HLA-DRB1 and rheumatoid arthritis: A common amino acid sequence extending from the 70th to 74th in the HLA-DRβ chain, which is known as the “shared epitope (SE)”, is considered to be the reason for the association between HLA-DRB1 and RA, and the association between the SE and RA has been reported to be ethnicity-independent [6]–[8].