PTPN22 and type 1 diabetes mellitus: In particular, Bottini et al., 2004, found that the rs2476601 polymorphism in the PTPN22 gene, encoding the lymphoid protein tyrosine phosphatase (LYP), was associated with T1DM in non-Hispanic North American Europeans; the rs2476601 polymorphism impairs the LYP–CSK complex formation, whose biological function is to inhibit T cell activation [39].