Pulmonary hypertension, primary, 1 (PPH1; MIM 178600) is an autosomal dominant pulmonary vascular disorder caused by mutations in the bone morphogenetic protein receptor, type II gene (BMPR2). PPH is characterized by the obstruction and obliteration of small pulmonary arteries, leading to pulmonary artery hypertension, right ventricular hypertrophy and right sided heart failure. Symptoms include syncope, dyspnea, fatigue, chest pain and edema. Females are two to four times more likely to be affected than males. About 70% of familial cases and 25% of simplex cases of PPH are caused by mutations in BMPR2. PPH is genetically heterogeneous. Less commonly, PPH is caused by mutations in SMAD9 (PPH2; MIM 615342), CAV1 (PPH3; MIM 615343) and KCNK3 (PPH4; MIM 615344). Mutations in ACVRL1 and ENG have also been described in PPH. Reduced penetrance is observed in PPH1 as only about 10 to 20% of patients with a BMPR2 mutation develop disease. The incidence of familial PPH is estimated at 1:100,000 to 1:1,000,000. BMPR2 mutations have also been defined in a subset of patients with hereditary hemorrhagic telangiectasia, a disorder also caused by mutations in ACVRL1, ENG, GDF2 and SMAD4. Pulmonary venoocclusive disease (PVOD) is a subtype of primary pulmonary hypertension. It accounts for about 10% of idiopathic cases of pulmonary arterial hypertension. PVOD develops because of widespread occlusion of many large and medium sized branches of the pulmonary veins resulting in occult alveolar hemorrhage. Pulmonary venoocclusive disease 1, autosomal dominant (PVOD1; MIM 265450) is caused by mutations in the BMPR2 gene and pulmonary venoocclusive disease 2, autosomal recessive (PVOD2; MIM 234810) is caused by mutations in the eukaryotic translation initiation factor 2-alpha kinase 4 gene (EIF2AK4).