GSTM1 and age-related macular degeneration: What has been already noted before, regarding the effect of DNA methylation changes and antioxidant gene expression in AMD, is that mRNA levels of glutathione S-transferase isoforms mu1 (GSTM1) and mu5 (GSTM5) were significantly reduced in AMD patients vs age-matched controls in the retinal pigment epithelium (RPE)/choroid and neurosensory retina.