HLA-DRB1 and mixed connective tissue disease: The diplotype frequency of HLA-DRB1*09:01-DQB1*03:03/DRB1*15:01-DQB1*06:02 was higher in MCTD patients (P = 0.0178, OR 3.72, 95% CI 1.28‒10.85), but DRB1*09:01-DQB1*03:03/DRB1*15:02-DQB1*06:01 was not.