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.
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.
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.
Interestingly, recent studies have not found association of IRF5 with the other autoimmune diseases, such as rheumatoid arthritis or psoriasis, suggesting the unique role for IRF5 in the development of lupus.