Multiple sclerorcis is an autoimmune disease. In an autoimmune disease, the body mistakes some part of itself as a foreign invader. With MS, the part of the body that is mistaken as an invader is the protective covering of nerve fibers, the myelin sheath. It's possible that the initial cause of MS could be an overreaction to a real foreign invader, such as a virus or bacteria. This overreaction could cause the immune system to attack myelin in addition to the invading virus or bacteria even after the foreign invader is gone. Our genes may have a key role in MS. People from different ethnic groups have different tendencies to develop MS. People usually of European descent are twice as likely to have MS as African Americans and Asian Americans.
