PTPN22 and type 1 diabetes mellitus: Although many of the genes in these two loci have polymorphisms between B6 and NOD, and are therefore positional candidates for altering susceptibility to T1D, we focused on Ptpn22 and Cd2 because these genes or the signaling pathways they are involved in have been associated with several human autoimmune diseases (18, 19, 35).