PRTN3 and rheumatoid arthritis: The first question found a partial answer in the strong association between ACPA-positive RA and specific HLA polymorphisms, especially the conserved region of HLA-DRB1*0104 allele: subjects who carry this allele have an higher risk of developing an erosive ACPA-positive RA, due to the ability of the HLA molecule coded by this specific haplotype to bind and present citrullinated antigens [55].