For example, HLA-A amino acid residue at position 77 with asparagine residue (i.e., HLA-A Asn77), HLA-B amino acid residue at position 9 with aspartic acid (i.e., HLA-B Asp9), and HLA-DPB1 amino acid residue at position 9 with phenylalanine residue (i.e., HLA-DPB1 Phe9) are associated with risk of developing ACPA-positive RA [17, 21]. This evidence concerns the gene PRTN3 and rheumatoid arthritis.