Myasthenia gravis is an autoimmune disease where antibodies block the acetylcholine receptors in the synapses of the nerves that control muscles. It is very rare, occurring in only about one out of every 1 to 10 million people, and can easily be mistaken for other diseases that affect nerves in muscles. It is very much an "equal opportunity" disease and has the same incidence in either sex, all ethnic groups, and all age groups. The symptoms of the disease may be intermittent and, in many cases, the disease will resolve itself after a few years even without treatment.