Health Watch -- Muscle Weakness

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A newly discovered cause for a muscle disorder could lead to new treatments.

About 37,000 Americans suffer from a condition called myasthenia gravis, which causes severe muscle weakness. People with this condition may have trouble walking long distances, holding up their arms or breathing. In some cases, facial muscles and the muscles that control swallowing are affected. It most often affects young women between the ages of 20 and 40, and older men.

This condition usually is the result of an autoimmune attack in which the body's own immune system attacks and damages the connection between nerves and muscles, so that the muscle never receives signals from nerves directing the muscles to move. In people without this disorder, the signal from the nerve causes a response in the muscle. That triggers electrical impulses that travel the length of the muscle.

But now researchers at UT Southwestern Medical Center at Dallas and the Mayo Clinic have found a new cause for this condition. They found a patient with a form of myasthenia gravis in which the connection between the nerves and the muscles was intact. The problem was that the signal didn't get transmitted the rest of the way through the muscles.

Researchers then found a genetic mutation that kept the "gate" to the rest of the muscle permanently closed so that electrical current wasn't carried throughout the muscle.
This discovery gives researchers another avenue to explore as they try to understand this condition. The result could be new treatment approaches.