Despite the strong association between BMPR2 mutations and the development of PAH, and despite the high frequency of BMPR2 mutations in heritable PAH, having a BMPR2 mutation alone is not sufficient; heterozygous carriers of deleterious BMPR2 mutations only have an approximately 20% lifetime risk of disease penetrance [15]. This evidence concerns the gene BMPR2 and pulmonary arterial hypertension.