Duchenne Muscular Dystrophy Gene Research Articles

Duchenne muscular dystrophy, one of the most complicated diseases for gene therapy

Gene therapy for Duchenne muscular dystrophy (DMD) is hindered by many pitfalls related in particular to the limitations of current technologies, the specificities of muscle and cardiac targets, and the disease itself, a chronic, multisystem, dystrophic and inflammatory disorder. Following RNA-based therapies, DNA gene transfer, mainly based on adeno-associated viral vectors, is now able to deliver therapeutic genetic sequences on a massive scale, and the first antisense and adeno-associated virus (AAV)-microdystrophin gene products are now reaching the marketing stage in Europe and/or in the US. However, only a subset of patients are eligible for those therapies. Many questions remain, such as the duration of the therapeutic effect, the burden of high doses of vectors, and the immunogenicity of viral capsids and therapeutic proteins, in the context of a disease-related inflammatory background. Evaluations of these treatments by the different biotech, pharma or non-for-profit sponsors also come up against the great clinical heterogeneity of patients. This review summarizes the significant progress made over the past three decades to optimize both the efficacy and safety of DMD gene therapies, as well as the remaining challenges, short-term prospects, and future directions such as more targeted vectors and combination therapies.

Rapid and scalable personalized ASO screening in patient-derived organoids.

Personalized antisense oligonucleotides (ASOs) have achieved positive results in the treatment of rare genetic disease1. As clinical sequencing technologies continue to advance, the ability to identify patients with rare disease harbouring pathogenic genetic variants amenable to this therapeutic strategy will probably improve. Here we describe a scalable platform for generating patient-derived cellular models and demonstrate that these personalized models can be used for preclinical evaluation of patient-specific ASOs. We describe protocols for delivery of ASOs to patient-derived organoid models and confirm reversal of disease-associated phenotypes in cardiac organoids derived from a patient with Duchenne muscular dystrophy (DMD) with a structural deletion in the gene encoding dystrophin (DMD) that is amenable to treatment with existing ASO therapeutics. Furthermore, we designed novel patient-specific ASOs for two additional patients with DMD (siblings) with a deep intronic variant in the DMD gene that gives rise to a novel splice acceptor site, incorporation of a cryptic exon and premature transcript termination. We showed that treatment of patient-derived cardiac organoids with patient-specific ASOs results in restoration of DMD expression and reversal of disease-associated phenotypes. The approach outlined here provides the foundation for an expedited path towards the design and preclinical evaluation of personalized ASO therapeutics for a broad range of rare diseases.

Treatment With Full-Spectrum Cannabidiol Oil Improved the Pathological Findings of Dystrophic Mutant Mice.

Duchenne muscular dystrophy (DMD) is caused by pathogenic variants in the DMD gene, making muscle fibers susceptible to contraction-induced membrane damage. Given the potential beneficial action of cannabidiol (CBD), we evaluated the invitro effect of full-spectrum CBD oil on the viability of dystrophic muscle fibers and the invivo effect on myopathy of the mdx mouse, a DMD model. In vitro, dystrophic cells from the mdx mouse were treated with full-spectrum CBD oil and assessed with cell viability and cytotoxic analyses. Invivo, fourteen-day-old mdx mice received 10 mg/kg/day of the full-spectrum CBD oil for 14 days. We analyzed creatine kinase (CK) levels, liver damage markers, and histopathology of the diaphragm (DIA) and quadriceps (QUA [myonecrotic fibers with positive IgG staining, regenerated fibers/central nuclei, the minimum Feret's diameter, the fibrosis area, the inflammatory area, the presence of macrophages, and NF-kappa B content]). In vitro treatment with full-spectrum CBD oil showed a dose-dependent cytotoxic effect; however, invivo 10 mg/kg treatment was safe and effectively improved DMD histopathological assessment parameters in DIA and QUA: reduction of central nuclei: 1.7% ± 2.0% versus 22.4% ± 5.3% and 11.1% ± 10.7% versus 32.3% ± 4.6%; reduction of IgG+ myofibers: 0.6% ± 0.7% versus 8.4% ± 1.6% and 0.9% ± 0.3% versus 7.5% ± 1.0%; increase in myofiber size: 85.2 ± 3.2 versus 64.3 ± 4.0 μm and 106.5 ± 8.6 versus 81.2 ± 4.8 μm; decrease in inflammatory area: 6.2% ± 2.7% versus 15.1% ± 2.6% and 5.3 ± 4.1 versus 17.3% ± 2.8%; reduced macrophage area: 0.05% ± 0.1% versus 10.8% ± 4.3% and 1.0% ± 0.7% versus 10.3% ± 4.9%; NF-κB levels: 0.6% ± 0.1% versus 1.7% ± 0.2% and 1.7% ± 0.1% versus 5.2% ± 2.1%; and fibrosis: 5.6% ± 1.8% versus 12.0% ± 3.7% and 1.3% ± 0.5% versus 4.7% ± 1.5%. It also reduced serum CK. Full-spectrum CBD oil may represent a promising new approach to treating DMD, but its potential toxicity must be considered.

Evaluation of Creatine Monohydrate Supplementation on the Gastrocnemius Muscle of Mice with Muscular Dystrophy: A Preliminary Study.

Background/Objectives: Duchenne muscular dystrophy (DMD) is a genetic disease characterized by a lack of dystrophin caused by mutations in the DMD gene, and some minor cases are due to decreased levels of dystrophin, leading to muscle weakness and motor impairment. Creatine supplementation has demonstrated several benefits for the muscle, such as increased strength, enhanced tissue repair, and improved ATP resynthesis. This preliminary study aimed to investigate the effects of creatine on the gastrocnemius muscle in dystrophy muscle (MDX) and healthy C57BL/10 mice. Methods: Twenty MDX and C57Bl/10 mice were organized into groups and supplemented or not with creatine in a dosage of 0.3 mg for 8 weeks. Gastrocnemius tissue was analyzed using histomorphology and histomorphometric techniques. Results: The results demonstrated potential anti-inflammatory effects of creatine, with less observation of inflammatory infiltrates, the preservation of intramuscular glycogen, and reduction in tissue fibrosis in supplemented animals. Conclusions: These findings suggest that creatine may enhance tissue function and slow the progression of DMD. However, further research, with more analysis, is needed to elucidate molecular mechanisms underlying creatine's effects on reducing mononuclear leukocytes and its role in mitigating tissue fibrosis.

Lower-Limb Orthoses in Duchenne Muscular Dystrophy

ABSTRACT Introduction Duchenne muscular dystrophy (DMD) is associated with a mutation in the DMD gene. It is a progressive disorder characterized by deficiency or absence of the production of dystrophin protein. The mechanical stress increased by muscle contractions causes damage to the muscle cell. Delayed ambulation, frequent falls, incompetence during climbing stairs, Gower’s sign, pseudohypertrophy of the calf, and proximal muscle weakness may be seen in children. Loss of ambulation, pulmonary failure, cardiomyopathy, and early mortality are expected in the natural process of the disease. The life expectancy is 30 years with the treatments and care applied nowadays. Materials and Methods Physiotherapy has a substantial place during aging. Physiotherapy approaches, orthoses, and self-help devices are utilized to prevent the development of contractures and deformities characterized by long-term fixed joint position, muscle imbalance, loss of joint range of motion, and fibrotic changes. Results It is observed that stretching exercises are noneffective in contracture and deformity management. It should be considered that the development of lower-limb contractures may occur in the early period. Orthotic approaches can be utilized to delay the loss of ambulation. Conclusions Lower-limb orthoses can be recommended for controlling contracture occurrence, providing postural control, ensuring and maintaining the correct position, continuity of function, ensuring ambulation or vertical position, and preserving surgical success. The use of personalized orthoses will enhance the success of rehabilitation. Orthoses should be used with other treatments to maintain functional mobility in accordance with the patient’s condition and should be reproduced according to the course of the disease. Clinical Relevance Ambulation level is important in choosing a lower-limb orthosis for patients with DMD. It is recommended that ankle-foot orthoses (AFOs) be preferred during the ambulatory period and knee-ankle-foot orthoses (KAFOs) or hip-knee-ankle-foot orthoses (HKAFOs) be preferred during the nonambulatory period.

Hydroxyapatite nanoparticle mediated delivery of full length dystrophin gene as a potential therapeutic for the treatment of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a severe genetic disorder characterized by progressive muscle degeneration, primarily affecting young males. In this study, we investigated arginine-modified hydroxyapatite nanoparticles (R-HAp) as a novel non-viral vector for DMD gene therapy, particularly for delivering the large 18.8 kb dystrophin gene. Addressing the limitations of traditional adeno-associated viral vectors, R-HAp demonstrated efficient binding and delivery of the dystrophin plasmid to DMD patient-derived skeletal muscle cells. Using confocal imaging and RT-PCR analysis, our results showed effective gene delivery and expression in both mouse myotubes and patient-derived cells, with sustained expression evident up to 5 days post transfection. The patient-derived myotubes also showed dystrophin protein production 7 days post transfection. These findings suggest R-HAp nanoparticles as a promising and cost-effective alternative for DMD treatment, highlighting their potential for overcoming current gene therapy challenges.

Phase 1/2 trial of brogidirsen: Dual-targeting antisense oligonucleotides for exon 44 skipping in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a severe muscle disorder caused by mutations in the DMD gene, leading to dystrophin deficiency. Antisense oligonucleotide (ASO)-mediated exon skipping offers potential by partially restoring dystrophin, though current therapies remain mutation specific with limited efficacy. To overcome those limitations, we developed brogidirsen, a dual-targeting ASO composed of two directly connected 12-mer sequences targeting exon 44 using phosphorodiamidate morpholino oligomers. An open-label, dose-escalation, phase 1/2 trial assessed the safety, pharmacokinetics, and efficacy of brogidirsen in six ambulant patients with DMD amenable to exon 44 skipping. Following dose escalation, extended 24-week treatment with 40mg/kg and 80mg/kg yielded dose-dependent increases in dystrophin (16.63% and 24.47% of normal). Functional assessments indicated motor stabilization, and plasma proteomics revealed reductions in peptidyl arginine deiminase 2 (PADI2), titin (TTN), and myomesin 2 (MYOM2), highlighting potential biomarkers. Brogidirsen's efficacy was supported invitro using urine-derived cells from patients with DMD. These promising results warrant a subsequent trial for DMD. This study was registered at ClinicalTrials.gov (NCT04129294).

Native DGC structure rationalizes muscular dystrophy-causing mutations.

Duchenne muscular dystrophy (DMD) is a severe X-linked recessive disorder marked by progressive muscle wasting leading to premature mortality1,2. Discovery of the DMD gene encoding dystrophin both revealed the cause of DMD and helped identify a family of at least ten dystrophin-associated proteins at the muscle cell membrane, collectively forming the dystrophin-glycoprotein complex (DGC)3-9. The DGC links the extracellular matrix to the cytoskeleton, but, despite its importance, its molecular architecture has remained elusive. Here we determined the native cryo-electron microscopy structure of rabbit DGC and conducted biochemical analyses to reveal its intricate molecular configuration. An unexpected β-helix comprising β-, γ- and δ-sarcoglycan forms an extracellular platform that interacts with α-dystroglycan, β-dystroglycan and α-sarcoglycan, allowing α-dystroglycan to contact the extracellular matrix. In the membrane, sarcospan anchors β-dystroglycan to the β-, γ- and δ-sarcoglycan trimer, while in the cytoplasm, β-dystroglycan's juxtamembrane fragment binds dystrophin's ZZ domain. Through these interactions, the DGC links laminin 2 to intracellular actin. Additionally, dystrophin's WW domain, along with its EF-hand 1 domain, interacts with α-dystrobrevin. A disease-causing mutation mapping to the WW domain weakens this interaction, as confirmed by deletion of the WW domain in biochemical assays. Our findings rationalize more than 110 mutations affecting single residues associated with various muscular dystrophy subtypes and contribute to ongoing therapeutic developments, including protein restoration, upregulation of compensatory genes and gene replacement.

Impact of distinct dystrophin gene mutations on behavioral phenotypes of Duchenne muscular dystrophy

ABSTRACT The severity of brain comorbidities in Duchenne muscular dystrophy (DMD) depends on the mutation position within the DMD gene and differential loss of distinct brain dystrophin isoforms (i.e. Dp427, Dp140, Dp71). Comparative studies of DMD mouse models with different mutation profiles may help to understand this genotype−phenotype relationship. The aim of this study was (1) to compare the phenotypes due to Dp427 loss in mdx5cv mice to those of mdx52 mice, which concomitantly lack Dp427 and Dp140; and (2) to evaluate replicability of phenotypes in separate laboratories. We show that mdx5cv mice displayed impaired fear conditioning and robust anxiety-related responses, the severity of which was higher in mdx52 mice. Depression-related phenotypes presented variably in these models and were difficult to replicate between laboratories. Recognition memory was unaltered or minimally affected in mdx5cv and mdx52 mice, at variance with the cognitive deficits described in the original Dp427-deficient mdx mouse, suggesting a difference related to its distinct genetic background. Our results confirm that Dp140 loss may increase the severity of emotional disturbances, and provide insights on the limits of the reproducibility of behavioral studies in DMD mouse models.

Safety and effectiveness of ataluren in patients with Duchenne muscular dystrophy: single-center experience from Saudi Arabia

Objective Duchenne muscular dystrophy (DMD) is a rare X-linked neurodegenerative disorder caused by mutations in the DMD gene. This study examined the efficacy and safety of ataluren, the first oral treatment for DMD with nonsense mutations (nmDMD), in patients in the Middle East. Methods This retrospective longitudinal study assessed the outcomes of seven boys with nmDMD who received treatment with ataluren and follow-up at a single center since 2016. Results The median patient age at treatment initiation was 8.04 years (range: 3.3–9.92), and the median duration of exposure was 3.95 years (interquartile range = 4.42 years). Five patients were still ambulatory at the last follow-up. Ataluren was more effective in individuals with baseline 6-min walking distance (6MWD) ≥300 m, as these patients had smaller declines in 6MWD and North Star Ambulatory Assessment scores. Pulmonary function was well preserved in all patients, with no patients having forced vital capacity <60% at their last follow-up. Six patients maintained normal cardiac function, whereas one patient developed heart failure before starting ataluren treatment. Conclusions Our results demonstrated both the efficacy and safety of ataluren. Early initiation of ataluren treatment delayed the loss of ambulation and cardiorespiratory milestones.

Biophysical characterization of the dystrophin C-terminal domain: Dystrophin interacts differentially with dystrobrevin isoforms

Duchenne muscular dystrophy (DMD) gene encodes dystrophin, a large multi-domain protein. Its non-functionality leads to dystrophinopathies like DMD and Becker muscular dystrophy (BMD), for which no cure is yet available. A few therapies targeted towards specific mutations can extend the lifespan of patients, although with limited efficacy and high costs, emphasizing the need for more general treatments. Dystrophin's complex structure with poorly understood domains and the presence of multiple isoforms with varied expression patterns in different tissues pose challenges in therapeutic development. The C-terminal (CT) domain of dystrophin is less understood in terms of its structure-function, although it has been shown to perform important functional roles by interacting with another cytosolic protein, dystrobrevin. Dystrophin and dystrobrevin stabilize the sarcolemma membrane by forming a multi-protein complex called dystrophin-associated glycoprotein complex (DAGC) that is destabilized in DMD. Dystrobrevin has two major isoforms, alpha and beta, with tissue-specific expression patterns. Here, we characterize the CT domain of dystrophin and its interactions with the two dystrobrevin isoforms. We show that the CT domain is non-globular and shows reversible urea denaturation as well as thermal denaturation. It interacts with dystrobrevin isoforms differentially, with differences in binding affinity and the mode of interaction. We further show that the amino acid differences in the C-terminal region of dystrobrevin isoforms contribute to these differences. These results have implications for the stability of DAGC in different tissues and explain the differing symptoms associated with DMD patients affecting organs beyond the skeletal muscles.

Golodirsen restores DMD transcript imbalance in Duchenne Muscular Dystrophy patient muscle cells

BackgroundAntisense oligonucleotides (AON) represent a promising treatment for Duchenne muscular dystrophy (DMD) carrying out-of-frame deletions, but also show limitations. In a completed clinical trial golodirsen, approved by FDA to induce skipping of DMD gene exon 53 in eligible patients, we demonstrated increase in DMD expression and protein production, albeit with inter-patient variability.MethodsHere, we investigate further the golodirsen mechanism of action using myotubes derived from MyoD transfected fibroblasts isolated from DMD patients at the baseline of the clinical trial SRP-4053.ResultsWe confirm golodirsen’s selectivity and efficiency in removing only exon 53. For the first time in human cells, we revealed a significant reduction in the so called DMD “transcript imbalance”, in golodirsen-treated DMD muscle cultures. The transcript imbalance is a unique DMD phenomenon characterized by non-homogeneous transcript expression along its entire length and responsible for the reduced stability of the transcript. Our in-vivo study also showed that the efficiency of exon skipping did not always correspond to a proportional restoration of the dystrophin protein. Predominant nuclear localization of the DMD transcript, observed in patients and animal models, persists even after exon skipping.ConclusionAll these findings suggest challenges other than AON delivery for high level of protein restoration in DMD, highlighting the importance of investigating the biological mechanisms upstream of protein production to further enhance the efficiency of any AON treatment in this condition.

Characterization of Nonclinical Drug Metabolism and Pharmacokinetic Properties of Phosphorodiamidate Morpholino Oligonucleotides, a Novel Drug Class for Duchenne Muscular Dystrophy.

Eteplirsen, golodirsen, and casimersen are phosphorodiamidate morpholino oligomers (PMOs) that are approved in the United States for the treatment of patients with Duchenne muscular dystrophy (DMD) with mutations in the DMD gene that are amenable to exon 51, 53, and 45 skipping, respectively. Here we report a series of in vivo and in vitro studies characterizing the drug metabolism and pharmacokinetic (DMPK) properties of these three PMOs. Following a single intravenous dose, plasma exposure was consistent for all three PMOs in mouse, rat, and nonhuman primate (NHP), and plasma half-lives were similar for eteplirsen (2.0-4.1 h) and golodirsen (2.1-8.7 h) across species and more variable for casimersen (3.2-18.1 h). Plasma protein binding was low (<40%) for all three PMOs in mouse, rat, NHP, and human and was largely concentration independent. In the mdx mouse model of DMD, following a single intravenous injection, extensive biodistribution was observed in the target skeletal muscle tissues and the kidney for all three PMOs; consistent with the latter finding, the predominant route of elimination was renal. In vitro studies using liver microsomes showed no evidence of hepatic metabolism, and none of the PMOs were identified as inhibitors or inducers of the human cytochrome P450 enzymes or membrane drug transporters tested at clinically relevant concentrations. These findings suggest that key DMPK features are consistent for eteplirsen, golodirsen, and casimersen and provide evidence for the concept of a PMO drug class with potential application to novel exon-skipping drug candidates. SIGNIFICANCE STATEMENT: The PMOs eteplirsen, golodirsen, and casimersen share similar absorption, distribution, metabolism, and excretion and DMPK properties, which provides evidence for the concept of a PMO treatment class. A PMO drug class may support a platform approach to enhance understanding of the pharmacokinetic and pharmacodynamic behavior of these molecules. The grouping of novel agent series into platforms could be beneficial in the development of drug candidates for populations in which traditional clinical trials are not feasible.

Angiopoietin 1 Attenuates Dysregulated Angiogenesis in the Gastrocnemius of DMD Mice.

Duchenne muscular dystrophy (DMD) is a degenerative neuromuscular disease caused by a lack of functional dystrophin. Ang 1 paracrine signalling maintains the endothelial barrier of blood vessels, preventing plasma leakage. Chronic inflammation, a consequence of DMD, causes endothelial barrier dysfunction in skeletal muscle. We aim to elucidate changes in the DMD mouse's gastrocnemius microvascular niche following local administration of Ang 1. Gastrocnemii were collected from eight-week-old mdx/utrn+/- and healthy mice. Additional DMD cohort received an intramuscular injection of Ang 1 to gastrocnemius and contralateral control. Gastrocnemii were collected for analysis after two weeks. Using immunohistochemistry and real-time quantitative reverse transcription, we demonstrated an abundance of endothelial cells in DMD mouse's gastrocnemius, but morphology and gene expression were altered. Myofiber perimeters were shorter in DMD mice. Following Ang 1 treatment, fewer endothelial cells were present, and microvessels were more circular. Vegfr1, Vegfr2, and Vegfa expression in Ang 1-treated gastronemii increased, while myofiber size distribution was consistent with vehicle-only gastrocnemii. These results suggest robust angiogenesis in DMD mice, but essential genes were underexpressed-furthermore, exogenous Ang 1 attenuated angiogenesis. Consequentially, gene expression increased. The impact must be investigated further, as Ang 1 therapy may be pivotal in restoring the skeletal muscle microvascular niche.

First, do no harm: the role of preclinical animal models in predicting adverse events in gene therapy clinical trials for Duchenne muscular dystrophy and X-Linked myotubular myopathy

The occurrence of severe adverse events (SAEs) in patients with Duchenne muscular dystrophy (DMD), X-linked myotubular myopathy (XLMTM), and other neuromuscular diseases treated with adeno-associated virus (AAV) constructs has prompted studies to improve the safety and efficacy of gene therapy. Physicians have weighed the medical tenet of “first, do no harm” against the perspective of patients with progressive life-threatening conditions who may accept greater risk. Regarding SAE pathogenesis, discussion has focused on total AAV exposure and patient mutations more likely to induce immunity, while stressing the limitations of animal models in predicting adverse events. Therapeutic strategies for reducing side effects have employed more myotropic AAV serotypes and efficient transgenes. Other recommendations include excluding certain DMD gene mutations associated with SAEs and substituting less immunogenic transgenes such as utrophin (DMD) and myotubularin-related protein (XLMTM). For the sake of preclinical studies, emphasis has been placed on outbred rodents and larger animals that better predict immunity. Here, the absence of side effects in canine DMD and XLMTM models might be explained partly by phenotypic differences between affected humans and dogs. Specifically, dystrophin- and myotubularin-deficient dogs exhibit milder lesions, including less muscle fat deposition and the absence of hepatopathy, respectively, which could lead to reduced immune responses to AAV constructs. To better predict future problems, thought should be given to tracking early subclinical markers of the innate immune response, especially complement activation. Regardless of steps taken to improve the predictive value of animal models for SAEs, some questions will only be answered through human clinical trials after carefully considering the risk-benefit ratio.

PTPN1/2 inhibition promotes muscle stem cell differentiation in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a lethal disease caused by mutations in the DMD gene that encodes dystrophin. Dystrophin deficiency also impacts muscle stem cells (MuSCs), resulting in impaired asymmetric stem cell division and myogenic commitment. Using MuSCs from DMD patients and the DMD mouse model mdx, we found that PTPN1 phosphatase expression is up-regulated and STAT3 phosphorylation is concomitantly down-regulated in DMD MuSCs. To restore STAT3-mediated myogenic signaling, we examined the effect of K884, a novel PTPN1/2 inhibitor, on DMD MuSCs. Treatment with K884 enhanced STAT3 phosphorylation and promoted myogenic differentiation of DMD patient-derived MuSCs. In MuSCs from mdx mice, K884 treatment increased the number of asymmetric cell divisions, correlating with enhanced myogenic differentiation. Interestingly, the pro-myogenic effect of K884 is specific to human and murine DMD MuSCs and is absent from control MuSCs. Moreover, PTPN1/2 loss-of-function experiments indicate that the pro-myogenic impact of K884 is mediated mainly through PTPN1. We propose that PTPN1/2 inhibition may serve as a therapeutic strategy to restore the myogenic function of MuSCs in DMD.

Two novel deep intronic variants cause Duchenne muscular dystrophy by splice-altering mechanism

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness, due to mutations in the DMD gene, which encodes the dystrophin protein. While mutations within the coding regions of DMD have been extensively studied, recent focus has shifted to deep intronic variants for their potential impact on disease severity. Here, we characterize two deep intronic variants, c.8669-19_8669-24del and c.6439-1016_6439-3376del, in unrelated DMD patients. These variants were identified using targeted long-read sequencing on patients' DNA. RNA sequencing/reverse transcription polymerase chain reaction on RNA extracted from muscle biopsies revealed the presence of a pseudoexon or retention of part of the intron in the transcript, resulting in the introduction of premature termination codons. This study enhances our understanding of pseudoexon activation mechanisms in DMD and underscores the diverse genetic abnormalities contributing to the disease's complexity.

AAV gene therapy for Duchenne muscular dystrophy: the EMBARK phase 3 randomized trial

Duchenne muscular dystrophy (DMD) is a rare, X-linked neuromuscular disease caused by pathogenic variants in the DMD gene that result in the absence of functional dystrophin, beginning at birth and leading to progressive impaired motor function, loss of ambulation and life-threatening cardiorespiratory complications. Delandistrogene moxeparvovec, an adeno-associated rh74-viral vector-based gene therapy, addresses absent functional dystrophin in DMD. Here the phase 3 EMBARK study aimed to assess the efficacy and safety of delandistrogene moxeparvovec in patients with DMD. Ambulatory males with DMD, ≥4 years to <8 years of age, were randomized and stratified by age group and North Star Ambulatory Assessment (NSAA) score to single-administration intravenous delandistrogene moxeparvovec (1.33 × 1014 vector genomes per kilogram; n = 63) or placebo (n = 62). At week 52, the primary endpoint, change from baseline in NSAA score, was not met (least squares mean 2.57 (delandistrogene moxeparvovec) versus 1.92 (placebo) points; between-group difference, 0.65; 95% confidence interval (CI), −0.45, 1.74; P = 0.2441). Secondary efficacy endpoints included mean micro-dystrophin expression at week 12: 34.29% (treated) versus 0.00% (placebo). Other secondary efficacy endpoints at week 52 (between-group differences (95% CI)) included: Time to Rise (−0.64 (−1.06, −0.23)), 10-meter Walk/Run (−0.42 (−0.71, −0.13)), stride velocity 95th centile (0.10 (0.00, 0.19)), 100-meter Walk/Run (−3.29 (−8.28, 1.70)), time to ascend 4 steps (–0.36 (−0.71, −0.01)), PROMIS Mobility and Upper Extremity (0.05 (−0.08, 0.19); −0.04 (−0.24, 0.17)) and number of NSAA skills gained/improved (0.19 (−0.67, 1.06)). In total, 674 adverse events were recorded with delandistrogene moxeparvovec and 514 with placebo. There were no deaths, discontinuations or clinically significant complement-mediated adverse events; 7 patients (11.1%) experienced 10 treatment-related serious adverse events. Delandistrogene moxeparvovec did not lead to a significant improvement in NSAA score at week 52. Some of the secondary endpoints numerically favored treatment, although no statistical significance can be claimed. Safety was manageable and consistent with previous delandistrogene moxeparvovec trials. ClinicalTrials.gov: NCT05096221

Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy

Becker muscular dystrophy (BMD) is an X-linked disorder due to in-frame mutations in the DMD gene, leading to a less abundant and truncated dystrophin. BMD is less common and severe than Duchenne muscular dystrophy (DMD) as well as less investigated. To accelerate the search for innovative treatments, we developed a rat model of BMD by deleting the exons 45–47 of the Dmd gene. Here, we report a functional and histopathological evaluation of these rats during their first year of life, compared to DMD and control littermates. BMD rats exhibit moderate damage to locomotor and diaphragmatic muscles but suffer from a progressive cardiomyopathy. Single nuclei RNA-seq analysis of cardiac samples revealed shared transcriptomic abnormalities in BMD and DMD rats and highlighted an altered end-addressing of TMEM65 and Connexin-43 at the intercalated disc, along with electrocardiographic abnormalities. Our study documents the natural history of a translational preclinical model of BMD and reports a cellular mechanism for the cardiac dysfunction in BMD and DMD offering opportunities to further investigate the organization role of dystrophin in intercellular communication.

CRISPR-mediated megabase-scale transgene de-duplication to generate a functional single-copy full-length humanized DMD mouse model

BackgroundThe development of sequence-specific precision treatments like CRISPR gene editing therapies for Duchenne muscular dystrophy (DMD) requires sequence humanized animal models to enable the direct clinical translation of tested strategies. The current available integrated transgenic mouse model containing the full-length human DMD gene, Tg(DMD)72Thoen/J (hDMDTg), has been found to have two copies of the transgene per locus in a tail-to-tail orientation, which does not accurately simulate the true (single) copy number of the DMD gene. This duplication also complicates analysis when testing CRISPR therapy editing outcomes, as large genetic alterations and rearrangements can occur between the cut sites on the two transgenes.ResultsTo address this, we performed long read nanopore sequencing on hDMDTg mice to better understand the structure of the duplicated transgenes. Following that, we performed a megabase-scale deletion of one of the transgenes by CRISPR zygotic microinjection to generate a single-copy, full-length, humanized DMD transgenic mouse model (hDMDTgSc). Functional, molecular, and histological characterisation shows that the single remaining human transgene retains its function and rescues the dystrophic phenotype caused by endogenous murine Dmd knockout.ConclusionsOur unique hDMDTgSc mouse model simulates the true copy number of the DMD gene, and can potentially be used for the further generation of DMD disease models that would be better suited for the pre-clinical assessment and development of sequence specific CRISPR therapies.