Many people only think about the debilitating disease muscular dystrophy during the Jerry Lewis Labor Day Telethon. Yet myotonic dystrophy, the most prevalent form of muscular dystrophy, affects one in 8,000 people worldwide.

In 1992 researchers identified the genetic mutation that causes myotonic dystrophy. But scientists have not yet been able to understand how the mutation on chromosome 19 causes the disease symptoms.

"We know the genetic mutation causes myotonic dystrophy," says Dr. Stephen Tapscott, associate member of the Fred Hutchinson Cancer Research Center and associate professor of neurology. "The question is, how can a single genetic mutation have so many clinical effects?"

The wide variety of myotonic dystrophy symptoms includes muscular weakness and degeneration, debilitating fatigue, cataracts and heart disorders. Considering the seemingly unrelated symptoms of the disease, Tapscott's research focuses on whether the mutation causes the disease by affecting the expression of neighboring genes.

"The muscle phenotype, cardiac phenotype and the optical cataracts are all characteristic of this disease," says Tapscott. "In a mouse model we found that the chromatin is more tightly compacted in the region of the mutation, suggesting that it might be shutting off other genes in the area."

Tapscott hypothesizes that the repeat expansion interferes with other genes while simultaneously producing a toxic effect on skeletal muscle tissue. The conundrum then is the few myotonic dystrophy patients who do not have the genetic mutation on chromosome 19.

"Our research emphasizes that one simple mutation can have several different mechanisms for creating very complex diseases such as myotonic dystrophy," says Tapscott. "The troublesome problem with this model is that some families with myotonic dystrophy do not have the specific mutation discovered in 1992. These families share another mutation that reproduces the various characteristic symptoms of the disease."

Tapscott received his Ph.D. in anatomy and M.D. from the University of Pennsylvania School of Medicine in 1982. He completed an internship and neurology residency at the Hospital of the University of Pennsylvania. Tapscott joined the Fred Hutchinson Cancer Research Center in 1986 as a staff scientist in the Basic Science Division. In 1986 he also became an acting instructor and senior fellow of medicine in the Division of Neurology.

Tapscott has received several awards, including a Clinical Investigator Development Award from the National Institutes of Health. He has been a member of several committees for the Muscular Dystrophy Association and was elected to active membership in the American Neurologic Association in 1999.