PRPH and age-related macular degeneration: In contrast to Global Up genes, Global Down genes are notfunctionally enriched, aside from three neurofilament-associated genes in the retina(NEFL, NEFM, PRPH), suggesting that AMD is associatedwith a general down-regulation of genes involved in diverse cellular processes.Notably, one gene present in both RPE-choroid and Retina Global Down modules,GSTT1 (glutathione S-transferase theta 1), is known to play a protectiverole in RPE oxidative stress, and reduced levels of this gene may be associated withboth advanced RPE aging [122] and AMD [85].