Mixed connective tissue disease (MCTD) is a rare autoimmune disorder that is characterized by features commonly seen in three different connective tissue disorders: systemic lupus erythematosus, scleroderma, and polymyositis. Some affected people may also have symptoms of rheumatoid arthritis. Although MCTD can affect people of all ages, it appears to be most common in women under age 30. Signs and symptoms vary but may include Raynaud’s phenomenon; arthritis; heart, lung and skin abnormalities; kidney disease; muscle weakness, and dysfunction of the esophagus. The cause of MCTD is currently unknown. There is no cure but certain medications may help manage the symptoms.