Mixed connective tissue disease (MCTD) is a rare autoimmune disease that has features of at least two connective tissue diseases, including systemic lupus erythematosus, systemic sclerosis, polymyositis, dermatomyositis, and rheumatoid arthritis. It is characterized by the presence of elevated blood levels of a specific autoantibody, anti-U1 ribonucleoprotein, along with a mix of symptoms. MCTD is sometimes called an overlap disease because it has signs and symptoms of a combination of disorders. The symptoms of the separate diseases usually dont appear all at once, but tend to occur over a number of years, which can complicate diagnosis. The typical symptoms of MCTD include Raynaud syndrome, swollen fingers, and joint pain. The cause of MCTD is unknown, but it is thought to be an autoimmune disease that occurs due to immune activation from environmental factors in people with genetic predisposition. There is no cure for MCTD, but treatment depends on how severe the disease is and the organs involved. Early diagnosis and targeted treatment are associated with a better outcome.