Genotype frequencies of HLA-DRB1*04:01/DRB1*15:01 (P = 0.0022, OR 33.08, 95% CI 1.77‒619.03) and DRB1*04:01/DRB1*15:02 (P = 0.0001, OR 48.65, 95% CI 2.72‒870.21) were higher in MCTD patients than in controls. The gene discussed is HLA-DRB1; the disease is mixed connective tissue disease.