HLA-DRB1 and rheumatoid arthritis: Previously, comprehensive research on all the functional HLA-DRB genes was lacking, or limited by the high cost of genotyping (resulting in small study sizes) [13,14] and the lack of imputation methods for HLA-DRB3, HLA-DRB4, and HLA-DRB5 [2–4], despite interest in the association of HLA-DR with RA and SLE.