Outcome reliability in non-ambulatory boys/men with Duchenne muscular dystrophy

INTRODUCTION

Therapeutic trials in Duchenne muscular dystrophy (DMD) often exclude non-ambulatory individuals. Here we establish optimal and reliable assessments in a multicenter trial.

METHODS

Non-ambulatory boys/men with DMD (N = 91; 16.7 ± 4.5 years of age) were assessed by trained clinical evaluators. Feasibility (percentage completing task) and reliability [intraclass correlation coefficients (ICCs) between morning and afternoon tests] were measured.

RESULTS

Forced vital capacity (FVC), assessed in all subjects, showed a mean of 47.8 ± 22% predicted (ICC 0.98). Brooke Upper Extremity Functional Rating (Brooke) and Egen Klassifikation (EK) scales in 100% of subjects showed ICCs ranging from 0.93 to 0.99. Manual muscle testing, range of motion, 9-hole peg test, and Jebsen-Taylor Hand Function Test (JHFT) demonstrated varied feasibility (99% to 70%), with ICCs ranging from 0.99 to 0.64. We found beneficial effects of different forms of corticosteroids for the Brooke scale, percent predicted FVC, and hand and finger strength.

CONCLUSIONS

Reliable assessment of non-ambulatory boys/men with DMD is possible. Clinical trials will have to consider corticosteroid use.

Dystrophin quantification: Biological and translational research implications

OBJECTIVE

We formed a multi-institution collaboration in order to compare dystrophin quantification methods, reach a consensus on the most reliable method, and report its biological significance in the context of clinical trials.

METHODS

Five laboratories with expertise in dystrophin quantification performed a data-driven comparative analysis of a single reference set of normal and dystrophinopathy muscle biopsies using quantitative immunohistochemistry and Western blotting. We developed standardized protocols and assessed inter- and intralaboratory variability over a wide range of dystrophin expression levels.

RESULTS

Results from the different laboratories were highly concordant with minimal inter- and intralaboratory variability, particularly with quantitative immunohistochemistry. There was a good level of agreement between data generated by immunohistochemistry and Western blotting, although immunohistochemistry was more sensitive. Furthermore, mean dystrophin levels determined by alternative quantitative immunohistochemistry methods were highly comparable.

CONCLUSIONS

Considering the biological function of dystrophin at the sarcolemma, our data indicate that the combined use of quantitative immunohistochemistry and Western blotting are reliable biochemical outcome measures for Duchenne muscular dystrophy clinical trials, and that standardized protocols can be comparable between competent laboratories. The methodology validated in our study will facilitate the development of experimental therapies focused on dystrophin production and their regulatory approval.

Ataluren treatment of patients with nonsense mutation dystrophinopathy

INTRODUCTION

Dystrophinopathy is a rare, severe muscle disorder, and nonsense mutations are found in 13% of cases. Ataluren was developed to enable ribosomal readthrough of premature stop codons in nonsense mutation (nm) genetic disorders.

METHODS

Randomized, double-blind, placebo-controlled study; males ≥ 5 years with nm-dystrophinopathy received study drug orally 3 times daily, ataluren 10, 10, 20 mg/kg (N=57); ataluren 20, 20, 40 mg/kg (N=60); or placebo (N=57) for 48 weeks. The primary endpoint was change in 6-Minute Walk Distance (6MWD) at Week 48.

RESULTS

Ataluren was generally well tolerated. The primary endpoint favored ataluren 10, 10, 20 mg/kg versus placebo; the week 48 6MWD Δ=31.3 meters, post hoc P=0.056. Secondary endpoints (timed function tests) showed meaningful differences between ataluren 10, 10, 20 mg/kg, and placebo.

CONCLUSIONS

As the first investigational new drug targeting the underlying cause of nm-dystrophinopathy, ataluren offers promise as a treatment for this orphan genetic disorder with high unmet medical need.

Translation from a DMD exon 5 IRES results in a functional dystrophin isoform that attenuates dystrophinopathy in humans and mice

Most mutations that truncate the reading frame of the DMD gene cause loss of dystrophin expression and lead to Duchenne muscular dystrophy. However, amelioration of disease severity has been shown to result from alternative translation initiation beginning in DMD exon 6 that leads to expression of a highly functional N-truncated dystrophin. Here we demonstrate that this isoform results from usage of an internal ribosome entry site (IRES) within exon 5 that is glucocorticoid inducible. We confirmed IRES activity by both peptide sequencing and ribosome profiling in muscle from individuals with minimal symptoms despite the presence of truncating mutations. We generated a truncated reading frame upstream of the IRES by exon skipping, which led to synthesis of a functional N-truncated isoform in both human subject-derived cell lines and in a new DMD mouse model, where expression of the truncated isoform protected muscle from contraction-induced injury and corrected muscle force to the same level as that observed in control mice. These results support a potential therapeutic approach for patients with mutations within the 5' exons of DMD.

Dexmedetomidine and ketamine sedation for muscle biopsies in patients with Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) possesses many potential challenges for anesthetic care. Invasive and noninvasive procedures with corresponding sedation or general anesthesia are frequent and necessary for affected patients. There remains a need for a better agent or agents for procedural sedation in patients with comorbid diseases. This study prospectively evaluated a combination of ketamine with two different doses of dexmedetomidine for sedation during muscle biopsy in patients with DMD.

METHODS

Dexmedetomidine 1.0 or 0.5 μg·kg(-1) was administered as a loading dose over 3 min followed by a continuous infusion of 1.0 or 0.5 μg·kg·h(-1). Ketamine (1 mg·kg(-1)) was administered along with the dexmedetomidine loading dose. As the procedure commenced, additional doses of ketamine (0.5 mg·kg(-1)) were administered as needed. Sedation scores, hemodynamic data, operative times, and recovery times were recorded.

RESULTS

The study cohort included a total of 53 bicep, deltoid, or anterior tibialis muscle biopsies in 19 boys including 24 in the dexmedetomidine 1.0 μg·kg(-1) group and 29 in the dexmedetomidine 0.5 μg·kg(-1) group. Mean age and weight were 9.7 ± 1.4 years and 33.3 ± 7.7 kg in the dexmedetomidine 1.0 μg·kg(-1) group and 8.8 ± 1.8 years and 30.2 ± 10.8 kg in the dexmedetomidine 0.5 μg·kg(-1) group. No significant changes in blood pressure were noted. A decrease in heart rate (HR) occurred after the loading dose of dexmedetomidine in both groups. The HR was significantly lower in the dexmedetomidine 1.0 μg·kg(-1) group compared with the dexmedetomidine 0.5 μg·kg(-1) group. Total recovery time to discharge was significantly shorter in the dexmedetomidine 0.5 μg·kg(-1) group than the dexmedetomidine 1.0 μg·kg(-1) group (146 ± 65 vs 174 ± 58 min; P = 0.03), although the total ketamine dose was significantly greater in the dexmedetomidine 0.5 μg·kg(-1) group (3.7 ± 1.0 vs 2.0 ± 0.5 mg·kg(-1); P < 0.01). There were no episodes of apnea or hypoventilation; however, a jaw thrust was needed in one patient in the dexmedetomidine 1.0 μg·kg(-1) group.

CONCLUSION

The combination of dexmedetomidine and ketamine is safe and effective for moderately painful procedures with limited respiratory and cardiovascular effects in a high-risk patient population. Dexmedetomidine 0.5 μg·kg(-1) as a loading dose with ketamine followed by a continuous infusion of dexmedetomidine at 0.5 μg·kg(-1) ·h(-1) achieved an adequate sedation level with shorter total recovery times in the perioperative unit compared with a higher dose regimen of dexmedetomidine (1.0 μg·kg(-1) loading dose followed by an infusion at 1.0 μg·kg(-1) ·h(-1)).

Position of glycine substitutions in the triple helix of COL6A1, COL6A2, and COL6A3 is correlated with severity and mode of inheritance in collagen VI myopathies

Glycine substitutions in the conserved Gly-X-Y motif in the triple helical (TH) domain of collagen VI are the most commonly identified mutations in the collagen VI myopathies including Ullrich congenital muscular dystrophy, Bethlem myopathy, and intermediate (INT) phenotypes. We describe clinical and genetic characteristics of 97 individuals with glycine substitutions in the TH domain of COL6A1, COL6A2, or COL6A3 and add a review of 97 published cases, for a total of 194 cases. Clinical findings include severe, INT, and mild phenotypes even from patients with identical mutations. INT phenotypes were most common, accounting for almost half of patients, emphasizing the importance of INT phenotypes to the overall phenotypic spectrum. Glycine substitutions in the TH domain are heavily clustered in a short segment N-terminal to the 17th Gly-X-Y triplet, where they are acting as dominants. The most severe cases are clustered in an even smaller region including Gly-X-Y triplets 10-15, accounting for only 5% of the TH domain. Our findings suggest that clustering of glycine substitutions in the N-terminal region of collagen VI is not based on features of the primary sequence. We hypothesize that this region may represent a functional domain within the triple helix.

Feasibility and safety of systemic rAAV9-hNAGLU delivery for treating mucopolysaccharidosis IIIB: toxicology, biodistribution, and immunological assessments in primates

No treatment is currently available for mucopolysaccharidosis (MPS) IIIB, a neuropathic lysosomal storage disease caused by autosomal recessive defect in α-N-acetylglucosaminidase (NAGLU). In anticipation of a clinical gene therapy treatment for MPS IIIB in humans, we tested the rAAV9-CMV-hNAGLU vector administration to cynomolgus monkeys (n=8) at 1E13 vg/kg or 2E13 vg/kg via intravenous injection. No adverse events or detectable toxicity occurred over a 6-month period. Gene delivery resulted in persistent global central nervous system and broad somatic transduction, with NAGLU activity detected at 2.9-12-fold above endogenous levels in somatic tissues and 1.3-3-fold above endogenous levels in the brain. Secreted rNAGLU was detected in serum. Low levels of preexisting anti-AAV9 antibodies (Abs) did not diminish vector transduction. Importantly, high-level preexisting anti-AAV9 Abs lead to reduced transduction in liver and other somatic tissues, but had no detectable impact on transgene expression in the brain. Enzyme-linked immunoabsorbent assay showed Ab responses to both AAV9 and rNAGLU in treated animals. Serum anti-hNAGLU Abs, but not anti-AAV9 Abs, correlated with the loss of circulating rNAGLU enzyme. However, serum Abs did not affect tissue rNAGLU activity levels. Weekly or monthly peripheral blood interferon-γ enzyme-linked immunospot assays detected a CD4(+) T-cell (Th-1) response to rNAGLU only at 4 weeks postinjection in one treated subject, without observable correlation to tissue transduction levels. The treatment did not result in detectable CTL responses to either AAV9 or rNAGLU. Our data demonstrate an effective and safe profile for systemic rAAV9-hNAGLU vector delivery in nonhuman primates, supporting its clinical potential in humans.

Recurrent central nervous system white matter changes in charcot-Marie-tooth type X disease

INTRODUCTION

X-linked Charcot-Marie-Tooth (CMT1X) disease is caused by mutations in the GJB1 gene. We describe a young man who presented with recurrent central nervous symptoms and transient white matter changes in the setting of a novel mutation in the GJB1 gene.

METHODS

Evaluation included clinical examination, neuroimaging, electrophysiological, and molecular genetic studies.

RESULTS

Clinical examination on 2 admissions 5 years apart demonstrated hemiparesis with findings of underlying peripheral neuropathy. Electrophysiologic studies revealed a sensorimotor polyneuropathy. MRI studies from both admissions revealed white matter changes, with improvement on an intervening study. Mutation analysis showed a novel mutation (c.98T>A; p.Ile33Asn) in the GJB1 gene.

CONCLUSIONS

Mutations in GJB1 can result in recurrent central nervous system symptoms with transient white matter signal changes on MRI. In patients presenting with hemiparesis, the presence of signs of a peripheral neuropathy may facilitate identification of CMT1X, and is likely to affect clinical management.

Exome sequencing identifies a DNAJB6 mutation in a family with dominantly-inherited limb-girdle muscular dystrophy

Limb-girdle muscular dystrophy primarily affects the muscles of the hips and shoulders (the "limb-girdle" muscles), although it is a heterogeneous disorder that can present with varying symptoms. There is currently no cure. We sought to identify the genetic basis of limb-girdle muscular dystrophy type 1 in an American family of Northern European descent using exome sequencing. Exome sequencing was performed on DNA samples from two affected siblings and one unaffected sibling and resulted in the identification of eleven candidate mutations that co-segregated with the disease. Notably, this list included a previously reported mutation in DNAJB6, p.Phe89Ile, which was recently identified as a cause of limb-girdle muscular dystrophy type 1D. Additional family members were Sanger sequenced and the mutation in DNAJB6 was only found in affected individuals. Subsequent haplotype analysis indicated that this DNAJB6 p.Phe89Ile mutation likely arose independently of the previously reported mutation. Since other published mutations are located close by in the G/F domain of DNAJB6, this suggests that the area may represent a mutational hotspot. Exome sequencing provided an unbiased and effective method for identifying the genetic etiology of limb-girdle muscular dystrophy type 1 in a previously genetically uncharacterized family. This work further confirms the causative role of DNAJB6 mutations in limb-girdle muscular dystrophy type 1D.

A comparative study of N-glycolylneuraminic acid (Neu5Gc) and cytotoxic T cell (CT) carbohydrate expression in normal and dystrophin-deficient dog and human skeletal muscle

The expression of N-glycolylneuraminic acid (Neu5Gc) and the cytotoxic T cell (CT) carbohydrate can impact the severity of muscular dystrophy arising from the loss of dystrophin in mdx mice. Here, we describe the expression of these two glycans in skeletal muscles of dogs and humans with or without dystrophin-deficiency. Neu5Gc expression was highly reduced (>95%) in muscle from normal golden retriever crosses (GR, n = 3) and from golden retriever with muscular dystrophy (GRMD, n = 5) dogs at multiple ages (3, 6 and 13 months) when compared to mouse muscle, however, overall sialic acid expression in GR and GRMD muscles remained high at all ages. Neu5Gc was expressed on only a minority of GRMD satellite cells, CD8⁺ T lymphocytes and macrophages. Human muscle from normal (no evident disease, n = 3), Becker (BMD, n = 3) and Duchenne (DMD, n = 3) muscular dystrophy individuals had absent to very low Neu5Gc staining, but some punctate intracellular muscle staining was present in BMD and DMD muscles. The CT carbohydrate was localized to the neuromuscular junction in GR muscle, while GRMD muscles had increased expression on a subset of myofibers and macrophages. In humans, the CT carbohydrate was ectopically expressed on the sarcolemmal membrane of some BMD muscles, but not normal human or DMD muscles. These data are consistent with the notion that altered Neu5Gc and CT carbohydrate expression may modify disease severity resulting from dystrophin deficiency in dogs and humans.

A randomized, double-blind trial of lisinopril and losartan for the treatment of cardiomyopathy in duchenne muscular dystrophy

OBJECTIVES

This study sought to compare the effectiveness and safety of an angiotensin converting enzyme inhibitor (ACE-I) (lisinopril) vs. an angiotensin receptor blocker (ARB) (losartan) for the treatment of cardiomyopathy (CM) in boys with Duchenne muscular dystrophy (DMD).

BACKGROUND

Development of CM is universal in boys with DMD. ACE-I and ARB have both been suggested as effective treatment options. ARBs have been associated with skeletal muscle regeneration in a mouse model of DMD. The question of which, if either, is more effective for CM treatment in DMD remains. The purpose of this multicenter double-blind prospective study was to compare efficacy and safety of lisinopril versus losartan in the treatment of newly diagnosed CM in boys with DMD.

METHODS

Echocardiographic technician inter- and intraobserver variability were tested on 2 separate days on 2 different boys with DMD CM. Results were compared with paired t-testing. Twenty-two boys with newly diagnosed DMD CM (echocardiographic ejection fraction (EF) 10% EF drop. Three boys in the aCE-I group had 3 visits, due to study funding termination. Two were withdrawn because of low EF. All their data are included in the analysis for as long as they remained in the study. Mean EF's were similar at baseline (47.5%- ACE-I, 48.4%- ARB). After 1 year each group significantly improved to 54.6% and 55.2% respectively (p=.02). There was no difference between the 2 treatment groups at 1 year.

CONCLUSIONS

Inter-observer and intra-observer reliability studies showed no differences between echocardiographers on serial examinations. EF improved equally in the two groups. There is no therapeutic difference in EF improvement between lisinopril and losartan over the one-year duration for treatment of boys with DMD-related CM.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01982695.

Phase 2a study of ataluren-mediated dystrophin production in patients with nonsense mutation Duchenne muscular dystrophy

Background

Approximately 13% of boys with Duchenne muscular dystrophy (DMD) have a nonsense mutation in the dystrophin gene, resulting in a premature stop codon in the corresponding mRNA and failure to generate a functional protein. Ataluren (PTC124) enables ribosomal readthrough of premature stop codons, leading to production of full-length, functional proteins.

Methods

This Phase 2a open-label, sequential dose-ranging trial recruited 38 boys with nonsense mutation DMD. The first cohort (n = 6) received ataluren three times per day at morning, midday, and evening doses of 4, 4, and 8 mg/kg; the second cohort (n = 20) was dosed at 10, 10, 20 mg/kg; and the third cohort (n = 12) was dosed at 20, 20, 40 mg/kg. Treatment duration was 28 days. Change in full-length dystrophin expression, as assessed by immunostaining in pre- and post-treatment muscle biopsy specimens, was the primary endpoint.

Findings

Twenty three of 38 (61%) subjects demonstrated increases in post-treatment dystrophin expression in a quantitative analysis assessing the ratio of dystrophin/spectrin. A qualitative analysis also showed positive changes in dystrophin expression. Expression was not associated with nonsense mutation type or exon location. Ataluren trough plasma concentrations active in the mdx mouse model were consistently achieved at the mid- and high- dose levels in participants. Ataluren was generally well tolerated.

Interpretation

Ataluren showed activity and safety in this short-term study, supporting evaluation of ataluren 10, 10, 20 mg/kg and 20, 20, 40 mg/kg in a Phase 2b, double-blind, long-term study in nonsense mutation DMD.

Trial Registration

ClinicalTrials.gov NCT00264888

The ZZ domain of dystrophin in DMD: making sense of missense mutations

Duchenne muscular dystrophy (DMD) is associated with the loss of dystrophin, which plays an important role in myofiber integrity via interactions with β-dystroglycan and other members of the transmembrane dystrophin-associated protein complex. The ZZ domain, a cysteine-rich zinc-finger domain near the dystrophin C-terminus, is implicated in forming a stable interaction between dystrophin and β-dystroglycan, but the mechanism of pathogenesis of ZZ missense mutations has remained unclear because not all such mutations have been shown to alter β-dystroglycan binding in previous experimental systems. We engineered three ZZ mutations (p.Cys3313Phe, p.Asp3335His, and p.Cys3340Tyr) into a short construct similar to the Dp71 dystrophin isoform for in vitro and in vivo studies and delineated their effect on protein expression, folding properties, and binding partners. Our results demonstrate two distinct pathogenic mechanisms for ZZ missense mutations. The cysteine mutations result in diminished or absent subsarcolemmal expression because of protein instability, likely due to misfolding. In contrast, the aspartic acid mutation disrupts binding with β-dystroglycan despite an almost normal expression at the membrane, confirming a role for the ZZ domain in β-dystroglycan binding but surprisingly demonstrating that such binding is not required for subsarcolemmal localization of dystrophin, even in the absence of actin binding domains.

Pharmacokinetics and safety of single doses of drisapersen in non-ambulant subjects with Duchenne muscular dystrophy: results of a double-blind randomized clinical trial

Duchenne muscular dystrophy (DMD) is a progressive, lethal neuromuscular disorder caused by the absence of dystrophin protein due to mutations of the dystrophin gene. Drisapersen is a 2′-O-methyl-phosphorothioate oligonucleotide designed to skip exon 51 in dystrophin pre-mRNA to restore the reading frame of the mRNA. This study assessed safety, tolerability, and pharmacokinetics of drisapersen after a single subcutaneous administration in non-ambulatory subjects. Eligible subjects were non-ambulant boys aged ≥9 years, in wheelchairs for ≥1 to ≤4 years, with a diagnosis of DMD resulting from a mutation correctable by drisapersen treatment. Four dose cohorts were planned (3, 6, 9 and 12 mg/kg), but study objectives were met with the 9 mg/kg dose. Less than proportional increase in exposure was demonstrated over the 3–9 mg/kg dose range, though post hoc analysis showed dose proportionality was more feasible over the 3–6 mg/kg range. Single doses of drisapersen at 3 and 6 mg/kg did not result in significant safety or tolerability concerns; however, at the 9 mg/kg dose, pyrexia and transient elevations in inflammatory parameters were seen. The maximum tolerated dose of 6 mg/kg drisapersen was identified for further characterization in multiple dose studies in the non-ambulant DMD population.

Eteplirsen for the treatment of Duchenne muscular dystrophy

OBJECTIVE

In prior open-label studies, eteplirsen, a phosphorodiamidate morpholino oligomer, enabled dystrophin production in Duchenne muscular dystrophy (DMD) with genetic mutations amenable to skipping exon 51. The present study used a double-blind placebo-controlled protocol to test eteplirsen's ability to induce dystrophin production and improve distance walked on the 6-minute walk test (6MWT).

METHODS

DMD boys aged 7 to 13 years, with confirmed deletions correctable by skipping exon 51 and ability to walk 200 to 400 m on 6 MWT, were randomized to weekly intravenous infusions of 30 or 50 mg/kg/wk eteplirsen or placebo for 24 weeks (n = 4/group). Placebo patients switched to 30 or 50 mg/kg eteplirsen (n=2/group) at week 25; treatment was open label thereafter. All patients had muscle biopsies at baseline and week 48. Efficacy included dystrophin-positive fibers and distance walked on the 6MWT.

RESULTS

At week 24, the 30 mg/kg eteplirsen patients were biopsied, and percentage of dystrophin-positive fibers was increased to 23% of normal; no increases were detected in placebo-treated patients (p≤0.002). Even greater increases occurred at week 48 (52% and 43% in the 30 and 50 mg/kg cohorts, respectively), suggesting that dystrophin increases with longer treatment. Restoration of functional dystrophin was confirmed by detection of sarcoglycans and neuronal nitric oxide synthase at the sarcolemma. Ambulation-evaluable eteplirsen-treated patients experienced a 67.3 m benefit compared to placebo/delayed patients (p≤0.001).

INTERPRETATION

Eteplirsen restored dystrophin in the 30 and 50 mg/kg/wk cohorts, and in subsequently treated, placebo-controlled subjects. Duration, more than dose, accounted for dystrophin production, also resulting in ambulation stability. No severe adverse events were encountered.

Anti-dystrophin T cell responses in Duchenne muscular dystrophy: prevalence and a glucocorticoid treatment effect

Duchenne muscular dystrophy (DMD) typically occurs as a result of truncating mutations in the DMD gene that result in a lack of expression of the dystrophin protein in muscle fibers. Various therapies under development are directed toward restoring dystrophin expression at the subsarcolemmal membrane, including gene transfer. In a trial of intramuscular adeno-associated virus (AAV)-mediated delivery of a therapeutic minidystrophin construct, we identified in two of six subjects the presence of a population of T cells that had been primed to recognize dystrophin epitopes before transgene delivery. As the presence of preexisting T cell immunity may have a significant effect on the success of therapeutic approaches for restoring dystrophin, we sought to determine the prevalence of such immunity within a DMD cohort from our Muscular Dystrophy Association clinic. Dystrophin-specific T cell immunity was evaluated in subjects with DMD who were either receiving the glucocorticoid steroid prednisone (n=24) or deflazacort (n=29), or who were not receiving steroids (n=17), as well as from normal age-matched control subjects (n=21). We demonstrate that increasing age correlates with an increased risk for the presence of anti-dystrophin T cell immunity, and that treatment with either corticosteroid decreases risk compared with no treatment, suggesting that steroid therapy in part may derive some of its benefit through modulation of T cell responses. The frequency of dystrophin-specific T cells detected by enzyme-linked immunospot assay was lower in subjects treated with deflazacort versus prednisone, despite similar overall corticosteroid exposure, suggesting that the effects of the two corticosteroids may not be identical in patients with DMD. T cells targeted epitopes upstream and downstream of the dystrophin gene mutation and involved the CD4⁺ helper and/or CD8⁺ cytotoxic subsets. Our data confirm the presence of preexisting circulating T cell immunity to dystrophin in a sizable proportion of patients with DMD, and emphasize the need to consider this in the design and interpretation of clinical gene therapy trials.

The TREAT-NMD Duchenne muscular dystrophy registries: conception, design, and utilization by industry and academia

Duchenne muscular dystrophy (DMD) is an X-linked genetic disease, caused by the absence of the dystrophin protein. Although many novel therapies are under development for DMD, there is currently no cure and affected individuals are often confined to a wheelchair by their teens and die in their twenties/thirties. DMD is a rare disease (prevalence <5/10,000). Even the largest countries do not have enough affected patients to rigorously assess novel therapies, unravel genetic complexities, and determine patient outcomes. TREAT-NMD is a worldwide network for neuromuscular diseases that provides an infrastructure to support the delivery of promising new therapies for patients. The harmonized implementation of national and ultimately global patient registries has been central to the success of TREAT-NMD. For the DMD registries within TREAT-NMD, individual countries have chosen to collect patient information in the form of standardized patient registries to increase the overall patient population on which clinical outcomes and new technologies can be assessed. The registries comprise more than 13,500 patients from 31 different countries. Here, we describe how the TREAT-NMD national patient registries for DMD were established. We look at their continued growth and assess how successful they have been at fostering collaboration between academia, patient organizations, and industry.

Identification of new dystroglycan complexes in skeletal muscle

The dystroglycan complex contains the transmembrane protein β-dystroglycan and its interacting extracellular mucin-like protein α-dystroglycan. In skeletal muscle fibers, the dystroglycan complex plays an important structural role by linking the cytoskeletal protein dystrophin to laminin in the extracellular matrix. Mutations that affect any of the proteins involved in this structural axis lead to myofiber degeneration and are associated with muscular dystrophies and congenital myopathies. Because loss of dystrophin in Duchenne muscular dystrophy (DMD) leads to an almost complete loss of dystroglycan complexes at the myofiber membrane, it is generally assumed that the vast majority of dystroglycan complexes within skeletal muscle fibers interact with dystrophin. The residual dystroglycan present in dystrophin-deficient muscle is thought to be preserved by utrophin, a structural homolog of dystrophin that is up-regulated in dystrophic muscles. However, we found that dystroglycan complexes are still present at the myofiber membrane in the absence of both dystrophin and utrophin. Our data show that only a minority of dystroglycan complexes associate with dystrophin in wild type muscle. Furthermore, we provide evidence for at least three separate pools of dystroglycan complexes within myofibers that differ in composition and are differentially affected by loss of dystrophin. Our findings indicate a more complex role of dystroglycan in muscle than currently recognized and may help explain differences in disease pathology and severity among myopathies linked to mutations in DAPC members.

Motor and cognitive assessment of infants and young boys with Duchenne Muscular Dystrophy: results from the Muscular Dystrophy Association DMD Clinical Research Network

Therapeutic trials in Duchenne Muscular Dystrophy (DMD) exclude young boys because traditional outcome measures rely on cooperation. The Bayley III Scales of Infant and Toddler Development (Bayley III) have been validated in developing children and those with developmental disorders but have not been studied in DMD. Expanded Hammersmith Functional Motor Scale (HFMSE) and North Star Ambulatory Assessment (NSAA) may also be useful in this young DMD population. Clinical evaluators from the MDA-DMD Clinical Research Network were trained in these assessment tools. Infants and boys with DMD (n = 24; 1.9 ± 0.7 years) were assessed. The mean Bayley III motor composite score was low (82.8 ± 8; p ≤ .0001) (normal = 100 ± 15). Mean gross motor and fine motor function scaled scores were low (both p ≤ .0001). The mean cognitive comprehensive (p=.0002), receptive language (p ≤ .0001), and expressive language (p = .0001) were also low compared to normal children. Age was negatively associated with Bayley III gross motor (r = -0.44; p = .02) but not with fine motor, cognitive, or language scores. HFMSE (n=23) showed a mean score of 31 ± 13. NSAA (n = 18 boys; 2.2 ± 0.4 years) showed a mean score of 12 ± 5. Outcome assessments of young boys with DMD are feasible and in this multicenter study were best demonstrated using the Bayley III.

Cardiac management in neuromuscular diseases

This article addresses the pathophysiology, diagnostic approaches, and therapeutic options in the more common forms of muscular dystrophy, especially those seen in pediatric and young adult populations. The major emphasis is on the dystrophinopathies because their treatment options are templates for those used in various other forms of dystrophy. Most patients with cardiomyopathy are treated with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, with other agents added as the disease progresses. Destination therapies and transplantation options are mentioned where appropriate. Some dystrophies can have significant conduction abnormalities requiring pacemaker treatment. Others with ventricular tachydysrhythmias may necessitate internal cardiac defibrillator placement.