CYP24A1 and age-related macular degeneration: A study performed in extremely discordant siblings (i.e., one sibling had the neovascular form of AMD while the discordant sibling had no sign of AMD and was older than 65 years) suggested that a single point variant in CYP24A1 (the gene encoding the catabolizing enzyme of the vitamin D pathway) influenced AMD risk, although this association has not been replicated [40].