GSTM1 and age-related macular degeneration: Regarding epigenetics, DNA methylation of glutathione S-transferase isoforms mu1 (GSTM1) and mu5 (GSTM5) has been reported to increase the susceptibility to oxidative stress in patients with AMD [6, 7], and cigarette smoke treatment of retinal pigment epithelium (RPE) decreased chromatin accessibility, also providing an epigenetic link between a known risk factor for AMD and AMD pathology [8].