Mixed connective tissue disease (MCTD), also known as Sharp syndrome, is an autoimmune overlap syndrome characterized by the presence of symptoms of systemic lupus erythematosus (SLE), systemic scleroderma, rheumatoid arthritis, and polymyositis. It was originally described as a distinct entity by Sharp et al in 1972.

The annual incidence of MCTD is estimated to be 1.9 per 100 000 population. MCTD is more common in females than males (5:1) and presents most commonly in the second and third decades of life.

The sequential appearance of symptoms makes diagnosis challenging, but the basic hallmarks include elevated antinuclear antibodies (ANA), hand / joint findings such as Raynaud phenomenon and swelling, and nonspecific symptoms including fever, fatigue, and myalgias. MCTD has a wide-ranging clinical presentation, from minimally symptomatic to life-threatening cardiac, kidney, or pulmonary involvement. Evolution to other connective diseases is infrequent. MCTD has been associated with HLA-DR4 and HLA-DR2.

Pulmonary hypertension is the most serious complication (occurring in up to 25% of patients) and a major cause of death in MCTD.