HLA-DRB1 and rheumatoid arthritis: However, associated amino acid residues 10, 11, 12, 13, 33, 57, 70, 96 and 98 of HLA-DRβ chain in Korean ACPA(+) RA [33] were more similar to the results (Figure 1B), reflecting the difference of DRB1 allele frequencies between European and Asian populations.