The Muscular Dystrophy Association (MDA) held its MDA Clinical & Scientific Conference from March 19-22, 2023 to share research, cutting-edge medical advancements, and clinical care practices within the muscular dystrophy sphere. During the conference, shares Muscular Dystrophy News, one presentation centered around long-term safety and efficacy data from a Phase 1/2a proof-of-concept study evaluating SRP-9001 (delandistrogene moxeparvovec) for children with Duchenne muscular dystrophy (DMD). 

SRP-9001: A Brief Overview 

Developed by Sarepta Therapeutics in conjunction with Roche, SRP-9001 is an adeno-associated virus (AAV) gene therapy. When administered, SRP-9001 delivers smaller but functional versions of dystrophin to the muscle. Sarepta is hoping that the U.S. FDA will approve SRP-9001 by May 2023. 

Study Findings

Altogether, four boys were treated within this study. Their data was compared to other children with DMD who did not receive SRP-9001 treatment. Four-year study data highlighted the potential benefits of intravenous SRP-9001. The four treated boys saw improved motor function, ambulation, and walking/climbing abilities. In particular, SRP-9001 significantly affected climbing abilities, with the four boys seeing around a 60% improvement. Treated patients also lost no muscle function during the study. The children who did not receive SRP-9001 saw significant declines in motor function and ambulation. 

SRP-9001 was also safe and well-tolerated. No new safety signals were identified. The most common side effect associated with treatment was vomiting. 

An additional presentation centered around the Phase 1b ENDEAVOR trial, which also evaluated SRP-9001 for DMD. The presentation included data from 20 children, aged 4-7, with DMD who were still able to walk. Similarly to the other trial, SRP-9001 improved ambulation and motor function. 

What is Duchenne Muscular Dystrophy (DMD)?

Duchenne muscular dystrophy (DMD) is a rare inherited disorder characterized by low to no dystrophin production. Normally, dystrophin acts in a protein complex that plays a role in muscle fiber strength. Because people with DMD do not have enough dystrophin, their muscles become weakened. While DMD can occur in females, it is extremely rare; DMD mostly presents in boys. This disorder manifests by 6 years old. Symptoms can, but do not always, include:

• Enlarged calf muscles
• Fatigue
• A waddling gait
• Difficulty moving, walking, climbing, or changing positions
• Frequent tripping 
• Learning disabilities 
• Progressive muscle weakness that begins in the legs, pelvis, and thighs
• Muscle pain and stiffness 

Due to muscle wasting and weakening, individuals with DMD may eventually experience heart disease and respiratory failure. Current treatment options include respiratory support, heart medication, and steroids (among others). Gene therapies are also being evaluated in a number of clinical studies.