The present results and our previous data showing CD154 association with systemic lupus erythematosus in Canary Islanders suggest that CD154 may commonly contribute to the pathophysiological process and common immunogenetic mechanisms underlying both autoimmune diseases, thus being in agreement with the hypothesis of the 'common genetic origin' of autoimmune diseases [55,56]. The gene discussed is CD40LG; the disease is systemic lupus erythematosus.