The majority of BMPR2 mutations result in a loss of function, but show low penetrance (∼20%) in more than 70% of patients with familial PAH and in 11–40% of patients with sporadic PAH, affecting only 20% of carriers during their lifetime (Lane et al., 2000; Machado et al., 2001). The gene discussed is BMPR2; the disease is pulmonary arterial hypertension.