HLA class 2 genes in Singaporean Chinese rheumatoid arthritis.

This study analysed HLA class 1 and 2 allele associations in Singaporean Chinese patients with RA. Seventy patients (ARA definite or classical) and 80 controls were typed for HLA class 1 alleles by serology and class 2 alleles by serology and the PCR/SSO method. RA patients had higher frequencies of DRB1*0405 (40 vs 12.5%; corrected probability value (PC) < 0.02, relative risk (RR) = 4.7, 95% confidence limit (CL) 2.1-10.6), DRB1*1001 (14.3 vs 1.3%; PC = 0.06, RR = 13.2, 95% CL 1.6-105.7), DQB1*0401 (38.6 vs 12.5%; P = 0.006, RR = 4.4, 95% CL 1.9-10.0) and DQB1*0501 (20 vs 5%; PC = 0.048, RR = 4.8, 95% CL 1.5-15.2). It is concluded that Chinese RA is associated primarily with HLA DRB1*0405 and DRB1*1001 which share common amino acid sequences in the third hypervariable region of the DR beta chains shown to be associated with RA in other ethnic groups. Patients without DRB1*0405 and *1001 had a higher frequency of DRB1*0901, which is in linkage disequilibrium with HLA B46 in the Chinese.