Therapeutic opportunities and clinical outcome measures in Duchenne muscular dystrophy

Mechanisms of cardiomyopathy in duchenne muscular dystrophy: A study using pluripotent stem cells derived from patients with severe and mild motor impairment

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder marked by progressive muscle degeneration and early cardiac involvement, with cardiac dysfunction as a major contributor to mortality. However, the molecular mechanisms underlying DMD-associated cardiac dysfunction remain unclear. This study aimed to elucidate these mechanisms and identify gene expression patterns associated with disease progression. Induced pluripotent stem cells (iPSCs) were derived from two patients with DMD exhibiting severe and mild motor impairment and differentiated into cardiomyocytes (iPSC-CMs). The resulting iPSC-CMs expressed myocardial markers, with genetic analysis confirmed dystrophin deficiency in DMD iPSC-CMs. Transcriptomic analysis revealed distinct gene expression profiles, with severe DMD iPSC-CMs exhibiting upregulation of the positive regulation of the transmembrane receptor protein serine/threonine kinase signaling pathway, leading to reduced proliferation, while mild DMD iPSC-CMs showed increased PI3K-Akt signaling and metabolic activity. Severe DMD iPSC-CMs also displayed more pronounced arrhythmicity, with significant correlation between dilated cardiomyopathy signaling changes and heart rate differences. This study establishes an iPSC-CM model for DMD cardiomyopathy, revealing altered gene expression and signaling pathways involved in cardiac dysfunction. Although non-allelic effects and unquantified differentiation efficiency may impact interpretation, these findings highlight key molecular alterations and offer potential therapeutic targets to improve cardiac outcomes in DMD.

Muscle weakness but also contractures contribute to the progressive gait pathology in children with Duchenne muscular dystrophy: a simulation study

BACKGROUND

Muscle weakness and contractures cause gait deficits in children with Duchenne muscular dystrophy (DMD) but their relative contributions are poorly understood and hence it is unclear whether contractures should be treated. Therefore, we aimed to differentiate the effect of muscle weakness in isolation from weakness and contractures combined on the gait patterns.

METHODS

We used computer simulations that generate gait patterns based on a musculoskeletal model (without relying on experimental data) to establish the relationship between muscle impairments and gait deviations. We previously collected a longitudinal database of 137 repeated measurements in 30 boys with DMD and found that the data measured through 3D gait analysis could be clustered in three gait patterns. We estimated weakness based on data from fixed dynamometry, and contractures based on goniometry and clinical measures. Foot deformities were modeled by reducing the height of all foot segments and decreasing the strength of the intrinsic foot muscles. We created musculoskeletal models that either represented (1) the mean weakness; (2) the mean weakness and contractures; or (3) the mean weakness, contractures and foot deformities, in each gait pattern.

RESULTS

Simulations based on models with both weakness and contractures captured most (but not all) experimentally observed gait deviations, demonstrating the validity of our approach. While muscle weakness was primarily responsible for gait deviations, muscle contractures and foot deformities further contributed to gait deviations. Interestingly, the simulations predict that the combination of increasing weakness and contractures rather than increasing weakness alone causes loss of ambulation for the most affected gait pattern.

CONCLUSIONS

Predictive simulations have the potential to elucidate causal relationships between muscle impairments and gait deviations in boys with DMD. In the future, they could be used to design targeted interventions (e.g. stretching, assistive devices) to prolong ambulation.

Longitudinal trajectories of muscle impairments in growing boys with Duchenne muscular dystrophy

BACKGROUND

Insights into the progression of muscle impairments in growing boys with Duchenne muscular dystrophy (DMD) remain incomplete due to the frequent oversight of normal maturation as a confounding factor, thereby restricting the delineation of sole pathological processes.

OBJECTIVE

To establish longitudinal trajectories for a comprehensive integrated set of muscle impairments, including muscle weakness, contractures and muscle size alterations, while correcting for normal maturation, in DMD.

METHODS

Thirty-three boys with DMD (aged 4.3-17 years) were included. Fixed dynamometry, goniometry, and 3D freehand ultrasound were used to repeatedly assess lower limb muscle strength, passive range of motion (ROM) and muscle size, resulting in 161, 178 and 64 assessments for the strength, ROM and ultrasound dataset, respectively. To account for natural strength development, ROM reduction, and muscle growth in growing children, muscle outcomes were converted to unit-less z-scores calculated in reference to typically developing (TD) peers. This allows the interpretation of the muscle outcomes as deficits or alterations with respect to TD. Mixed-effect models estimated the longitudinal change in muscle impairments.

RESULTS

At 4.3-4.9 years of age, all muscle strength outcomes and several ROMs (i.e., dorsiflexion, hamstrings, and hip extension) showed deficits relative to TD, while m. medial gastrocnemius size was increased. Most muscle outcomes remained stable or slightly improved until the ages of 6.6-9.4 years (except knee flexion strength). After this period, muscle strength (-0.27 to -0.45 z-score/year; p < 0.0044), dorsiflexion ROM (-0.23 to -0.33 z-score/year; p < 0.0007), m. medial gastrocnemius size (-0.56 z-score/year; p = 0.0022), and m. rectus femoris size (-0.36 z-score/year; p = 0.0054) declined.

CONCLUSIONS

The current study established longitudinal trajectories of muscle impairments in boys with DMD. The results provided enriched history data and revealed promising outcome measures that could enhance the detection of the efficacy of novel therapeutic strategies. Future studies are necessary to validate these outcomes.

Early Cardiac Dysfunction in Duchenne Muscular Dystrophy: A Case Report and Literature Update

Duchenne Muscular Dystrophy (DMD) is a severe X-linked recessive disorder characterized by progressive muscle degeneration due to dystrophin deficiency. Cardiac involvement, particularly dilated cardiomyopathy, significantly impacts morbidity and mortality, typically manifesting after age 10. This case report presents a rare instance of early-onset cardiac involvement in a 3-year-old male with a confirmed deletion in exon 55 of the dystrophin gene. The patient developed dilated cardiomyopathy at 3 years and 8 months, with progressive left ventricular dysfunction despite early treatment with corticosteroids, ACE inhibitors, and beta-blockers. Genetic mechanisms and genotype-phenotype correlations related to cardiac involvement were reviewed, highlighting emerging therapies such as exon skipping, vamorolone, ifetroban, and rimeporide. Studies indicate that variants in exons 12, 14-17, 31-42, 45, and 48-49 are associated with more severe cardiac impairment. This case emphasizes the need for early, ongoing cardiac assessment and personalized treatment to address disease heterogeneity. While current DMD care standards improve survival, optimizing management through early intervention and novel therapies remains essential. Further research is needed to better understand genotype-phenotype correlations and improve cardiac outcomes for patients with DMD.

Is there a decline in speech and swallowing in Amyotrophic Lateral Sclerosis over ten years?

PURPOSE

To analyze the evolution of speech and swallowing decline in patients with amyotrophic lateral sclerosis (ALS) over a ten-year period.

METHODS

A retrospective and longitudinal cohort study. Data were collected using the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) from 101 medical records of ALS patients treated at the multidisciplinary neuromuscular diseases clinic of a University Hospital over a ten-year period. The data were statistically analyzed, adopting a significance level of p<0.05.

RESULTS

The analysis of the studied functions indicated that speech, swallowing, and salivation are altered over ten years in ALS. There are differences in patterns between the variables sex and disease type concerning symptoms related to dysarthria and dysphagia in these individuals, which may indicate the rate of progression over a given time interval.

CONCLUSION

There is a decline in speech and swallowing over ten years in ALS. The bulbar type leads to a faster decline in the studied functions than the spinal type.

Use of assistive technology to assess distal motor function in subjects with neuromuscular disease

Among the 32 items of the Motor Function Measure scale, 3 concern the assessment of hand function on a paper-based support. Their characteristics make it possible to envisage the use of a tablet instead of the original paper-based support for their completion. This would then make it possible to automate the score to reduce intra- and inter-individual variability. The main objective of the present study was to validate the digital completion of items 18, 19, and 22 by measuring the agreement of the scores obtained using a digital tablet with those obtained using the original paper-based support in children and adults with various neuromuscular diseases (NMD). The secondary objective is to calibrate an algorithm for the automatic items scoring.

DESIGN

Prospective, multicentre, non-interventional study.

METHODS

Ninety-eight subjects aged 5 to 60 years with a confirmed NMD completed MFM items 18, 19, and 22 both on a paper support and a digital tablet.

RESULTS

The median age of included subjects was 16.2 years. Agreement between scores as assessed using the weighted Kappa coefficient was almost perfect for the scores of items 18 and 22 (K = 0.93, and 0.95, respectively) and substantial for item 19 (K = 0.70). In all cases of disagreement, the difference was of 1 point. The most frequent disagreement concerned item 19; mainly in the direction of a scoring of 1 point less on the tablet. An automatic analysis algorithm was tested on 82 recordings to suggest improvements.

CONCLUSION

The switch from original paper-based support to the tablet results in minimal and acceptable differences, and maintains a valid and reproducible measure of the 3 items. The developed algorithm for automatic scoring appears feasible with the perspective to include them in a digital application that will make it easier to monitor patients.

Givinostat: First Approval

Givinostat (DUVYZAT™), an orally available histone deacetylase inhibitor, is being developed by Italfarmaco for the treatment of muscular dystrophy and polycythemia vera. Givinostat received its first approval on 21 March 2024, in the USA, for the treatment of Duchenne muscular dystrophy (DMD) in patients 6 years of age and older. Approval was based on the results of the multinational phase III EPIDYS trial, in which givinostat recipients showed less decline than placebo recipients in the time taken to perform a functional task. Givinostat represents the first nonsteroidal treatment for DMD to be approved for use in patients irrespective of the specific genetic variant underlying their disease. Givinostat is available as an oral suspension to be administered twice daily with food. The recommended dosage is based on the body weight of the patient. In the EU, regulatory review of givinostat in DMD is currently underway. This article summarizes the milestones in the development of givinostat leading to this first approval for DMD.

Physiological stress improves stem cell modeling of dystrophic cardiomyopathy

Heart failure contributes to Duchenne muscular dystrophy (DMD), which arises from mutations that ablate dystrophin, rendering the plasma membrane prone to disruption. Cardiomyocyte membrane breakdown in patients with DMD yields a serum injury profile similar to other types of myocardial injury with the release of creatine kinase and troponin isoforms. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly useful but can be improved. We generated hiPSC-CMs from a patient with DMD and subjected these cells to equibiaxial mechanical strain to mimic in vivo stress. Compared to healthy cells, DMD hiPSC-CMs demonstrated greater susceptibility to equibiaxial strain after 2 h at 10% strain. We generated an aptamer-based profile of proteins released from hiPSC-CMs both at rest and subjected to strain and identified a strong correlation in the mechanical stress-induced proteome from hiPSC-CMs and serum from patients with DMD. We exposed hiPSC-CMs to recombinant annexin A6, a protein resealing agent, and found reduced biomarker release in DMD and control hiPSC-CMs subjected to strain. Thus, the application of mechanical strain to hiPSC-CMs produces a model that reflects an in vivo injury profile, providing a platform to assess pharmacologic intervention.

Gait classification for growing children with Duchenne muscular dystrophy

Classifying gait patterns into homogeneous groups could enhance communication among healthcare providers, clinical decision making and clinical trial designs in boys with Duchenne muscular dystrophy (DMD). Sutherland's classification has been developed 40 years ago. Ever since, the state-of-the-art medical care has improved and boys with DMD are now longer ambulatory. Therefore, the gait classification requires an update. The overall aim was to develop an up-to-date, valid DMD gait classification. A total of 137 three-dimensional gait analysis sessions were collected in 30 boys with DMD, aged 4.6-17 years. Three classes were distinguished, which only partly aligned with increasing severity of gait deviations. Apart from the mildly affected pattern, two more severely affected gait patterns were found, namely the tiptoeing pattern and the flexion pattern with distinct anterior pelvic tilt and posterior trunk leaning, which showed most severe deviations at the ankle or at the proximal segments/joints, respectively. The agreement between Sutherland's and the current classification was low, suggesting that gait pathology with the current state-of-the-art medical care has changed. However, overlap between classes, especially between the two more affected classes, highlights the complexity of the continuous gait changes. Therefore, caution is required when classifying individual boys with DMD into classes.

Hybrid QUS Radiomics: A Multimodal-Integrated Quantitative Ultrasound Radiomics for Assessing Ambulatory Function in Duchenne Muscular Dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder that affects ambulatory function. Quantitative ultrasound (QUS) imaging, utilizing envelope statistics, has proven effective in diagnosing DMD. Radiomics enables the extraction of detailed features from QUS images. This study further proposes a hybrid QUS radiomics and explores its value in characterizing DMD.

METHODS

Patients (n = 85) underwent ultrasound examinations of gastrocnemius through Nakagami, homodyned K (HK), and information entropy imaging. The hybrid QUS radiomics extracted, selected, and integrated the retained features derived from each QUS image for classification of ambulatory function using support vector machine. Nested five fold cross-validation of the data was conducted, with the rotational process repeated 50 times. The performance was assessed by averaging the areas under the receiver operating characteristic curve (AUROC).

RESULTS

Radiomics enhanced the average AUROC of B-scan, Nakagami, HK, and entropy imaging to 0.790, 0.911, 0.869, and 0.890, respectively. By contrast, the hybrid QUS radiomics using HK and entropy images for diagnosing ambulatory function in DMD patients achieved a superior average AUROC of 0.971 (p < 0.001 compared with conventional radiomics analysis).

CONCLUSIONS

The proposed hybrid QUS radiomics incorporates microstructure-related backscattering information from various envelope statistics models to effectively enhance the performance of DMD assessment.

N-terminal titin fragment: a non-invasive, pharmacodynamic biomarker for microdystrophin efficacy

BACKGROUND

Multiple clinical trials to assess the efficacy of AAV-directed gene transfer in participants with Duchenne muscular dystrophy (DMD) are ongoing. The success of these trials currently relies on standard functional outcome measures that may exhibit variability within and between participants, rendering their use as sole measures of drug efficacy challenging. Given this, supportive objective biomarkers may be useful in enhancing observed clinical results. Creatine kinase (CK) is traditionally used as a diagnostic biomarker of DMD, but its potential as a robust pharmacodynamic (PD) biomarker is difficult due to the wide variability seen within the same participant over time. Thus, there is a need for the discovery and validation of novel PD biomarkers to further support and bolster traditional outcome measures of efficacy in DMD.

METHOD

Potential PD biomarkers in DMD participant urine were examined using a proteomic approach on the Somalogic platform. Findings were confirmed in both mdx mice and Golden Retriever muscular dystrophy (GRMD) dog plasma samples.

RESULTS

Changes in the N-terminal fragment of titin, a well-known, previously characterized biomarker of DMD, were correlated with the expression of microdystrophin protein in mice, dogs, and humans. Further, titin levels were sensitive to lower levels of expressed microdystrophin when compared to CK.

CONCLUSION

The measurement of objective PD biomarkers such as titin may provide additional confidence in the assessment of the mechanism of action and efficacy in gene therapy clinical trials of DMD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03368742.

Gain and loss of upper limb abilities in Duchenne muscular dystrophy patients: A 24-month study

Duchenne muscular dystrophy (DMD) is a neuromuscular condition characterized by muscle weakness. The Performance of upper limb (PUL) test is designed to evaluate upper limb function in DMD patients across three domains. The aim of this study is to identify frequently lost or gained PUL 2.0 abilities at distinct functional stages in DMD patients. This retrospective study analyzed prospectively collected data on 24-month PUL 2.0 changes related to ambulatory function. Ambulant patients were categorized based on initial 6MWT distance, non-ambulant patients by time since ambulation loss. Each PUL 2.0 item was classified as shift up, no change, or shift down. The study's cohort incuded 274 patients, with 626 paired evaluations at the 24-month mark. Among these, 55.1 % had activity loss, while 29.1 % had gains. Ambulant patients showed the lowest loss rates, mainly in the shoulder domain. The highest loss rate was in the shoulder domain in the transitioning subgroup and in elbow and distal domains in the non-ambulant patients. Younger ambulant patients demonstrated multiple gains, whereas in the other functional subgroups there were fewer gains, mostly tied to singular activities. Our findings highlight divergent upper limb domain progression, partly linked to functional status and baseline function.

Early Cost-Utility Analysis of Ataluren and Eteplirsen in the Treatment of Duchenne Muscular Dystrophy in Egypt

OBJECTIVES

Ataluren and eteplirsen are orphan drugs that delay progression of Duchenne muscular dystrophy in mutation-specific subgroups. They have yet to be approved in Egypt but are expected to reach the market soon. This study describes 2 cost-utility models comparing the drugs with the standard of care.

METHODS

We used a partition-survival model with 5 states based on the ambulatory status to model a cohort of ambulatory patients at the age of 5 years. Baseline curves were obtained from a published model; then the ambulation loss curve was updated using the Kaplan-Meier curve of the standard of care from a study by McDonald et al. Other curves were updated by calibration to this curve. Costs and utilities were from a local study. Deterministic and probabilistic sensitivity analyses were conducted. Prices were estimated based on other orphan drugs' prices.

RESULTS

In the base case, ataluren 1000 mg and eteplirsen 50 mg/mL resulted in an incremental cost-effectiveness ratio of EGP 51 745 605 and EGP 69 652 533/quality-adjusted life-year, respectively, at their hypothetical prices of EGP 308 600 for ataluren 30-sachet pack and EGP 62 800 for eteplirsen 10 mL vial. The incremental cost-effectiveness ratio was sensitive to health state utilities but not to state costs. At EGP 911 719/quality-adjusted life-year threshold, the value-based prices were EGP 4680 for ataluren 1000 mg and EGP 733 for eteplirsen 10 mL vial.

CONCLUSIONS

Based on these models, there is a huge gap between the prices of orphan drugs and their value-based prices, which highlights the need for major policy reforms in the assessment and pricing of orphan drugs.