Importantly, we did not detect significant confounding for association of rs231778 when our patients were stratified by level of European admixture or by RA subclassification such as presence of the HLA-DRB1 shared epitope (SE) or anti-cyclic citrullinated peptide (anti-CCP) antibodies [20]. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.