HLA-DRB1 and rheumatoid arthritis: The vast majority of patients with rheumatoid arthritis (RA) carry human leukocyte antigen-DRB1 (HLA-DRB1) alleles encoding QKRAA, QRRAA, or RRRAA amino acid sequences in positions 70 to 74 of the DR-β chain, a motif commonly known as the RA 'shared epitope' (SE) [1].