TPH2: Tryptophan hydroxylase 2, also known as neuronal tryptophan hydroxylase (NTPH), the key rate-limiting enzyme in the synthesis of serotonin (5-hydroxytryptamine, or 5HT). 5HT is causally involved in numerous activities in the central nervous system, and it also has other functions including the maintenance of vascular tone and gut motility. The TPH2 gene is on chromosome 12.
A functional genetic polymorphism (variation) in the TPH2 gene results in the substitution of a single amino acid in the TPH2 protein. This minute change in TPH2 leads to decreased brain serotonin levels and provides direct evidence for a fundamental role of TPH2 in the production of serotonin in the brain. Dysregulation of brain serotonin contributes to some psychiatric disorders.