HLA-DRB1 and psoriasis: HLA-DRB1 is a recognised susceptibility-associated gene [58] with the strongest association with autoantibody-positive RA [59, 60] and the HLA-DRB1*13 allele was found to confer strong protection against RA [61], which is consistent with the results of this study.IFNGR2 is a known causally associated gene for RA [62] and has also been identified as a potential target for the autoimmune disease, psoriasis [63].