PRTN3 and rheumatoid arthritis: Moreover, studies by Kapitany and Snir found a significant correlation between HLA-DR4 and HLA-DRB1 and the ACPA titers, respectively [112,113]; hence it has been concluded that HLA-DR4 and HLA-DRB1 allele positivity poses an increased risk for developing RA because of their association with high ACPA titers.