PTPN22 and type 1 diabetes mellitus: There are three main chromosomal regions that are reproducibly and statistically significantly associated with T1DM: the region of human leukocyte antigen (HLA) on chromosome 6p21, the gene for protein tyrosin-phosphatase non-receptor-type 22 (PTPN22) on chromosome 1p13, and the region of insulin (INS) gene on chromosome 11p15 [1,2].