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. In a study appearing this week in the online early edition of Proceedings of the National Academy of Sciences, researchers unveil a new cause discovered 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," said Dr. Stephen Cannon, chairman of neurology at UT Southwestern, who studied the consequences of the genetic mutation. "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 discovery may open new avenues of investigation into the disease and, possibly, new therapeutic approaches, said Dr. Cannon.

The patient in whom the genetic mutation was discovered is a 20-year-old woman diagnosed with congenital myasthenic syndrome a subset of illness under the disease known as myasthenia gravis. Myasthenia gravis, which literally means grave muscle weakness, affects about 37,000 Americans. People who have this disease 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 both genders. It most commonly affects young adult women between the ages of 20 and 40 and older men in their 50s and 60s, but it can occur at a
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Contact: Rachel Horton
rachel.horton@utsouthwestern.edu
214-648-3404
UT Southwestern Medical Center
19-May-2003