THBS1 and pulmonary arterial hypertension: Thbs1 is maintained at low levels in the postnatal vessels and elevated in various vascular diseases, including pulmonary arterial hypertension (Kumar et al., 2017), aortic aneurysms (Kessler et al., 2014), atherosclerosis (Moura et al., 2008), cerebral cavernous malformations (Lopez-Ramirez et al., 2017) and ischemia reperfusion injury (Favier et al., 2005).