Interrelationship of major histocompatibility complex class II alleles and autoantibodies in four ethnic groups with various forms of myositis

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Abstract
Objective. To examine interrelationships among myositis subsets, autoantibodies, and major histocompatibility complex (MHC) class II alleles across ethnic lines, and to localize genetic susceptibility (presence of HLA–DR versus DQ) to myositis within the MHC class II region. Methods. MHC class II alleles (HLA–DRB1, DQA1, and DQB1, detected by DNA oligotyping) and myositis-specific autoantibodies (MSA) were determined in 224 patients with various myositis syndromes, including 89 whites, 89 African-Americans, 25 Mexican-Americans, and 21 Japanese. Results. Anti–Jo-1 (histidyl–transfer RNA [tRNA] synthetase) and other MSAs (anti–PL-12, anti–PL-7, anti-OJ, anti-EJ, anti-KJ, anti-tRNA, and anti–signal recognition particle) were equally distributed among the races, but occurred more often in patients with polymyositis (PM) than in those with dermatomyositis (DM) or other myositis syndromes. MSA frequencies were significantly positively associated with anti–Ro (SS-A) (P = 0.002), and significantly negatively associated with anti–U1 RNP (P = 0.003). Frequencies of the HLA–DRB1*0301 (DR3), DQA1*0501, and DQB1*0201 (DQ2) alleles (and haplotype) were each increased in white patients with myositis, especially those with PM, but most strikingly in those with MSAs. However, in the other ethnic groups, except the Japanese group, only frequencies of HLA–DQA1*0501 and the structurally similar DQA1*0401 alleles were significantly increased. The presence of HLA–DQA1*0501 or *0401 was most significantly associated with anti–Jo-1, anti–PL-12, and other MSAs, compared with myositis patients without MSAs (P = 0.0008, Pcorr = 0.01, odds ratio [OR] = 3.7), and with normal, ethnically matched controls (P = 3 × 10−7, Pcorr = 1 × 10−6, OR = 6.5). Among MSA-positive patients who were negative for HLA–DQA1*0501 and *0401, including Japanese patients, the HLA–DQA1*0101 and *0103 alleles predominated. In addition, there appeared to be a negative association of the HLA–DR2 alleles (DRB1*1501 and *1503) with PM (P = 0.007, Pcorr not significant, OR = 0.39), but not with DM or myositis overall. Conclusion. By transracial gene mapping, genetic susceptibility to anti–Jo-1 and other MSAs in patients with myositis can be localized within the MHC region to the HLA–DQA1 locus.

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