What Is It?
Myasthenia gravis is a chronic (long-lasting) and rare disease that affects the way muscles respond to signals from nerves, leading to muscle weakness. The disease can occur at any age, but it mainly affects women between ages 20 and 40. After age 50, men are more likely to get the disease.
Normal muscle movement relies on chemical signals from the nerves. Nerve signals cause the nerve endings to release a chemical called acetylcholine into the small space between the nerve and the muscle. This chemical binds to special acetylcholine receptors on the muscle cells and causes the muscle to contract.