Recent genome-wide association scans and replication studies of European populations have disclosed several single-nucleotide polymorphisms (SNPs) associated with rheumatoid arthritis (RA) susceptibility. The aim of this study was to evaluate the RA-associated loci by genotyping previously reported SNPs and additional tag SNPs in a Korean population.
A total of 1,316 unrelated RA patients and 1,006 controls were genotyped for 12 SNPs identified in genome-wide scans and for 12 additional tag SNPs in IL2RB, OLIG3-TNFAIP3, PTPN22, and TRAF1-C5, and the findings were statistically compared.
None of the SNPs tested was associated with RA susceptibility, except rs7021206 in TRAF1 intron 3 (P = 0.0032) and, among the SNPs previously reported, rs6457617 in HLA (P = 4.6 x 10(-35)). The association of rs7021206 was positive in patients who were seropositive for rheumatoid factor (P = 0.0051) or for anti-cyclic citrullinated peptide autoantibodies (P = 0.0062). However, Korean patients were negative for the association of rs3761847 in the TRAF1-C5 intergenic region previously reported in Caucasians. Linkage disequilibrium between rs3761847 and rs7021206 was not as high in Koreans (r(2) = 0.37) as in Caucasians (r(2) = 0.67), which explains the lack of association of rs3761847 in Koreans. Accordingly, RA susceptibility was localized to an extended haplotype marked by rs7021206 rather than rs3761847, and SNPs highly correlated with rs7021206 (r(2) > or = 0.81) extended from rs1953126 in the PHF19-TRAF1 intergenic region to rs2900180 in the TRAF1-C5 intergenic region, spanning 66 kb.
Our results demonstrate that within and around TRAF1, excluding PHF19 and C5, SNPs highly correlated with rs7021206, but not those correlated with rs3761847, are associated with RA in both Asians and Caucasians and are possibly correlated with causative variations.