Human leukocyte antigen in Japanese patients with idiopathic inflammatory myopathy

<b>Objective:</b> The human leukocyte antigen (HLA) is the strongest genetic risk factor for idiopathic inflammatory myopathy (IIM), and different <i>HLA</i> alleles have been reported to be associated with IIM susceptibility among different ethnic groups. In this study, we have investigated HLA alleles associated with IIM in Japanese patients. <b>Methods:</b> Genotyping of <i>HLA-DRB1</i> and <i>DPB1</i> were performed in 252 Japanese IIM patients (166 dermatomyositis [DM] and 86 polymyositis [PM] patients) and the association was analyzed with comparison to controls (<i>n</i> = 1026 for <i>DRB1</i> and <i>n</i> = 413 for <i>DPB1</i>). <b>Results:</b><i>DRB1*08:03</i> was associated with IIM (<i>p</i> = 1.60 × 10⁻⁵, <i>p</i>c = .0005, odds ratio [OR] 2.11, 95% confidence interval [CI] 1.52–2.92) and DM (<i>p</i> = .0004, <i>p</i>c = .0128, OR 2.06, 95%CI 1.40–3.02). <i>DPB1*05:01</i> was also associated with IIM (<i>p</i> = .0001, <i>p</i>c = .0021, OR 1.96, 95%CI 1.38–2.77) and DM (<i>p</i> = .0005, <i>p</i>c = .0075, OR 2.05, 95%CI 1.37–3.08). <i>DRB1*09:01</i> (<i>p</i> = .0012, <i>p</i>c = .0368, OR 0.35, 95% CI 0.18–0.69) and <i>DPB1*04:01</i>(<i>p</i> = .0004, <i>p</i>c = .0057, OR 0.05, 95% CI 0.00–0.85) were protectively associated with PM. Two locus analyses suggested that <i>DRB1*09:01</i> and <i>DPB1*04:01</i> were independently associated with PM. <b>Conclusion:</b> Protective associations of <i>HLA</i> were detected in Japanese PM patients.