Assessing Pharmacogenomic loci Associated with the Pharmacokinetics of Vamorolone in Boys with Duchenne Muscular Dystrophy

Human genetic variation (polymorphisms) in genes coding proteins involved in the absorption, distribution, metabolism, and elimination (ADME) of drugs can have a strong effect on drug exposure and downstream efficacy and safety outcomes. Vamorolone, a dissociative steroidal anti-inflammatory drug for treating Duchenne muscular dystrophy (DMD), primarily undergoes oxidation by CYP3A4 and CYP3A5 and glucuronidation by UDP-glucuronosyltransferases. This work assesses the pharmacokinetics (PKs) of vamorolone and sources of interindividual variability (IIV) in 81 steroid-naïve boys with DMD aged 4 to <7 years old considering the genetic polymorphisms of CYPS3A4 (CYP3A4*22, CYP3A4*1B), CYP3A5 (CYP3A5*3), and UGT1A1 (UGT1A1*60) utilizing population PK modeling. A one-compartment model with zero-order absorption (Tk0, duration of absorption), linear clearance (CL/F), and volume (V/F) describes the plasma PK data for boys with DMD receiving a wide range of vamorolone doses (0.25-6 mg/kg/day). The typical CL/F and V/F values of vamorolone were 35.8 L/h and 119 L, with modest IIV. The population Tk0 was 3.14 h yielding an average zero-order absorption rate (k0) of 1.16 mg/kg/h with similar absorption kinetics across subjects at the same vamorolone dose (i.e., no IIV on Tk0). The covariate analysis showed that none of the genetic covariates had any significant impact on the PKs of vamorolone in boys with DMD. Thus, the PKs of vamorolone is very consistent in these young boys with DMD.

Efficacy and Safety of Vamorolone Over 48 Weeks in Boys With Duchenne Muscular Dystrophy: A Randomized Controlled Trial

BACKGROUND AND OBJECTIVES

Vamorolone is a dissociative agonist of the glucocorticoid receptor that has shown similar efficacy and reduced safety concerns in comparison with prednisone in Duchenne muscular dystrophy (DMD). This study was conducted to determine the efficacy and safety of vamorolone over 48 weeks and to study crossover participants (prednisone to vamorolone; placebo to vamorolone).

METHODS

A randomized, double-blind, placebo-controlled and prednisone-controlled clinical trial of 2 doses of vamorolone was conducted in participants with DMD, in the ages from 4 years to younger than 7 years at baseline. The interventions were 2 mg/kg/d of vamorolone and 6 mg/kg/d of vamorolone for 48 weeks (period 1: 24 weeks + period 2: 24 weeks) and 0.75 mg/kg/d of prednisone and placebo for the first 24 weeks (before crossover). Efficacy was evaluated through gross motor outcomes and safety through adverse events, growth velocity, body mass index (BMI), and bone turnover biomarkers. This analysis focused on period 2.

RESULTS

A total of 121 participants with DMD were randomized. Vamorolone at a dose of 6 mg/kg/d showed maintenance of improvement for all motor outcomes to week 48 (e.g., for primary outcome, time to stand from supine [TTSTAND] velocity, week 24 least squares mean [LSM] [SE] 0.052 [0.0130] rises/s vs week 48 LSM [SE] 0.0446 [0.0138]). After 48 weeks, vamorolone at a dose of 2 mg/kg/d showed similar improvements as 6 mg/kg/d for North Star Ambulatory Assessment (NSAA) (vamorolone 6 mg/kg/d-vamorolone 2 mg/kg/d LSM [SE] 0.49 [1.14]; 95% CI -1.80 to 2.78, p = 0.67), but less improvement for other motor outcomes. The placebo to vamorolone 6 mg/kg/d group showed rapid improvements after 20 weeks of treatment approaching benefit seen with 48-week 6 mg/kg/d of vamorolone treatment for TTSTAND, time to run/walk 10 m, and NSAA. There was significant improvement in linear growth after crossover in the prednisone to vamorolone 6 mg/kg/d group, and rapid reversal of prednisone-induced decline in bone turnover biomarkers in both crossover groups. There was an increase in BMI after 24 weeks of treatment that then stabilized for both vamorolone groups.

DISCUSSION

Improvements of motor outcomes seen with 6 mg/kg/d of vamorolone at 24 weeks of treatment were maintained to 48 weeks of treatment. Vamorolone at a dose of 6 mg/kg/d showed better maintenance of effect compared with vamorolone at a dose of 2 mg/kg/d for most (3/5) motor outcomes. Bone morbidities of prednisone (stunting of growth and declines in serum bone biomarkers) were reversed when treatment transitioned to vamorolone.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT03439670.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for boys with DMD, the efficacy of vamorolone at a dose of 6 mg/kg/d was maintained over 48 weeks.

Diagnostic outcome of pro bono neurogenetic diagnostic service in Sri Lanka: A wealth creation

The inherited disease community in Sri Lanka has been widely neglected. This article aimed to present accumulated knowledge in establishing a pro bono cost-effective national, island-wide, free-of-charge molecular diagnostic service, suggesting a model for other developing countries. The project provided 637 molecular diagnostic tests and reports free of charge to a nation with limited resources. We pioneered the implementation of mobile clinics and home visits, where the research team acted as barefoot doctors with the concept of the doctor and the researcher at the patient's doorstep. Establishing pro bono, cost-effective molecular diagnostics is feasible in developing countries with limited resources and state funding through the effort of dedicated postgraduate students. This service could provide an accurate molecular diagnosis of Duchenne muscular dystrophy, Huntington's disease, Spinocerebellar ataxia, and Spinal muscular atrophy, a diagnostic yield of 54% (343/637), of which 43% (147/343) of the patients identified as amenable for available gene therapies. Initiated human resource development by double doctoral degree opportunities with international collaborations. Established a neurobiobank and a national registry in Sri Lanka, a rich and unique repository, wealth creation for translational collaborative research and sharing of information in neurological diseases, as well as a lodestar for aspiring initiatives from other developing countries.

Title-molecular diagnostics of dystrophinopathies in Sri Lanka towards phenotype predictions: an insight from a South Asian resource limited setting

BACKGROUND

The phenotype of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) patients is determined by the type of DMD gene variation, its location, effect on reading frame, and its size. The primary objective of this investigation was to determine the frequency and distribution of DMD gene variants (deletions/duplications) in Sri Lanka through the utilization of a combined approach involving multiplex polymerase chain reaction (mPCR) followed by Multiplex Ligation Dependent Probe Amplification (MLPA) and compare to the international literature. The current consensus is that MLPA is a labor efficient yet expensive technique for identifying deletions and duplications in the DMD gene.

METHODOLOGY

Genetic analysis was performed in a cohort of 236 clinically suspected pediatric and adult myopathy patients in Sri Lanka, using mPCR and MLPA. A comparative analysis was conducted between our findings and literature data.

RESULTS

In the entire patient cohort (n = 236), mPCR solely was able to identify deletions in the DMD gene in 131/236 patients (DMD-120, BMD-11). In the same cohort, MLPA confirmed deletions in 149/236 patients [DMD-138, BMD -11]. These findings suggest that mPCR has a detection rate of 95% (131/138) among all patients who received a diagnosis. The distal and proximal deletion hotspots for DMD were exons 45-55 and 6-15. Exon 45-60 identified as a novel in-frame variation hotspot. Exon 45-59 was a hotspot for BMD deletions. Comparisons with the international literature show significant variations observed in deletion and duplication frequencies in DMD gene across different populations.

CONCLUSION

DMD gene deletions and duplications are concentrated in exons 45-55 and 2-20 respectively, which match global variation hotspots. Disparities in deletion and duplication frequencies were observed when comparing our data to other Asian and Western populations. Identified a 95% deletion detection rate for mPCR, making it a viable initial molecular diagnostic approach for low-resource countries where MLPA could be used to evaluate negative mPCR cases and cases with ambiguous mutation borders. Our findings may have important implications in the early identification of DMD with limited resources in Sri Lanka and to develop tailored molecular diagnostic algorithms that are regional and population specific and easily implemented in resource limited settings.

A population-based study of children suggests blunted morning cortisol rhythms are associated with alterations of the systemic inflammatory state

BACKGROUND

In children, digital media, lifestyle, and the COVID pandemic have impacted sunlight exposure, exercise, and diet patterns - cues that entrain the circadian clock. We hypothesized that low morning cortisol reflects a weak circadian clock, impacting the pro-inflammatory state. The primary objective was to test relationships between diurnal cortisol fluctuations and the inflammatory state in children as a means of providing indirect support for this hypothesis.

METHODS

The Cardiovascular Health Intervention Program (CHIP) was a population-based cross-sectional and longitudinal study of circadian health in public elementary school children in Southern Maine, USA (recruitment period 2012-2017). Participants were 689 students in 4th grade (baseline; age=9.2 ± 0.4 years), and 647 students in 5th grade (age=10.5 ± 0.5 years). Nine salivary cortisol measures per child (2 awakening and 1 prior to bed for 3 sequential days) (n = 1336 child phenotype days; n = 7987 cortisol assays), 10 cytokines measured in morning and evening saliva samples (n = 202 child phenotype days), and lipids were measured. Clinical outcomes were blood pressure, weight and height (body mass index [BMI]; BMI = kg/m2), among others.

FINDINGS

Upon-waking cortisol levels were 0.28 ± 0.13 µg/dL, 30-minute post-waking 0.33 ± 0.15 µg/dL, and evening 0.08 ± 0.10 µg/dL. Salivary cytokine levels (n = 202) showed interleukins (IL) IL-1β and IL-8 were highest in early morning (upon awakening; AM), and IL-6 and tumor necrosis factor (TNF) TNF-α highest before bed (PM) (IL-1β AM > PM [-4.02 fold; p < 0.001]; IL-8 AM > PM [-1.36 fold; p < 0.001]; IL-6 AM < PM [+1.49 fold; p < 0.001]; TNF-α AM < PM [+1.73 fold; p = 0.03]. Regression modeling showed high morning cortisol was associated with high morning IL-1β (p = 3.82 ×10-6), but low evening IL-1β (p = 6.27 ×10-4). Regression modeling of BMI z-score as the response variable showed the expected significant relationships to high density lipoprotein (HDL) (negative; p < 0.001), mean arterial pressure (positive; p < 0.001), and morning cortisol (negative; p = 0.01) but only weak relationships to either evening cortisol (p = 0.1) or cytokine (positive; p = 0.02; from the model with smallest Rsquared) levels.

INTERPRETATION

We provide preliminary data on diurnal fluctuations of inflammatory cytokines in saliva in a population-based cohort of children. Correlation of morning and evening cortisol levels with inflammatory cytokines in the same saliva samples showed that high morning cortisol was associated with high morning IL-1β and low evening IL-1β. Future studies may test the hypothesis that strong diurnal cycling of IL-1β may serve as a homeostatic mechanism keeping the immune system in check, and that low morning cortisol (possible circadian misalignment) may lead to less stringent control of inflammatory networks.

Characterization of the dystrophin-associated protein complex by mass spectrometry

The dystrophin-associated protein complex (DAPC) is a highly organized multiprotein complex that plays a pivotal role in muscle fiber structure integrity and cell signaling. The complex is composed of three distinct interacting subgroups, intracellular peripheral proteins, transmembrane glycoproteins, and extracellular glycoproteins subcomplexes. Dystrophin protein nucleates the DAPC and is important for connecting the intracellular actin cytoskeletal filaments to the sarcolemma glycoprotein complex that is connected to the extracellular matrix via laminin, thus stabilizing the sarcolemma during muscle fiber contraction and relaxation. Genetic mutations that lead to lack of expression or altered expression of any of the DAPC proteins are associated with different types of muscle diseases. Hence characterization of this complex in healthy and dystrophic muscle might bring insights into its role in muscle pathogenesis. This review highlights the role of mass spectrometry in characterizing the DAPC interactome as well as post-translational glycan modifications of some of its components such as α-dystroglycan. Detection and quantification of dystrophin using targeted mass spectrometry are also discussed in the context of healthy versus dystrophic skeletal muscle.

The IAAM LTBP4 Haplotype is Protective Against Dystrophin-Deficient Cardiomyopathy

Background

Dilated cardiomyopathy (DCM) is a major complication of, and leading cause of mortality in Duchenne muscular dystrophy (DMD). Its severity, age at onset, and rate of progression display wide variability, whose molecular bases have been scarcely elucidated. Potential DCM-modifying factors include glucocorticoid (GC) and cardiological treatments, DMD mutation type and location, and variants in other genes.

Methods and Results

We retrospectively collected 3138 echocardiographic measurements of left ventricular ejection fraction (EF), shortening fraction (SF), and end-diastolic volume (EDV) from 819 DMD participants, 541 from an Italian multicentric cohort and 278 from the Cooperative International Neuromuscular Group Duchenne Natural History Study (CINRG-DNHS). Using generalized estimating equation (GEE) models, we estimated the yearly rate of decrease of EF (-0.80%) and SF (-0.41%), while EDV increase was not significantly associated with age. Utilizing a multivariate generalized estimating equation (GEE) model we observed that mutations preserving the expression of the C-terminal Dp71 isoform of dystrophin were correlated with decreased EDV (-11.01 mL/m2, p = 0.03) while for dp116 were correlated with decreased EF (-4.14%, p = <0.001). The rs10880 genotype in the LTBP4 gene, previously shown to prolong ambulation, was also associated with increased EF and decreased EDV (+3.29%, p = 0.002, and -10.62 mL/m2, p = 0.008) with a recessive model.

Conclusions

We quantitatively describe the progression of systolic dysfunction progression in DMD, confirm the effect of distal dystrophin isoform expression on the dystrophin-deficient heart, and identify a strong effect of LTBP4 genotype of DCM in DMD.

Duchenne Muscular Dystrophy from Brain to Muscle: The Role of Brain Dystrophin Isoforms in Motor Functions

Brain function and its effect on motor performance in Duchenne muscular dystrophy (DMD) is an emerging concept. The present study explored how cumulative dystrophin isoform loss, age, and a corticosteroid treatment affect DMD motor outcomes. A total of 133 genetically confirmed DMD patients from Sri Lanka were divided into two groups based on whether their shorter dystrophin isoforms (Dp140, Dp116, and Dp71) were affected: Group 1, containing patients with Dp140, Dp116, and Dp71 affected (n = 98), and Group 2, containing unaffected patients (n = 35). A subset of 52 patients (Group 1, n = 38; Group 2, n = 14) was followed for up to three follow-ups performed in an average of 28-month intervals. The effect of the cumulative loss of shorter dystrophin isoforms on the natural history of DMD was analyzed. A total of 74/133 (56%) patients encountered developmental delays, with 66/74 (89%) being in Group 1 and 8/74 (11%) being in Group 2 (p < 0.001). Motor developmental delays were predominant. The hip and knee muscular strength, according to the Medical Research Council (MRC) scale and the North Star Ambulatory Assessment (NSAA) activities, "standing on one leg R", "standing on one leg L", and "walk", declined rapidly in Group 1 (p < 0.001 In the follow-up analysis, Group 1 patients became wheelchair-bound at a younger age than those of Group 2 (p = 0.004). DMD motor dysfunction is linked to DMD mutations that affect shorter dystrophin isoforms. When stratifying individuals for clinical trials, considering the DMD mutation site and its impact on a shorter dystrophin isoform is crucial.

Is it time for genetic modifiers to predict prognosis in Duchenne muscular dystrophy?

Patients with Duchenne muscular dystrophy (DMD) show clinically relevant phenotypic variability, despite sharing the same primary biochemical defect (dystrophin deficiency). Factors contributing to this clinical variability include allelic heterogeneity (specific DMD mutations), genetic modifiers (trans-acting genetic polymorphisms) and variations in clinical care. Recently, a series of genetic modifiers have been identified, mostly involving genes and/or proteins that regulate inflammation and fibrosis - processes increasingly recognized as being causally linked with physical disability. This article reviews genetic modifier studies in DMD to date and discusses the effect of genetic modifiers on predicting disease trajectories (prognosis), clinical trial design and interpretation (inclusion of genotype-stratified subgroup analyses) and therapeutic approaches. The genetic modifiers identified to date underscore the importance of progressive fibrosis, downstream of dystrophin deficiency, in driving the disease process. As such, genetic modifiers have shown the importance of therapies aimed at slowing this fibrotic process and might point to key drug targets.

Efficacy and Safety of Viltolarsen in Boys With Duchenne Muscular Dystrophy: Results From the Phase 2, Open-Label, 4-Year Extension Study

Background: Duchenne muscular dystrophy (DMD) is caused by DMD gene mutations, resulting in absence of functional dystrophin protein. Viltolarsen, an exon 53 skipping therapy, significantly increased dystrophin levels in patients with DMD. Presented here are completed study results of >4 years of functional outcomes in viltolarsen-treated patients compared to a historical control group (Cooperative International Neuromuscular Research Group Duchenne Natural History Study [CINRG DNHS]). Objective: To evaluate the efficacy and safety of viltolarsen for an additional 192 weeks in boys with DMD. Methods: This phase 2, open-label, 192-week long-term extension (LTE) study (NCT03167255) evaluated the efficacy and safety of viltolarsen in participants aged 4 to <10 years at baseline with DMD amenable to exon 53 skipping. All 16 participants from the initial 24-week study enrolled into this LTE. Timed function tests were compared to the CINRG DNHS group. All participants received glucocorticoid treatment. The primary efficacy outcome was time to stand from supine (TTSTAND). Secondary efficacy outcomes included additional timed function tests. Safety was continuously assessed. Results: For the primary efficacy outcome (TTSTAND), viltolarsen-treated patients showed stabilization of motor function over the first two years and significant slowing of disease progression over the following two years compared with the CINRG DNHS control group which declined. Viltolarsen was well tolerated, with most reported treatment-emergent adverse events being mild or moderate. No participants discontinued drug during the study. Conclusions: Based on the results of this 4-year LTE, viltolarsen can be an important treatment strategy for DMD patients amenable to exon 53 skipping.

Loss of calpain3b in Zebrafish, a Model of Limb-Girdle Muscular Dystrophy, Increases Susceptibility to Muscle Defects Due to Elevated Muscle Activity

Limb-Girdle Muscular Dystrophy Type R1 (LGMDR1; formerly LGMD2A), characterized by progressive hip and shoulder muscle weakness, is caused by mutations in CAPN3. In zebrafish, capn3b mediates Def-dependent degradation of p53 in the liver and intestines. We show that capn3b is expressed in the muscle. To model LGMDR1 in zebrafish, we generated three deletion mutants in capn3b and a positive-control dmd mutant (Duchenne muscular dystrophy). Two partial deletion mutants showed transcript-level reduction, whereas the RNA-less mutant lacked capn3b mRNA. All capn3b homozygous mutants were developmentally-normal adult-viable animals. Mutants in dmd were homozygous-lethal. Bathing wild-type and capn3b mutants in 0.8% methylcellulose (MC) for 3 days beginning 2 days post-fertilization resulted in significantly pronounced (20-30%) birefringence-detectable muscle abnormalities in capn3b mutant embryos. Evans Blue staining for sarcolemma integrity loss was strongly positive in dmd homozygotes, negative in wild-type embryos, and negative in MC-treated capn3b mutants, suggesting membrane instability is not a primary muscle pathology determinant. Increased birefringence-detected muscle abnormalities in capn3b mutants compared to wild-type animals were observed following induced hypertonia by exposure to cholinesterase inhibitor, azinphos-methyl, reinforcing the MC results. These mutant fish represent a novel tractable model for studying the mechanisms underlying muscle repair and remodeling, and as a preclinical tool for whole-animal therapeutics and behavioral screening in LGMDR1.

Modeling Early Heterogeneous Rates of Progression in Boys with Duchenne Muscular Dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) exhibits substantial variability in rates of disease progression and response to treatment. This has hindered treatment development and complicated interpretation of drug effects in clinical trials.

OBJECTIVE

We hypothesized that a multivariate combination of early-age clinical outcome measurements can explain differential disease progression.

METHODS

Data on boys with DMD (ages 4-<10 years), both treated with steroidal anti-inflammatories and untreated, were obtained from CINRG Duchenne Natural History Study (n = 209) and vamorolone VBP15-002/003/LTE (n = 46) studies. Velocities from three timed function tests (TFTs; stand from supine, run/walk 10 meters, and climb 4 stairs) were simultaneously modeled in a longitudinal latent class analysis.

RESULTS

Three classes of differentially progressing early age DMD motor trajectories were identified. Quicker decline/progression was associated with lower baseline TFT velocities, earlier loss of ability to finish a TFT, and lower predicted velocities. Earlier substantial steroid exposure was associated with greater TFT velocities while the moderate progression class was observed to have the largest difference in performance between boys treated early with steroids vs. not. Sample size calculations with the class showing the largest treatment response showed a large reduction in required sample size as compared to using summaries from all participants. Gene mutations were also investigated in post-hoc analyses, with mutations near the beginning of the DMD gene (Dp427 absent and Dp140/Dp71 present) found to be enriched in the slowest progressing class.

CONCLUSIONS

This study provides insight into the variation in DMD progression through a latent class analysis. Our findings show class-related trajectories of motor outcomes and pharmacological response to corticosteroids, and suggest that enrichment strategies and/or subgroup analyses could be considered further in design of therapeutic interventions in DMD.

A novel estrogen receptor 1-sphingomyelin phosphodiesterase acid like 3B pathway mediates rituximab response in myositis patients

OBJECTIVES

The B cell depleting biologic, rituximab, is used to treat refractory autoimmune myositis. However, the beneficial effects of rituximab appear to outweigh the known contribution of B-cells in myositis. We aimed to elucidate how myositis patients respond differently to rituximab and possible alternative mechanisms of action.

METHODS

Here we have: a) comprehensively investigated concurrent mRNA and microRNA expression in muscle biopsies taken at baseline and 16 weeks post treatment in ten patients who were part of the rituximab in myositis (RIM) trial; and b) investigated the beneficial effect of rituximab on myositis muscle cells.

RESULTS

Our analyses identified an increased number of changes in gene expression in biopsies from patients who had a clinical response to rituximab (n = 5) compared with non-responders (n = 5). The two groups had completely different changes in microRNA and mRNA expression following rituximab therapy, with the exception of one mRNA, BHMT2. Networks of mRNA and microRNA with opposite direction of expression changes highlighted ESR1 as upregulated in responders. We confirmed ESR1 upregulation upon rituximab treatment of immortalized myotubes and primary human dermatomyositis muscle cells in vitro, demonstrating a direct effect of rituximab on muscle cells. Notably, despite showing a response to rituximab, human dermatomyositis primary muscle cells did not express the rituximab target, CD20. However, these cells expressed a possible alternative target of rituximab, sphingomyelinase-like phosphodiesterase 3 b (SMPDL3B).

CONCLUSION

In addition to B cell depletion, rituximab may be beneficial in myositis due to increased ESR1 signalling mediated by rituximab binding to SMPDL3B on skeletal muscle cells.

Influence of β1 Adrenergic Receptor Genotype on Longitudinal Measures of Left Ventricular Ejection Fraction and Responsiveness to ß-Blocker Therapy in Patients With Duchenne Muscular Dystrophy

The purpose of this study was to determine whether the longitudinal progression of decline in left ventricular ejection fraction (LVEF) in Duchenne muscular dystrophy (DMD) patients is moderated by ADRB1 genotype and whether the efficacy of ß-blocker therapy is influenced by genotype status. About 147 DMD patients (6-34 years.) were analyzed with a focus on β₁ adrenergic receptor (ADRB1) genotype variants. Patients were grouped by ADRB1 genotype resulting in Gly389 patients and Arg389 patients. A generalized additive mixed effects model was used to examine differences in the nonlinear trend of LVEF across patient ages between genotype groups and for ß-blocker use. Both genotype groups displayed a progressive decline in LVEF starting around the mean age of ambulation loss (~12 years). However, there was no difference between genotype groups in the progression of decline in LVEF. There was a significant effect of ß-blocker use on longitudinal LVEF, wherein patients on ß-blockers had systematically lower LVEF when compared to patients not on ß-blockers. However, the effect of ß-blocker therapy on LVEF was not affected by ADRB1 genotype. The current study did not demonstrate an influence of patient ADRB1 genotype on longitudinal LVEF in our cohort. Despite previous literature suggesting a positive influence of ß-blocker use on cardiac function in DMD patients and of an ADRB1 genotypic difference in responsiveness to ß-blocker use, we did not observe this in our cohort. Interestingly, our cohort did not demonstrate a positive influence of ß-blocker use on LVEF measures.

Efficacy and Safety of Vamorolone vs Placebo and Prednisone Among Boys With Duchenne Muscular Dystrophy: A Randomized Clinical Trial

Question

For steroidal anti-inflammatory drugs, can efficacy be retained while safety concerns are reduced among boys with Duchenne muscular dystrophy (DMD) with the novel partial receptor agonist vamorolone?

Findings

A randomized, double-blind, placebo- and prednisone-controlled trial of vamorolone (2 dose groups) was carried out in 121 patients with DMD. The trial met the primary (time to stand velocity after 24 weeks for vamorolone, 6 mg/kg per day vs placebo) and first 4 sequential secondary motor function end points; vamorolone showed loss of bone morbidities compared with prednisone, with no stunting of growth and no deleterious changes in bone biomarkers.

Meaning

This study found that vamorolone, a dissociative steroidal anti-inflammatory, was able to reduce bone morbidities while retaining efficacy.

Importance

Corticosteroidal anti-inflammatory drugs are widely prescribed but long-term use shows adverse effects that detract from patient quality of life.

Objective

To determine if vamorolone, a structurally unique dissociative steroidal anti-inflammatory drug, is able to retain efficacy while reducing safety concerns with use in Duchenne muscular dystrophy (DMD).

Design, Setting, and Participants

Randomized, double-blind, placebo- and prednisone-controlled 24-week clinical trial, conducted from June 29, 2018, to February 24, 2021, with 24 weeks of follow-up. This was a multicenter study (33 referral centers in 11 countries) and included boys 4 to younger than 7 years of age with genetically confirmed DMD not previously treated with corticosteroids.

Interventions

The study included 4 groups: placebo; prednisone, 0.75 mg/kg per day; vamorolone, 2 mg/kg per day; and vamorolone, 6 mg/kg per day.

Main Outcomes and Measures

Study outcomes monitored (1) efficacy, which included motor outcomes (primary: time to stand from supine velocity in the vamorolone, 6 mg/kg per day, group vs placebo; secondary: time to stand from supine velocity [vamorolone, 2 mg/kg per day], 6-minute walk distance, time to run/walk 10 m [vamorolone, 2 and 6 mg/kg per day]; exploratory: NorthStar Ambulatory Assessment, time to climb 4 stairs) and (2) safety, which included growth, bone biomarkers, and a corticotropin (ACTH)–challenge test.

Results

Among the 133 boys with DMD enrolled in the study (mean [SD] age, 5.4 [0.9] years), 121 were randomly assigned to treatment groups, and 114 completed the 24-week treatment period. The trial met the primary end point for change from baseline to week 24 time to stand velocity for vamorolone, 6 mg/kg per day (least-squares mean [SE] velocity, 0.05 [0.01] m/s vs placebo −0.01 [0.01] m/s; 95% CI, 0.02-0.10; P = .002) and the first 4 sequential secondary end points: time to stand velocity, vamorolone, 2 mg/kg per day, vs placebo; 6-minute walk test, vamorolone, 6 mg/kg per day, vs placebo; 6-minute walk test, vamorolone, 2 mg/kg per day, vs placebo; and time to run/walk 10 m velocity, vamorolone, 6 mg/kg per day, vs placebo. Height percentile declined in prednisone-treated (not vamorolone-treated) participants (change from baseline [SD]: prednisone, −1.88 [8.81] percentile vs vamorolone, 6 mg/kg per day, +3.86 [6.16] percentile; P = .02). Bone turnover markers declined with prednisone but not with vamorolone. Boys with DMD at baseline showed low ACTH-stimulated cortisol and high incidence of adrenal insufficiency. All 3 treatment groups led to increased adrenal insufficiency.

Conclusions and Relevance

In this pivotal randomized clinical trial, vamorolone was shown to be effective and safe in the treatment of boys with DMD over a 24-week treatment period. Vamorolone may be a safer alternative than prednisone in this disease, in which long-term corticosteroid use is the standard of care.

Trial Registration

ClinicalTrials.gov Identifier: NCT03439670

Long-Term Functional Efficacy and Safety of Viltolarsen in Patients with Duchenne Muscular Dystrophy

Background: Duchenne muscular dystrophy (DMD) is a rare, genetic disease caused by mutations in the DMD gene resulting in an absence of functional dystrophin protein. Viltolarsen, an exon 53 skipping therapy, has been shown to increase endogenous dystrophin levels. Herein, long-term (>2 years) functional outcomes in viltolarsen treated patients were compared to a matched historical control group. Objective: To evaluate long-term efficacy and safety of the anti-sense oligonucleotide viltolarsen in the treatment of patients with DMD amenable to exon 53 skipping therapy. Methods: This trial (NCT03167255) is the extension of a previously published 24-week trial in North America (NCT02740972) that examined dystrophin levels, timed function tests compared to a matched historical control group (Cooperative International Neuromuscular Research Group Duchenne Natural History Study, CINRG DNHS), and safety in boys 4 to <  10 years (N = 16) with DMD amenable to exon 53 skipping who were treated with viltolarsen. Both groups were treated with glucocorticoids. All 16 participants elected to enroll in this long-term trial (up to 192 weeks) to continue evaluation of motor function and safety. Results: Time to stand from supine and time to run/walk 10 meters showed stabilization from baseline through week 109 for viltolarsen-treated participants whereas the historical control group showed decline (statistically significant differences for multiple timepoints). Safety was similar to that observed in the previous 24-week trial, which was predominantly mild. There have been no treatment-related serious adverse events and no discontinuations. Conclusions: Based on these results at over 2 years, viltolarsen can be a new treatment option for patients with DMD amenable to exon 53 skipping.

Mechanism of action and therapeutic route for a muscular dystrophy caused by a genetic defect in lipid metabolism

CHKB encodes one of two mammalian choline kinase enzymes that catalyze the first step in the synthesis of the membrane phospholipid phosphatidylcholine. In humans and mice, inactivation of the CHKB gene (Chkb in mice) causes a recessive rostral-to-caudal muscular dystrophy. Using Chkb knockout mice, we reveal that at no stage of the disease is phosphatidylcholine level significantly altered. We observe that in affected muscle a temporal change in lipid metabolism occurs with an initial inability to utilize fatty acids for energy via mitochondrial β-oxidation resulting in shunting of fatty acids into triacyglycerol as the disease progresses. There is a decrease in peroxisome proliferator-activated receptors and target gene expression specific to Chkb^−/− affected muscle. Treatment of Chkb^−/− myocytes with peroxisome proliferator-activated receptor agonists enables fatty acids to be used for β-oxidation and prevents triacyglyerol accumulation, while simultaneously increasing expression of the compensatory choline kinase alpha (Chka) isoform, preventing muscle cell injury.

Mutations in the CHKB gene cause muscular dystrophy. Here, the authors show that in mouse models of the disease changes in lipid metabolism are associated with decreased PPAR signaling, and show PPAR agonists can rescue expression of injury markers in myocytes in vitro.

Acute serum protein and cytokine response of single dose of prednisone in adult volunteers

Pharmacological glucocorticoids are the most prescribed anti-inflammatory medications, and are chemical variants of cortisol, the circadian and stress hormone. Both endogenous and pharmacological glucocorticoids bind the glucocorticoid receptor (NR3C1) with high affinity, and both then bind downstream gene promoter elements (GRE) to drive positive gene transcription of many proteins. Glucocorticoid/GR complexes also bind distinct negative gene promoter elements (nGRE) to inhibit expression of genes involved in NF-κB innate immunity signaling. We sought to define the acute response of a single dose of prednisone (0.2 mg/kg) in young adult volunteers, with blood samples taken at baseline, 2, 3, 4 and 6 h post-oral dose. To control for circadian morning cortisol hitting the same molecular pathways, a day of blood draws was done without oral prednisone (same time of day), one day prior to drug day. Serum samples were processed for steroid hormone profiles (mass spectrometry; 9 steroidal hormones), proteomics (SOMAscan aptamer panels, 1,305 proteins), and inflammatory markers (Meso Scale Discovery; 10 pro-inflammatory cytokines). The pharmacological effect of the prednisone dose was shown by significant declines of adrenal steroids by 3 h after dosing. IL-10 showed drug-related increase to 4 hrs, then decrease to 6 hrs. IL-8 showed drug-related decrease in serum by 4 h, consistent with direct negative action of GR/ligand on IL-8 gene promoter. Proteomics data showed beta-2 microglobulin, TNFSF15, TSH, CST3, NBL1 to show time-related decreases with prednisone, while CXCL13 showed increases, although these require validation. In summary, a single low dose of prednisone leads to broad suppression of the adrenal axis within 3 h, and down-regulation of inflammatory serum proteins by 6 h.

Efficacy and Safety of Vamorolone in Duchenne Muscular Dystrophy: A 30-Month Nonrandomized Controlled Open-Label Extension Trial

IMPORTANCE

Vamorolone is a synthetic steroidal drug with potent anti-inflammatory properties. Initial open-label, multiple ascending dose-finding studies of vamorolone among boys with Duchenne muscular dystrophy (DMD) found significant motor function improvement after 6 months treatment in higher-dose (ie, ≥2.0 mg/kg/d) groups.

OBJECTIVE

To investigate outcomes after 30 months of open-label vamorolone treatment.

DESIGN, SETTING, AND PARTICIPANTS

This nonrandomized controlled trial was conducted by the Cooperative International Neuromuscular Research Group at 11 US and non-US study sites. Participants were 46 boys ages 4.5 to 7.5 years with DMD who completed the 6-month dose-finding study. Data were analyzed from July 2020 through November 2021.

INTERVENTIONS

Participants were enrolled in a 24-month, long-term extension (LTE) study with vamorolone dose escalated to 2.0 or 6.0 mg/kg/d.

MAIN OUTCOMES AND MEASURES

Change in time-to-stand (TTSTAND) velocity from dose-finding baseline to end of LTE study was the primary outcome. Efficacy assessments included timed function tests, 6-minute walk test, and NorthStar Ambulatory Assessment (NSAA). Participants with DMD treated with glucocorticoids from the Duchenne Natural History Study (DNHS) and NorthStar United Kingdom (NSUK) Network were matched and compared with participants in the LTE study receiving higher doses of vamorolone.

RESULTS

Among 46 boys with DMD who completed the dose-finding study, 41 boys (mean [SD] age, 5.33 [0.96] years) completed the LTE study. Among 21 participants treated with higher-dose (ie, ≥2.0 mg/kg/d) vamorolone consistently throughout the 6-month dose-finding and 24-month LTE studies with data available at 30 months, there was a decrease in mean (SD) TTSTAND velocity from baseline to 30 months (0.206 [0.070] rises/s vs 0.189 (0.124) rises/s), which was not a statistically significant change (-0.011 rises/s; CI, -0.068 to 0.046 rises/s). There were no statistically significant differences between participants receiving higher-dose vamorolone and matched participants in the historical control groups receiving glucocorticoid treatment (75 patients in DNHS and 110 patients in NSUK) over a 2-year period in NSAA total score change (0.22 units vs NSUK; 95% CI, -4.48 to 4.04]; P = .92), body mass index z score change (0.002 vs DNHS SD/mo; 95% CI, -0.006 to 0.010; P = .58), or timed function test change. Vamorolone at doses up to 6.0 mg/kg/d was well tolerated, with 5 of 46 participants discontinuing prematurely and for reasons not associated with study drug. Participants in the DNHS treated with glucocorticoids had significant growth delay in comparison with participants treated with vamorolone who had stable height percentiles (0.37 percentile/mo; 95% CI, 0.23 to 0.52 percentile/mo) over time.

CONCLUSIONS AND RELEVANCE

This study found that vamorolone treatment was not associated with a change in TTSTAND velocity from baseline to 30 months among boys with DMD aged 4 to 7 years at enrollment. Vamorolone was associated with maintenance of muscle strength and function up to 30 months, similar to standard of care glucocorticoid therapy, and improved height velocity compared with growth deceleration associated with glucocorticoid treatment, suggesting that vamorolone may be an attractive candidate for treatment of DMD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03038399.

Serum biomarkers associated with baseline clinical severity in young steroid-naïve Duchenne muscular dystrophy boys

Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin in muscle, and while all patients share the primary gene and biochemical defect, there is considerable patient–patient variability in clinical symptoms. We sought to develop multivariate models of serum protein biomarkers that explained observed variation, using functional outcome measures as proxies for severity. Serum samples from 39 steroid-naïve DMD boys 4 to <7 years enrolled into a clinical trial of vamorolone were studied (NCT02760264). Four assessments of gross motor function were carried out for each participant over a 6-week interval, and their mean was used as response for biomarker models. Weighted correlation network analysis was used for unsupervised clustering of 1305 proteins quantified using SOMAscan^® aptamer profiling to define highly representative and connected proteins. Multivariate models of biomarkers were obtained for time to stand performance (strength phenotype; 17 proteins) and 6 min walk performance (endurance phenotype; 17 proteins) including some shared proteins. Identified proteins were tested with associations of mRNA expression with histological severity of muscle from dystrophinopathy patients (n = 28) and normal controls (n = 6). Strong associations predictive of both clinical and histological severity were found for ERBB4 (reductions in both blood and muscle with increasing severity), SOD1 (reductions in muscle and increases in blood with increasing severity) and CNTF (decreased levels in blood and muscle with increasing severity). We show that performance of DMD boys was effectively modeled with serum proteins, proximal strength associated with growth and remodeling pathways and muscle endurance centered on TGFβ and fibrosis pathways in muscle.

Human muscle stem cells are refractory to aging

Age-related loss of muscle mass and strength is widely attributed to limitation in the capacity of muscle resident satellite cells to perform their myogenic function. This idea contains two notions that have not been comprehensively evaluated by experiment. First, it entails the idea that we damage and lose substantial amounts of muscle in the course of our normal daily activities. Second, it suggests that mechanisms of muscle repair are in some way exhausted, thus limiting muscle regeneration. A third potential option is that the aged environment becomes inimical to the conduct of muscle regeneration. In the present study, we used our established model of human muscle xenografting to test whether muscle samples taken from cadavers, of a range of ages, maintained their myogenic potential after being transplanted into immunodeficient mice. We find no measurable difference in regeneration across the range of ages investigated up to 78 years of age. Moreover, we report that satellite cells maintained their myogenic capacity even when muscles were grafted 11 days postmortem in our model. We conclude that the loss of muscle mass with increasing age is not attributable to any intrinsic loss of myogenicity and is most likely a reflection of progressive and detrimental changes in the muscle microenvironment such as to disfavor the myogenic function of these cells.

Blunted circadian cortisol in children is associated with poor cardiovascular health and may reflect circadian misalignment

OBJECTIVES

Circadian cues in children (sunlight, exercise, diet patterns) may be associated with health outcomes. The primary objective was to assess associations of daily cortisol fluctuations (morning, night) with cardiovascular health outcomes. A secondary objective was to determine if 1-year longitudinal changes in circadian cortisol levels are associated with longitudinal changes in health outcomes.

STUDY DESIGN

The Cardiovascular Health Intervention Program (CHIP) was a cross-sectional and longitudinal study of cardiovascular risk profiles in public elementary school children in Southern Maine. Participants were 689 students in 4th grade (baseline; age = 9.20 ± 0.41 years), and 647 students in 5th grade (age = 10.53 ± 0.52 years). Longitudinal data (4th and 5th grade) was available for 347 participants. Clinical outcomes were blood pressure, hip/waist ratios, body mass index, percent fat. Laboratory measures were fasting glucose, lipids, and salivary cortisol measures (morning and evening).

RESULTS

Lower first-in-morning diurnal cortisol levels were associated with increased blood pressure (β -0.23 ± 0.05; p < 0.001), increased body fat (β -0.22 ± 0.05; p < 0.001), and poor lipid profiles (β -0.15 ± 0.07; p < 0.05). Inclusion of night cortisol in the model (stress-related) improved associations of the model with bodyfat composition (morning β -0.27 ± 0.05; p < 0.001; night β +0.16 ± 0.06; p < 0.01). Adjustments for potential confounding variables improved associations of morning cortisol with lipids (β -0.19 ± 0.07; p < 0.01). Longitudinal analysis showed that lower morning diurnal cortisol in 4th grade was associated with increases in blood pressure a year later (β -0.18 ± 0.08; p = 0.017) after adjusting for confounding variables.

CONCLUSION

Data presented suggest adding circadian misalignment (lower amplitude of first-in-morning cortisol) to existing models of metabolic syndrome in children. Further, circadian misalignment may be a factor contributing to high blood pressure.

Exon-Skipping in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a devastating, rare disease. While clinically described in the 19^th century, the genetic foundation of DMD was not discovered until more than 100 years later. This genetic understanding opened the door to the development of genetic treatments for DMD. Over the course of the last 30 years, the research that supports this development has moved into the realm of clinical trials and regulatory drug approvals. Exon skipping to therapeutically restore the frame of an out-of-frame dystrophin mutation has taken center stage in drug development for DMD. The research reviewed here focuses on the clinical development of exon skipping for the treatment of DMD. In addition to the generation of clinical treatments that are being used for patient care, this research sets the stage for future therapeutic development with a focus on increasing efficacy while providing safety and addressing the multi-systemic aspects of DMD.

Safety, Tolerability, and Efficacy of Viltolarsen in Boys With Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A Phase 2 Randomized Clinical Trial

Question

What are the safety, tolerability, and efficacy of viltolarsen in boys with Duchenne muscular dystrophy (DMD) amenable to exon 53 skipping?

Findings

Results of this 4-week randomized clinical trial for safety followed by a 20-week open-label treatment period in 16 patients with DMD indicated significant drug-induced dystrophin production in both viltolarsen groups (40 mg/kg per week and 80 mg/kg week) after 20 to 24 weeks of treatment. Timed function tests provided supportive evidence of treatment-related clinical improvement, and viltolarsen was well tolerated.

Meaning

Viltolarsen may provide a new therapeutic option for patients with DMD amenable to exon 53 skipping.

Importance

An unmet need remains for safe and efficacious treatments for Duchenne muscular dystrophy (DMD). To date, there are limited agents available that address the underlying cause of the disease.

Objective

To evaluate the safety, tolerability, and efficacy of viltolarsen, a novel antisense oligonucleotide, in participants with DMD amenable to exon 53 skipping.

Design, Setting, and Participants

This phase 2 study was a 4-week randomized clinical trial for safety followed by a 20-week open-label treatment period of patients aged 4 to 9 years with DMD amenable to exon 53 skipping. To enroll 16 participants, with 8 participants in each of the 2 dose cohorts, 17 participants were screened. Study enrollment occurred between December 16, 2016, and August 17, 2017, at sites in the US and Canada. Data were collected from December 2016 to February 2018, and data were analyzed from April 2018 to May 2019.

Interventions

Participants received 40 mg/kg (low dose) or 80 mg/kg (high dose) of viltolarsen administered by weekly intravenous infusion.

Main Outcomes and Measures

Primary outcomes of the trial included safety, tolerability, and de novo dystrophin protein production measured by Western blot in participants’ biceps muscles. Secondary outcomes included additional assessments of dystrophin mRNA and protein production as well as clinical muscle strength and function.

Results

Of the 16 included boys with DMD, 15 (94%) were white, and the mean (SD) age was 7.4 (1.8) years. After 20 to 24 weeks of treatment, significant drug-induced dystrophin production was seen in both viltolarsen dose cohorts (40 mg/kg per week: mean [range] 5.7% [3.2-10.3] of normal; 80 mg/kg per week: mean [range] 5.9% [1.1-14.4] of normal). Viltolarsen was well tolerated; no treatment-emergent adverse events required dose reduction, interruption, or discontinuation of the study drug. No serious adverse events or deaths occurred during the study. Compared with 65 age-matched and treatment-matched natural history controls, all 16 participants treated with viltolarsen showed significant improvements in timed function tests from baseline, including time to stand from supine (viltolarsen: −0.19 s; control: 0.66 s), time to run/walk 10 m (viltolarsen: 0.23 m/s; control: −0.04 m/s), and 6-minute walk test (viltolarsen: 28.9 m; control: −65.3 m) at the week 25 visit.

Conclusions and Relevance

Systemic treatment of participants with DMD with viltolarsen induced de novo dystrophin production, and clinical improvement of timed function tests was observed.

Trial Registration

ClinicalTrials.gov Identifier: NCT02740972

Elevation of fast but not slow troponin I in the circulation of patients with Becker and Duchenne muscular dystrophy

Introduction

One of the hallmarks of injured skeletal muscle is the appearance of elevated skeletal muscle proteins in circulation. Human skeletal muscle generally consists of a mosaic of slow (type I) and fast (type IIa, IIx/d) fibers, defined by their myosin isoform expression. Recently, measurement of circulating fiber‐type specific isoforms of troponin I has been used as a biomarker to suggest that muscle injury in healthy volunteers (HV) results in the appearance of muscle proteins from fast but not slow fibers. We sought to understand if this is also the case in severe myopathy patients with Becker and Duchenne muscular dystrophy (BMD, DMD).

Methods

An enzyme‐linked immunosorbent assay (ELISA) that selectively measures fast and slow skeletal troponin I (TNNI2 and TNNI1) was used to measure a cross‐section of patient plasma samples from HV (N = 50), BMD (N = 49), and DMD (N = 132) patients. Creatine kinase (CK) activity was also measured from the same samples for comparison.

Results

TNNI2 was elevated in BMD and DMD and correlated with the injury biomarker, CK. In contrast, TNNI1 levels were indistinguishable from levels in HV. There was an inverse relationship between CK and TNNI2 levels and age, but no relationship for TNNI1.

Discussion

We define a surprising discrepancy between TNNI1 and TNNI2 in patient plasma that may have implications for the interpretation of elevated muscle protein levels in dystrophinopathies.

See Editorial on pages 4–5 in this issue.

Biomarker-focused multi-drug combination therapy and repurposing trial in mdx mice

Duchenne muscular dystrophy is initiated by dystrophin deficiency, but downstream pathophysiological pathways such as membrane instability, NFĸB activation, mitochondrial dysfunction, and induction of TGFβ fibrosis pathways are thought to drive the disability. Dystrophin replacement strategies are hopeful for addressing upstream dystrophin deficiency; however, all methods to date use semi-functional dystrophin proteins that are likely to trigger downstream pathways. Thus, combination therapies that can target multiple downstream pathways are important in treating DMD, even for dystrophin-replacement strategies. We sought to define blood pharmacodynamic biomarkers of drug response in the mdx mouse model of Duchenne muscular dystrophy using a series of repurposed drugs. Four-week-old mdx mice were treated for four weeks with four different drugs singly and in combination: vehicle, prednisolone, vamorolone, rituximab, β-aminoisobutyric acid (BAIBA) (11 treatment groups; n = 6/group). Blood was collected via cardiac puncture at study termination, and proteomic profiling was carried out using SOMAscan aptamer panels (1,310 proteins assayed). Prednisolone was tested alone and in combination with other drugs. It was found to have a good concordance of prednisolone-responsive biomarkers (56 increased by prednisolone, 39 decreased) focused on NFκB and TGFβ cascades. Vamorolone shared 45 (80%) of increased biomarkers and 13 (33%) of decreased biomarkers with prednisolone. Comparison of published human corticosteroid-responsive biomarkers to our mdx data showed 14% (3/22) concordance between mouse and human. Rituximab showed fewer drug-associated biomarkers, with the most significant being human IgG. On the other hand, BAIBA treatment (high and low dose) showed a drug-associated increase in 40 serum proteins and decreased 5 serum proteins. Our results suggest that a biomarker approach could be employed for assessing drug combinations in both mouse and human studies.

Causes of clinical variability in Duchenne and Becker muscular dystrophies and implications for exon skipping therapies

Becker muscular dystrophy is caused by mutations in the DMD gene that permit significant residual dystrophin protein expression in patient muscle. This is in contrast to DMD gene mutations in Duchenne muscular dystrophy where little or no dystrophin is produced (typically < 3% normal levels). Clinically, Becker muscular dystrophy is extremely variable, from slightly milder than DMD, to asymptomatic hyperCKemia at old age. The factors driving clinical variability in Becker muscular dystrophy have now been studied in some depth, and the findings are likely highly relevant to anticipated clinical findings in exon skipping therapy in DMD. The specific mutations in Becker dystrophy play an important role, and clinical variability is less with high frequency mutations (deletions exons 45-47, 45-48). The percentage of dystrophin content in patient muscle is not well-correlated with clinical findings. Muscle MRI findings (degree of fibrofatty replacement) are very well-correlated with the degree of patient disability, regardless of mutation or muscle dystrophin content. Taken together, data to date suggest that the main determinant driving clinical disability in Becker dystrophy patients is the degree of fibrofatty replacement in muscle. Thus, as with DMD, DMD gene mutations and resulting dystrophin protein abnormalities initiate the disease process, but downstream tissue pathophysiology plays a dominant role in disease progression. Factors influencing the age-dependent rate of fibrofatty replacement of muscles are responsible for much of the clinical variability seen in Becker dystrophy, as well as Duchenne dystrophy. These fibrosis-related factors include genetic modifiers, degree of muscle inflammation, and induction of microRNAs in muscle that bind to dystrophin mRNA and down-regulate dystrophin protein content in patient muscle. Studies to date regarding clinical variability in Becker dystrophy suggest that exon skipping therapy in DMD may show variable efficacy from patient to patient.

Novel mutation identification and copy number variant detection via exome sequencing in congenital muscular dystrophy

Background

Congenital muscular dystrophy type 1A (MDC1A), also termed merosin‐deficient congenital muscular dystrophy (CMD), is a severe form of CMD caused by mutations in the laminin α2 gene (LAMA2). Of the more than 300 likely pathogenic variants found in the Leiden Open Variant Database, the majority are truncating mutations leading to complete LAMA2 loss of function, but multiple copy number variants (CNVs) have also been reported with variable frequency.

Methods

We collected a cohort of individuals diagnosed with likely MDC1A and sought to identify both single nucleotide variants and small and larger CNVs via exome sequencing by extending the analysis of sequencing data to detect splicing changes and CNVs.

Results

Standard exome analysis identified multiple novel LAMA2 variants in our cohort, but only four cases carried biallelic variants. Since likely truncating LAMA2 variants are often found in heterozygosity without a second allele, we performed additional splicing and CNV analysis on exome data and identified one splice change outside of the canonical sequences and three CNVs, in the remaining four cases.

Conclusions

Our findings support the expectation that a portion of MDC1A cases may be caused by at least one CNV allele and show how these changes can be effectively identified by additional analysis of existing exome data.

Developmental Pharmacodynamics and Modeling in Pediatric Drug Development

Challenges in pediatric drug development include small patient numbers, limited outcomes research, ethical barriers, and sparse biosamples. Increasingly, pediatric drug development is focusing on extrapolation: leveraging knowledge about adult disease and drug responses to inform projections of drug and clinical trial performance in pediatric subpopulations. Pharmacokinetic-pharmacodynamic (PK-PD) modeling and extrapolation aim to reduce the numbers of patients and data points needed to establish efficacy. Planning for PK-PD and biomarker studies should begin early in the adult drug development program. Extrapolation relies on the assumption that both the underlying disease and the mechanism of action of the drug used to treat that disease are similar in adults and pediatric subpopulations. Clearly, developmental changes in PK and PD need to be considered to enhance the quality of PK-PD modeling and, therefore, increase the success of extrapolation. This article focuses on the influence of differences in PD between adults and pediatric subpopulations that are highly relevant for the use of extrapolation.

Efficacy and safety of vamorolone in Duchenne muscular dystrophy: An 18-month interim analysis of a non-randomized open-label extension study

BACKGROUND

Treatment with corticosteroids is recommended for Duchenne muscular dystrophy (DMD) patients to slow the progression of weakness. However, chronic corticosteroid treatment causes significant morbidities. Vamorolone is a first-in-class anti-inflammatory investigational drug that has shown evidence of efficacy in DMD after 24 weeks of treatment at 2.0 or 6.0 mg/kg/day. Here, open-label efficacy and safety experience of vamorolone was evaluated over a period of 18 months in trial participants with DMD.

METHODS AND FINDINGS

A multicenter, open-label, 24-week trial (VBP15-003) with a 24-month long-term extension (VBP15-LTE) was conducted by the Cooperative International Neuromuscular Research Group (CINRG) and evaluated drug-related effects of vamorolone on motor outcomes and corticosteroid-associated safety concerns. The study was carried out in Canada, US, UK, Australia, Sweden, and Israel, from 2016 to 2019. This report covers the initial 24-week trial and the first 12 months of the VBP15-LTE trial (total treatment period 18 months). DMD trial participants (males, 4 to <7 years at entry) treated with 2.0 or 6.0 mg/kg/day vamorolone for the full 18-month period (n = 23) showed clinical improvement of all motor outcomes from baseline to month 18 (time to stand velocity, p = 0.012 [95% CI 0.010, 0.068 event/second]; run/walk 10 meters velocity, p < 0.001 [95% CI 0.220, 0.491 meters/second]; climb 4 stairs velocity, p = 0.001 [95% CI 0.034, 0.105 event/second]; 6-minute walk test, p = 0.001 [95% CI 31.14, 93.38 meters]; North Star Ambulatory Assessment, p < 0.001 [95% CI 2.702, 6.662 points]). Outcomes in vamorolone-treated DMD patients (n = 46) were compared to group-matched participants in the CINRG Duchenne Natural History Study (corticosteroid-naïve, n = 19; corticosteroid-treated, n = 68) over a similar 18-month period. Time to stand was not significantly different between vamorolone-treated and corticosteroid-naïve participants (p = 0.088; least squares [LS] mean 0.042 [95% CI -0.007, 0.091]), but vamorolone-treated participants showed significant improvement compared to group-matched corticosteroid-naïve participants for run/walk 10 meters velocity (p = 0.003; LS mean 0.286 [95% CI 0.104, 0.469]) and climb 4 stairs velocity (p = 0.027; LS mean 0.059 [95% CI 0.007, 0.111]). The vamorolone-related improvements were similar in magnitude to corticosteroid-related improvements. Corticosteroid-treated participants showed stunting of growth, whereas vamorolone-treated trial participants did not (p < 0.001; LS mean 15.86 [95% CI 8.51, 23.22]). Physician-reported incidences of adverse events (AEs) for Cushingoid appearance, hirsutism, weight gain, and behavior change were less for vamorolone than published incidences for prednisone and deflazacort. Key limitations to the study were the open-label design, and use of external comparators.

CONCLUSIONS

We observed that vamorolone treatment was associated with improvements in some motor outcomes as compared with corticosteroid-naïve individuals over an 18-month treatment period. We found that fewer physician-reported AEs occurred with vamorolone than have been reported for treatment with prednisone and deflazacort, and that vamorolone treatment did not cause the stunting of growth seen with these corticosteroids. This Phase IIa study provides Class III evidence to support benefit of motor function in young boys with DMD treated with vamorolone 2.0 to 6.0 mg/kg/day, with a favorable safety profile. A Phase III RCT is underway to further investigate safety and efficacy.

TRIAL REGISTRATION

Clinical trials were registered at www.clinicaltrials.gov, and the links to each trial are as follows (as provided in manuscript text): VBP15-002 [NCT02760264] VBP15-003 [NCT02760277] VBP15-LTE [NCT03038399].

The discovery of dystrophin, the protein product of the Duchenne muscular dystrophy gene

Duchenne muscular dystrophy was a well‐established medical and genetic enigma by the 1970s. Why was the new mutation rate so high in all world populations? Why were affected boys doing well in early childhood, but then showed relentless progression of muscle wasting? What was wrong with the muscle? The identification of the first fragments of DMD gene cDNA in 1986, prediction of the entire 3685 amino acid protein sequence, and production of antibodies to dystrophin, both in 1987, provided key tools to understand DMD genetics and molecular pathology. The identification of dystrophin nucleated extensive research on myofiber membrane cytoskeleton, membrane repair, muscle regeneration, and failure of regeneration. This in turn led to molecular therapeutics based on understanding of dystrophin structure and function. This historical perspective describes the events surrounding the initial identification of the dystrophin protein.

A long-read RNA-seq approach to identify novel transcripts of very large genes

RNA-seq is widely used for studying gene expression, but commonly used sequencing platforms produce short reads that only span up to two exon junctions per read. This makes it difficult to accurately determine the composition and phasing of exons within transcripts. Although long-read sequencing improves this issue, it is not amenable to precise quantitation, which limits its utility for differential expression studies. We used long-read isoform sequencing combined with a novel analysis approach to compare alternative splicing of large, repetitive structural genes in muscles. Analysis of muscle structural genes that produce medium (Nrap: 5 kb), large (Neb: 22 kb), and very large (Ttn: 106 kb) transcripts in cardiac muscle, and fast and slow skeletal muscles identified unannotated exons for each of these ubiquitous muscle genes. This also identified differential exon usage and phasing for these genes between the different muscle types. By mapping the in-phase transcript structures to known annotations, we also identified and quantified previously unannotated transcripts. Results were confirmed by endpoint PCR and Sanger sequencing, which revealed muscle-type-specific differential expression of these novel transcripts. The improved transcript identification and quantification shown by our approach removes previous impediments to studies aimed at quantitative differential expression of ultralong transcripts.

Muscle Weakness in Myositis: MicroRNA-Mediated Dystrophin Reduction in a Myositis Mouse Model and Human Muscle Biopsies

Objective

Muscle inflammation is a feature in myositis and Duchenne muscular dystrophy (DMD). Autoimmune mechanisms are thought to contribute to muscle weakness in patients with myositis. However, a lack of correlation between the extent of inflammatory cell infiltration and muscle weakness indicates that nonimmune pathologic mechanisms may play a role. The present study focused on 2 microRNA (miRNA) sets previously identified as being elevated in the muscle of patients with DMD—an “inflammatory” miRNA set that is dampened with glucocorticoids, and a “dystrophin‐targeting” miRNA set that inhibits dystrophin translation—to test the hypothesis that these miRNAs are similarly dysregulated in the muscle of patients with myositis, and could contribute to muscle weakness and disease severity.

Methods

A major histocompatibility complex class I–transgenic mouse model of myositis was utilized to study gene and miRNA expression and histologic features in the muscle tissue, with the findings validated in human muscle biopsy tissue from 6 patients with myositis. Mice were classified as having mild or severe myositis based on transgene expression, body weight, histologic disease severity, and muscle strength/weakness.

Results

In mice with severe myositis, muscle tissue showed mononuclear cell infiltration along with elevated expression of type I interferon and NF‐κB–regulated genes, including Tlr7 (3.8‐fold increase, P < 0.05). Furthermore, mice with severe myositis showed elevated expression of inflammatory miRNAs (miR‐146a, miR‐142‐3p, miR‐142‐5p, miR‐455‐3p, and miR‐455‐5p; ~3–40‐fold increase, P < 0.05) and dystrophin‐targeting miRNAs (miR‐146a, miR‐146b, miR‐31, and miR‐223; ~3–38‐fold increase, P < 0.05). Bioinformatics analyses of chromatin immunoprecipitation sequencing (ChIP‐seq) data identified at least one NF‐κB consensus element within the promoter/enhancer regions of these miRNAs. Western blotting and immunofluorescence analyses of the muscle tissue from mice with severe myositis demonstrated reduced levels of dystrophin. In addition, elevated levels of NF‐κB–regulated genes, TLR7, and miRNAs along with reduced dystrophin levels were observed in muscle biopsy tissue from patients with histologically severe myositis.

Conclusion

These data demonstrate that an acquired dystrophin deficiency may occur through NF‐κB–regulated miRNAs in myositis, thereby suggesting a unifying theme in which muscle injury, inflammation, and weakness are perpetuated both in myositis and in DMD.

Exposure-Response Analysis of Vamorolone (VBP15) in Boys With Duchenne Muscular Dystrophy

Exposure-response relationships of vamorolone, a novel dissociative steroidal anti-inflammatory drug, were investigated in clinical trials in boys with Duchenne muscular dystrophy. Variables were clinical outcome measures, Fridericia-corrected QT (QTcF) duration, and pharmacodynamic (PD) biomarkers. Exposure metrics were area under the plasma concentration time curve (AUC) and maximum plasma concentration (C_max ), with a sigmoid E_max model applied. Significant improvement in clinical efficacy outcomes was observed after 24 weeks of daily dosing. The primary outcome, time to stand from supine velocity, exhibited the highest sensitivity to vamorolone, with the lowest AUC value providing 50% of maximum effect (E₅₀  = 186 ng·h/mL), followed by time to climb 4 stairs (E₅₀  = 478 ng·h/mL), time to run/walk 10 m (E₅₀  = 1220 ng·h/mL), and 6-minute walk test (E₅₀  = 1770 ng·h/mL). Week 2 changes of proinflammatory PD biomarkers showed exposure-dependent decreases. The E₅₀ was 260 ng·h/mL for insulin-like growth factor-binding protein 2, 1200 ng·h/mL for matrix metalloproteinase 12, 1260 ng·h/mL for lymphotoxin α1/β2, 1340 ng·h/mL for CD23, 1420 ng·h/mL for interleukin-22-binding protein, and 1600 ng·h/mL for macrophage-derived chemokine/C-C motif chemokine 22. No relationship was found between QTcF interval changes from baseline and C_max in week 2 or 24. This analysis showed that improvements in clinical efficacy end points in week 24 and PD biomarkers in week 2 were achieved at typical vamorolone exposure of 2 mg/kg daily dose with a median AUC dose of 6 mg/kg (3651 ng·h/mL), corresponding to approximately 95% of maximum effects for most response variables.

Genetic modifiers of respiratory function in Duchenne muscular dystrophy

Objective

Respiratory insufficiency is a major complication of Duchenne muscular dystrophy (DMD). Its progression shows considerable interindividual variability, which has been less thoroughly characterized and understood than in skeletal muscle. We collected pulmonary function testing (PFT) data from a large retrospective cohort followed at Centers collaborating in the Italian DMD Network. Furthermore, we analyzed PFT associations with different DMD mutation types, and with genetic variants in SPP1, LTBP4, CD40, and ACTN3, known to modify skeletal muscle weakness in DMD. Genetic association findings were independently validated in the Cooperative International Neuromuscular Research Group Duchenne Natural History Study (CINRG‐DNHS).

Methods and Results

Generalized estimating equation analysis of 1852 PFTs from 327 Italian DMD patients, over an average follow‐up time of 4.5 years, estimated that forced vital capacity (FVC) declined yearly by −4.2%, forced expiratory volume in 1 sec by −5.0%, and peak expiratory flow (PEF) by −2.9%. Glucocorticoid (GC) treatment was associated with higher values of all PFT measures (approximately + 15% across disease stages). Mutations situated 3’ of DMD intron 44, thus predicted to alter the expression of short dystrophin isoforms, were associated with lower (approximately −6%) PFT values, a finding independently validated in the CINRG‐DNHS. Deletions amenable to skipping of exon 51 and 53 were independently associated with worse PFT outcomes. A meta‐analysis of the two cohorts identified detrimental effects of SPP1 rs28357094 and CD40 rs1883832 minor alleles on both FVC and PEF.

Interpretation

These findings support GC efficacy in delaying respiratory insufficiency, and will be useful for the design and interpretation of clinical trials focused on respiratory endpoints in DMD.

MicroRNA Profiling in Adipose Before and After Weight Loss Highlights the Role of miR-223-3p and the NLRP3 Inflammasome

OBJECTIVE

Adipose tissue plays a key role in obesity-related metabolic dysfunction. MicroRNA (miRNA) are gene regulatory molecules involved in intercellular and inter-organ communication. It was hypothesized that miRNA levels in adipose tissue would change after gastric bypass surgery and that this would provide insights into their role in obesity-induced metabolic dysregulation.

METHODS

miRNA profiling (Affymetrix GeneChip miRNA 2.0 Array) of omental and subcutaneous adipose (n = 15 females) before and after gastric bypass surgery was performed.

RESULTS

One omental and thirteen subcutaneous adipose miRNAs were significantly differentially expressed after gastric bypass, including downregulation of miR-223-3p and its antisense relative miR-223-5p in both adipose tissues. mRNA levels of miR-223-3p targets NLRP3 and GLUT4 were decreased and increased, respectively, following gastric bypass in both adipose tissues. Significantly more NLRP3 protein was observed in omental adipose after gastric bypass (P = 0.02). Significant hypomethlyation of NLRP3 and hypermethylation of miR-223 were observed in both adipose tissues after gastric bypass. In subcutaneous adipose, significant correlations were observed between both miR-223-3p and miR-223-5p and glucose and between NLRP3 mRNA and protein levels and blood lipids.

CONCLUSIONS

This is the first report detailing genome-wide miRNA profiling of omental adipose before and after gastric bypass, and it further highlights the association of miR-223-3p and the NLRP3 inflammasome with obesity.

Absolute quantification of dystrophin protein in human muscle biopsies using parallel reaction monitoring (PRM)

The need for a reliable and accurate method to quantify dystrophin proteins in human skeletal muscle biopsies has become crucial in order to assess the efficacy of dystrophin replacement therapies in Duchenne muscular dystrophy as well as to gain insight into the relationship between dystrophin levels and disease severity in Becker's muscular dystrophy. Current methods to measure dystrophin such as western blot and immunofluorescence, while straightforward and simple, lack precision and sometimes specificity. Here, we standardized a targeted mass spectrometry method to determine the absolute amount of dystrophin in ng/mg of muscle using full-length ¹³ C6-Arg- and ¹³ C6,¹⁵ N2-Lys-labeled dystrophin and parallel reaction monitoring (PRM). The method was found to be reproducible with a limit of quantification as low as 30 pg of dystrophin protein per mg of total muscle proteins. The method was then tested to measure levels of dystrophin in muscle biopsies from a healthy donor and from Duchenne and Becker's muscular dystrophy patients.

Report of a TREAT-NMD/World Duchenne Organisation Meeting on Dystrophin Quantification Methodology

Representatives of academia, patient organisations, industry and the United States Food and Drug Administration attended a workshop on dystrophin quantification methodology. The aims of the workshop were to provide an overview of methods used to quantify dystrophin levels in human skeletal muscle and their applicability to clinical trial samples, outline the gaps with regards to validating the methods for robust clinical applications prior to regulatory agency review, and to align future efforts towards further optimizing these methods. The workshop facilitated a constructive but also critical discussion on the potential and limitations of techniques currently used in the field of translational research (western blot and immunofluorescence analysis) and emerging techniques (mass spectrometry and capillary western immunoassay). Notably, all participants reported variation in dystrophin levels between muscle biopsies from different healthy individuals and agreed on the need for a common reference sample.

TCTEX1D1 is a genetic modifier of disease progression in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by pathogenic variants in the DMD gene leading to the lack of dystrophin. Variability in the disease course suggests that other factors influence disease progression. With this study we aimed to identify genetic factors that may account for some of the variability in the clinical presentation. We compared whole-exome sequencing (WES) data in 27 DMD patients with extreme phenotypes to identify candidate variants that could affect disease progression. Validation of the candidate SNPs was performed in two independent cohorts including 301 (BIO-NMD cohort) and 109 (CINRG cohort of European ancestry) DMD patients, respectively. Variants in the Tctex1 domain containing 1 (TCTEX1D1) gene on chromosome 1 were associated with age of ambulation loss. The minor alleles of two independent variants, known to affect TCTEX1D1 coding sequence and induce skipping of its exon 4, were associated with earlier loss of ambulation. Our data show that disease progression of DMD is affected by a new locus on chromosome 1 and demonstrate the possibility to identify genetic modifiers in rare diseases by studying WES data in patients with extreme phenotypes followed by multiple layers of validation.

Pharmacotherapy of Duchenne Muscular Dystrophy

Drug development and pharmacotherapy of rare pediatric diseases have significantly expanded over the last decade, in part due to incentives and financial support provided by governments, regulators, and nonprofit foundations. Duchenne muscular dystrophy (DMD) is among the most common rare pediatric disorders, and clinical trials of therapeutic approaches have seen dramatic expansion. Pharmacotherapeutic standard of care has been limited to off-label prescription of high-dose, daily corticosteroids (prednisone, deflazacort). Deflazacort received FDA approval for DMD in 2016, although the price increases associated with formal FDA approval and the severe side effects associated with corticosteroid use have limited patient/physician uptake and insurance coverage in the USA. In Europe, EMA has given conditional marketing authorization for prescription of Translarna (a stop codon read-through drug prescribed to ~10% of DMD patients), although there is not yet evidence of clinical efficacy. The FDA awarded conditional approval to etiplirsen, an exon-skipping oligonucleotide drug, based on accelerated pathways (increased dystrophin production in patient muscle). Evidence of clinical efficacy remains the focus of post-marketing studies. There are many innovative pharmacotherapies under clinical development for DMD (Phase I, II, and III clinical trials). All are "disease modifying" in the sense that none seek to replace the full-length, normal DMD gene or dystrophin protein, but instead either seek to introduce an abnormal "Becker-like" version of the gene or protein or target pathophysiological pathways downstream of the primary defect. It is envisioned that the most significant benefit to DMD patients will be through multidrug approaches simultaneously aiming to introduce partially functional dystrophin in patient muscle while also targeting both chronic inflammation and the fibrofatty replacement of muscle.

Influence of β2 adrenergic receptor genotype on risk of nocturnal ventilation in patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease resulting in severe respiratory derangements. As such, DMD patients are at a high risk of nocturnal hypoventilation, thereby requiring nocturnal ventilation (NV). To this end, NV is an important clinical milestone in the management of DMD. Emerging evidence suggests that ß₂ adrenergic receptors (ADRB2) may play a role in determining respiratory function, whereby more functional ADRB2 genotype variants (e.g., Gly16) are associated with improved pulmonary function and respiratory muscle strength. These findings suggest that the more functional ADRB2 genotype may help to preserve respiratory function in patients with DMD. The purpose of this study was to identify the influence of ADRB2 genotype on the risk of NV use in DMD. Data from the CINRG Duchenne Natural History Study including 175 DMD patients (3–25 yrs) were analyzed focusing on ADRB2 genotype variants. Time-to-event analyses were used to examine differences in the age at prescription of full-time NV use between genotypes. There were no differences between genotype groups in age, height, weight, corticosteroid use, proportion of ambulatory patients, or age at loss of ambulation. DMD patients expressing the Gly16 polymorphism had a significantly (P < 0.05) lower mean age at NV prescription compared with those patients expressing the Arg16 polymorphism (21.80 ± 0.59 yrs. vs 25.91 ± 1.31 yrs., respectively). In addition, a covariate-adjusted Cox model revealed that the Gly16 variant group possessed a 6.52-fold higher risk of full-time NV use at any given age compared with the Arg16 polymorphism group. These data suggest that genetic variations in the ADRB2 gene may influence the age at which DMD patients are first prescribed NV, whereby patients with the Gly16 polymorphism are more likely to require NV assistance at an earlier age than their Arg16 counterparts.

Vamorolone trial in Duchenne muscular dystrophy shows dose-related improvement of muscle function

Objective

To study vamorolone, a first-in-class steroidal anti-inflammatory drug, in Duchenne muscular dystrophy (DMD).

Methods

An open-label, multiple-ascending-dose study of vamorolone was conducted in 48 boys with DMD (age 4–<7 years, steroid-naive). Dose levels were 0.25, 0.75, 2.0, and 6.0 mg/kg/d in an oral suspension formulation (12 boys per dose level; one-third to 10 times the glucocorticoid dose in DMD). The primary goal was to define optimal doses of vamorolone. The primary outcome for clinical efficacy was time to stand from supine velocity.

Results

Oral administration of vamorolone at all doses tested was safe and well tolerated over the 24-week treatment period. The 2.0–mg/kg/d dose group met the primary efficacy outcome of improved muscle function (time to stand; 24 weeks of vamorolone treatment vs natural history controls), without evidence of most adverse effects of glucocorticoids. A biomarker of bone formation, osteocalcin, increased in vamorolone-treated boys, suggesting possible loss of bone morbidities seen with glucocorticoids. Biomarker outcomes for adrenal suppression and insulin resistance were also lower in vamorolone-treated patients with DMD relative to published studies of glucocorticoid therapy.

Conclusions

Daily vamorolone treatment suggested efficacy at doses of 2.0 and 6.0 mg/kg/d in an exploratory 24-week open-label study.

Classification of evidence

This study provides Class IV evidence that for boys with DMD, vamorolone demonstrated possible efficacy compared to a natural history cohort of glucocorticoid-naive patients and appeared to be tolerated.

Congenital Titinopathy: Comprehensive characterization and pathogenic insights

OBJECTIVE

Comprehensive clinical characterization of congenital titinopathy to facilitate diagnosis and management of this important emerging disorder.

METHODS

Using massively parallel sequencing we identified 30 patients from 27 families with 2 pathogenic nonsense, frameshift and/or splice site TTN mutations in trans. We then undertook a detailed analysis of the clinical, histopathological and imaging features of these patients.

RESULTS

All patients had prenatal or early onset hypotonia and/or congenital contractures. None had ophthalmoplegia. Scoliosis and respiratory insufficiency typically developed early and progressed rapidly, whereas limb weakness was often slowly progressive, and usually did not prevent independent walking. Cardiac involvement was present in 46% of patients. Relatives of 2 patients had dilated cardiomyopathy. Creatine kinase levels were normal to moderately elevated. Increased fiber size variation, internalized nuclei and cores were common histopathological abnormalities. Cap-like regions, whorled or ring fibers, and mitochondrial accumulations were also observed. Muscle magnetic resonance imaging showed gluteal, hamstring and calf muscle involvement. Western blot analysis showed a near-normal sized titin protein in all samples. The presence of 2 mutations predicted to impact both N2BA and N2B cardiac isoforms appeared to be associated with greatest risk of cardiac involvement. One-third of patients had 1 mutation predicted to impact exons present in fetal skeletal muscle, but not included within the mature skeletal muscle isoform transcript. This strongly suggests developmental isoforms are involved in the pathogenesis of this congenital/early onset disorder.

INTERPRETATION

This detailed clinical reference dataset will greatly facilitate diagnostic confirmation and management of patients, and has provided important insights into disease pathogenesis. Ann Neurol 2018;83:1105-1124.

Orthogonal analysis of dystrophin protein and mRNA as a surrogate outcome for drug development

Aim: Detection of drug-induced dystrophin in patient muscle biopsy is a surrogate outcome measure for Duchenne muscular dystrophy. We sought to establish and validate an orthogonal approach to measurement of dystrophin protein and RNA in muscle biopsies. Materials & methods: Validated methods were developed for dystrophin western blotting, mass spectrometry, immunostaining and reverse transcriptase PCR of biopsy mRNA using muscle biopsy standards. Results: Both western blotting and mass spectrometry validated methods demonstrated good linearity, and acceptable precision and accuracy with a lower limit of quantitation at 1%. Immunostaining and reverse transcriptase PCR methods were shown to be reliable. Conclusion: The described orthogonal approach is sufficient to support measures of dystrophin as a surrogate outcome in a clinical trial.

Discovery of potential urine-accessible metabolite biomarkers associated with muscle disease and corticosteroid response in the mdx mouse model for Duchenne

Urine is increasingly being considered as a source of biomarker development in Duchenne Muscular Dystrophy (DMD), a severe, life-limiting disorder that affects approximately 1 in 4500 boys. In this study, we considered the mdx mice-a murine model of DMD-to discover biomarkers of disease, as well as pharmacodynamic biomarkers responsive to prednisolone, a corticosteroid commonly used to treat DMD. Longitudinal urine samples were analyzed from male age-matched mdx and wild-type mice randomized to prednisolone or vehicle control via liquid chromatography tandem mass spectrometry. A large number of metabolites (869 out of 6,334) were found to be significantly different between mdx and wild-type mice at baseline (Bonferroni-adjusted p-value < 0.05), thus being associated with disease status. These included a metabolite with m/z = 357 and creatine, which were also reported in a previous human study looking at serum. Novel observations in this study included peaks identified as biliverdin and hypusine. These four metabolites were significantly higher at baseline in the urine of mdx mice compared to wild-type, and significantly changed their levels over time after baseline. Creatine and biliverdin levels were also different between treated and control groups, but for creatine this may have been driven by an imbalance at baseline. In conclusion, our study reports a number of biomarkers, both known and novel, which may be related to either the mechanisms of muscle injury in DMD or prednisolone treatment.