Idiopathic (IPAH) and heritable PAH (HPAH), included within group one, have been classically associated with BMPR2 mutations [4], with a penetrance of 20%, which means that approximately 80% of individuals with BMPR2 will not develop clinically detectable PAH [5]. Here, BMPR2 is linked to idiopathic pulmonary arterial hypertension.