PTPN22 and type 1 diabetes mellitus: Only five type 1 diabetes loci with compelling evidence had been identified before the advent of GWA studies: the HLA class II genes on chromosome 6p21 [2]; the insulin gene (INS) on 11p15 [3]; CTLA4 on 2q33 [4]; PTPN22 on 1q13 [5,6]; and, IL2RA/CD25 on 10p15 [7,8].