On a molecular basis, the 5-HT1b-receptor after stimulation with 5-HT shows altered epigenetic response in covalent modifications of nuclear proteins in cells similar to pulmonary vascular cells from patients with pulmonary hypertension, supporting a clinically relevant role of 5-HT in pulmonary hypertension at least [251]. The gene discussed is HTR5A; the disease is pulmonary arterial hypertension.