Multiple dysregulated signalling pathways have been identified in PAH patients, and a significant portion of disease-specific therapeutic agents have an influence on the course of the disease through these routes, namely the nitric oxide (NO) pathway (I), the prostacyclin (II) and endothelin-1 pathways (III) [5,6,7,8]. The gene discussed is EDN1; the disease is pulmonary arterial hypertension.