Our data suggest that a small increase in circulating sENG concentrations in some patient groups, such as changes from ∼4 ng/mL in healthy controls to ∼8 ng/mL as measured in PAH patients (6), more likely reflects the consequence of endothelial dysfunction and increased shedding of cell-surface receptors, rather than sENG directly contributing to the disease pathogenesis. This evidence concerns the gene CD177 and pulmonary arterial hypertension.