Background: * Like other complex diseases, autoimmune diseases are the result of numerous causes, including genetic and environmental factors. Some researchers believe that people who are susceptible to autoimmune disorders develop them when the body reacts to environmental or other factors by creating white blood cells that attack the body s own tissues, which then progresses to autoimmune diseases. These im...

Summary: This study will evaluate subjects with adult- and childhood-onset myositis to learn more about their cause and the immune system changes and medical problems associated with them. Myositis is an inflammatory muscle disease that can damage muscles and other organs, resulting in significant disability. Children or adults with polymyositis or dermatomyositis or a related condition may be evaluated un...