Debilitating condition traced to mutation.

• Position: Muscular System - Myasthenia

A novel genetic mutation that leads to a debilitating muscle condition known as myasthenia has been discovered by researchers from the University of Texas Southwestern Medical Center at Dallas and the Mayo Clinic, Minneapolis, Minn. Myasthenia, a severe form of muscle weakness, usually results from an autoimmune attack against the nerve-muscle junction in which the nerve's communication to the muscle is broken down.

A unique cause for this disease has been identified in a single patient: a genetic mutation leading to a shutdown in muscle responsiveness to the nerve's electrical impulses. "This was a surprise in that it's a totally different mechanism for a well researched disease," attests Stephen Cannon, chairman of neurology at UT Southwestern. "Until this study, every single case of myasthenia ever examined had been attributed to a reduction in what's called the safety factor of neurotransmission, or how reliably the nerve talks to the muscle."

The advance may open new avenues of investigation into the disease and, possibly, new therapeutic approaches. The patient in whom this mutation was traced is a 20-year-old woman diagnosed with congenital myasthenic syndrome. Myasthenia gravis, which literally means grave muscle weakness, affects about 37,000 Americans. People afflicted often cannot walk long distances or hold up their arms, and some have difficulty breathing. Muscles that control eye and eyelid movements, facial expression, chewing, talking, and swallowing are often, but not always, involved.

Myasthenia gravis occurs in all ethnic groups and in both men and women. It most commonly affects young adult females between the ages of 20 and 40 and older males...