A new gene therapy technique that has shown promise in skin disease and hemophilia might one day be useful for treating muscular dystrophy, according to a new study by researchers at Stanford University School of Medicine.
In the study, scheduled to be published online in the Proceedings of the National Academy of Sciences the week of Jan. 2, the researchers used gene therapy to introduce a healthy copy of the gene dystrophin into mice with a condition that mimics muscular dystrophy. The dystrophin gene is mutated and as a result produces a defective protein in the roughly 20,000 people in the United States with the most common form of the disease.
Using gene therapy to treat muscular dystrophy isn't a new idea. Thomas Rando, MD, PhD, associate professor of neurology and neurological sciences, said that researchers have tried several different techniques with variable success. One hurdle is getting genes into muscle cells all over the body. Another is convincing those cells to permanently produce the therapeutic protein made by those genes.
The gene therapy technique Rando and postdoctoral fellow Carmen Bertoni, PhD, used was developed by Michele Calos, PhD, associate professor of genetics. One of the main advantages of this method is that it could potentially provide a long-term fix for a variety of genetic diseases, including muscular dystrophy.
In muscular dystrophy, the muscle cells break down and are slowly replaced by fat. Eventually people with the disease are confined to a wheelchair and usually die in their 20s. There is currently no effective treatment for the disease, which explains why gene therapy remains a hope despite the significant hurdles.
Rando said the PNAS paper highlights an additional requirement for any gene therapy to be successful: the introduced gene must produce healthy dystrophin protein in large quantities in order to repair the entire muscle cell. Previous muscular dystrophy gene therapy studies did not look at whether the introduced dystrophin spread along the entire length of the muscle cell, which can be many millimeters long in mice or inches long in humans.
In the upcoming paper Bertoni used a standard gene therapy method to introduce two genes - dystrophin and a gene that makes a glowing protein - into mice with a mouse version of muscular dystrophy. She found that in mice producing insufficient dystrophin, she could see the glowing protein slowly leak out of the cell. This leakiness is a sign that the cell is not healed. In contrast, when she used Calos' gene therapy technique to introduce the genes, the muscle cell contained high levels of dystrophin distributed along the length of the cell and the glowing protein stayed within the cell, suggesting that the abundant dystrophin repaired the ailing muscle.