Additionally, the frequency of HLA-DRB1*04:01–DQB1*03:01, DRB1*09:01–DQB1*03:03/DRB1*15:01–DQB1*06:02, DRB1*15:02–DQB1*06:01 was higher in MCTD patients (P = 4.97 × 10–6, OR 5.17, 95% CI 2.58‒10.35). This evidence concerns the gene HLA-DRB1 and mixed connective tissue disease.