PTPN22 and type 1 diabetes mellitus: The nsSNP located at 1858bp (C/T) within PTPN22 results in substitution of Arginine (Arg) (CGG) to a tryptophan (Trp) (TGG) at codon 620 (R620W) (rs2476601) and was first associated with T1D susceptibility in two independent case-control cohorts of North American (P=10-3) and Sardinian (P<0.05) background [68].