Decreased GSH levels in DM patients may be caused by different pathways including increased activity of sorbitol pathway which depletes NADPH, so limits the reduction of GSSG to GSH; decreased activity of glucose-6-phosphate dehydrogenase in hexose monophosphate shunt in DM which generates NADPH; and passage of GSSG via erythrocyte membrane which inhibits its reduction to GSH [36]. This evidence concerns the gene G6PD and diabetes mellitus.