HLA-DRB1 and mixed connective tissue disease: The frequency of HLA-DRB1*09:01/DRB1*15:01 (P = 0.0112, OR 3.75, 95% CI 1.38‒10.22) was also higher in MCTD patients, but that of DRB1*09:01/DRB1*15:02 was not.