The genetic interactions between IRF5 and STAT4 polymorphisms in SLE and RA susceptibility were examined using the epistasis options in PLINK software.
The strongest association was detected for a functionally relevant four SNP haplotype of IRF5, which comprised a protective effect (p = 0.0000897, p (corrected) = 0.0012, OR 0.73, 95% CI 0.62-0.85) similar to those previously seen in RA and SLE.
All of the remaining RA patients (ACPA- or SE+) showed a strong association with IRF5 SNPs, which followed a complex pattern of opposing effects mediated by independent haplotypes.
We also identified non-MHC epistatic interactions between RA susceptible loci LOC100506023 and IRF5 with Immunochip-wide significance (p < 1.1e-08) and between 2 neighboring single-nucleotide polymorphism near PTPN22 that were in low linkage disequilibrium with independent interaction (p < 1.0e-05).
Given the fact that anti-CCP-negative RA differs from anti-CCP-positive RA with respect to genetic and environmental risk factor profiles, our results indicate that genetic variants of IRF5 contribute to a unique disease etiology and pathogenesis in anti-CCP-negative RA.
Polymorphisms in the interferon regulatory factor 5 (IRF5) gene are associated with susceptibility to systemic lupus erythematosus, rheumatoid arthritis and other diseases through independent risk and protective haplotypes.
Two of the IRF5 polymorphisms, CGGGGindel (OR 1.38, 95% CI 1.09-1.76, pcorr = 0.04) and rs2004640 (OR 1.36, 95% CI 1.09-1.68, pcorr = 0.03), and one haplotype, including the rs2004640 and the CGGGGindel, ht3 (A-Del-T-C-del-A-T) (OR 1.39, 95% CI 1.09-1.79, pcorr = 0.04) were significantly associated with an increased risk of RA.