Protective effect of the HLA-DRB1*13:02 allele in Japanese rheumatoid arthritis patients.

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease. Certain HLA-DRB1 "shared-epitope" alleles are reported to be positively associated with increased RA susceptibility, whereas some of the other alleles may be negatively associated. However, studies on the latter are rare. Here, we focus on the protective effects of DRB1 alleles in Japanese RA patients in an association study. Relative predispositional effects (RPE) were analyzed by sequential elimination of carriers of each allele with the strongest association. The protective effects of DRB1 alleles were investigated in patients stratified according to whether they possessed anti-citrullinated peptide antibodies (ACPA). The DRB1*13:02 allele was found to be negatively associated with RA (P = 4.59×10(-10), corrected P (Pc) = 1.42×10(-8), odds ratio [OR] 0.42, 95% CI 0.32-0.55, P [RPE] = 1.27×10(-6)); the genotypes DRB1*04:05/*13:02 and *09:01/*13:02 were also negatively associated with RA. The protective effect of *13:02 was also present in ACPA-positive patients (P = 3.95×10(-8), Pc = 1.22×10(-6), OR 0.42, 95%CI 0.31-0.58) whereas *15:02 was negatively associated only with ACPA-negative RA (P = 8.87×10(-5), Pc = 0.0026, OR 0.26, 95%CI 0.12-0.56). Thus, this study identified a negative association of DRB1*13:02 with Japanese RA; our findings support the protective role of DRB1*13:02 in the pathogenesis of ACPA-positive RA.