DMD genotype correlations from the Duchenne Registry: Endogenous exon skipping is a factor in prolonged ambulation for individuals with a defined mutation subtype

Association of DMD Gene Variant Classes With Motor Outcomes in a Drug Registration Clinical Trial Setting

Background and Objectives

Duchenne muscular dystrophy (DMD) is caused by pathogenic variants of the DMD gene, leading to the loss of dystrophin. Clinical variability in DMD can complicate interpretation of interventional data in clinical trials. One source of clinical variability is allelic heterogeneity (different pathogenic variants with different effects on dystrophin protein expression). We sought to determine whether gene variant classes in clinical trial participants potentially affect clinical trial data interpretation.

Methods

We analyzed 186 vamorolone trial participants with DMD (VBP15-002/003; VBP15-004) who were 4 to <7 years old and steroid-naïve at baseline. We stratified participants into gene variant classes by either variant location in the gene affecting different gene promoters (5' [Dp427-only] vs 3' [Dp427+other isoforms]) or residual dystrophin levels (null vs possible non-null [5' gene variants, exon 44 skippable, splice site]). We evaluated associations with baseline motor outcomes and treatment response (prednisone and vamorolone).

Results

Participants with variants in ex63 and downstream (null for Dp427+Dp140+Dp71 protein isoforms) showed poorer baseline motor outcomes for time to stand from supine velocity than those with variants in ex1-44 (Dp427 only). No significant baseline differences were found between likely null and possible non-null variants. Participants with only Dp427 involvement showed significantly better treatment response for the 6-minute walk distance. Most of the comparisons of baseline motor function and treatment response were similar between variant classes.

Discussion

The large variation in baseline motor function in young, steroid-naïve patients with DMD is only minimally explained by different gene variant classes. While there is strong literature support for 3' variants leading to a more severe motor and cognitive DMD phenotype, we found this variant class under-represented in our clinical trials. This suggests that they may fail inclusion criteria (failure to follow commands; poor motor function). Subgroup analyses in DMD clinical trials at a young age range based on gene variant class may not reveal significant differences and would be relatively noninformative.

AOC 1044 induces exon 44 skipping and restores dystrophin protein in preclinical models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe disorder caused by mutations in the dystrophin gene, resulting in loss of functional dystrophin protein in muscle. While phosphorodiamidate morpholino oligomers (PMOs) are promising exon-skipping therapeutics aimed at restoring dystrophin expression, their effectiveness is often limited by poor muscle delivery. We developed AOC 1044, an antibody-oligonucleotide conjugate (AOC) that combines a PMO-targeting exon 44 with an antibody against the transferrin receptor (TfR1), enhancing delivery to muscle tissues for patients with DMD amenable to exon 44 skipping (DMD44). AOC 1044 induces dose-dependent exon 44 skipping and its mouse-active variant elicited dose-dependent dystrophin restoration in skeletal and cardiac muscle in a DMD mouse model. This treatment also reduced muscle damage, as evidenced by decreases in serum creatine kinase and key liver enzymes, suggesting that restored dystrophin is functionally active. In nonhuman primates, single or repeated AOC 1044 doses resulted in dose-dependent increases in PMO concentration and exon 44 skipping across a range of muscle tissues, including the heart. Collectively, these findings highlight AOC 1044 as a promising therapeutic candidate for patients with DMD44, offering improved muscle targeting and meaningful dystrophin restoration, with potential clinical benefits in reducing muscle degeneration.

Dystrophin isoform deficiency and upper-limb and respiratory function in Duchenne muscular dystrophy

AIM

To investigate the associations between mutations expected to differentially affect Dp140 expression and long-term trajectories of respiratory and upper-limb motor outcomes in Duchenne muscular dystrophy (DMD).

METHOD

In a retrospective analysis of population-based longitudinal data from three real-world and natural history data sources, individuals with DMD aged 5 years to 18 years were subdivided according to the predicted effects of the participants' DMD mutation on dystrophin isoform expression (group 1, Dp427 absent, Dp140/Dp71 present; group 2, Dp427/Dp140 absent, Dp71 present).

RESULTS

A total of 459 participants were studied, with upper-limb outcomes assessed in 71 (27 in group 1 and 44 in group 2) and forced vital capacity percentage predicted (%pred) assessed in 434 (224 in group 1 and 210 in group 2). Mean grip strength %pred was on average 7.1 percentage points lower in group 2 than in group 1 (p = 0.03). Mean pinch strength %pred was on average 9.2 percentage points lower in group 2 than in group 1 (p = 0.04). Mean forced vital capacity %pred was on average 4.3 percentage points lower in group 2 than in group 1 (p = 0.01).

INTERPRETATION

In individuals with DMD, DMD mutations predicted to affect Dp140 expression were associated with more severe trajectories of respiratory and upper-limb motor outcomes.

Biological biomarkers in muscle diseases relevant for follow-up and evaluation of treatment

Muscle diseases cover a diverse group of disorders that, in most cases, are hereditary. The rarity of the individual muscle diseases provides a challenge for researchers when wanting to establish natural history of the conditions and when trying to develop diagnostic tools, therapies, and outcome measures to evaluate disease progression. With emerging molecular therapies in many genetic muscle diseases, as well as biological therapies for the immune-mediated diseases, biological biomarkers play an important role in both drug development and evaluation. In this review, we focus on the role of biological biomarkers in muscle diseases and discuss their utility as surrogate end points in therapeutic trials. We categorize these as either (i) disease unspecific markers; (ii) markers of specific pathways that may be used for more than one disease; or (iii) disease-specific markers. We also propose that evaluation of specific therapeutic interventions benefits from biological markers that match the intervention.

The impact of genotype on age at loss of ambulation in individuals with Duchenne muscular dystrophy treated with corticosteroids: A single-center study of 555 patients

INTRODUCTION/AIMS

Studies have demonstrated that certain genotypes in Duchenne muscular dystrophy (DMD) have milder or more severe phenotypes. These studies included individuals treated and not treated with corticosteroids and multiple sites with potentially varying standards of care. We aimed to assess genotype-phenotype correlations for age at loss of ambulation (LoA) in a large cohort of individuals with DMD treated with corticosteroids at one center.

METHODS

In this retrospective review of medical records, encounters were included for individuals diagnosed with DMD if prescribed corticosteroids, defined as daily deflazacort or prednisone or high-dose weekend prednisone, for 12 consecutive months. Encounters were excluded if the participants were taking disease-modifying therapy. Data were analyzed using survival analysis for LoA and Fisher's exact tests to assess the percentage of late ambulatory (>14 years old) individuals for selected genotypes.

RESULTS

Overall, 3948 encounters from 555 individuals were included. Survival analysis showed later age at LoA for exon 44 skip amenable (p = .004), deletion exons 3-7 (p < .001) and duplication exon 2 (p = .043) cohorts and earlier age at LoA for the exon 51 skip amenable cohort (p < .001) when compared with the rest of the cohort. Individuals with deletions of exons 3-7 had significantly more late ambulatory individuals than other cohorts (75%), while those with exon 51 skip amenable deletions had significantly fewer (11.9%) compared with other cohorts.

DISCUSSION

This confirms previous observations of genotype-phenotype correlations in DMD and enhances information for trial design and clinical management.

Skeletal muscle symptoms and quantitative MRI in females with dystrophinopathy

INTRODUCTION/AIMS

The dystrophinopathies primarily affect males; however, female carriers of pathogenic dystrophin variants can develop skeletal muscle symptoms. This study aimed to evaluate muscle involvement and symptoms in females with dystrophinopathy using quantitative magnetic resonance imaging (MRI), functional assessments, and patient-reported outcomes.

METHODS

Controls and females with dystrophinopathy with muscle symptoms of pain, weakness, fatigue, or excessive tightness were enrolled in this cross-sectional study. Participants underwent lower extremity MRI to quantify muscle inflammation, replacement by fat, and disease asymmetry. Cardiac MRI, functional ability, muscle symptoms, and serum creatine kinase levels were also evaluated.

RESULTS

Six pediatric females with dystrophinopathy (mean age: 11.7 years), 11 adult females with dystrophinopathy (mean age: 41.3 years), and seven controls enrolled. The mean fat fraction was increased in females with dystrophinopathy compared to controls in the soleus (0.11 vs. 0.03, p = .0272) and vastus lateralis (0.16 vs. 0.03, p = .004). Magnetic resonance spectroscopy water T2, indicative of muscle inflammation, was elevated in the soleus and/or vastus lateralis in 11 of 17 individuals. North Star Ambulatory Assessment score was lower in the dystrophinopathy group compared to controls (29 vs. 34 points, p = .0428). From cardiac MRI, left ventricle T1 relaxation times were elevated in females with dystrophinopathy compared to controls (1311 ± 55 vs. 1263 ± 25 ms, p < .05), but ejection fraction and circumferential strain did not differ.

DISCUSSION

Symptomatic females with dystrophinopathy quantitatively demonstrate muscle replacement by fat and inflammation, along with impairments in functional ability and cardiac function. Additional research is needed to evaluate how symptoms and muscle involvement change longitudinally.

Respiratory performance in Duchenne muscular dystrophy: Clinical manifestations and lessons from animal models

Duchenne muscular dystrophy (DMD) is a fatal genetic neuromuscular disease. Lack of dystrophin in skeletal muscles leads to intrinsic weakness, injury, subsequent degeneration and fibrosis, decreasing contractile function. Dystropathology eventually presents in all inspiratory and expiratory muscles of breathing, severely curtailing their critical function. In people with DMD, premature death is caused by respiratory or cardiac failure. There is an urgent need to develop therapies that improve quality of life and extend life expectancy in DMD. Surprisingly, there is a dearth of information on respiratory control in animal models of DMD, and respiratory outcome measures are often limited or absent in clinical trials. Characterization of respiratory performance in murine and canine models has revealed extensive remodelling of the diaphragm, the major muscle of inspiration. However, significant compensation by extradiaphragmatic muscles of breathing is evident in early disease, contributing to preservation of peak respiratory system performance. Loss of compensation afforded by accessory muscles in advanced disease is ultimately associated with compromised respiratory performance. A new and potentially more translatable murine model of DMD, the D2.mdx mouse, has recently been developed. Respiratory performance in D2.mdx mice is yet to be characterized fully. However, based on histopathological features, D2.mdx mice might serve as useful preclinical models, facilitating the testing of new therapeutics that rescue respiratory function. This review summarizes the pathophysiological mechanisms associated with DMD both in humans and in animal models, with a focus on breathing. We consider the translational value of each model to human DMD and highlight the urgent need for comprehensive characterization of breathing in representative preclinical models to better inform human trials.

Large scale serum proteomics identifies proteins associated with performance decline and clinical milestones in Duchenne muscular dystrophy

Serum biomarkers are promising minimally invasive outcome measures in clinical studies in Duchenne muscular dystrophy (DMD). However, biomarkers strongly associated with clinical progression and predicting performance decline are lacking. In this study we aimed to identify serum biomarkers associated with clinical performance and able to predict clinical milestones in DMD. Towards this aim we present a retrospective multi-center cohort study including serum samples and clinical data collected in research participants with DMD as part of a natural history study at the University of Florida (UF) and real-world observations at Leiden University Medical Center (LUMC) between 2009-2022. The 7K SomaScan® assay was used to analyse protein levels in in individual serum samples. Serum biomarkers predicted age at loss of ambulation (LoA), age at loss of overhead reach (OHR) and age at loss of hand to mouth function (HTM). Secondary outcomes were the association of biomarkers with age, corticosteroid (CS) usage, and clinical performance based on the North Star Ambulatory Assessment (NSAA), 10 meter run velocity (10mrv), 6 minute walk (6MWT) and Performance of the Upper Limb (PUL2.0). A total of 716 serum samples were collected in 79 participants at UF and 74 at LUMC (mean[SD] age; 10.9[3.2] vs 8.4[3.4]). 244 serum proteins showed an association with CS usage in both cohorts independent of CS type and regimen, including MMP3 and IGLL1. 318 probes (corresponding to 294 proteins) showed significant associations with NSAA, 10mrv, 6MWT and/or PUL2.0 across both cohorts. The expression of 38 probes corresponding to 36 proteins such as RGMA, EHMT2, ART3, ANTXR2 and DLK1 was associated with risk of both lower and upper limb clinical milestones in both the LUMC and UF cohort. In conclusion, multiple biomarkers were associated with CS use, motor function and upper lower and upper limb disease milestones in DMD. These biomarkers were validated across two independent cohorts, increasing their likelihood of translation for use within the broader DMD population.

The complex landscape of DMD mutations: moving towards personalized medicine

Duchenne muscular dystrophy (DMD) is a severe genetic disorder characterized by progressive muscle degeneration, with respiratory and cardiac complications, caused by mutations in the DMD gene, encoding the protein dystrophin. Various DMD mutations result in different phenotypes and disease severity. Understanding genotype/phenotype correlations is essential to optimize clinical care, as mutation-specific therapies and innovative therapeutic approaches are becoming available. Disease modifier genes, trans-active variants influencing disease severity and phenotypic expressivity, may modulate the response to therapy, and become new therapeutic targets. Uncovering more disease modifier genes via extensive genomic mapping studies offers the potential to fine-tune prognostic assessments for individuals with DMD. This review provides insights into genotype/phenotype correlations and the influence of modifier genes in DMD.

Quantifying Variability in Motor Function in Duchenne Muscular Dystrophy: UK Centiles for the NorthStar Ambulatory Assessment, 10 m Walk Run Velocity and Rise from Floor Velocity in GC Treated Boys

Background Boys with Duchenne Muscular Dystrophy (DMD) display heterogeneous motor function trajectory in clinics, which represents a significant obstacle to monitoring.

OBJECTIVE

In this paper, we present the UK centiles for the North Star Ambulatory Assessment (NSAA), the 10 m walk/run time (10MWR) and velocity (10MWRV), and the rise from floor time (RFF) and velocity (RFFV) created from a cohort of glucocorticoid treated DMD boys between the age of 5 and 16 years.

METHODS

Participants were included from the UK NorthStar registry if they had initiated steroids (primarily deflazacorts/prednisolone, intermittent/daily) and were not enrolled in an interventional trial. Assessments were included if the participant had a complete NSAA, the timed tests had been completed or the corresponding items were 0, or the participant was recorded as non-ambulant, in which case the NSAA was assumed 0.

RESULTS

We analysed 3987 assessments of the NSAA collected from 826 participants. Of these, 1080, 1849 and 1199 were imputed as 0 for the NSAA, RFFV and 10MWRV respectively. The 10th, 25th, 50th, 75th and 90th centiles were presented. The NSAA centiles showed a peak score of 14, 20, 26, 30 and 32 respectively, with loss of ambulation at 10.7, 12.2 and 14.3 years for the 25th, 50th and 75th centiles, respectively. The centiles showed loss of rise from floor at 8.6, 10.1 and 11.9 years and a loss of 10MWR of 0 at 8.9, 10.3 and 13.8 years for the 25th, 50th and 75th centiles, respectively. The centiles were pairwise less correlated than the raw scores, suggesting an increased ability to detect variability in the DMD cohort.

CONCLUSIONS

The NSAA, 10MWR and RFF centiles may provide insights for clinical monitoring of DMD boys, particularly in late ambulatory participants who are uniformly declining. Future work will validate the centiles in national and international natural history cohorts.

Developing a Natural History Model for Duchenne Muscular Dystrophy

BACKGROUND

The aim of this study was to pool multiple data sets to build a patient-centric, data-informed, natural history model (NHM) for Duchenne muscular dystrophy (DMD) to estimate disease trajectory across patient lifetime under current standard of care in future economic evaluations. The study was conducted as part of Project HERCULES, a multi-stakeholder collaboration to develop tools to support health technology assessments of new treatments for DMD.

METHODS

Health states were informed by a review of NHMs for DMD and input from clinicians, patients and caregivers, and defined using common outcomes in clinical trials and real-world practice. The primary source informing the NHM was the Critical Path Institute Duchenne Regulatory Science Consortium (D-RSC) database. This was supplemented with expert input obtained via an elicitation exercise, and a systematic literature review and meta-analysis of mortality data.

RESULTS

The NHM includes ambulatory, transfer and non-ambulatory phases, which capture loss of ambulation, ability to weight bear and upper body and respiratory function, respectively. The NHM estimates patients spend approximately 9.5 years in ambulatory states, 1.5 years in the transfer state and the remainder of their lives in non-ambulatory states. Median predicted survival is 34.8 years (95% CI 34.1-35.8).

CONCLUSION

The model includes a detailed disease pathway for DMD, including the clinically and economically important transfer state. The NHM may be used to estimate the current trajectory of DMD in economic evaluations of new treatments, facilitating inclusion of a lifetime time horizon, and will help identify areas for further research.

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.

Predictors of Loss of Ambulation in Duchenne Muscular Dystrophy: A Systematic Review and Meta-Analysis

Objective

The objective of this study was to describe predictors of loss of ambulation in Duchenne muscular dystrophy (DMD).

Methods

This systematic review and meta-analysis included searches of MEDLINE ALL, Embase, and the Cochrane Database of Systematic Reviews from January 1, 2000, to December 31, 2022, for predictors of loss of ambulation in DMD. Search terms included "Duchenne muscular dystrophy" as a Medical Subject Heading or free text term, in combination with variations of the term "predictor". Risk of bias was assessed using the Newcastle-Ottawa Scale. We performed meta-analysis pooling of hazard ratios of the effects of glucocorticoids (vs. no glucocorticoid therapy) by fitting a common-effect inverse-variance model.

Results

The bibliographic searches resulted in the inclusion of 45 studies of children and adults with DMD from 17 countries across Europe, Asia, and North America. Glucocorticoid therapy was associated with delayed loss of ambulation (overall meta-analysis HR deflazacort/prednisone/prednisolone: 0.44 [95% CI: 0.40-0.48]) (n = 25 studies). Earlier onset of first signs or symptoms, earlier loss of developmental milestones, lower baseline 6MWT (i.e.,<350 vs. ≥350 metres and <330 vs. ≥330 metres), and lower baseline NSAA were associated with earlier loss of ambulation (n = 5 studies). Deletion of exons 3-7, proximal mutations (upstream intron 44), single exon 45 deletions, and mutations amenable of skipping exon 8, exon 44, and exon 53, were associated with prolonged ambulation; distal mutations (intron 44 and downstream), deletion of exons 49-50, and mutations amenable of skipping exon 45, and exon 51 were associated with earlier loss of ambulation (n = 13 studies). Specific single-nucleotide polymorphisms in CD40 gene rs1883832, LTBP4 gene rs10880, SPP1 gene rs2835709 and rs11730582, and TCTEX1D1 gene rs1060575 (n = 7 studies), as well as race/ethnicity and level of family/patient deprivation (n = 3 studies), were associated with loss of ambulation. Treatment with ataluren (n = 2 studies) and eteplirsen (n = 3 studies) were associated with prolonged ambulation. Magnetic resonance biomarkers (MRI and MRS) were identified as significant predictors of loss of ambulation (n = 6 studies). In total, 33% of studies exhibited some risk of bias.

Conclusion

Our synthesis of predictors of loss of ambulation in DMD contributes to the understanding the natural history of disease and informs the design of new trials of novel therapies targeting this heavily burdened patient population.

Trajectories of motor function in children with Duchenne muscular dystrophy: A longitudinal study on a Colombian population

Duchenne Muscular Dystrophy (DMD) is characterized by an initial increase in motor function followed by a plateau phase and then entering a phase of steady decline. However, motor evolution of DMD have not been evaluated in developing countries. Therefore, this study aims to evaluate the trajectory of motor function in a sample of Colombian children with DMD. We included 119 children with DMD aged 4.8-19.3 years (mean follow-up = 1.7 years). A linear mixed model was used with age as the time scale and adjusted for covariates using a stepwise regression. Participants showed a progressive decline in motor skills from the age of 5 years with a decrease in speed around the age of 11 years (p < 0.001). After age 11, the decline in motor function was observed to continue until age 20 but at a slower rate (βAge = -9.64. and βAge2 = 0.18, p < 0.001 for both). Educational inclusion, glucocorticoid treatment and the number of mutated exons were shown to be associated with the motor performance. These findings may indicate that the evolution of DMD maintains similar patterns between high income countries and the Colombian population. They allow us to adapt and develop treatments that impact the population with DMD in Colombia, based in international evidence.

Long-term Observation in Patients with Duchenne Muscular Dystrophy with Early Introduction of a Standing Program Using Knee-ankle-foot Orthoses

Objectives

This study investigated the outcomes of the early introduction of a standing program for patients with Duchenne muscular dystrophy (DMD).

Methods

This was a retrospective observational study of 41 outpatients with DMD aged 15-20 years. We introduced the standing program using knee-ankle-foot orthoses (KAFO) to slow the progression of scoliosis when ankle dorsiflexion became less than 0° in the ambulatory period.

Results

Thirty-two patients with DMD were offered the standing program with KAFO; 12 continued the program until the age of 15 years (complete group) and 20 discontinued the program before the age of 15 years (incomplete group). The non-standing program group included 9 patients. The standing program with KAFO was significantly associated with the Cobb angle at the age of 15 years after adjustment for the duration of corticosteroid use and DMD mutation type (P=0.0004). At the age of 15 years, significant correlations were found between the ankle dorsiflexion range of motion (ROM) and non-ambulatory period (P=0.0010), non-ambulatory period and Cobb angle (P<0.0001), Cobb angle and percent predicted forced vital capacity (P=0.0004), and ankle dorsiflexion ROM and Cobb angle (P=0.0066). In the complete group, the age at ambulation loss (log-rank P=0.0015), scoliosis progression (log-rank P=0.0032), and pulmonary dysfunction (log-rank P=0.0006) were significantly higher than in the non-standing program group.

Conclusions

The early introduction of a standing program for DMD patients may prolong the ambulation period and slow the progression of scoliosis and pulmonary dysfunction.

Real-world evidence of eteplirsen treatment effects in patients with Duchenne muscular dystrophy in the USA

Aim: To evaluate treatment effects of eteplirsen among patients with Duchenne muscular dystrophy. Methods: Using real-world claims and electronic medical record data, this retrospective comparative analysis assessed eteplirsen-treated and control cohorts matched by age, disease progression state, and pre-index period healthcare resource utilization. Poisson regression was used to evaluate eteplirsen effects on healthcare resource utilization outcomes. Results: Eteplirsen was associated with statistically significant reductions in rates of hospital encounters (31%), emergency room visits (31%), need for pulmonary management (33%), cardiac management (21%), tracheostomy (86%), and assisted ventilation (39%) versus the control group. Other assessed outcomes favored eteplirsen numerically but did not all reach statistical significance. Conclusion: Eteplirsen-treated patients had reduced rates of multiple healthcare resource utilization measures versus matched controls.

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.

Exploring the relationship between North Star Ambulatory Assessment and Health Utilities Index scores in Duchenne muscular dystrophy

BACKGROUND

The North Star Ambulatory Assessment (NSAA) documents motor performance in ambulatory individuals with Duchenne muscular dystrophy (DMD). Health Utilities Index (HUI) scores, reflecting preferences for health-related quality-of-life (HRQoL) implications of health states, are commonly estimated within trials. This study sought to characterize the relationship between the NSAA score and utility in DMD.

METHODS

Family members serving as proxy respondents for placebo-treated ambulatory individuals with DMD (NCT01254019; BioMarin Pharmaceuticals Inc) completed the HUI and the NSAA (score range, 0-34). Mean change over time on these measures was estimated, and the correlation between changes in NSAA score and a) HUI utility; b) HUI3 ambulation and HUI2 mobility attribute scores, over 48 weeks was calculated.

RESULTS

Baseline mean (range) age was 8.0 years (5-16; n = 61) and mean (standard deviation [SD]) scores were 0.87 (0.13; HUI2), 0.82 (0.19; HUI3), and 21.0 (8.1; NSAA). Mean (SD) change over 48 weeks was -0.05 (0.14; HUI2), -0.06 (0.19; HUI3), and -2.9 (4.7; NSAA). Weak positive correlations were observed between baseline NSAA score and HUI utility (HUI2: r = 0.29; HUI3: r = 0.17) and for change over 48 weeks (HUI2: r = 0.16; HUI3: r = 0.15). Stronger correlations were observed between change in NSAA score and the HUI3 ambulation (r = 0.41) and HUI2 mobility (r = 0.41) attributes.

CONCLUSIONS

Among ambulatory individuals with DMD, NSAA score is weakly correlated with HUI utility, suggesting that motor performance alone does not fully explain HRQoL. Stronger relationships were observed between HUI ambulation and mobility attributes, and NSAA. Although unidimensional measures like the NSAA are informative for documenting disease-specific health impacts, they may not correlate well with measures of overall health status; requiring use in conjunction with other patient-reported and preference-based outcomes.

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.

Expanding genotype-phenotype correlations in FOXG1 syndrome: results from a patient registry

BACKGROUND

We refine the clinical spectrum of FOXG1 syndrome and expand genotype-phenotype correlations through evaluation of 122 individuals enrolled in an international patient registry.

METHODS

The FOXG1 syndrome online patient registry allows for remote collection of caregiver-reported outcomes. Inclusion required documentation of a (likely) pathogenic variant in FOXG1. Caregivers were administered a questionnaire to evaluate clinical severity of core features of FOXG1 syndrome. Genotype-phenotype correlations were determined using nonparametric analyses.

RESULTS

We studied 122 registry participants with FOXG1 syndrome, aged < 12 months to 24 years. Caregivers described delayed or absent developmental milestone attainment, seizures (61%), and movement disorders (58%). Participants harbouring a missense variant had a milder phenotype. Compared to individuals with gene deletions (0%) or nonsense variants (20%), missense variants were associated with more frequent attainment of sitting (73%). Further, individuals with missense variants (41%) achieved independent walking more frequently than those with gene deletions (0%) or frameshift variants (6%). Presence of epilepsy also varied by genotype and was significantly more common in those with gene deletions (81%) compared to missense variants (47%). Individuals with gene deletions were more likely to have higher seizure burden than other genotypes with 53% reporting daily seizures, even at best control. We also observed that truncations preserving the forkhead DNA binding domain were associated with better developmental outcomes.

CONCLUSION

We refine the phenotypic spectrum of neurodevelopmental features associated with FOXG1 syndrome. We strengthen genotype-driven outcomes, where missense variants are associated with a milder clinical course.

DMD Gene and Dystrophinopathy Phenotypes Associated With Mutations: A Systematic Review for Clinicians

ABSTRACT

The diagnosis of Duchenne and Becker muscular dystrophy (DBMD) is made by genetic testing in approximately 95% of cases. Although specific mutations can be associated with skeletal muscle phenotype, pulmonary and cardiac comorbidities (leading causes of death in Duchenne) have not been associated with Duchenne muscular dystrophy mutation type or location and vary within families. Therefore, identifying predictors for phenotype severity beyond frameshift prediction is important clinically. We performed a systematic review assessing research related to genotype-phenotype correlations in DBMD. While there are severity differences across the spectrum and within mild and severe forms of DBMD, few protective or exacerbating mutations within the dystrophin gene were reported. Except for intellectual disability, clinical test results reporting genotypic information are insufficient for clinical prediction of severity and comorbidities and the predictive validity is too low to be useful when advising families. Including expanded information coupled with proposed severity predictions in clinical genetic reports for DBMD is critical for improving anticipatory guidance.

A genome-wide association analysis of loss of ambulation in dystrophinopathy patients suggests multiple candidate modifiers of disease severity

The major determinant of disease severity in Duchenne muscular dystrophy (DMD) or milder Becker muscular dystrophy (BMD) is whether the dystrophin gene (DMD) mutation truncates the mRNA reading frame or allows expression of a partially functional protein. However, even in the complete absence of dystrophin, variability in disease severity is observed, and candidate gene studies have implicated several genes as modifiers. Here we present the largest genome-wide search to date for loci influencing severity in N = 419 DMD patients. Availability of subjects for such studies is quite limited, leading to modest sample sizes, which present a challenge for GWAS design. We have therefore taken special steps to minimize heterogeneity within our dataset at the DMD locus itself, taking a novel approach to mutation classification to effectively exclude the possibility of residual dystrophin expression, and utilized statistical methods that are well adapted to smaller sample sizes, including the use of a novel linear regression-like residual for time to ambulatory loss and the application of evidential statistics for the GWAS approach. Finally, we applied an unbiased in silico pipeline, utilizing functional genomic datasets to explore the potential impact of the best supported SNPs. In all, we obtained eight SNPs (out of 1,385,356 total) with posterior probability of trait-marker association (PPLD) ≥ 0.4, representing six distinct loci. Our analysis prioritized likely non-coding SNP regulatory effects on six genes (ETAA1, PARD6G, GALNTL6, MAN1A1, ADAMTS19, and NCALD), each with plausibility as a DMD modifier. These results support both recurrent and potentially new pathways for intervention in the dystrophinopathies.

Next steps for the optimization of exon therapy for Duchenne muscular dystrophy

INTRODUCTION

It is established that the exon-skipping approach can restore dystrophin in Duchenne muscular dystrophy (DMD) patients. However, dystrophin restoration levels are low, and the field is evolving to provide solutions for improved exon skipping. DMD is a neuromuscular disorder associated with chronic muscle tissue loss attributed to the lack of dystrophin, which causes muscle inflammation, fibrosis formation, and impaired regeneration. Currently, four antisense oligonucleotides (AONs) based on phosphorodiamidate morpholino oligomer (PMO) chemistry are approved by US Food and Drug Administration for exon skipping therapy of eligible DMD patients.

AREAS COVERED

This review describes a preclinical and clinical experience with approved and newly developed AONs for DMD, outlines efforts that have been done to enhance AON efficiency, reviews challenges of clinical trials, and summarizes the current state of the exon skipping approach in the DMD field.

EXPERT OPINION

The exon skipping approach for DMD is under development, and several chemical modifications with improved properties are under (pre)-clinical investigation. Despite existing advantages of these modifications, their safety and effectiveness have to be examined in clinical trials, which are planned or ongoing. Furthermore, we propose clinical settings using natural history controls to facilitate studying the functional effect of the therapy.

Machine Learning Guides Peptide Nucleic Acid Flow Synthesis and Sequence Design

Peptide nucleic acids (PNAs) are potential antisense therapies for genetic, acquired, and viral diseases. Efficiently selecting candidate PNA sequences for synthesis and evaluation from a genome containing hundreds to thousands of options can be challenging. To facilitate this process, this work leverages machine learning (ML) algorithms and automated synthesis technology to predict PNA synthesis efficiency and guide rational PNA sequence design. The training data is collected from individual fluorenylmethyloxycarbonyl (Fmoc) deprotection reactions performed on a fully automated PNA synthesizer. The optimized ML model allows for 93% prediction accuracy and 0.97 Pearson's r. The predicted synthesis scores are validated to be correlated with the experimental high-performance liquid chromatography (HPLC) crude purities (correlation coefficient R² = 0.95). Furthermore, a general applicability of ML is demonstrated through designing synthetically accessible antisense PNA sequences from 102 315 predicted candidates targeting exon 44 of the human dystrophin gene, SARS-CoV-2, HIV, as well as selected genes associated with cardiovascular diseases, type II diabetes, and various cancers. Collectively, ML provides an accurate prediction of PNA synthesis quality and serves as a useful computational tool for informing PNA sequence design.

Evaluating Genetic Modifiers of Duchenne Muscular Dystrophy Disease Progression Using Modeling and MRI

BACKGROUND AND OBJECTIVES

Duchenne muscular dystrophy (DMD) is a progressive muscle degenerative disorder with a well-characterized disease phenotype but considerable interindividual heterogeneity that is not well understood. The aim of this study was to evaluate the effects of dystrophin variations and genetic modifiers of DMD on rate and age of muscle replacement by fat.

METHODS

One hundred seventy-five corticosteroid treated participants from the ImagingDMD natural history study underwent repeated magnetic resonance spectroscopy (MRS) of the vastus lateralis (VL) and soleus (SOL) to determine muscle fat fraction (FF). MRS was performed annually in most instances; however, some individuals had additional visits at 3 or 6 monthss intervals. FF changes over time were modeled using nonlinear mixed effects to estimate disease trajectories based on the age that the VL or SOL reached half-maximum change in FF (mu) and the time required for FF change (sigma). Computed mu and sigma values were evaluated for dystrophin variations that have demonstrated the ability to lead to a mild phenotype as well as compared between different genetic polymorphism groups.

RESULTS

Participants with dystrophin gene deletions amenable to exon 8 skipping (n = 4) had minimal increases in SOL FF and had an increase in VL mu value by 4.4 years compared with a reference cohort (p = 0.039). Participants with nonsense variations within exons that may produce milder phenotypes (n = 11) also had minimal increases in SOL and VL FFs. No differences in estimated FF trajectories were seen for individuals amenable to exon 44 skipping (n = 10). Modeling of the SPP1, LTBP4, and thrombospondin-1 (THBS1) genetic modifiers did not result in significant differences in muscle FF trajectories between genotype groups (p > 0.05); however, trends were noted for the polymorphisms associated with long-range regulation of LTBP4 and THBS1 that deserve further follow-up.

DISCUSSION

The results of this study link the historically mild phenotypes seen in individuals amenable to exon 8 skipping and with certain nonsense variations with alterations in trajectories of lower extremity muscle replacement by fat.

Associations Between Self-Reported Behavioral and Learning Concerns and DMD Isoforms in Duchenne Muscular Dystrophy

Background: Duchenne muscular dystrophy (DMD) is an X-linked recessive neuromuscular disorder resulting from loss of dystrophin. In addition to its role in muscle, isoforms of dystrophin are expressed in different cell types of the brain, and DMD has been linked to language delays, behavioral abnormalities and learning disabilities. Objective: To determine whether disruption of specific DMD isoforms, age, corticosteroid use, ambulation status, or country are associated with behavioral and/or learning concerns in DMD. Methods: De-identified data were collected from the Duchenne Registry from 2007– 2019. Females, patients with BMD, and those without genetic testing reports were excluded from the cohort. For the genetic analysis, patients were divided into four subgroups based on the location of their mutation and the predicted isoforms affected. Bivariate analysis was conducted using chi-square for categorical variables. Two multivariate logistic regressions were used to assess independent associations with behavioral and learning concerns, respectively, and to estimate the effect size of each variable. Results: DMD mutations disrupting expression of Dp140 and Dp71 were associated with a higher likelihood of reported behavioral and learning concerns. Corticosteroid use, categorical age, and country were other factors associated with behavior and learning concerns. Conclusion: This data adds to our current understanding of DMD isoforms, their mutational consequence and impact on behavior and learning.

LTBP4, SPP1, and CD40 Variants: Genetic Modifiers of Duchenne Muscular Dystrophy Analyzed in Serbian Patients

BACKGROUND

Clinical course variability in Duchenne muscular dystrophy (DMD) is partially explained by the mutation location in the DMD gene and variants in modifier genes. We assessed the effect of the SPP1, CD40, and LTBP4 genes and DMD mutation location on loss of ambulation (LoA).

METHODS

SNPs in SPP1-rs28357094, LTBP4-rs2303729, rs1131620, rs1051303, rs10880, and CD40-rs1883832 were genotyped, and their effect was assessed by survival and hierarchical cluster analysis.

RESULTS

Patients on glucocorticoid corticosteroid (GC) therapy experienced LoA one year later (p = 0.04). The modifying effect of SPP1 and CD40 variants, as well as LTBP4 haplotypes, was not observed using a log-rank test and multivariant Cox regression analysis. Cluster analysis revealed two subgroups with statistical trends in differences in age at LoA. Almost all patients in the cluster with later LoA had the protective IAAM LTBP4 haplotype and statistically significantly fewer CD40 genotypes with harmful T allele and "distal" DMD mutations.

CONCLUSIONS

The modifying effect of SPP1, CD40, and LTBP4 was not replicated in Serbian patients, although our cohort was comparable in terms of its DMD mutation type distribution, SNP allele frequencies, and GC-positive effect with other European cohorts. Cluster analysis may be able to identify patient subgroups carrying a combination of the genetic variants that modify LoA.

Newborn screening for Duchenne muscular dystrophy-early detection and diagnostic algorithm for female carriers of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most common pediatric-onset form of muscular dystrophy, occurring in 1 in 5,000 live male births. DMD is a multi-system disease resulting in muscle weakness with progressive deterioration of skeletal, heart, and smooth muscle, and learning disabilities. Pathogenic/likely pathogenic (P/LP) variants in the DMD gene, which encodes dystrophin protein, cause dystrophinopathy. All males with a P/LP variant in the X-linked DMD gene are expected to be affected. Two to 20% of female heterozygotes with a P/LP variant develop symptoms of dystrophinopathy ranging from mild muscle weakness to significant disability similar to Becker muscular dystrophy. Recently, with improvements in therapies and testing methodology, there is stronger evidence supporting newborn screening (NBS) for DMD for males and females because females may also develop symptoms. A consented pilot study to screen newborns for DMD was initiated in New York State (NYS) and conducted from 2019 to 2021. The identification of female carriers and the realization of the subsequent uncertainty of providers concerning follow-up during the pilot led to the development of algorithms for screening and diagnosis of carrier females, including both NBS and cascade molecular testing of family members.

Genetic modifiers of upper limb function in Duchenne muscular dystrophy

Genetic modifiers of Duchenne muscular dystrophy (DMD) are variants located in genes different from the disease-causing gene DMD, but associated with differences in disease onset, progression, or response to treatment. Modifiers described so far have been tested mainly for associations with ambulatory function, while their effect on upper limb function, which is especially relevant for quality of life and independence in non-ambulatory patients, is unknown. We tested genotypes at several known modifier loci (SPP1, LTBP4, CD40, ACTN3) for association with Performance Upper Limb version 1.2 score in an Italian multicenter cohort, and with Brooke scale score in the Cooperative International Neuromuscular Group Duchenne Natural History Study (CINRG-DNHS), using generalized estimating equation (GEE) models of longitudinally collected data, with age and glucocorticoid treatment as covariates. CD40 rs1883832, previously linked to earlier loss of ambulation, emerged as a modifier of upper limb function, negatively affecting shoulder and distal domains of PUL (p = 0.023 and 0.018, respectively) in the Italian cohort, as well as of Brooke score (p = 0.018) in the CINRG-DNHS. These findings will be useful for the design and interpretation of clinical trials in DMD, especially for non-ambulatory populations.

Modeling Patient-Specific Muscular Dystrophy Phenotypes and Therapeutic Responses in Reprogrammed Myotubes Engineered on Micromolded Gelatin Hydrogels

In vitro models of patient-derived muscle allow for more efficient development of genetic medicines for the muscular dystrophies, which often present mutation-specific pathologies. One popular strategy to generate patient-specific myotubes involves reprogramming dermal fibroblasts to a muscle lineage through MyoD induction. However, creating physiologically relevant, reproducible tissues exhibiting multinucleated, aligned myotubes with organized striations is dependent on the introduction of physicochemical cues that mimic the native muscle microenvironment. Here, we engineered patient-specific control and dystrophic muscle tissues in vitro by culturing and differentiating MyoD–directly reprogrammed fibroblasts isolated from one healthy control subject, three patients with Duchenne muscular dystrophy (DMD), and two Limb Girdle 2A/R1 (LGMD2A/R1) patients on micromolded gelatin hydrogels. Engineered DMD and LGMD2A/R1 tissues demonstrated varying levels of defects in α-actinin expression and organization relative to control, depending on the mutation. In genetically relevant DMD tissues amenable to mRNA reframing by targeting exon 44 or 45 exclusion, exposure to exon skipping antisense oligonucleotides modestly increased myotube coverage and alignment and rescued dystrophin protein expression. These findings highlight the value of engineered culture substrates in guiding the organization of reprogrammed patient fibroblasts into aligned muscle tissues, thereby extending their value as tools for exploration and dissection of the cellular and molecular basis of genetic muscle defects, rescue, and repair.

Diversity of Dystrophin Gene Mutations and Disease Progression in a Contemporary Cohort of Duchenne Muscular Dystrophy

Abnormal dystrophin production due to mutations in the dystrophin gene causes Duchenne Muscular Dystrophy (DMD). Cases demonstrate considerable genetic and disease progression variability. It is unclear if specific gene mutations are prognostic of outcomes in this population. We conducted a retrospective cohort study of DMD patients followed at 17 centers across the USA and Canada from 2005 to 2015 with goal of understanding the genetic variability of DMD and its impact on clinical outcomes. Cumulative incidence of clinically relevant outcomes was stratified by genetic mutation type, exon mutation location, and extent of exon deletion. Of 436 males with DMD, 324 (74.3%) underwent genetic testing. Deletions were the most common mutation type (256, 79%), followed by point mutations (45, 13.9%) and duplications (23, 7.1%). There were 131 combinations of mutations with most mutations located along exons 45 to 52. The number of exons deleted varied between 1 and 52 with a median of 3 exons deleted (IQR 1-6). Subjects with mutations starting at exon positions 40-54 had a later onset of arrhythmias occurring at median age 25 years (95% CI 18-∞), p = 0.01. Loss of ambulation occurred later at median age of 13 years (95% CI 12-15) in subjects with mutations that started between exons 55-79, p = 0.01. There was no association between mutation type or location and onset of cardiac dysfunction. We report the genetic variability in DMD and its association with timing of clinical outcomes. Genetic modifiers may explain some phenotypic variability.

Prognostic indicators of disease progression in Duchenne muscular dystrophy: A literature review and evidence synthesis

BACKGROUND

Duchenne muscular dystrophy (DMD) is a rare, severely debilitating, and fatal neuromuscular disease characterized by progressive muscle degeneration. Like in many orphan diseases, randomized controlled trials are uncommon in DMD, resulting in the need to indirectly compare treatment effects, for example by pooling individual patient-level data from multiple sources. However, to derive reliable estimates, it is necessary to ensure that the samples considered are comparable with respect to factors significantly affecting the clinical progression of the disease. To help inform such analyses, the objective of this study was to review and synthesise published evidence of prognostic indicators of disease progression in DMD. We searched MEDLINE (via Ovid), Embase (via Ovid) and the Cochrane Library (via Wiley) for records published from inception up until April 23 2021, reporting evidence of prognostic indicators of disease progression in DMD. Risk of bias was established with the grading system of the Centre for Evidence-Based Medicine (CEBM).

RESULTS

Our search included 135 studies involving 25,610 patients from 18 countries across six continents (Africa, Asia, Australia, Europe, North America and South America). We identified a total of 23 prognostic indicators of disease progression in DMD, namely age at diagnosis, age at onset of symptoms, ataluren treatment, ATL1102, BMI, cardiac medication, DMD genetic modifiers, DMD mutation type, drisapersen, edasalonexent, eteplirsen, glucocorticoid exposure, height, idebenone, lower limb surgery, orthoses, oxandrolone, spinal surgery, TAS-205, vamorolone, vitlolarsen, ventilation support, and weight. Of these, cardiac medication, DMD genetic modifiers, DMD mutation type, and glucocorticoid exposure were designated core prognostic indicators, each supported by a high level of evidence and significantly affecting a wide range of clinical outcomes.

CONCLUSION

This study provides a current summary of prognostic indicators of disease progression in DMD, which will help inform the design of comparative analyses and future data collection initiatives in this patient population.

Dystrophin genetic variants and autism

Loss-of-function variants in the dystrophin gene, a well-known cause of muscular dystrophies, have emerged as a mutational risk mechanism for autism spectrum disorder (ASD), which in turn is a highly prevalent (~ 1%) genetically heterogeneous neurodevelopmental disorder. Although the association of intellectual disability with the dystrophinopathies Duchenne (DMD) and Becker muscular dystrophy (BMD) has been long established, their association with ASD is more recent, and the dystrophin genotype-ASD phenotype correlation is unclear. We therefore present a review of the literature focused on the ASD prevalence among dystrophinopathies, the relevance of the dystrophin isoforms, and most particularly the relevance of the genetic background to the etiology of ASD in these patients. Four families with ASD-DMD/BMD patients are also reported here for the first time. These include a single ASD individual, ASD-discordant and ASD-concordant monozygotic twins, and non-identical ASD triplets. Notably, two unrelated individuals, which were first ascertained because of the ASD phenotype at ages 15 and 5 years respectively, present rare dystrophin variants still poorly characterized, suggesting that some dystrophin variants may compromise the brain more prominently. Whole exome sequencing in these ASD-DMD/BMD individuals together with the literature suggest, although based on preliminary data, a complex and heterogeneous genetic architecture underlying ASD in dystrophinopathies, that include rare variants of large and medium effect. The need for the establishment of a consortia for genomic investigation of ASD-DMD/BMD patients, which may shed light on the genetic architecture of ASD, is discussed.

Development of a model-based clinical trial simulation platform to optimize the design of clinical trials for Duchenne muscular dystrophy

Early clinical trials of therapies to treat Duchenne muscular dystrophy (DMD), a fatal genetic X‐linked pediatric disease, have been designed based on the limited understanding of natural disease progression and variability in clinical measures over different stages of the continuum of the disease. The objective was to inform the design of DMD clinical trials by developing a disease progression model‐based clinical trial simulation (CTS) platform based on measures commonly used in DMD trials. Data were integrated from past studies through the Duchenne Regulatory Science Consortium founded by the Critical Path Institute (15 clinical trials and studies, 1505 subjects, 27,252 observations). Using a nonlinear mixed‐effects modeling approach, longitudinal dynamics of five measures were modeled (NorthStar Ambulatory Assessment, forced vital capacity, and the velocities of the following three timed functional tests: time to stand from supine, time to climb 4 stairs, and 10 meter walk‐run time). The models were validated on external data sets and captured longitudinal changes in the five measures well, including both early disease when function improves as a result of growth and development and the decline in function in later stages. The models can be used in the CTS platform to perform trial simulations to optimize the selection of inclusion/exclusion criteria, selection of measures, and other trial parameters. The data sets and models have been reviewed by the US Food and Drug Administration and the European Medicines Agency; have been accepted into the Fit‐for‐Purpose and Qualification for Novel Methodologies pathways, respectively; and will be submitted for potential endorsement by both agencies.

Phenotypic Spectrum of Dystrophinopathy Due to Duchenne Muscular Dystrophy Exon 2 Duplications

BACKGROUND AND OBJECTIVES

To describe the phenotypic spectrum of dystrophinopathy in a large cohort of individuals with DMD exon 2 duplications (Dup2), who may be particularly amenable to therapies directed at restoring expression of either full-length dystrophin or nearly full-length dystrophin through utilization of the DMD exon 5 internal ribosome entry site (IRES).

METHODS

In this retrospective observational study, we analyzed data from large genotype-phenotype databases (the United Dystrophinopathy Project [UDP] and the Italian DMD network) and classified participants into Duchenne muscular dystrophy (DMD), intermediate muscular dystrophy (IMD), or Becker muscular dystrophy (BMD) phenotypes. Log-rank tests for time-to-event variables were used to compare age at loss of ambulation (LOA) in participants with Dup2 vs controls without Dup2 in the UDP database and for comparisons between steroid-treated vs steroid-naive participants with Dup2.

RESULTS

Among 66 participants with Dup2 (UDP = 40, Italy = 26), 61% were classified as DMD, 9% as IMD, and 30% as BMD. Median age at last observation was 15.4 years (interquartile range 8.79-26.0) and 75% had been on corticosteroids for at least 6 months. Age at LOA differed significantly between participants with Dup2 DMD and historical controls without Dup2 DMD (p < 0.001). Valid spirometry was limited but suggested a delay in the typical age-related decline in forced vital capacity and 24 of 55 participants with adequate cardiac data had cardiomyopathy.

DISCUSSION

Some patients with Dup2 display a milder disease course than controls without Dup2 DMD, and prolonged ambulation with corticosteroids suggests the potential of IRES activation as a molecular mechanism. As Dup2-targeted therapies reach clinical applications, this information is critical to aid in the interpretation of the efficacy of new treatments.

Antisense and Gene Therapy Options for Duchenne Muscular Dystrophy Arising from Mutations in the N-Terminal Hotspot

Duchenne muscular dystrophy (DMD) is a fatal genetic disease affecting children that is caused by a mutation in the gene encoding for dystrophin. In the absence of functional dystrophin, patients experience progressive muscle deterioration, leaving them wheelchair-bound by age 12 and with few patients surviving beyond their third decade of life as the disease advances and causes cardiac and respiratory difficulties. In recent years, an increasing number of antisense and gene therapies have been studied for the treatment of muscular dystrophy; however, few of these therapies focus on treating mutations arising in the N-terminal encoding region of the dystrophin gene. This review summarizes the current state of development of N-terminal antisense and gene therapies for DMD, mainly focusing on exon-skipping therapy for duplications and deletions, as well as microdystrophin therapy.

Clinical and Genetic Characteristics in Young, Glucocorticoid-Naive Boys With Duchenne Muscular Dystrophy

BACKGROUND AND OBJECTIVES

Duchenne muscular dystrophy (DMD) is a pediatric neuromuscular disorder caused by mutations in the dystrophin gene. Genotype-phenotype associations have been examined in glucocorticoid-treated boys, but there are few data on the young glucocorticoid-naive DMD population. A sample of young glucocorticoid-naive DMD boys is described, and genotype-phenotype associations are investigated.

METHODS

Screening and baseline data were collected for all the participants in the Finding the Optimum Corticosteroid Regime for Duchenne Muscular Dystrophy (FOR-DMD) study, an international, multicenter, randomized, double-blind, clinical trial comparing 3 glucocorticoid regimens in glucocorticoid-naive, genetically confirmed boys with DMD between 4 and <8 years of age.

RESULTS

One hundred ninety-six boys were recruited. The mean ± SD age at randomization was 5.8 ± 1.0 years. The predominant mutation type was out-of-frame deletions (67.4%, 130 of 193), of which 68.5% (89 of 130) were amenable to exon skipping. The most frequent mutations were deletions amenable to exon 51 skipping (13.0%, 25 of 193). Stop codon mutations accounted for 10.4% (20 of 193). The mean age at first parental concerns was 29.8 ± 18.7 months; the mean age at genetic diagnosis was 53.9 ± 21.9 months; and the mean diagnostic delay was 25.9 ± 18.2 months. The mean diagnostic delay for boys diagnosed after an incidental finding of isolated hyperCKemia (n = 19) was 6.4 ± 7.4 months. The mean ages at independent walking and talking in sentences were 17.1 ± 4.2 and 29.0 ± 10.7 months, respectively. Median height percentiles were below the 25th percentile regardless of age group. No genotype-phenotype associations were identified expect for boys with exon 8 skippable deletions, who had better performance on time to walk/run 10 m (p = 0.02) compared to boys with deletions not amenable to skipping.

DISCUSSION

This study describes clinical and genetic characteristics of a sample of young glucocorticoid-naive boys with DMD. A low threshold for creatine kinase testing can lead to an earlier diagnosis. Motor and speech delays were common presenting symptoms. The effects of low pretreatment height on growth and adult height require further study. These findings may promote earlier recognition of DMD and inform study design for future clinical trials. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov Identifier: NCT01603407.

The impact of genotype on outcomes in individuals with Duchenne muscular dystrophy: A systematic review

Duchenne muscular dystrophy (DMD) is associated with progressive muscle weakness, loss of ambulation (LOA), and early mortality. In this review we have synthesized published data on the clinical course of DMD by genotype. Using a systematic search implemented in Medline and Embase, 53 articles were identified that describe the clinical course of DMD, with pathogenic variants categorizable by exon skip or stop-codon readthrough amenability and outcomes presented by age. Outcomes described included those related to ambulatory, cardiac, pulmonary, or cognitive function. Estimates of the mean (95% confidence interval) age at LOA ranged from 9.1 (8.7-9.6) years among 90 patients amenable to skipping exon 53 to 11.5 (9.5-13.5) years among three patients amenable to skipping exon 8. Although function worsened with age, the impact of genotype was less clear for other outcomes (eg, forced vital capacity and left ventricular ejection fraction). Understanding the distribution of pathogenic variants is important for studies in DMD, as this research suggests major differences in the natural history of disease. In addition, specific details of the use of key medications, including corticosteroids, antisense oligonucleotides, and cardiac medications, should be reported.

Long-Term Safety and Efficacy Data of Golodirsen in Ambulatory Patients with Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A First-in-human, Multicenter, Two-Part, Open-Label, Phase 1/2 Trial

The aim of this Phase 1/2, 2-part, multicenter trial was to report clinical safety and efficacy of long-term golodirsen treatment among ambulatory patients with exon 53 skip-amenable Duchenne muscular dystrophy (DMD). Part 1 was a 12-week, randomized, double-blind, placebo-controlled, dose-titration study followed by 9-week safety review. Part 2 was a 168-week, open-label evaluation of golodirsen 30 mg/kg. Part 1 primary endpoint was safety. Part 2 primary endpoints were dystrophin protein expression and 6-minute walk test (6MWT); secondary endpoints were percent predicted forced vital capacity (FVC%p) and safety. Post hoc ambulation analyses used mutation-matched external natural history controls. All patients from Part 1 (golodirsen, n = 8; placebo, n = 4) plus 13 additional patients entered Part 2; 23 completed the study. Adverse events were generally mild, nonserious, and unrelated to golodirsen, with no safety-related discontinuations or deaths. Golodirsen increased dystrophin protein (16.0-fold; P < 0.001) and exon skipping (28.9-fold; P < 0.001). At 3 years, 6MWT change from baseline was −99.0 m for golodirsen-treated patients versus −181.4 m for external controls (P = 0.067), and loss of ambulation occurred in 9% versus 26% (P = 0.21). FVC%p declined 8.4% over 3 years in golodirsen-treated patients, comparing favorably with literature-reported rates. This study provides evidence for golodirsen biologic activity and long-term safety in a declining DMD population and suggests functional benefit versus external controls. Clinical Trial Registration number: NCT02310906.

A Combined Prospective and Retrospective Comparison of Long-Term Functional Outcomes Suggests Delayed Loss of Ambulation and Pulmonary Decline with Long-Term Eteplirsen Treatment

Background:

Studies 4658-201/202 (201/202) evaluated treatment effects of eteplirsen over 4 years in patients with Duchenne muscular dystrophy and confirmed exon-51 amenable genetic mutations. Chart review Study 4658-405 (405) further followed these patients while receiving eteplirsen during usual clinical care.

Objective:

To compare long-term clinical outcomes of eteplirsen-treated patients from Studies 201/202/405 with those of external controls.

Methods:

Median total follow-up time was approximately 6 years of eteplirsen treatment. Outcomes included loss of ambulation (LOA) and percent-predicted forced vital capacity (FVC%p). Time to LOA was compared between eteplirsen-treated patients and standard of care (SOC) external controls and was measured from eteplirsen initiation in 201/202 or, in the SOC group, from the first study visit. Comparisons were conducted using univariate Kaplan-Meier analyses and log-rank tests, and multivariate Cox proportional hazards models with regression adjustment for baseline characteristics. Annual change in FVC%p was compared between eteplirsen-treated patients and natural history study patients using linear mixed models with repeated measures.

Results:

Data were included from all 12 patients in Studies 201/202 and the 10 patients with available data from 405. Median age at LOA was 15.16 years. Eteplirsen-treated patients experienced a statistically significant longer median time to LOA by 2.09 years (5.09 vs. 3.00 years, p < 0.01) and significantly attenuated rates of pulmonary decline vs. natural history patients (FVC%p change: –3.3 vs. –6.0 percentage points annually, p < 0.0001).

Conclusions:

Study 405 highlights the functional benefits of eteplirsen on ambulatory and pulmonary function outcomes up to 7 years of follow-up in comparison to external controls.

Genetic Modifiers and Phenotype of Duchenne Muscular Dystrophy: A Systematic Review and Meta-Analysis

The transforming growth factor beta (TGFβ) pathway could modulate the Duchenne muscular dystrophy (DMD) phenotype. This meta-analysis aims to estimate the association of genetic variants involved in the TGFβ pathway, including the latent transforming growth factor beta binding protein 4 (LTBP4) and secreted phosphoprotein 1 (SPP1) genes, among others, with age of loss of ambulation (LoA) and cardiac function in patients with DMD. Meta-analyses were conducted for the hazard ratio (HR) of LoA for each genetic variant. A subgroup analysis was performed in patients treated exclusively with glucocorticoids. Eight studies were included in the systematic review and four in the meta-analyses. The systematic review suggests a protective effect of LTBP4 haplotype IAAM (recessive model) for LoA. It is also suggested that the SPP1 rs28357094 genotype G (dominant model) is associated with early LoA in glucocorticoids-treated patients. The meta-analysis of the LTBP4 haplotype IAAM showed a protective association with LoA, with an HR = 0.78 (95% CI: 0.67–0.90). No association with LoA was observed for the SPP1 rs28357094. The LTBP4 haplotype IAAM is associated with a later LoA, especially in the Caucasian population, while the SPP1 rs28357094 genotype G could be associated with a poor response to glucocorticoids. Future research is suggested for SPP1 rs11730582, LTBP4 rs710160, and THBS1 rs2725797.

Longitudinal motor function in proximal versus distal DMD pathogenic variants

INTRODUCTION/AIMS

There is considerable heterogenicity in clinical outcomes in Duchenne muscular dystrophy (DMD). The aim of this study was to assess whether dystrophin gene (DMD) pathogenic variant location influences upper or lower extremity motor function outcomes in a large prospective cohort.

METHODS

We used longitudinal timed and quantitative motor function measurements obtained from 154 boys with DMD over a 10-y period by the Cooperative International Neuromuscular Research Group Duchenne Natural History Study (CINRG-DNHS) to understand how the trajectories of motor function differ based on proximal versus distal DMD pathogenic variants. Proximal variants were defined as located proximal to 5' DMD intron 44, and distal variants as those including nucleotides 3' DMD including intron 44. Distal DMD variants are predicted to alter the expression of short dystrophin isoforms (Dp140, Dp116, and Dp71). We compared various upper extremity and lower extremity motor function measures in these two groups, after adjusting for total lifetime corticosteroid use.

RESULTS

The time to loss-of-ambulation and timed motor function measurements of both upper and lower limbs over a 10-y period were comparable between boys with proximal (n = 53) and distal (n = 101) DMD pathogenic variants. Age had a significant effect on several motor function outcomes. Boys younger than 7 y of age (n = 49) showed gain in function whereas boys 7 y and older (n = 71) declined, regardless of dystrophin pathogenic variant location.

DISCUSSION

The longitudinal decline in upper and lower motor function is independent of proximal versus distal location of DMD pathogenic variants.

Efficient correction of Duchenne muscular dystrophy mutations by SpCas9 and dual gRNAs

CRISPR gene therapy is one promising approach for treatment of Duchenne muscular dystrophy (DMD), which is caused by a large spectrum of mutations in the dystrophin gene. To broaden CRISPR gene editing strategies for DMD treatment, we report the efficient restoration of dystrophin expression in induced myotubes by SpCas9 and dual guide RNAs (gRNAs). We first sequenced 32 deletion junctions generated by this editing method and revealed that non-homologous blunt-end joining represents the major indel type. Based on this predictive repair outcome, efficient in-frame deletion of a part of DMD exon 51 was achieved in HEK293T cells with plasmids expressing SpCas9 and dual gRNAs. More importantly, we further corrected a frameshift mutation in human DMD (exon45del) fibroblasts with SpCas9-dual gRNA ribonucleoproteins. The edited DMD fibroblasts were transdifferentiated into myotubes by lentiviral-mediated overexpression of a human MYOD transcription factor. Restoration of DMD expression at both the mRNA and protein levels was confirmed in the induced myotubes. With further development, the combination of SpCas9-dual gRNA-corrected DMD patient fibroblasts and transdifferentiation may provide a valuable therapeutic strategy for DMD.

The clinical course of Duchenne muscular dystrophy in the corticosteroid treatment era: a systematic literature review

Background

Duchenne muscular dystrophy (DMD) is a severe rare progressive inherited neuromuscular disorder, leading to loss of ambulation (LOA) and premature mortality. The standard of care for patients with DMD has been treatment with corticosteroids for the past decade; however a synthesis of contemporary data describing the clinical course of DMD is lacking. The objective was to summarize age at key clinical milestones (loss of ambulation, scoliosis, ventilation, cardiomyopathy, and mortality) in the corticosteroid-treatment-era.

Methods

A systematic review was conducted using MEDLINE and EMBASE. The percentage experiencing key clinical milestones, and the mean or median age at those milestones, was synthesized from studies from North American populations, published between 2007 and 2018.

Results

From 5637 abstracts, 29 studies were included. Estimates of the percentage experiencing key clinical milestones, and age at those milestones, showed heterogeneity. Up to 30% of patients lost ambulation by age 10 years, and up to 90% by 15 years of age. The mean age at scoliosis onset was approximately 14 years. Ventilatory support began from 15 to 18 years, and up to half of patients required ventilation by 20 years of age. Registry-based estimates suggest that 70% had evidence of cardiomyopathy by 15 years and almost all by 20 years of age. Finally, mortality rates up to 16% by age 20 years were reported; among those surviving to adulthood mortality was up to 60% by age 30 years.

Conclusions

Contemporary natural history studies from North America report that LOA on average occurs in the early teens, need for ventilation and cardiomyopathy in the late teens, and death in the third or fourth decade of life. Variability in rates may be due to differences in study design, treatment with corticosteroids or other disease-modifying agents, variations in clinical practices, and dystrophin mutations. Despite challenges in synthesizing estimates, these findings help characterize disease progression among contemporary North American DMD patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01862-w.

Genotype characterization and delayed loss of ambulation by glucocorticoids in a large cohort of patients with Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common genetic muscle disease in human. We aimed to describe the genotype distribution in a large cohort of Chinese DMD patients and their delayed loss of ambulation by glucocorticoid (GC) treatments. This is to facilitate protocol designs and outcome measures for the emerging DMD clinical trials.

RESULTS

A total of 1163 patients with DMD were recruited and genotyped. Genotype variations were categorized as large deletions, large duplications, and small mutations. Large deletions were further analyzed for those amenable to exon-skipping therapies. Participants aged 5 years or older were grouped into GC-treated and GC-naïve groups. Clinical progression among different genotypes and their responses to GC treatments were measured by age at loss of ambulation (LOA). Among the mutation genotypes, large deletions, large duplications, and small mutations accounted for 68.79%, 7.14%, and 24.07%, respectively. The mean age at diagnosis was 4.59 years; the median ages at LOA for the GC-naïve, prednisone/prednisolone-treated, and deflazacort-treated groups were 10.23, 12.02, and 13.95 years, respectively. The "deletion amenable to skipping exon 44" subgroup and the nonsense-mutation subgroup had older ages at LOA than the "other deletions" subgroup. Subgroups were further analyzed by both genotypes and GC status. All genotypes showed significant beneficial responses to GC treatment. Deletions amenable to skipping exon 44 showed a lower hazard ratio (0.155). The mean age at death was 18.57 years in this DMD group.

CONCLUSION

Genotype variation influences clinical progression in certain DMD groups. Beneficial responses to GC treatment were observed among all DMD genotypes. Compared with other genotypes, deletions amenable to skipping exon 44 had a lower hazard ratio, which may indicate a stronger protective effect of GC treatments on this subgroup. These data are valuable for designing future clinical trials, as clinical outcomes may be influenced by the genotypes.

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

The nonsense mutation stop+4 model correlates with motor changes in Duchenne muscular dystrophy

The aim was to assess 3-year longitudinal data using 6MWT in 26 ambulant boys affected by DMD carrying nonsense mutations and to compare their results to other small mutations. We also wished to establish, within the nonsense mutations group, patterns of change according to several variables. Patients with nonsense mutations were categorized according to the stop codon type newly created by the mutation and also including the adjacent 5' (upstream) and 3' (downstream) nucleotides. No significant difference was found between nonsense mutations and other small mutations (p > 0.05) on the 6MWT. Within the nonsense mutations group, there was no difference in 6MWT when the patients were subdivided according to: Type of stop codon, frame status of exons involved, protein domain affected. In contrast, there was a difference when the stop codon together with the 3' adjacent nucleotide ("stop+4 model") was considered (p < 0.05) with patients with stop codon TGA and 3' adjacent nucleotide G (TGAG) having a more rapid decline. Our finding suggest that the stop+4 model may help in predicting functional changes. This data will be useful at the time of interpreting the long term follow up of patients treated with Ataluren that are becoming increasingly available.

Association of genetic mutations and loss of ambulation in childhood-onset dystrophinopathy

BACKGROUND

Quantifying associations between genetic mutations and loss of ambulation (LoA) among males diagnosed with childhood-onset dystrophinopathy is important for understanding variation in disease progression and may be useful in clinical trial design.

METHODS

Genetic and clinical data from the Muscular Dystrophy Surveillance, Tracking, and Research Network for 358 males born and diagnosed from 1982 to 2011 were analyzed. LoA was defined as the age at which independent ambulation ceased. Genetic mutations were defined by overall type (deletion/duplication/point mutation) and among deletions, those amenable to exon-skipping therapy (exons 8, 20, 44-46, 51-53) and another group. Cox proportional hazards regression modeling was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Mutation type did not predict time to LoA. Controlling for corticosteroids, Exons 8 (HR = 0.22; 95% CI = 0.08, 0.63) and 44 (HR = 0.30; 95% CI = 0.12, 0.78) were associated with delayed LoA compared to other exon deletions.

CONCLUSIONS

Delayed LoA in males with mutations amenable to exon-skipping therapy is consistent with previous studies. These findings suggest that clinical trials including exon 8 and 44 skippable males should consider mutation information prior to randomization.