Recessive mutations in the EIF2AK4 gene (encoding GCN2) and resultant reduction of GCN2 protein expression are linked to heritable pulmonary veno-occlusive disease (PVOD), a rare subgroup of severe PAH, which is characterized by intimal proliferation and fibrosis of septal veins and preseptal venules (31). The gene discussed is EIF2AK4; the disease is pulmonary venoocclusive disease.