In anti-citrullinated protein antibody positive rheumatoid arthritis (ACPA-positive RA), a particular subset of 
We computed the attributable proportion (AP) due to additive interaction at genome-wide level for two independent ACPA-positive RA cohorts: the Swedish epidemiological investigation of rheumatoid arthritis (EIRA) and the North American rheumatoid arthritis consortium (NARAC). Then, we tested for differences in the AP p value distributions observed for two groups of SNPs, non-associated and associated with disease. We also evaluated whether the SNPs in interaction with 
We found a strong enrichment of significant interactions (AP p<0.05) between the 
Our data demonstrate that there are massive genetic interactions between the 