PAH and vitiligo: The etiology of vitiligo is still not known, but, it is believed to be associated with the metabolic functions of phenylalanine hydroxylase (PAH), an H4Bip-dependent enzyme of the initial stage of melanogenesis, and tyrosinase (EC 1.14.18.1)) [251,252], as well as with photochemical reactions of H4Bip and oxidized pterins [29,253].