The CD40 gene has been previously identified as a risk gene for multiple sclerosis (MS) [1–4] and other autoimmune diseases, including Graves’ disease (GD) [5–8], rheumatoid arthritis (RA) [9–12], systemic lupus erythematosus (SLE) [13] and Crohn’s disease (CD) [3]. Here, CD40 is linked to rheumatoid arthritis.