Novel susceptibility alleles in HLA region for myositis and myositis specific autoantibodies in Korean patients

Objectives: HLA genes are a major genetic risk factor for myositis and myositis specific antibodies (MSAs), exhibiting unique HLA backgrounds for myositis in different ethnic groups. This is the first large scale Korean study to genotype the HLA-DRB1 and -DPB1 alleles and to examine their association with myositis and MSAs. Methods: HLA-DRB1 and HLA-DPB1 alleles and MSAs were examined in 179 patients with dermatomyositis (DM, n = 129) or polymyositis (PM, n = 50) and healthy controls (n = 800 for HLA-DRB1, n = 548 for HLA-DPB1). Associations between individual HLA alleles and myositis/MSA were examined. Bonferroni correction was applied for multiple testing comparing patients and controls. Results: A total of 33 HLA-DRB1 and 24 HLA-DPB1 alleles were genotyped in patients and controls. MSAs were found in 67.0% of patients. Anti-MDA5 (26.8%) and anti-aminoacyl-tRNA synthetase antibodies (15.6%) were most common, followed by anti-Mi2 (9.5%) and anti-TIF1γ antibodies (8.9%). HLA-DRB1*12:02 and HLA-DRB1*14:03 were associated with DM and PM, respectively. HLA-DRB1*12:02 was associated with anti-MDA5, HLA-DRB1*08:03 with anti-ARS, HLA-DRB1*14:03 with anti-SRP, and HLA-DRB1*07:01 with anti-Mi2 antibodies. Although HLA-DRB1*13:01 was associated with anti-TIF1γ antibodies, the frequency of HLA-DRB1*13:01 was rare. HLA-DPB1*02:01 was negatively associated with myositis and PM while HLA-DPB1*17:01 was associated with anti-Mi2 positive DM. Conclusions: Unique immunogenetic background was observed for Korean patients with myositis. Novel myositis susceptibility alleles, HLA-DRB1*12:02 and HLA-DRB1*14:03, were identified, together with MSA-associated HLA alleles unique to Korean patients with myositis.