Polymorphism in the immunoglobulin VH gene V1-69 affects susceptibility to rheumatoid arthritis in subjects lacking the HLA-DRB1 shared epitope

Abstract

Objective. To investigate the contribution of polymorphism in the immunoglobulin heavy chain variable region VI-69 gene set to genetic susceptibility to rheumatoid arthritis (RA) in Czech and British patients. Methods. We used V1-69 gene sequence-specific polymerase chain reaction (PCR) and restriction enzyme digestion to study polymorphism in the V1-69 gene set in germline DNA of 109 Czech and 159 British RA patients and 164 ethnically matched controls. Polymorphism was further studied by nucleotide sequencing of the V1-69 gene locus in germline DNA. Results. We found that all patients and controls had at least one V1-69 gene copy. In the Czech RA cohort, the dimorphic nucleotide in codon 73 of V1-69 (GAA or AAA) was present in the homozygous form 73A/A in 31 of 109 (28.4%) RA patients vs 12 of 79 (15.2%) controls [odds ratio (OR) = 2.22, P < 0.001]. When the RA patients and controls were classified according to HLA shared epitope (SE) status, 73A/A was found in 18 of 76 (23.7%) SE+ patients compared with 13 of 38 (34.2%) SE- patients, four of 12 (18.2) SE+ controls and eight of 57 (14%) SE- controls. This suggests that homozygosity for the dimorphic sequence 73A contributed to susceptibility to RA in SE- Czech individuals (OR = 3.2, P < 0.001). The most striking observation was that none of the 38 SE- Czech patients, compared with 11 of 76 (14.5%) SE+ RA patients, three of 22 (13.6%) SE+ and 11 of 57 (19.3%) SE- ethnically matched controls, were homozygous for the alternative dimorphic sequence 73G/G (OR = 9.1, P < 0.05). These data, however, were not replicated in a Caucasoid British RA population. Conclusion. The dimorphic sequence at codon 73 (73A/A) of the V1-69 gene contributes to genetic susceptibility in SE- Czech RA patients.