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Gene Pinpointed in Adult Muscular Dystrophy

Causes of two related forms of disease linked

FRIDAY, Aug. 3, 2001 (HealthDayNews) -- Scientists say they've pinpointed the gene for an elusive form of myotonic dystrophy, the most common adult version of muscular dystrophy.

The finding now connects two forms of the muscle disorder to errors in RNA, which translates information from its DNA sister molecules into the proteins that carry out genetic instructions. These particular illnesses are caused by problems in stretches of DNA that have no known function.

The discovery appears in today's issue of Science.

Myotonic dystrophy, or DM, affects about one in every 8,000 adults. The disorder causes muscular dystrophy's characteristic muscle wasting and other symptoms, including cataracts, faulty heartbeats, muscle spasms and an increased risk of diabetes.

Most muscular dystrophy cases are the result of flaws in a protein called dystrophin, which is key to healthy muscle function.

That turned out not to be the case with two types of DM.

Scientists first discovered a gene defect for one form of DM in 1992, but the error involved a stretch of genetic material that didn't code for a protein at all. What's more, many people with symptoms of the disease failed to test positive for the mutation, leading researchers to hunt for something else to explain both illnesses.

The general area of the DM2 mutation was first identified in 1998. In the latest work, Laura P.W. Ranum and her colleagues at the University of Minnesota found the more precise culprit: a massively elongated chain of repetitious genetic material in a gene that produces a molecule that helps regulate other genes.

When RNA translates a DNA information, filler material usually is destroyed, leaving only the RNA necessary for protein synthesis.

"But in DM2, the RNA is made and it accumulates in the nucleus of cell," Ranum says. The same goes for DM1.

"The extra RNA binds to proteins that it normally wouldn't, and that messes up the biology of the cell," Ranum says.

But researchers aren't sure whether the globs of RNA protect or destroy the cells. Only more studies will tell.

Susan Hesterlee, director of research development for the Muscular Dystrophy Association of America, says the finding is an important step in identifying patients with DM.

"We think probably the most immediate benefit is likely the increased diagnosis in people who test negative for the first form" of the condition. Both varieties are difficult to identify by symptoms alone.

"The other major implication is that this is the first evidence that RNA on its own can be the cause of a disease," Hesterlee says.

What To Do

For more on DM, visit the International Myotonic Dystrophy Organization.

To learn more about DM and other forms of muscular dystrophy, try the National Institutes of Health or the Muscular Dystrophy Association of America.

SOURCES: Interviews with Laura P. W. Ranum, Ph.D., associate professor, genetics, cell biology and development, University of Minnesota, Minneapolis; Susan Hesterlee, Ph.D., director of research development, Muscular Dystrophy Association of America, Tucson, Ariz.; Aug. 3, 2001 Science
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