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.
Myasthenia gravis is an autoimmune disease, which means the body's defense mechanism, the immune system, begins to attack the body's own tissues instead of foreign invaders, such as viruses. In myasthenia gravis, the immune system attacks the acetylcholine receptors with specific antibodies. Some of the receptors are destroyed or blocked, which means that the chemical message cannot be received. Therefore, muscles do not contract properly and become weak. It has been estimated that up to 80% of the receptors can be damaged in this disease.
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