Year 1

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophies and the most common fatal genetic disorder of childhood. Approximately one in every 5,000 boys worldwide is affected with DMD often caused by spontaneous mutations. Extrapolating from population based studies, there are over 15,000 people currently living with DMD in the US alone. DMD is a devastating and incurable muscle-wasting disease caused by genetic mutations in the gene that codes for dystrophin, a protein that plays a key role in muscle cell health. Children with DMD are typically weaker than normal by age three, and progressive muscle weakness of the legs, pelvis, arms, neck and other areas result in most patients requiring full-time use of a wheelchair by age 11. Eventually, the disease progresses to complete paralysis and increasing difficulty in breathing due to respiratory muscle dysfunction and heart failure, with death usually occuring before the age of 25. While corticosteroids can slow disease progression and supportive care can extend lifespan and improve quality of life, no therapies exist that address the primary defect or dramatically alter the debilitating disease course.
Exon-skipping is a promising therapy that aims to repair the expression of the dystrophin protein by repairing the RNA. We have identified a combination therapy that improves the effectiveness of exon-skipping therapy in mouse muscle and in human DMD patient stem cell derived muscle cells in culture. In exon skipping the genetic defect is directly repaired inside of each muscle cell. Thus, this therapy is predicted to lessen the disease severity.
Early research on this combination therapy for Duchenne used human DMD patient stem cells including: reprogrammed patient fibroblasts converted into muscle-like cells in culture or when transplanted in mice. We have made a panel of these cells with different mutations to assess efficacy in a range of DMD mutations. These cells are necessary because each patient’s mutation in the dystrophin gene is different. In order to know who will or will not benefit from the exon-skipping therapy, individualized cell culture and mouse transplant models from a number of DMD patients must be created to effectively characterize the combination therapy. At 12 months of the CIRM-funded research program, we have established optimal oral dosing of dantrolene that is compatible with 6 month long-term testing in dystrophic mice and optimal dosing of morpholino antisense oligo. The combination therapy is well tolerated by mice, and dystrophin rescue is increased in short term experiments. 6 month treatment experiments are being initiated that will test if the induction of dystrophin can reduce the severity of the disease in the dystrophic mice. Since exon-skipping therapy relies on knowing individual patients exact DNA mutation, this is a form of personalized genetic medicine. While the specific combination therapy being developed here will treat up to 13% of DMD patients, the strategy is likely to be generalized to be able to treat up to 70% of DMD patients.