The frequencies of heterozygosity for HLA-DRB1*04:01/*15 (P = 1.88 × 10–7, OR 81.54, 95% CI 4.74‒1402.63) and DRB1*09:01/*15 (P = 0.0061, OR 2.94, 95% CI 1.38‒6.25) were also higher in MCTD patients. This evidence concerns the gene HLA-DRB1 and mixed connective tissue disease.