By using the DNA methylation microarray and bisulfite pyrosequencing applied to frozen human RPE/choroid samples (donors), Hunter and coworkers observed the hypermethylation of glutathione S-transferase isoforms mu1 and mu5 (GSTM1 and GSTM5) in AMD compared with age-matched control tissues (Hunter et al., 2012). Here, GSTM5 is linked to age-related macular degeneration.