Evaluation of: Remmers EF, Plenge RM, Lee AT et al.: STAT4 and the risk of rheumatoid arthritis and systemic lupus erythematosus. N. Engl. J. Med. 6(10), 977–986 (2007). Rheumatoid arthritis is an autoimmune disease with a strong genetic component. The genetic component of rheumatoid arthritis is thought to be complex, with a wide number of predisposing alleles, each of them conferring a modest risk. The identification of the genetic component of complex diseases is of great interest, since a fuller understanding of disease etiology and pathogenesis is expected to lead to improved risk predictions for susceptibility, severity and outcome and, ultimately, may lead to the development of novel therapies. Until very recently, only two reproducible genetic associations were described. For 30 years, only HLA genes have been identified as sufficiently validated rheumatoid arthritis genetic risk factors. A second, more modest, association has been recently identified with the PTPN22 gene. In the study by Remmers et al., a new susceptibility marker for rheumatoid arthritis is identified, the STAT4 rs7574865 polymorphism. Interestingly, this SNP is also associated with systemic lupus erythematosus.