Myasthenia gravis, or MG, is a type of autoimmune disease. It stops nerve signals that normally travel to certain muscles. This causes the muscles to become weak. The muscles tend to get weaker in periods of activity and get stronger after periods of rest. There is no cure for MG, but long-term remission is possible. Remission is a period of time with no symptoms. MG can affect people of any age or ethnic group, but it’s more common in people in their 20s, 60s, and 70s.