PRTN3 and rheumatoid arthritis: For instance, the polymorphic amino acid residues at position 11 (e.g., valine, HLA-DRB1 Val11 or leucine, HLA-DRB1 Leu11) within HLA-DRB1 protein explained most of the genetic risk of developing ACPA-positive RA [17, 19–21], instead of the amino acid residues previously defined at positions 71 and 74, the conserved amino acid region of the SE alleles [2].