The genetic predisposition for RA has been linked to variants in the MHC class II genes (the so-called shared epitope HLA-DR alleles)7,8, while SpA is linked more closely to the MHC class I pathway with HLA-B27 and the proteasome components encoded by ARTS-1 as the major disease predisposing genes6. This evidence concerns the gene HLA-C and rheumatoid arthritis.