SLC6A4 and pulmonary arterial hypertension: Pulmonary arterial hypertension has demonstrated multi-serotonin receptor pathologies, characterized by increased tone (5-HT1B receptor) and complex lesions (SERT, 5-HT1B, 5-HT2B receptors) of the pulmonary vasculature together with right ventricular hypertrophy, ischemia and fibrosis (5-HT2B receptor) (Thomas et al., 2013).