Efficacy and safety of deflazacort vs prednisone and placebo for Duchenne muscular dystrophy

Duchenne and Becker Muscular Dystrophies: A Review of Animal Models, Clinical End Points, and Biomarker Quantification

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are neuromuscular disorders that primarily affect boys due to an X-linked mutation in the DMD gene, resulting in reduced to near absence of dystrophin or expression of truncated forms of dystrophin. Some newer therapeutic interventions aim to increase sarcolemmal dystrophin expression, and accurate dystrophin quantification is critical for demonstrating pharmacodynamic relationships in preclinical studies and clinical trials. Current challenges with measuring dystrophin include the variation in protein expression within individual muscle fibers and across whole muscle samples, the presence of preexisting dystrophin-positive revertant fibers, and trace amounts of residual dystrophin. Immunofluorescence quantification of dystrophin can overcome many of these challenges, but manual quantification of protein expression may be complicated by variations in the collection of images, reproducible scoring of fluorescent intensity, and bias introduced by manual scoring of typically only a few high-power fields. This review highlights the pathology of DMD and BMD, discusses animal models of DMD and BMD, and describes dystrophin biomarker quantitation in DMD and BMD, with several image analysis approaches, including a new automated method that evaluates protein expression of individual muscle fibers.

Seeking a better landscape for therapy development in neuromuscular disorders

Although the neuromuscular field has seen accelerated approval of a drug for Duchenne muscular dystrophy (DMD) and full approval of one for spinal muscular atrophy, these experiences have shown that objective data and an adequate level of effect are essential for drug approval and reimbursement. The appropriateness and validity of biomarkers and clinically meaningful endpoints and an understanding of disease progression rates all played essential roles in the levels of evidence for these drugs. Such tools are best developed through integration of clinical data. The siloing of clinical data for rare neuromuscular diseases represents a considerable barrier to achieving better care and novel therapies for patients living with neuromuscular diseases. We discuss a data-sharing model implemented for DMD and urge cultural changes in the ways natural history and clinical trial data are collected and shared across all neuromuscular diseases in order to benefit the primary stakeholder, the patient. Muscle Nerve 57: 16-19, 2018.

Newborn screening for Duchenne muscular dystrophy in China: follow-up diagnosis and subsequent treatment

BACKGROUND

Newborn screening for Duchenne muscular dystrophy (DMD) is currently being initiated in Zhejiang Province, China and is under consideration in other countries, including the United States. As China begins to implement DMD newborn screening (DMD-NBS), there is ongoing discussion regarding the steps forward for follow up care of positively identified patients as well as false positive and false negative results.

DATA SOURCES

Relevant papers related to DMD-NBS, and NBS in China were reviewed in PubMed.

RESULTS

The current state of DMD-NBS is discussed, along with the steps needed to effectively screen infants for this disease in China, recommendations for establishment of follow up care in patients with positive and negative screens, and measurement of patient outcomes.

CONCLUSIONS

Zhejiang Province, China is ready to implement DMD-NBS. Future challenges that exist for this program, and other countries, include the ability to track patients, assist with access to care, and ensure adequate follow-up care according to evidence-based guidelines. In addition, China's large rural population, lack of specialty providers, and difficulty in educating patients regarding the benefits of treatment create challenges that will need to be addressed.

Intermittent glucocorticoid steroid dosing enhances muscle repair without eliciting muscle atrophy

Glucocorticoid steroids such as prednisone are prescribed for chronic muscle conditions such as Duchenne muscular dystrophy, where their use is associated with prolonged ambulation. The positive effects of chronic steroid treatment in muscular dystrophy are paradoxical because these steroids are also known to trigger muscle atrophy. Chronic steroid use usually involves once-daily dosing, although weekly dosing in children has been suggested for its reduced side effects on behavior. In this work, we tested steroid dosing in mice and found that a single pulse of glucocorticoid steroids improved sarcolemmal repair through increased expression of annexins A1 and A6, which mediate myofiber repair. This increased expression was dependent on glucocorticoid response elements upstream of annexins and was reinforced by the expression of forkhead box O1 (FOXO1). We compared weekly versus daily steroid treatment in mouse models of acute muscle injury and in muscular dystrophy and determined that both regimens provided comparable benefits in terms of annexin gene expression and muscle repair. However, daily dosing activated atrophic pathways, including F-box protein 32 (Fbxo32), which encodes atrogin-1. Conversely, weekly steroid treatment in mdx mice improved muscle function and histopathology and concomitantly induced the ergogenic transcription factor Krüppel-like factor 15 (Klf15) while decreasing Fbxo32. These findings suggest that intermittent, rather than daily, glucocorticoid steroid regimen promotes sarcolemmal repair and muscle recovery from injury while limiting atrophic remodeling.

Progress toward Gene Therapy for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) has been a major target for gene therapy development for nearly 30 years. DMD is among the most common genetic diseases, and isolation of the defective gene (DMD, or dystrophin) was a landmark discovery, as it was the first time a human disease gene had been cloned without knowledge of the protein product. Despite tremendous obstacles, including the enormous size of the gene and the large volume of muscle tissue in the human body, efforts to devise a treatment based on gene replacement have advanced steadily through the combined efforts of dozens of labs and patient advocacy groups. Progress in the development of DMD gene therapy has been well documented in Molecular Therapy over the past 20 years and will be reviewed here to highlight prospects for success in the imminent human clinical trials planned by several groups.

Emerging new tools to study and treat muscle pathologies: genetics and molecular mechanisms underlying skeletal muscle development, regeneration, and disease

Skeletal muscle is the most abundant tissue in our body, is responsible for generating the force required for movement, and is also an important thermogenic organ. Skeletal muscle is an enigmatic tissue because while on the one hand, skeletal muscle regeneration after injury is arguably one of the best-studied stem cell-dependent regenerative processes, on the other hand, skeletal muscle is still subject to many degenerative disorders with few therapeutic options in the clinic. It is important to develop new regenerative medicine-based therapies for skeletal muscle. Future therapeutic strategies should take advantage of rapidly developing technologies enabling the differentiation of skeletal muscle from human pluripotent stem cells, along with precise genome editing, which will go hand in hand with a steady and focused approach to understanding underlying mechanisms of skeletal muscle development, regeneration, and disease. In this review, I focus on highlighting the recent advances that particularly have relied on developmental and molecular biology approaches to understanding muscle development and stem cell function. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.