PTPN22 and systemic lupus erythematosus: This hypothesis is supported by reports on genes found to be associated with more than one autoimmune disease in experimental models of RA and MS.12 Shared genes in autoimmune diseases are becoming apparent also in humans, such as PTPN22 in RA and SLE,13MHC2TA in RA and MS,14 and recently the suggested involvement of CD24 in MS and SLE.15