GSTM1 and type 2 diabetes mellitus: The genes encoding the GST enzymes are polymorphic, therefore determining changes in the metabolic activity of each enzyme regarding the clearance of toxic DNA intermediates, and seem to determine the susceptibility of an individual's pancreatic β cells to oxidative stress and possibly the predisposition for T2DM's microvascular complications [23]. GSTM1 null and GSTT1 null genotypes determine the enzymatic inactivity of the proteins encoded by these genes.