GSTM1 and type 2 diabetes mellitus: An Iranian study showed that the presence of GSTM1 null genotype and the synergic effect of GSTM1 null and GSTT1 null genotypes were associated with an increased risk of T2DM development but there was no significant correlation observed between GSTM1 null and GSTT1 null genotypes and the risk of DR occurrence [37].