BMPR2 and pulmonary arterial hypertension: In addition to germline mutations, BMPR2 expression and BMPR2 signal transduction is universally impaired in all PAH forms, including APAH (16, 18–20) and other precapillary PH forms such as chronic thromboembolic PH and interstitial lung disease associated PH (21, 22) by a plethora of pathological mechanisms [reviewed in (23)].