Polymorphisms in the interferon‐γ/interleukin‐26 gene region contribute to sex bias in susceptibility to rheumatoid arthritis

Objective To determine whether polymorphisms in the interferon‐γ (IFNγ)/interleukin‐26 (IL‐26; formerly, AK155) gene cluster contribute to sex‐based differential susceptibility to rheumatoid arthritis (RA). Methods Four microsatellite markers, located in a 118‐kb interval that contains both the IFNγ and IL‐26 genes on chromosome 12q15, were typed in 251 patients with RA and 198 unrelated healthy controls (all of whom lived in Northern Ireland) by means of polymerase chain reaction–based fragment analysis. Results Marker D12S2510 , which is located 3 kb 3′ from the IL‐26 gene, was significantly associated with RA in women (corrected P [ P corr ] = 0.008, 2 degrees of freedom [2 df]) but not in men ( P = 0.99, 2 df). A 3‐marker haplotype, IFNGCA*13;D12S2510*8;D12S2511*9, was inferred that showed significant underrepresentation in women with RA (odds ratio 0.50, 95% confidence interval 0.32–0.78; P = 0.002, P corr = 0.03) but not in men with RA. Conclusion Our results demonstrate that common polymorphisms in the IFNγ/IL‐26 gene region may contribute to sex bias in susceptibility to RA, by distorting the propensity of female carriers versus male carriers to contract this disease. These results conform to our recent observations of a role for this gene cluster in sex‐based differential susceptibility to another Th1‐type inflammatory disease, multiple sclerosis.