in part, determined genetically, thus sle is more likely in patients with hla-dr3 and scleroderma in patients with hla-dr5. epidemiology the prevalence of mctd is higher than that of dermatomyositis and lower than that of sle. in a 2011 norwegian study, the prevalence of mctd was 3.8 per 100,000 adults, with an incidence of 2.1 per million per year. mctd is much more frequent in women than in men at between a 3:1 to 16:1 ratio, and in women younger than 50. the general age at onset is around 15–25 years old.