Dr. Jerry Mendell of Nationwide Children’s Research Institute recently presented data from a ground-breaking PPMD-funded study demonstrating that a modified virus carrying the gene for follistatin can improve performance on the 6 minute walk test in study participants with Becker muscular dystrophy. This is the first time a gene therapy has demonstrated an improvement in function in a muscular dystrophy.
Previously, animal studies demonstrated that a molecule called follistatin could be used to block myostatin in the muscles, leading to increased muscle size and strength, even in mice that lacked dystrophin. For the clinical study, Dr. Mendell and colleagues injected the modified virus into 12 places in the quadriceps muscle in 6 men with Becker muscular dystrophy, where it entered the muscle cells and allowed those cells to make and secrete follistatin. The investigators chose to start with Becker muscular dystrophy because those with BMD have significantly weak quadriceps muscles compared to the surrounding leg muscles and improving quad strength should lead to improved walking abilitly. The participants were all over 18 years of age and had to be able to complete the 6 minute timed walk. The first three participants received a low dose of gene therapy and the second three participants received a higher dose.
From the group that received the low dose, at the end of the first year one participant was able to walk 58 meters longer, one could walk 125 meters longer and the third saw no change in walking ability. In the high dose group, similarly, one participant could walk 30 meters longer, one could walk 108 meters longer and the third saw no change. When magnetic resonance imaging was used to visualize the participants’ muscle, it was clear that the two participants who showed no change in walking ability also has the greatest amount of fibrosis in their muscles. Muscle biopsies showed a decrease in fibrosis compared to the start in the two participants who improved the most in their 6 minute timed walk tests. Importantly, there has been speculation that forcing the muscle cells to become larger and stronger without fixing the underlying lack of dystrophin may overtax the muscle repair system. Dr. Mendell showed that there was no evidence that the muscle satellite stem cells that are involved in muscle repair were reduced in number.
Dr. Mendell is currently planning a similar trial in Duchenne muscular dystrophy, but will plan to inject the follistatin gene into gluteal muscles, thigh muscles and the tiabialis anterior muscles because all of these muscle groups are strongly affected in Duchenne. He speculates that even muscle groups that are not injected directly may show some benefit since follistatin is secreted and can circulate through the body. Animal studies showed evidence of these “remote effects” away from the site of injection.
As always, PPMD will keep you up to date on the next steps in this exciting research.