Pulmonary veno-occlusive disease (PVOD) is a rare and devastating cause of pulmonary hypertension that is characterized histologically by widespread fibrous intimal proliferation of septal veins and preseptal venules and is frequently associated with pulmonary capillary dilatation and proliferation. PVOD is categorized into a separate pulmonary arterial hypertension-related group in the current classification of pulmonary hypertension. PVOD presents either sporadically or as familial cases with a seemingly recessive mode of transmission. Using whole-exome sequencing, we detected recessive mutations in EIF2AK4 (also called GCN2) that cosegregated with PVOD in all 13 families studied. We also found biallelic EIF2AK4 mutations in 5 of 20 histologically confirmed sporadic cases of PVOD. All mutations, either in a homozygous or compound-heterozygous state, disrupted the function of the gene. These findings point to EIF2AK4 as the major gene that is linked to PVOD development and contribute toward an understanding of the complex genetic architecture of pulmonary hypertension.

SummaryRNase E contains a large non-catalytic region that binds RNA and the protein components of the Escherichia coli RNA degradosome. The rne gene was replaced with alleles encoding deletions in the noncatalytic part of RNase E. All the proteins are stable in vivo . RNase E activity was tested using a P T7 -lacZ reporter gene, the message of which is particularly sensitive to degradation because translation is uncoupled from transcription. The non-catalytic region has positive and negative effectors of mRNA degradation. Disrupting RhlB and enolase binding resulted in hypoactivity, whereas disrupting PNPase binding resulted in hyperactivity. Expression of the mutant proteins in vivo anticorrelates with activity showing that autoregulation compensates for defective function. There is no simple correlation between RNA binding and activity in vivo . An allele ( rne131 ), expressing the catalytic domain alone, was put under P lac control. In contrast to rne + , low expression of rne131 severely affects growth. Even with autoregulation, all the mutants are less fit when grown in competition with wild type. Although the catalytic domain of RNase E is sufficient for viability, our work demonstrates that elements in the non-catalytic part are necessary for normal activity in vivo .