The complication of interstitial lung disease (ILD) in polymyositis/dermatomyositis (PM/DM) is associated with anti–aminoacyl–transfer RNA synthetase (anti‐aaRS) antibody or anti–melanoma differentiation–associated gene 5 (anti–MDA‐5) antibody positivity. Anti–MDA‐5 antibody is associated with clinically amyopathic DM and fatal outcome due to rapidly progressive ILD in Asian populations. The association between genetic factors and anti–MDA‐5 antibody–positive DM is unclear. This study was undertaken to investigate the HLA–DRB1 genotype in patients with anti–MDA‐5 antibody–positive DM.

We examined genetic differences among 17 patients with anti–MDA‐5 antibody–positive DM, 33 patients with anti‐aaRS antibody–positive PM/DM, 33 patients with PM/DM without anti‐aaRS antibody or ILD, and 265 healthy controls.

The frequencies of HLA–DRB1*0101 and DRB1*0405 were 29% and 71%, respectively, in patients with anti–MDA‐5 antibody–positive DM, which were higher than the frequencies in healthy controls (10% and 25%, respectively). Among the 17 patients with anti–MDA‐5 antibody–positive DM, 16 (94%) harbored either the DRB1*0101 or DRB1*0405 allele. The combined frequency of the DRB1*0101 allele and the DRB1*0405 allele was significantly higher in patients with anti–MDA‐5 antibody–positive DM than in patients with PM/DM without anti‐aaRS antibody or ILD, with an odds ratio (OR) of 42.7 (95% confidence interval [95% CI] 4.9–370.2) (P = 1.1 × 10⁻⁵), or in patients with anti‐aaRS antibody–positive PM/DM (OR 13.3 [95% CI 1.6–112.6], P = 4.5 × 10⁻³).

Our findings indicate that HLA–DRB1*0101/*0405 is associated with susceptibility to anti–MDA‐5 antibody–positive DM in the Japanese population.