The catabolic pathways of amino acids are affected by malnutrition (Val/Gly ratio), inflammation and acidosis, renal enzyme activity modified by kidney disease (glycine hydroxymethyltransferase: Gly→Ser; phenylalanine 4-hydroxylase: Phe→Tyr) or intestinal microbiota (Trp) [26,35]. The gene discussed is PAH; the disease is Acidosis.