Mixed connective tissue disease (MCTD) is a autoimmune disorder that causes overlapping features of three connective tissue disorders: lupus, scleroderma, and polymyositis. MCTD may also have features of rheumatoid arthritis. This condition is most often diagnosed in women in their 20’s and 30’s. Occasionally, children are affected. At this time the cause of this condition is unknown.
Source: NIH.gov