Myasthenia gravis is an autoimmune disorder that causes muscle weakness. An autoimmune disorder is one in which the body produces antibodies against its own tissues.

What is going on in the body?

For unknown reasons, myasthenia gravis causes a person's immune system to produce antibodies that attack the muscles in his or her body. The antibodies destroy the part of the muscle that receives signals from the nerves. When a muscle is used a great deal, it may not work properly. After a period of rest, the muscle generally improves.

What are the causes and risks of the disease?

No one knows why a person with myasthenia gravis produces antibodies that attack the muscles. This disorder occurs more often in women than in men. It usually starts in women during their childbearing years. In men, the disease most often starts in middle age. Rarely, a child may be born with myasthenia gravis from a genetic defect.

New research findings suggest that autoimmune disorders may be set off by a transfer of cells between the fetus and the mother during pregnancy. The study involved women with scleroderma, an autoimmune disorder that affects the skin. These women have more fetal cells in their blood even decades after a pregnancy than women who don't have scleroderma. While further research is needed to confirm these findings, the study does offer an explanation for the much higher incidence of autoimmune disorders in women than in men.

Symptoms can be worsened by a number of factors, such as: