A study of lung tissue from people with different forms of PH showed that Ang-1 was overexpressed and linked to exaggerated pulmonary smooth muscle cell hyperplasia and downregulation of the bone morphogenetic protein receptor (BMPR) 1A, a component of the BMPR complex which is also inactivated in hereditary PAH (by mutation of BMPR2) [20]. Here, BMPR2 is linked to pulmonary arterial hypertension.