The TPH2-R439H mouse, an analogous mutation to the R441H mutation found in human depressive patients, not only lacked TPH2 but also exhibited increased depression and anxiety-like behaviors, reduced levels of 5-HT and 5-HIAA in the brain (67), and fewer enteric neuronal 5-HT in the gut (68). The gene discussed is HTR5A; the disease is depressive disorder.