Long-term natural history data in Duchenne muscular dystrophy ambulant patients with mutations amenable to skip exons 44, 45, 51 and 53

Early motor, cognitive, language, behavioural and social emotional development in infants and young boys with Duchenne Muscular Dystrophy- A systematic review

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive disorder caused by mutations in the dystrophin gene. Deficiency of the dystrophin protein causes not only motor, but also cognitive, language, behavioural and social emotional problems. This is the first systematic review investigating five early developmental domains in boys with DMD between 0 and 6 years old. Interactions between different domains and links with mutation types and sites were explored. A systematic search was performed in PubMed, Web of Science and Scopus. An adapted version of the Scottish Intercollegiate Guidelines Network (SIGN) Checklists for case-control and cohort studies was used to evaluate quality. Fifty-five studies of high or acceptable quality were included. One was an RCT of level 1b; 50 were cohort studies of level 2b; and four were an aggregation of case-control and cohort studies receiving levels 2b and 3b. We found that young boys with DMD experienced problems in all five developmental domains, with significant interactions between these. Several studies also showed relationships between mutation sites and outcomes. We conclude that DMD is not only characterised by motor problems but by a more global developmental delay with a large variability between boys. Our results emphasise the need for harmonisation in evaluation and follow-up of young boys with DMD. More high-quality research is needed on the different early developmental domains in young DMD to facilitate early detection of difficulties and identification of associated early intervention strategies.

Comprehensive analysis of 2097 patients with dystrophinopathy based on a database from 2011 to 2021

BACKGROUND

An increasing number of clinical trials for new therapeutic strategies are underway or being considered for dystrophinopathy. Having detailed data on the natural progression of this condition is crucial for assessing the effectiveness of new drugs. However, there's a lack of data regarding the long-term data on the natural course and how it's managed in China. In this study, we offer a comprehensive overview of clinical and molecular findings, as well as treatment outcomes in the Chinese population.

METHODS

Institutional data on all patients with dystrophinopathy from August 2011 to August 2021 were retrospectively reviewed. The data included geographic distribution, age at diagnosis, molecular findings, and treatment options, such as corticosteroids, cardiac interventions, and clinical outcomes.

RESULTS

In total, 2097 patients with dystrophinopathy, including 1703 cases of Duchenne muscular dystrophy (DMD), 311 cases of Becker muscular dystrophy (BMD), 46 cases of intermediate muscular dystrophy (IMD), and 37 cases categorized as "pending" (individuals with an undetermined phenotype), were registered in the Children's Hospital of Fudan University database for dystrophinopathy from August 2011 to August 2021. The spectrum of identified variants included exonic deletions (66.6%), exonic duplications (10.7%), nonsense variants (10.3%), splice-site variants (4.5%), small deletions (3.5%), small insertions/duplications (1.8%), and missense variants (0.9%). Four deep intronic variants and two inversion variants were identified. Regarding treatment, glucocorticoids were administered to 54.4% of DMD patients and 39.1% of IMD patients. The median age at loss of ambulation was 2.5 years later in DMD patients who received glucocorticoid treatment. Overall, one cardiac medicine at least was prescribed to 7.4% of DMD patients, 8.3% of IMD patients, and 2.6% of BMD patients. Additionally, ventilator support was required by four DMD patients. Eligibility for exon skipping therapy was found in 55.3% of DMD patients, with 12.9%, 10%, and 9.6% of these patients being eligible for skipping exons 51, 53, and 45, respectively.

CONCLUSIONS

This is one of the largest studies to have evaluated the natural history of dystrophinopathy in China, which is particularly conducive to the recruitment of eligible patients for clinical trials and the provision of real-world data to support drug development.

Survival among patients receiving eteplirsen for up to 8 years for the treatment of Duchenne muscular dystrophy and contextualization with natural history controls

INTRODUCTION/AIMS

Eteplirsen, approved in the US for patients with Duchenne muscular dystrophy (DMD) with exon 51 skip-amenable variants, is associated with attenuated ambulatory/pulmonary decline versus DMD natural history (NH). We report overall survival in a US cohort receiving eteplirsen and contextualize these outcomes versus DMD NH.

METHODS

US patients with DMD receiving eteplirsen were followed through a patient support program, with data collected on ages at eteplirsen initiation and death/end of follow-up. Individual DMD NH data were extracted by digitizing Kaplan-Meier (KM) curves from published systematic and targeted literature reviews. Overall survival age was analyzed using KM curves and contextualized with DMD NH survival curves; subanalyses considered age groups and duration of eteplirsen exposure. Overall survival time from treatment initiation was also evaluated.

RESULTS

A total of 579 eteplirsen-treated patients were included. During a total follow-up of 2119 person-years, median survival age was 32.8 years. DMD NH survival curves extracted from four publications (follow-up for 1224 DMD NH controls) showed overall pooled median survival age of 27.4 years. Eteplirsen-treated patients had significantly longer survival from treatment initiation versus age-matched controls (age-adjusted hazard ratio [HR], 0.65; 95% confidence interval [CI], 0.44-0.98; p < .05). Longer treatment exposure was associated with improved survival (HR, 0.15; 95% CI, 0.05-0.41; p < .001). Comparisons using different DMD NH cohorts to address common risks of bias yielded consistent findings.

DISCUSSION

Data suggest eteplirsen may prolong survival in patients with DMD across a wide age range. As more data become available, the impact of eteplirsen on survival will be further elucidated.

Factors Associated With Early Motor Function Trajectories in DMD After Glucocorticoid Initiation: Post Hoc Analysis of the FOR-DMD Trial

BACKGROUND AND OBJECTIVES

Clinical trials in Duchenne muscular dystrophy (DMD) require 3-6 months of stable glucocorticoids, and the primary outcome is explored at 48-52 weeks. The factors that influence the clinical outcome assessment (COA) trajectories soon after glucocorticoid initiation are relevant for the design and analysis of clinical trials of novel drugs. We describe early COA trajectories, associated factors, and the time from glucocorticoid initiation to COA peak.

METHODS

This was a prospective 18-month analysis of the Finding the Optimum Corticosteroid Regimen for Duchenne Muscular Dystrophy study. Four COAs were investigated: rise from supine velocity (RFV), 10-meter walk/run velocity (10MWRV), North Star Ambulatory Assessment (NSAA) total score, and 6-minute walk test distance (6MWT). The relationships of baseline age (4-5 vs 6-7 years), COA baseline performance, genotype, and glucocorticoid regimen (daily vs intermittent) with the COA trajectories were evaluated using linear mixed-effects models.

RESULTS

One hundred ninety-six glucocorticoid-naïve boys with DMD aged 4-7 years were enrolled. The mean age at baseline was 5.9 ± 1.0 years, 66% (n = 130) were on daily regimens, 55% (n = 107) showed a 6MWT distance >330 metres; 41% (n = 78) showed RFV >0.2 rise/s; 76% (n = 149) showed 10MWRV >0.142 10m/s, and 41.0% (n = 79) showed NSAA total score >22 points. Mean COA trajectories differed by age at glucocorticoid initiation (p < 0.01 for RFV, 10MWRV, and NSAA; p < 0.05 for 6MWT) and regimen (p < 0.01 for RFV, 10MWRV, and NSAA). Boys younger than 6 years reached their peak performance 12-18 months after glucocorticoid initiation. Boys aged 6 years or older on a daily regimen peaked between months 9 and 12 and those on an intermittent regimen by 9 months. The baseline COA performance was associated with the NSAA (p < 0.01) and the 6MWT trajectory in boys younger than 6 years on a daily regimen (p < 0.01). Differences in the mean trajectories by genotype were not significant.

DISCUSSION

Glucocorticoid regimen, age, duration of glucocorticoid exposure, and baseline COA performance need to be considered in the design and analysis of clinical trials in young boys with DMD.

Longitudinal data of serum creatine kinase levels and motor, pulmonary, and cardiac functions in 337 patients with Duchenne muscular dystrophy

INTRODUCTION/AIMS

Duchenne muscular dystrophy (DMD) presents with skeletal muscle weakness, followed by cardiorespiratory involvement. The need for longitudinal data regarding DMD that could serve as a control for determining treatment efficacy in clinical trials has increased notably. The present study examined the longitudinal data of Japanese DMD patients collectively and assessed individual patients with pathogenic variants eligible for exon-skipping therapy.

METHODS

Patients with DMD who visited Kobe University Hospital between March 1991 and March 2019 were enrolled. Data between the patients' first visit until age 20 years were examined.

RESULTS

Three hundred thirty-seven patients were included. Serum creatine kinase levels showed extremely high values until the age of 6 years and a rapid decline from ages 7-12 years. Both the median 10-m run/walk velocity and rise-from-floor velocity peaked at the age of 4 years and declined with age. The values for respiratory function declined from the age of 11 years. The median left ventricular ejection fraction was >60% until the age of 12 years and rapidly declined from ages 13-15 years. Examination of the relationship between pathogenic variants eligible for exon-skipping therapy and longitudinal data revealed no characteristic findings.

DISCUSSION

We found that creatine kinase levels and motor, respiratory, and cardiac functions each exhibited various changes over time. These findings provide useful information about the longitudinal data of several outcome measures for patients with DMD not receiving corticosteroids. These data may serve as historical controls in comparing the natural history of DMD patients not on regular steroid use in appropriate clinical trials.

Duchenne muscular dystrophy: promising early-stage clinical trials to watch

INTRODUCTION

Current therapies are unable to cure Duchenne muscular dystrophy (DMD), a severe and common form of muscular dystrophy, and instead aim to delay disease progression. Several treatments currently in phase I trials could increase the number of therapeutic options available to patients.

AREAS COVERED

This review aims to provide an overview of current treatments undergoing or having recently undergone early-stage trials. Several exon-skipping and gene therapy approaches are currently being investigated at the clinical stage to address an unmet need for DMD treatments. This article also covers Phase I trials from the last 5 years that involve inhibitors, small molecules, a purified synthetic flavanol, a cell-based therapy, and repurposed cardiac or tumor medications.

EXPERT OPINION

With antisense oligonucleotide (AON) treatments making up the majority of conditionally approved DMD therapies, most of the clinical trials occurring within the last 5 years have also evaluated exon-skipping AONs. The approval of Elevidys, a micro-dystrophin therapy, is reflected in a recent trend toward gene transfer therapies in phase I DMD clinical trials, but their safety and efficacy are being established in this phase of development. Other Phase I clinical-stage approaches are diverse, but have a range in efficacy, safety, and endpoint measures.

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.

The Dutch Dystrophinopathy Database: A National Registry with Standardized Patient and Clinician Reported Real-World Data

Background

Duchenne and Becker muscular dystrophy lack curative treatments. Registers can facilitate therapy development, serving as a platform to study epidemiology, assess clinical trial feasibility, identify eligible candidates, collect real-world data, perform post-market surveillance, and collaborate in (inter)national data-driven initiatives.

Objective

In addressing these facets, it's crucial to gather high-quality, interchangeable, and reusable data from a representative population. We introduce the Dutch Dystrophinopathy Database (DDD), a national registry for patients with DMD or BMD, and females with pathogenic DMD variants, outlining its design, governance, and use.

Methods

The design of DDD is based on a system-independent information model that ensures interoperable and reusable data adhering to international standards. To maximize enrollment, patients can provide consent online and participation is allowed on different levels with contact details and clinical diagnosis as minimal requirement. Participants can opt-in for yearly online questionnaires on disease milestones and medication and to have clinical data stored from visits to one of the national reference centers. Governance involves a general board, advisory board and database management.

Results

On November 1, 2023, 742 participants were enrolled. Self-reported data were provided by 291 Duchenne, 122 Becker and 38 female participants. 96% of the participants visiting reference centers consented to store clinical data. Eligible patients were informed about clinical studies through DDD, and multiple data requests have been approved to use coded clinical data for quality control, epidemiology and natural history studies.

Conclusion

The Dutch Dystrophinopathy Database captures long-term patient and high-quality standardized clinician reported healthcare data, supporting trial readiness, post-marketing surveillance, and effective data use using a multicenter design that is scalable to other neuromuscular disorders.

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.

Model-Informed Approaches and Innovative Clinical Trial Design for Adeno-Associated Viral Vector-Based Gene Therapy Product Development: A White Paper

The promise of viral vector-based gene therapy (GT) as a transformative paradigm for treating severely debilitating and life-threatening diseases is slowly coming to fruition with the recent approval of several drug products. However, they have a unique mechanism of action often necessitating a tortuous clinical development plan. Expertise in such complex therapeutic modality is still fairly limited in this emerging class of adeno-associated virus (AAV) vector-based gene therapies. Because of the irreversible mode of action and incomplete understanding of genotype-phenotype relationship and disease progression in rare diseases careful considerations should be given to GT product's benefit-risk profile. In particular, special attention needs to be paid to safe dose selection, reliable dose exposure response (including clinically relevant endpoints), or creative approaches in study design targeting small patient populations during clinical development. We believe that quantitative tools encompassed within model-informed drug development (MIDD) framework fits quite well in the development of such novel therapies, as they enable us to benefit from the totality of data approach in order to support dose selection as well as optimize clinical trial designs, end point selection, and patient enrichment. In this thought leadership paper, we provide our collective experiences, identify challenges, and suggest areas of improvement in applications of modeling and innovative trial design in development of AAV-based GT products and reflect on the challenges and opportunities for incorporating MIDD tools and more in rational development of these products.

Efficacy and safety of hydrokinesitherapy in patients with dystrophinopathy

Duchenne muscular dystrophy (DMD) is one of the most common forms of hereditary muscular dystrophies in childhood and is characterized by steady progression and early disability. It is known that physical therapy can slow down the rate of progression of the disease. According to global recommendations, pool exercises, along with stretching, are preferable for children with DMD, as these types of activities have a balanced effect on skeletal muscles and allow simultaneous breathing exercises. The present study aimed to evaluate the effectiveness of regular pool exercises in patients with Duchenne muscular dystrophy who are capable of independent movement during 4 months of training. 28 patients with genetically confirmed Duchenne muscular dystrophy, who were aged 6.9 ± 0.2 years, were examined. A 6-min distance walking test and timed tests, namely, rising from the floor, 10-meter running, and stair climbing and descending, muscle strength of the upper and lower extremities were assessed on the baseline and during dynamic observation at 2 and 4 months. Hydrorehabilitation course lasted 4 months and was divided into two stages: preparatory and training (depend on individual functional heart reserve (IFHR)). Set of exercises included pool dynamic aerobic exercises. Quantitative muscle MRI of the pelvic girdle and thigh was performed six times: before training (further BT) and after training (further AT) during all course. According to the results of the study, a statistically significant improvement was identified in a 6-min walking test, with 462.7 ± 6.2 m on the baseline and 492.0 ± 6.4 m after 4 months (p < 0.001). The results from the timed functional tests were as follows: rising from the floor test, 4.5 ± 0.3 s on the baseline and 3.8 ± 0.2 s after 4 months (p < 0.001); 10 meter distance running test, 4.9 ± 0.1 s on the baseline and 4.3 ± 0.1 s after 4 months (p < 0.001); 4-stair climbing test, 3.7 ± 0.2 s on the baseline and 3.2 ± 0.2 s after 4 months (p < 0.001); and 4-stair descent test, 3.9 ± 0.1 s on the baseline and 3.2 ± 0.1 s after 4 months (p < 0.001). Skeletal muscle quantitative MRI was performed in the pelvis and the thighs in order to assess the impact of the procedures on the muscle structure. Muscle water T2, a biomarker of disease activity, did not show any change during the training period, suggesting the absence of deleterious effects and negative impact on disease activity. Thus, a set of dynamic aerobic exercises in water can be regarded as effective and safe for patients with DMD.

Antisense Oligonucleotide Therapy for the Nervous System: From Bench to Bedside with Emphasis on Pediatric Neurology

Antisense oligonucleotides (ASOs) are disease-modifying agents affecting protein-coding and noncoding ribonucleic acids. Depending on the chemical modification and the location of hybridization, ASOs are able to reduce the level of toxic proteins, increase the level of functional protein, or modify the structure of impaired protein to improve function. There are multiple challenges in delivering ASOs to their site of action. Chemical modifications in the phosphodiester bond, nucleotide sugar, and nucleobase can increase structural thermodynamic stability and prevent ASO degradation. Furthermore, different particles, including viral vectors, conjugated peptides, conjugated antibodies, and nanocarriers, may improve ASO delivery. To date, six ASOs have been approved by the US Food and Drug Administration (FDA) in three neurological disorders: spinal muscular atrophy, Duchenne muscular dystrophy, and polyneuropathy caused by hereditary transthyretin amyloidosis. Ongoing preclinical and clinical studies are assessing the safety and efficacy of ASOs in multiple genetic and acquired neurological conditions. The current review provides an update on underlying mechanisms, design, chemical modifications, and delivery of ASOs. The administration of FDA-approved ASOs in neurological disorders is described, and current evidence on the safety and efficacy of ASOs in other neurological conditions, including pediatric neurological disorders, is reviewed.

Peak functional ability and age at loss of ambulation in Duchenne muscular dystrophy

AIM

To correlate the North Star Ambulatory Assessment (NSAA) and timed rise from floor (TRF) recorded at age of expected peak with age at loss of ambulation (LOA) in Duchenne muscular dystrophy (DMD).

METHOD

Male children with DMD enrolled in the UK North Start Network database were included according to the following criteria: follow-up longer than 3 years, one NSAA record between 6 years and 7 years 6 months (baseline), at least one visit when older than 8 years. Data about corticosteroid treatment, LOA, genotype, NSAA, and TRF were analysed. Age at LOA among the different groups based on NSAA and TRF was determined by log-rank tests. Cox proportional hazard models were used for multivariable analysis.

RESULTS

A total of 293 patients from 13 different centres were included. Mean (SD) age at first and last visit was 5 years 6 months (1 year 2 months) and 12 years 8 months (2 years 11 months) (median follow-up 7 years 4 months). Higher NSAA and lower TRF at baseline were associated with older age at LOA (p<0.001). Patients scoring NSAA 32 to 34 had a probability of 0.61 of being ambulant when older than 13 years compared with 0.34 for those scoring 26 to 31. In multivariable analysis, NSAA, TRF, and corticosteroid daily regimen (vs intermittent) were all independently associated with outcome (p=0.01).

INTERPRETATION

Higher functional abilities at peak are associated with older age at LOA in DMD. This information is important for counselling families. These baseline measures should also be considered when designing clinical trials.

Therapeutic Strategies for Dystrophin Replacement in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked hereditary disease characterized by progressive muscle wasting due to modifications in the DMD gene (exon deletions, nonsense mutations, intra-exonic insertions or deletions, exon duplications, splice site defects, and deep intronic mutations) that result in a lack of functional dystrophin expression. Many therapeutic approaches have so far been attempted to induce dystrophin expression and improve the patient phenotype. In this manuscript, we describe the relevant updates for some therapeutic strategies for DMD aiming to restore dystrophin expression. We also present and analyze in vitro and in vivo ongoing experimental approaches to treat the disease.

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.

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.

Recent Advances in RNA Therapy and Its Carriers to Treat the Single-Gene Neurological Disorders

The development of new sequencing technologies in the post-genomic era has accelerated the identification of causative mutations of several single gene disorders. Advances in cell and animal models provide insights into the underlining pathogenesis, which facilitates the development and maturation of new treatment strategies. The progress in biochemistry and molecular biology has established a new class of therapeutics—the short RNAs and expressible long RNAs. The sequences of therapeutic RNAs can be optimized to enhance their stability and translatability with reduced immunogenicity. The chemically-modified RNAs can also increase their stability during intracellular trafficking. In addition, the development of safe and high efficiency carriers that preserves the integrity of therapeutic RNA molecules also accelerates the transition of RNA therapeutics into the clinic. For example, for diseases that are caused by genetic defects in a specific protein, an effective approach termed “protein replacement therapy” can provide treatment through the delivery of modified translatable mRNAs. Short interference RNAs can also be used to treat diseases caused by gain of function mutations or restore the splicing aberration defects. Here we review the applications of newly developed RNA-based therapeutics and its delivery and discuss the clinical evidence supporting the potential of RNA-based therapy in single-gene neurological disorders.

CPP Applications in Immune Modulation and Disease Therapy

About 30 years ago, the discovery of CPP improved the therapeutic approach to treat diseases and extended the range of potential targets to intracellular molecules. There are potential drug candidates for FDA approval based on active studies in basic research, preclinical, and clinical trials. Various attempts by CPP application to control the diseases such as allergy, autoimmunity, cancer, and infection demonstrated a strategy to make a new drug pipeline for successful discovery of a biologic drug for immune modulation. However, there are still no CPP-based drug candidates for immune-related diseases in the clinical stage. To control immune responses successfully, not only increasing delivery efficiency of CPPs but also selecting potential target cells and cargoes could be important issues. In particular, as it becomes possible to control intracellular targets, efforts to find various novel potential target are being attempted. In this chapter, we focused on CPP-based approaches to treat diseases through modulation of immune responses and discussed for perspectives on future direction of the research for successful application of CPP technology to immune modulation and disease therapy in clinical trial.

Walking alone milestone combined reading-frame rule improves early prediction of Duchenne muscular dystrophy

OBJECTIVE

To explore the potential of walking alone milestone combined reading-frame rule to improve the early diagnosis of Duchenne muscular dystrophy (DMD).

METHOD

To retrospectively describe the genotype and phenotype of Duchenne and Becker muscular dystrophies (BMD) patients with deletions and duplicates in the dystrophin gene. The sensitivity and specificity of the reading frame rule were calculated and compared to that of the combined reading frame rule and walking alone milestone. The diagnostic coincidence rate of two different methods was analyzed.

RESULT

One hundred sixty-nine male DMD/BMD patients were enrolled, including 17 cases of BMD and 152 cases of DMD. The diagnostic coincidence rate, diagnostic sensitivity, and specificity of the reading-frame rule for DMD/BMD were 85.2, 86.8, and 70.59%, respectively. The sensitivity and specificity of the reading frame principle combined with the walking alone milestone for DMD/BMD were 96.05 and 70.59%, respectively. The diagnostic coincidence rate increased to 93.49%, significantly different from that predicted by reading- frame rule (P < 0.05).

CONCLUSION

The reading-frame rule combined with the walking alone milestone significantly improved the early diagnosis rate of DMD.

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.

Lessons Learned From Translational Research in Neuromuscular Diseases: Impact on Study Design, Outcome Measures and Managing Expectation

Spinal Muscular Atrophy (SMA) and Duchenne Muscular Dystrophy (DMD), two of the most common, child onset, rare neuromuscular disorders, present a case study for the translation of preclinical research into clinical work. Over the past decade, well-designed clinical trials and innovative methods have led to the approval of several novel therapies for SMA and DMD, with many more in the pipeline. This review discusses several features that must be considered during trial design for neuromuscular diseases, as well as other rare diseases, to maximise the possibility of trial success using historic examples. These features include well-defined inclusion criteria, matching criteria, alternatives to placebo-controlled trials and the selection of trial endpoints. These features will be particularly important in the coming years as the investigation into innovative therapy approaches for neuromuscular diseases continues.

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.

Genotype-related respiratory progression in Duchenne muscular dystrophy-A multicenter international study

INTRODUCTION/AIMS

Mutations amenable to skipping of specific exons have been associated with different motor progression in Duchenne muscular dystrophy (DMD). Less is known about their association with long-term respiratory function. In this study we investigated the features of respiratory progression in four DMD genotypes relevant in ongoing exon-skipping therapeutic strategies.

METHODS

This was a retrospective longitudinal study including DMD children followed by the UK NorthStar Network and international AFM Network centers (May 2003 to October 2020). We included boys amenable to skip exons 44, 45, 51, or 53, who were older than 5 years of age and ambulant at first recorded visit. Subjects who were corticosteroid-naive or enrolled in interventional clinical trials were excluded. The progression of respiratory function (absolute forced vital capacity [FVC] and calculated as percent predicted [FVC%]) was compared across the four subgroups (skip44, skip45, skip51, skip53).

RESULTS

We included 142 boys in the study. Mean (standard deviation) age at first visit was 8.6 (2.5) years. Median follow-up was 3 (range, 0.3-8.3) years. In skip45 and skip51, FVC% declined linearly from the first recorded visit. From the age of 9 years, FVC% declined linearly in all genotypes. Skip44 had the slowest (2.7%/year) and skip51 the fastest (5.9%/year) annual FVC% decline. The absolute FVC increased progressively in skip44, skip45, and skip51. In skip53, FVC started declining from 14 years of age.

DISCUSSION

The progression of respiratory dysfunction follows different patterns for specific genotype categories. This information is valuable for prognosis and for the evaluation of exon-skipping therapies.

Fondazione Telethon and Unione Italiana Lotta alla Distrofia Muscolare, a successful partnership for neuromuscular healthcare research of value for patients

In 2001, Fondazione Telethon and the Italian muscular dystrophy patient organisation Unione Italiana Lotta alla Distrofia Muscolare joined their efforts to design and launch a call for grant applications specifically dedicated to clinical projects in the field of neuromuscular disorders. This strategic initiative, run regularly over the years and still ongoing, aims at supporting research with impact on the daily life of people with a neuromuscular condition and is centred on macro-priorities identified by the patient organisation. It is investigator-driven, and all proposals are peer-reviewed for quality and feasibility. Over the years, this funding program contributed to strengthening the activities of the Italian neuromuscular clinical network, reaching many achievements in healthcare research. Moreover, it has been an enabling factor for innovative therapy experimentation at international level and prepared the clinical ground to make therapies available to Italian patients. The ultimate scope of healthcare research is to ameliorate the delivery of care. In this paper, the achievements of the funded studies are analysed also from this viewpoint, to ascertain to which extent they have fulfilled the original goals established by the patient organisation. The evidence presented indicates that this has been a highly fruitful program. Factors that contributed to its success, lessons learned, challenges, and issues that remain to be addressed are discussed to provide practical examples of an experience that could inspire also other organizations active in the field of rare disease research.

Upper limb disease evolution in exon 53 skipping eligible patients with Duchenne muscular dystrophy

OBJECTIVE

To understand the natural disease upper limb progression over 3 years of ambulatory and non-ambulatory patients with Duchenne muscular dystrophy (DMD) using functional assessments and quantitative magnetic resonance imaging (MRI) and to exploratively identify prognostic factors.

METHODS

Forty boys with DMD (22 non-ambulatory and 18 ambulatory) with deletions in dystrophin that make them eligible for exon 53-skipping therapy were included. Clinical assessments, including Brooke score, motor function measure (MFM), hand grip and key pinch strength, and upper limb distal coordination and endurance (MoviPlate), were performed every 6 months and quantitative MRI of fat fraction (FF) and lean muscle cross sectional area (flexor and extensor muscles) were performed yearly.

RESULTS

In the whole population, there were strong nonlinear correlations between outcome measures. In non-ambulatory patients, annual changes over the course of 3 years were detected with high sensitivity standard response mean (|SRM| ≥0.8) for quantitative MRI-based FF, hand grip and key pinch, and MFM. Boys who presented with a FF<20% and a grip strength >27% were able to bring a glass to their mouth and retained this ability in the following 3 years. Ambulatory patients with grip strength >35% of predicted value and FF <10% retained ambulation 3 years later.

INTERPRETATION

We demonstrate that continuous decline in upper limb strength, function, and MRI measured muscle structure can be reliably measured in ambulatory and non-ambulatory boys with DMD with high SRM and strong correlations between outcomes. Our results suggest that a combination of grip strength and FF can be used to predict important motor milestones.

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.

North Star Ambulatory Assessment changes in ambulant Duchenne boys amenable to skip exons 44, 45, 51, and 53: A 3 year follow up

Introduction

The aim of this study was to report 36-month longitudinal changes using the North Star Ambulatory Assessment (NSAA) in ambulant patients affected by Duchenne muscular dystrophy amenable to skip exons 44, 45, 51 or 53.

Materials and methods

We included 101 patients, 34 had deletions amenable to skip exon 44, 25 exon 45, 19 exon 51, and 28 exon 53, not recruited in any ongoing clinical trials. Five patients were counted to skip exon 51 and 53 since they had a single deletion of exon 52.

Results

The difference between subgroups (skip 44, 45, 51 and 53) was significant at 12 (p = 0.043), 24 (p = 0.005) and 36 months (p≤0.001).

Discussion

Mutations amenable to skip exons 53 and 51 had lower baseline values and more negative changes than the other subgroups while those amenable to skip exon 44 had higher scores both at baseline and at follow up.

Conclusion

Our results confirm different progression of disease in subgroups of patients with deletions amenable to skip different exons. This information is relevant as current long term clinical trials are using the NSAA in these subgroups of mutations.

Open-Label Evaluation of Eteplirsen in Patients with Duchenne Muscular Dystrophy Amenable to Exon 51 Skipping: PROMOVI Trial

Background

Eteplirsen received accelerated FDA approval for treatment of Duchenne muscular dystrophy (DMD) with mutations amenable to exon 51 skipping, based on demonstrated dystrophin production.

Objective

To report results from PROMOVI, a phase 3, multicenter, open-label study evaluating efficacy and safety of eteplirsen in a larger cohort.

Methods

Ambulatory patients aged 7–16 years, with confirmed mutations amenable to exon 51 skipping, received eteplirsen 30 mg/kg/week intravenously for 96 weeks. An untreated cohort with DMD not amenable to exon 51 skipping was also enrolled.

Results

78/79 eteplirsen-treated patients completed 96 weeks of treatment. 15/30 untreated patients completed the study; this cohort was considered an inappropriate control group because of genotype-driven differences in clinical trajectory. At Week 96, eteplirsen-treated patients showed increased exon skipping (18.7-fold) and dystrophin protein (7-fold) versus baseline. Post-hoc comparisons with patients from eteplirsen phase 2 studies (4658-201/202) and mutation-matched external natural history controls confirmed previous results, suggesting clinically notable attenuation of decline on the 6-minute walk test over 96 weeks (PROMOVI: –68.9 m; phase 2 studies: –67.3 m; external controls: –133.8 m) and significant attenuation of percent predicted forced vital capacity annual decline (PROMOVI: –3.3%, phase 2 studies: –2.2%, external controls: –6.0%; p < 0.001). Adverse events were generally mild to moderate and unrelated to eteplirsen. Most frequent treatment-related adverse events were headache and vomiting; none led to treatment discontinuation.

Conclusions

This large, multicenter study contributes to the growing body of evidence for eteplirsen, confirming a positive treatment effect, favorable safety profile, and slowing of disease progression versus natural history.

Bone density and bone health alteration in boys with Duchenne Muscular Dystrophy: a prospective observational study

OBJECTIVES

Boys with Duchenne Muscular Dystrophy (DMD) are at increased risk for compromised bone health, manifesting as low-impact trauma long bone fractures and vertebral compression fractures.

METHODS

In a prospective observational study, we studied bone health parameters in North Indian boys with DMD. We consecutively enrolled ambulatory boys with DMD on glucocorticoid therapy. Bone health was evaluated with X-ray spine, Dual-energy X-ray absorptiometry (DXA), serum calcium, vitamin D3 (25[OH]D), 1,25-dihyroxyvitamin D3 (1,25[OH]₂D₃), serum osteocalcin, osteopontin, and N terminal telopeptide of type 1 collagen (Ntx) levels.

RESULTS

A total of 76 boys with DMD were enrolled. The median age was 8.5 (interquartile range [IQR] 7.04-10.77) years. Among these, seven (9.2%) boys had long bone fractures, and four (5.3%) had vertebral compression fractures. Fifty-four (71%) boys underwent DXA scan, and among these 31 (57%) had low bone mineral density (BMD, ≤-2 z-score) at the lumbar spine. The mean BMD z-score at the lumbar spine was -2.3 (95% confidence interval [CI] = -1.8, -2.8), and at the femoral neck was -2.5 (95% CI = -2, -2.9). 25(OH)D levels were deficient in 68 (89.5%, n=76) boys, and 1,25(OH)₂D₃ levels were deficient in all. Mean serum osteocalcin levels were 0.68 ± 0.38 ng/mL (n=54), serum osteopontin levels were 8.6 ± 4.6 pg/mL (n=54) and serum Ntx levels were 891 ± 476 nmol/L (n=54). Boys with low BMD received glucocorticoids for longer duration, in comparison to those with normal BMD (median, IQR [16.9 (6-34) months vs. 7.8 (4.8-13.4) months]; p=0.04).

CONCLUSIONS

Bone health is compromised in North Indian boys with DMD. BMD at the lumbar spine is reduced in more than half of boys with DMD and nearly all had vitamin D deficiency on regular vitamin D supplements. Longer duration of glucocorticoid therapy is a risk factor for low BMD in our cohort.

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.

The administration of antisense oligonucleotide golodirsen reduces pathological regeneration in patients with Duchenne muscular dystrophy

During the last decade, multiple clinical trials for Duchenne muscular dystrophy (DMD) have focused on the induction of dystrophin expression using different strategies. Many of these trials have reported a clear increase in dystrophin protein following treatment. However, the low levels of the induced dystrophin protein have raised questions on its functionality. In our present study, using an unbiased, high-throughput digital image analysis platform, we assessed markers of regeneration and levels of dystrophin associated protein via immunofluorescent analysis of whole muscle sections in 25 DMD boys who received 48-weeks treatment with exon 53 skipping morpholino antisense oligonucleotide (PMO) golodirsen. We demonstrate that the de novo dystrophin induced by exon skipping with PMO golodirsen is capable of conferring a histological benefit in treated patients with an increase in dystrophin associated proteins at the dystrophin positive regions of the sarcolemma in post-treatment biopsies. Although 48 weeks treatment with golodirsen did not result in a significant change in the levels of fetal/developmental myosins for the entire cohort, there was a significant negative correlation between the amount of dystrophin and levels of regeneration observed in different biopsy samples. Our results provide, for the first time, evidence of functionality of induced dystrophin following successful therapeutic intervention in the human.

Genotype-Phenotype Correlations in Duchenne and Becker Muscular Dystrophy Patients from the Canadian Neuromuscular Disease Registry

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disorder generally caused by out-of-frame mutations in the DMD gene. In contrast, in-frame mutations usually give rise to the milder Becker muscular dystrophy (BMD). However, this reading frame rule does not always hold true. Therefore, an understanding of the relationships between genotype and phenotype is important for informing diagnosis and disease management, as well as the development of genetic therapies. Here, we evaluated genotype-phenotype correlations in DMD and BMD patients enrolled in the Canadian Neuromuscular Disease Registry from 2012 to 2019. Data from 342 DMD and 60 BMD patients with genetic test results were analyzed. The majority of patients had deletions (71%), followed by small mutations (17%) and duplications (10%); 2% had negative results. Two deletion hotspots were identified, exons 3-20 and exons 45-55, harboring 86% of deletions. Exceptions to the reading frame rule were found in 13% of patients with deletions. Surprisingly, C-terminal domain mutations were associated with decreased wheelchair use and increased forced vital capacity. Dp116 and Dp71 mutations were also linked with decreased wheelchair use, while Dp140 mutations significantly predicted cardiomyopathy. Finally, we found that 12.3% and 7% of DMD patients in the registry could be treated with FDA-approved exon 51- and 53-skipping therapies, respectively.

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.

Increased dystrophin production with golodirsen in patients with Duchenne muscular dystrophy

Objective

To report safety, pharmacokinetics, exon 53 skipping, and dystrophin expression in golodirsen-treated patients with Duchenne muscular dystrophy (DMD) amenable to exon 53 skipping.

Methods

Part 1 was a randomized, double-blind, placebo-controlled, 12-week dose titration of once-weekly golodirsen; part 2 is an ongoing, open-label evaluation. Safety and pharmacokinetics were primary and secondary objectives of part 1. Primary biological outcome measures of part 2 were blinded exon skipping and dystrophin protein production on muscle biopsies (baseline, week 48) evaluated, respectively, using reverse transcription PCR and Western blot and immunohistochemistry.

Results

Twelve patients were randomized to receive golodirsen (n = 8) or placebo (n = 4) in part 1. All from part 1 plus 13 additional patients received 30 mg/kg golodirsen in part 2. Safety findings were consistent with those previously observed in pediatric patients with DMD. Most of the study drug was excreted within 4 hours following administration. A significant increase in exon 53 skipping was associated with ∼16-fold increase over baseline in dystrophin protein expression at week 48, with a mean percent normal dystrophin protein standard of 1.019% (range, 0.09%–4.30%). Sarcolemmal localization of dystrophin was demonstrated by significantly increased dystrophin-positive fibers (week 48, p < 0.001) and a positive correlation (Spearman r = 0.663; p < 0.001) with dystrophin protein change from baseline, measured by Western blot and immunohistochemistry.

Conclusion

Golodirsen was well-tolerated; muscle biopsies from golodirsen-treated patients showed increased exon 53 skipping, dystrophin production, and correct dystrophin sarcolemmal localization.

Clinicaltrials.gov identifier

NCT02310906.

Classification of evidence

This study provides Class I evidence that golodirsen is safe and Class IV evidence that it induces exon skipping and novel dystrophin as confirmed by 3 different assays.

Fibrogenesis in LAMA2-Related Muscular Dystrophy Is a Central Tenet of Disease Etiology

LAMA2-related congenital muscular dystrophy, also known as MDC1A, is caused by loss-of-function mutations in the alpha2 chain of Laminin-211. Loss of this protein interrupts the connection between the muscle cell and its extracellular environment and results in an aggressive, congenital-onset muscular dystrophy characterized by severe hypotonia, lack of independent ambulation, and early mortality driven by respiratory complications and/or failure to thrive. Of the pathomechanisms of MDC1A, the earliest and most prominent is widespread and rampant fibrosis. Here, we will discuss some of the key drivers of fibrosis including TGF-beta and renin–angiotensin system signaling and consequences of these pathways including myofibroblast transdifferentiation and matrix remodeling. We will also highlight some of the differences in fibrogenesis in congenital muscular dystrophy (CMD) with that seen in Duchenne muscular dystrophy (DMD). Finally, we will connect the key signaling pathways in the pathogenesis of MDC1A to the current status of the therapeutic approaches that have been tested in the preclinical models of MDC1A to treat fibrosis.