Protein tyrosine phosphatase, non-receptor type 22 (PTPN22) gene polymorphism (rs2476601), is significantly associated with the progression from islet autoimmunity to clinical T1D [67] and rs45450798 in PTPN22 is affecting the β-cell destruction early after the initial seroconversion [16]. This evidence concerns the gene PTPN22 and type 1 diabetes mellitus.