HLA-DRB1 and rheumatoid arthritis: Comparison of HLA-DRB1 associations with RA in different ethnic groups helped to support the original “shared epitope” hypothesis of RA susceptibility [3] based on an amino acid risk motif at positions 67–74 in the third hypervariable region (HVR3) of the class II MHC molecule, encoded by HLA-DRB1. The group of RA “shared epitope” alleles now includes HLA-DRB1*01:01, HLA-DRB1*04:01, HLA-DRB1*04:04, HLA-DRB1*04:08, and HLA-DRB1*10:01; other alleles provide weaker protective effects, additional to the risk effects of the “shared epitope” [4].