical stress during contraction or exertion. Muscle may undergo repeated damage resulting in a loss of muscle fibers followed by a process of recovery initiated by satellite cells. In the course of DMD, the process is brought into play very early and initially enables compensation for the necrotic lesions related to the absence of dystrophin. However, since the pathological process is permanent, the ability of muscle to regenerate becomes exhausted. The imbalance between muscle degeneration and regeneration induces inflammation and endomysial fibrosis with gradual replacement of the muscle fibers by fibrous and adipose tissue, and loss of muscle function. This explains the late onset of the initial symptoms of the disease and its exacerbation in the event of excessive exercise.

    Statement of interests

    References

    [1] Blake DJ, Weir A, Newey SE, Davies KE. Function and genetics of dystrophin and dystrophin-related proteins in muscle. Physiol Rev 2002;82:291-329.

    [2] Gao QQ, McNally EM. The Dystrophin complex: structure, function, and implications for therapy. Compr Physiol 2015;1;5:1223- 39.

    [3] Koenig M, Kunkel LM. Detailed analysis of the repeat domain of dystrophin reveals four potential hinge segments that may confer flexibility. J Biol Chem 1990;265:4560-66.

    [4] Koenig M, Monaco AP, Kunkel LM. The complete sequence of dystrophin predicts a rod-shaped cytoskeletal protein. Cell 1988;53:219-2.

    [5] Huang X, Poy F, Zhang R, et al. Structure of aWW domain containing fragment of dystrophin in complex with β-dystroglycan. Nat Struct Biol 2000;7:634-38.

    [6] Le Rumeur E, Winder SJ, Hubert JF. Dystrophin: more than just the sum of its parts. Biochim Biophys Acta 2010;1804:1713-22.

    [7] Ervasti JM, Campbell KP. A role for the dystrophin-glycoprotein complex as a transmembrane linker between laminin and actin. J Cell Biol 1993;122:809-23.

    [8] Vallejo-Illarramendi A, Toral-Ojeda I, Aldanondo G et al. Dysregulation of calcium homeostasis in muscular dystrophies. Exp Rev Molec Med 2014;16:e16.

    [9] Campbell KP. Three muscular dystrophies: Loss of cytoskeleton extracellular matrix linkage. Cell 1995;80:675-9.

    [10] Petrof BJ, Shrager JB, Stedman HH, et al. Dystrophin protects the sarcolemma from stresses developed during muscle contraction. Proc Natl Acad Sci USA 1993;90: 3710-14.

    [11] Hamer PW, Mc Geachie JM, Davies MJ, Grounds MD. Evans Blue Dye as an in vivo marker of myofibre damage: Optimizing parameters for detecting initial myofibre membrane permeability. J Anat 2002;200:69-79.

    [12] Bodensteiner J.B. Engel, A.G. Intracellular calcium accumulation in Duchenne dystrophy and othermyopathies: a study of 567,000 muscle fibers in 114 biopsies. Neurology 1978;28:439-46.

    [13] Carafoli E, Molinari M. Calpain: A protease in search of a function? Biochem Biophys Res Commun 1998;247:193-203.

    [14] Allen DG, Whitehead NP. Duchenne muscular dystrophy--what causes the increased membrane permeability in skeletal muscle? Int J Biochem Cell Biol 2011;43:290-4.

    [15] Vandebrouck C. Martin D, Colson-Van Schoor M, et al. Involvement of TRPC in the abnormal calcium influx observed in dystrophic (mdx) mouse skeletal muscle fibers. J Cell Biol 2002;158:1089-96.

    [16] Gailly P. TRP channels in normal and dystrophic skeletal muscle. Curr Opin Pharmacol 2012;12:326-34.

    [17] Zhao X, Moloughney JG, Zhang S, et al. Orai1 mediates exacerbated Ca(2+) entry in dystrophic skeletal muscle. PLoS ONE 2012;7:e49862.

    [18] Sander M, Chavoshan B, Harris SA, et al. Functional muscle ischemia in neuronal nitric oxide synthase-deficient skeletal muscle of children with Duchenne muscular dystrophy. Proc Natl Acad Sci USA 2000;97:13818-23.

    [19] Terrill JR, Radley-Crabb HG, Iwasaki T, et al. Oxidative stress and pathology in muscular dystrophies: focus on protein thiol oxidation and dysferlinopathies. FEBS J 2013;280:4149-64.

    [20] Dadgar S,Wang Z, Johnston H, et al. Asynchronous remodeling is a driver of failed regeneration in Duchenne muscular dystrophy. J Cell Biol 2014;207:139-58.

    [21] Pétrilli V, Dostert C, Muruve DA, et al. The inflammasome: A danger sensing complex triggering innate immunity. Curr Opin Immunol 2007;19:615-22.

    [22] Rosenberg AS, Puig M, Nagaraju K et al. Immune-mediated pathology in Duchenne muscular dystrophy. Sci Translat Med 2015;7:299rv4.

    [23] Deconinck N, Dan B. Pathophysiology of Duchenne muscular dystrophy: current hypotheses. Pediatr Neurol 2007;36:1-7.

    [24] Li H, Mittal A, Makonchuk DY, et al. Matrix metalloproteinase-9 inhibition ameliorates pathogenesis and improves skeletal muscle regeneration in muscular dystrophy. Hum Mol Genet 2009;18:2584-98.

  • Genetic counseling in dystrophinopathies

    C. Coubes

    Centre de Référence « Anomalies du développement et syndromes malformatifs », Département de génétique médicale, CHU Arnaud de Villeneuve, 371, avenue du doyen Gaston-Giraud, 34295 Montpellier cedex 5, France

    Summary

    Genetic counseling in dystrophinopathies enables carrier diagnosis, assessment of the risk for descendents, and discussion of the various possibilities for having a boy free from the disease: prenatal diagnosis, preimplantation diagnosis, ovocyte donation, and adoption. The various stages of each proposal are described. Prenatal diagnosis and preimplantation diagnosis can only occur within a strictly defined legal framework. Invasive prenatal diagnosis in particular brings up the risk of miscarriage or termination of pregnancy for medical reasons. Preimplantation diagnosis (PID) is the study of the genetic characteristics of a 3-day-old embryo. PID is suggested to couples who risk transmitting a particularly serious genetic disease to their child as an alternative to prenatal diagnosis. PID requires resort to medically assisted reproduction for couples who do not necessarily present with sterility problems. Preimplantation diagnosis requires a highly committed clinical and biological multidisciplinary team. It is very stressful for couples, both physically and psychologically. Technological advances (new-generation sequencing) suggest that noninvasive prenatal diagnosis may be possible in the future.

    © 2017 Elsevier Masson SAS. All rights reserved

    Résumé

    Le conseil génétique dans les dystrophinopathies permet de diagnostiquer les conductrices, évaluer les risques pour la descendance, discuter de différentes possibilités d’avoir un garçon non atteint: diagnostic prénatal, diagnostic préimplantatoire, don d’ovocytes, adoption. Les différentes étapes de chaque proposition sont détaillées. Le diagnostic prénatal et le diagnostic préimplantatoire ne s’entendent que dans un cadre légal très défini. Le diagnostic prénatal invasif fait discuter en particulier le risque de fausse couche, d’interruption médicale de grossesse. Le diagnostic préimplantatoire (DPI) est l’étude des caractéristiques génétiques d’un embryon âgé de trois jours. Il est proposé aux couples qui risquent de transmettre à leur enfant une maladie génétique d’une particulière gravité, en alternative au diagnostic prénatal. Il impose le recours à une aide médicale à la procréation à des couples qui ne présentent pas obligatoirement des problèmes de stérilité. La réalisation d’un DPI nécessite une équipe multidisciplinaire clinique et biologique très impliquée. Il sollicite très fortement physiquement et psychologiquement les couples demandeurs. L’évolution des technologies (séquençage nouvelle génération) laisse entrevoir la possibilité d’un diagnostic prénatal non invasif dans les années à venir.

    © 2017 Elsevier Masson SAS. Tous droits réservés.

    1. Introduction

    In the context of dystrophinopathies, genetic counseling consists in meeting with the families in order to review the history of the index case (clinical diagnosis, muscle biopsy and molecular genetics), com-pile a genealogical tree and screen carrier women while explaining the X linked transmission mode.

    Mandatory carriers consist in the mothers of an affected boy with an affected relative in the maternal line. Women with two or more affected boys and no familial history, have a germinal mutation or mosaicism. If the index case is isolated, he may have a germinal mutation, or his mother may carry a de novo mutation, or his mother may have inherited the mutation. The risk for a carrier woman of having an affected child is 25% at each pregnancy; if she is expecting a boy, the risk of him being affected is 50%. The risk of germinal mosaicism is estimated to be between 15 and 20%. Carrier detection is thus of the greatest importance for accurate genetic counseling. It enables evaluation of the risks for the offspring and discussion of the various possibilities for having an unaffected boy. The following are to be addressed by genetic counseling: prenatal diagnosis (PND), preimplantation diagnosis (PID), oocyte donation and adoption.

    2. Ethical aspects

    The legal context is the same for PND and PID. Duchenne muscu-lar dystrophy (DMD) is expressed early and is rapidly progressive with a low survival rate after 20 years; death is due to respiratory and cardiac complications. Accordingly, given the seriousness and frequency of DMD, it is one of the disease that most frequently gives rise to PID [1]. Becker muscular dystrophy (BMD) is cha-racterized by later onset progressive muscle weakness; dilated cardiomyopathy is a usual cause of morbidity and the most frequent cause of death is heart failure after age of 35 years. BMD may be considered a disease that emerges late and is of variable expression depending on the family. The variable expression and the complexity of cardiac management have resulted in BMD being considered as an indication for PND and PID by most of the teams involved in those procedures [2] (Pluridisciplinary Centers for Prenatal Diagnosis under the supervision of the Biomedicines Agency).

    3. Prenatal diagnosis

    Prenatal diagnosis consists in medical practices designed for the intrauterine detection of particularly serious disease in the embryo or fetus.

    3.1. Genetic counseling

    Ideally, genetic counseling is provided before every pregnancy, if not before every prenatal diagnosis. Counseling consists in explaining the procedure, disadvantages (risk of miscarriage), ovule retrieval, potential technical failure, and the results of the tests conducted and their consequences. All prescriptions of an investigation desi-gned to define genetic characteristics necessitate the pregnant woman’s written consent (Article R.162-16-1 of the French Code of Public Health).

    3.2. PND implementation

    After ultrasound dating of the pregnancy, the procedure consists in genotypic determination of fetal gender, which is conducted on maternal serum at 10 weeks of amenorrhea (WA). If the result is in favor of female gender, the pregnancy is followed up normally. An interim ultrasound toward 16 WA is recommended in order to confirm fetal gender.

    If the embryo is male, ovular sampling is proposed. A trophoblast biopsy is conducted at 12 WA in order to determine whether the embryo carries the familial mutation. If the pregnancy is discovered late, the embryo’s familial gene status may be determined on an amniotic fluid sample obtained by amniocentesis. If the mutation is detected, the Pluridisciplinary Center for Prenatal Diagnosis may be requested to conduct an abortion. Two physicians who are members of the Center’s team certify, when the team has formulated its advisory opinion, that “there is a high probability that the unborn child suffers from a particularly serious disease known to be incurable at the time of diagnosis”. Except in the event of a medical emergency, the pregnant woman is then given at least a week to decide whether to terminate or pursue her pregnancy (article L.2213-1).

    4. Preimplantation diagnosis

    PID is a long process necessitating in vitro fertilization (IVF) with intracytoplasmic spermatozoid injection (ICSI). Several stages related to medically assisted procreation (MAP) and genetic diagnosis of the embryo are necessary before transfer of the mutation-free embryo [3]. PID implementation necessitates a multidisciplinary team and close cooperation between the clinicians (geneticists, gynecologists, midwives, psychologists) and laboratories specializing in the fields of in vitro fertilization (IVF), cytogenetics and molecular biology, working within a clearly defined legal framework. The couple’s strong physical and psychological commitment is also sought.

    4.1. PID legislation

    In France, PID is authorized pursuant to act No. 94-654 dated July 29, 1994, relating to the donation and use of human tissues and organs, and to medically assisted procreation and prenatal diagnosis. Pursuant to L.2131-4, biological diagnosis conducted on cells taken from an embryo in vitro is only authorized as an exceptional procedure under the following conditions: “A physician practicing in a Pluridisciplinary Center for Prenatal Diagnosis (CPDPN) is to certify that the couple, due to its familial situation, has a high probability of giving birth to a child suffering from a particularly serious genetic disease considered to be incurable at the time of diagnosis. Diagnosis can only be conducted when the disease has been previously and accurately identified in one of the parents. Diagnosis cannot have any aim other than investigating for the pertinent disease. Diagnosis can only be implemented in an establishment specifically authorized to conduct the procedure pursuant to a ruling by the Biomedicines Agency”.

    The legislation thus only authorizes recourse to PID in an exceptional manner, and only to prevent the birth of a seriously ill or handicapped child. The objectives of the PID act are to prevent any eugenic drift through assessment of the seriousness of the disease, prior identification of the genetic defect in the family, restriction of the diagnosis to the pertinent disease, and providing the couple with guidance. At the present time in France, four centers have been accredited by the Biomedicines Agency (Paris, Strasbourg, Montpellier, Nantes).

    4.2. Candidate couples

    Candidate couples are those not wishing to resort to prenatal diagnosis for ethical or religious reasons (rejection of abortion) or those having experienced an abortion after prenatal diagnosis. Candidates may also consist in couples with low fertility, in itself grounds for IVF, and in which a genetic risk has been identified. The law requires candidates to be living persons of procreational age who certify in writing that they live together. The couple submits a written application to the PID center. The application may be spontaneous or, more commonly, follow referral by a physician (geneticist, gynecologist). Given the complexity of the procedure, it is highly advisable to ascertain the couple’s degree of awareness of PID: risk of recurrence of the pertinent disease, motivation, awareness of the broad lines of the procedure, and other solutions (prenatal diagnosis, gamete donation, adoption). Both members of the couple are to consent in writing to implementation of the diagnostic procedure.

    4.3. Medical and genetic feasibility

    In vitro fertilization with ICSI enables couples at risk of transmitting a genetic disease to obtain several embryos with a view to establishing their genetic status and thus only transferring a healthy embryo or embryos. An adequate cohort of embryos is indispensable in order to obtain at least one healthy embryo. Several tests prescribed by the PID center enable determination of whether the methods of medically assisted procreation are applicable: for the woman: hormone assays and follicle count on day 3 of the menstrual cycle (ovarian reserve determination); for the man: spermiogram. An additional workup may be prescribed subsequently. If the results are positive, the center’s genetics team evaluates the feasibility of genetic diagnosis. Blood tests for dystrophinopathies are thus conducted on the couple and possibly on their parents. Chromosome analyses are conducted on both members of the couple to check that reciprocal and robertsonian translocations are absent (their presence would raise the question of a second PID indication).

    4.4. Pluridisciplinary consultation

    With the agreement of the CPDPN and providing the medical and genetic conditions are fulfilled, the couple attends a pluridisciplinary consultation at the PID center, most frequently in the presence of a geneticist, gynecologist, midwife, anesthetist, biologist and psychologist. The aim of the consultation is to explain to the couple how the various phases of IVF are implemented (stages, efficacy, risks of failure, etc.), the genetic diagnosis and the various potential results. At the end of the consultation, the couple sign consent forms stating that they have received the relevant information and agree to pursue the procedure.

    4.5. PID implementation (fig. 1)

    4.5.1. First stage: medically assisted procreation

    4.5.1.1. Ovarian stimulation

    The protocol, drugs and dosages depend on the patient’s age, hormone results on day 3 of the cycle, and body mass index. Except in special cases, long protocols combining GnRH agonists and FSH are selected on the basis of their performance and scope for scheduling. Scheduling is, in fact, essential since PID implementation necessitates the commitment of an indissociable team at a given time (clinician, biologist, geneticist). The follicles are regularly monitored by ultrasound (growth) and hormone assays (secretion). When the follicles are mature, ovulation is triggered by hCG injection. The follicles are sampled 36 hours later by the vaginal route under ultrasound guidance and under general or local anesthesia.

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    Figure 1. PID preparation and implementation (Biomedicines Agency)

    4.5.1.2. Spermatozoid collection

    The spermatozoids are collected on the day of oocyte sampling: the patient’s partner’s sperm is collected by masturbation. Frozen sperm may also be used (the straws are thawed on the day of oocyte collection.

    4.5.1.3. IVF-ICSI and embryo culturing

    In vitro fertilization is conducted on the day of oocyte collection. ICSI is indispensable in order to prevent contamination by spermatozoids bound to the pellucid zone.

    4.5.2. Second stage: collection and identification of genetic disease free embryos

    4.5.2.1. Embryo biopsy

    Only well developed embryo may be biopsied (stage: 6-8 cells). Biopsy is conducted three days after fertilization, and consists in sampling one or two cells (blastomers) from the embryo for genetic analysis (fig. 2).

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    Figure 2. Blastomer biopsy

    4.5.2.2. Genetic diagnosis

    Genetic diagnosis is conducted on the day of biopsy (24 - 36 h). The method used is the polymerase chain reaction (PCR), which enables exponential in vitro amplification of fragments of the gene of interest through serial cycles of hybridization and dehybridization. It is advisable to sample and independently analyze two blastomers from the same embryo, in order to enhance the reliability of the diagnosis.

    Several difficulties inherent in the analysis of a single cell are now well known: total absence of amplification; potential test sample contamination; allele dropout phenomenon (non amplification or non detection of one of the two alleles at a given locus in a heterozygous cell) [4]; preferential amplification of one of the two alleles. These difficulties are to be taken into account in the overall PID procedure and are to be explained to the couple. In the case of dystrophinopathies an additional test is conducted (amelogenin) to distinguish between male and female embryos (fig. 3).

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    Figure 3. PID for a couple in which the woman is a carrier (heterozygous) of a deletion of exons 3 to 47 of the DMD gene
    Above: female embryo (1 “amelo” allele) not a carrier for the familial deletion. Below: male embryo (2 “amelo” alleles and Y-specific DYS388) with DMD and with deletion of exons E44-E45 and microsatellite markers located in the deleted region (for introns I45-44-4-25 and 41). The amplification of the sequences located outside of the deletion (control) ensures the quality of the results (images and commentary kindly provided by Dr. Anne Girardet)

    4.5.2.3. Embryo transfer

    For DMD/BMD, depending on the legal framework, the following are proposed: transfer of female embryos (mutated or non mutated) and transfer of non mutated male embryos. Transfer consists of placing the embryo in the uterus using a thin flexible catheter inserted by the vaginal route. After the transfer, the probability of pregnancy is about 30%. About two weeks after the transfer, an initial pregnancy test is conducted on a blood sample. If the test confirms pregnancy, ultrasound is conducted to determine whether the pregnancy is single or multiple and whether the embryo(s) is (are) developing correctly.

    4.5.3. Third stage: results

    4.5.3.1. Prenatal diagnosis

    The risk of error is not nil [5]. This is to be discussed with the couple on a case by case basis. In light of that risk, the center biologist who conducted preimplantation genetic diagnosis evaluates the interest of conducting prenatal diagnosis during the pregnancy in order to confirm the PID result.

    4.5.3.2. Follow-up

    In 8 cases out of 10 the pregnancy is followed by birth since the spontaneous miscarriage rate is about 20%, as is the case for naturally induced pregnancies. The results of the PID conducted in Europe are regularly collated and studies by the European Society for Human Reproduction and Embryology (ESHRE) [6]. Follow-up of the children born post-PID has shown that their preand post-natal growth and development were similar to those of children born after IVF-ICSI. PID does not appear to be associated with an increased health risk in that population [7].

    5. Non invasive prenatal diagnosis (NIPND): the future?

    The presence of circulating fetal DNA in maternal plasma affords the potential for development of non-invasive prenatal genetic diagnosis. Following the development of non-invasive diagnosis of aneuploidies, studies are beginning to suggest that it would be possible to determine, by targeted new generation sequencing on maternal plasma, the status with respect to carrying a familial deletion/duplication or point mutation at about 7 weeks of gestation [1].

    6. Conclusions

    While considerable technological progress has been made, particularly in the last ten years [8], it should not be forgotten that PND and PID (and NlPND?) address couples who have often already been greatly distressed by loss of a sick child. The procedures are proposed within a strict legal framework and call for great rigor with respect to the information given and attentive psychological support.

    Statement of interests

    The author has no interests related to this article.

    References

    [1] Yoo SK, Lim BC, Byeun J et al. Noninvasive prenatal diagnosis of Duchenne muscular dystrophy: comprehensive genetic diagnosis in carrier, proband, and fœtus. Clin Chem 2015;61:829-37.

    [2] Bonneau D, Marlin S, Sanlaville et al. Les tests génétiques à l’heure de la deuxième révision des lois de bioéthique. Pathol Biol (Paris) 2010;58:396-401.

    [3] Handyside AH, Kontogianni EH, Hardy K, et al. Pregnancies from biopsied human preimplantation embryos sexed by Y-specific DNA amplification. Nature 1990;344:768-70.

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    [7] Desmyttere S, Bonduelle M, Nekkebroeck J et al. Growth and health outcome of 102 2-year-old children conceived after preimplantation genetic diagnosis or screening. Early Hum Dev 2009;85:755-9.

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    Find out more

    [1] Agence de la biomédecine: www.agence-biomedecine.fr.
    [2] Légifrance: www.legifrance.gouv.fr.

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