Epidemiology

Rigorous epidemiologic studies on the incidence and prevalence of overlap syndromes have not been done, and data are lacking. However, they are all rare conditions. One population-based study following a US cohort between 1985-2014 found the annual incidence of mixed connective tissue disease (MCTD) was 1.9 per 100,000.[5]​ At a tertiary US referral center, it was found to be less common than systemic lupus erythematosus (SLE), as common as systemic sclerosis, and more common than polymyositis.[6]​ Like SLE, MCTD is far more common in women (female to male ratio ranging from 3.3:1 to 5:1).[5][7]​​​[8]​​​​ No familial clustering has been noted.

Antisynthetase antibodies (including anti-Jo-1, an antibody directed against histidyl-tRNA synthetase) are found in 5% to 20% of patients with polymyositis or dermatomyositis.[9]

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