Analyses of families with multiple autoimmune disorders have revealed a functional polymorphism, 620W, in the intracellular tyrosine phosphatase gene PTPN22 as a predisposing factor for type 1 diabetes, seropositive rheumatoid arthritis, systemic lupus erythematosus, and Hashimoto thyroiditis, and the presence of the PTPN22 protein appears to herald the development of autoantibodies in these disorders