PTPN22 and rheumatoid arthritis: The allelic variation of the PTPN22 gene, 1858T, has been found associated with several autoimmune disorders: rheumatoid arthritis [3-7], systemic lupus erythematosus [4], Wegener's granulomatosis [8] and myasthenia gravis [9] among them, but no association was found with either multiple sclerosis [10] or celiac disease [11].