SAN FRANCISCO, Oct. 19 -- Animal muscles crippled due to a form of muscular dystrophy can be repaired, both in size and strength, through an innovative gene therapy, according to a team of investigators from the Children's National Medical Center in Washington, D.C., and the University of Pittsburgh. The results, presented Friday, Oct. 22, at the annual meeting of the American Society of Human Genetics (ASHG) in San Francisco, offer the first evidence that whole muscles can be functionally rescued in any type of muscular dystrophy using an extremely safe gene vector.
"We are very excited by these preliminary results, which suggest that we can use a non-toxic virus to safely shuttle a gene for an important muscle protein that is improperly made in people suffering limb girdle muscular dystrophy," said Devin Dressman, who is presenting the results and who is a graduate student at the Center for Genetic Medicine, Children's National Medical Center, and the University of Pittsburgh's School of Medicine. "These findings demonstrate the feasibility of using the gene therapy approach in treating affected patients."
In their experiments, the investigators used a non-replicating adeno-associated virus (AAV) to carry a gene for the sarcoglycan protein, an important constituent of skeletal muscle. Unlike several other available viral vectors, AAV does not provoke an immune response from the body, either by itself or when it resides within cells. Furthermore, it can infect non-dividing cells and it takes up residence permanently, thus allowing long-term production of a critical protein.
In a collaborative effort, Xiao Xiao, Ph.D., assistant professor of molecular genetics and biochemistry at the University of Pittsburgh, injected this AAV-sarcoglycan gene combination into hamster leg muscles ravaged by limb girdle dystrophy. After one month, Jon Watchko, M.D., associate professor of pediatrics and of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh, tested the treated muscles and found that they increased nearly 100 percent in strength and resumed normal size.
Limb girdle muscular dystrophy affects several thousand people in the United States, causing rapid degeneration of the large muscles attached to the shoulders and hips. Currently no effective treatment exists for this fatal disorder. The Children's/Pitt team of investigators is currently planning a gene therapy treatment protocol based on the experimental findings. This approach may be applied to other forms of muscular dystrophy as well, such as the more common lethal condition, Duchenne muscular dystrophy, which affects 20,000 boys in this country and is considered one of the most prevalent diseases to result from a single gene defect.
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