Tryptophan hydroxylase (TPH) is an enzyme responsible for neuronal serotonin (5-HT) synthesis and it is encoded by two genes, TPH1 and TPH2. While TPH1 is primarily expressed in the periphery, TPH2 is predominantly expressed in the brain. Polymorphisms in TPH2 are associated with a range of behavioural traits and psychiatric disorders.41,42 Chen and colleagues demonstrated that the 90 A/G polymorphism at the 5′UTR of the THP2 mRNA alters the mRNA structure and/or RNA–protein interaction, thus affecting TPH2 gene expression at the post-transcriptional level.43
