AQP1 and idiopathic pulmonary arterial hypertension: In a minority of IPAH cases, (potentially) associated variants have been reported in several genes including KCNK3 (encoding a PH sensitive potassium channel), CAV1 (encoding an integral membrane protein), TBX4 (playing a critical role in the development of respiratory system), GDF2 (also called BMP9 and a member of the highly conserved transforming growth factor-β superfamily), AQP1 (encoding aquaporin-1), SOX17 (encoding a transcription factor involved in Wnt/β-catenin and Notch signaling during development), and BMPR1B (encoding a type I BMP receptor) [5,9,11].