Eligibility Criteria

• Individuals meeting probable or definite criteria for Idiopathic Inflammatory Myopathies (IIM).
• Patient or parent/guardian must give informed consent to all or part of the study.
• Selected patients with undefined illnesses who may have weakness, myalgias, or an elevated CK may be evaluated to establish a diagnosis and, if they are found to have IIM, would be offered the opportunity to enter the study.
• For patients with at least one first-degree relative affected with IIIM, we will enroll all available first degree relatives (affected and unaffected) to participate in the genetics portion of the protocol.
• Severe medical disease requiring intensive care or any other conditions in which the drawing of blood or undergoing procedures needed for the study is not deemed medically appropriate will be excluded from the study.