Since the presence of the SE has been associated with susceptibility to RA in our population [23] and known to confound association with RA at other immunologically relevant loci such as PTPN22[27], we evaluated our findings in CTLA4 for possible confounding by the HLA-DRB1 SE, the strongest known genetic risk factor for RA. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.