The expression levels of six known RA susceptibility genes, PADI2 (Fig. 4C), TRAF1 (Fig. 5B), HLA-A, HLA-DRB1, HLA-DPB1 and HLA-B (Supplementary Table S5), in blood cells were significantly associated with RA. Here, HLA-DRB1 is linked to rheumatoid arthritis.