PXK and rheumatoid arthritis: These SNPs are present in close proximity to genes of known immune function, namely, IL6ST, SPRED2, RBPJ, CCR6, IRF5 and PXK. However, HLA-DRB1 and PTPN22 together explain around 50% of the heritable risk to RA [6] and the effects of other genes are weak (odds ratio (OR) <1.3).