Knockout mouse points to second form of tryptophan hydroxylase.

A second form of tryptophan hydroxylase (TPH) is expressed in the brain by the gene Tph2. The presence of the gene was discovered when Tph 1(-/-)mice were found to express normal amounts of serotonin in brain, but not in the periphery. Additionally, Tph1(-/-) mice showed no observed behavioral differences from wild-type littermates. Veenstra-Vanderweele and Cook discuss the ramifications of these findings and what they might mean for designing drugs that target the expression and activity of TPH in differing tissues.