EIF2AK4 and pulmonary venoocclusive disease: Given that the KO mice used in these studies have genetic deletion of exon 12 of the Eif2ak4 gene encoding amino acids 606–648, an essential region for its kinase activity (14), it is possible that the N-terminal 605 amino acids may retain some of the GCN2 functional domains, which are sufficient to inhibit PVOD development.