There is no clear distinction between the markers and biomarkers of endothelial cells uncontrolled proliferation, as some are expressed on the cell surface and can also be released into the bloodstream through a process called shedding (such as ACE, VWF, ADAMTS-13, soluble adhesion molecules, and others), and there is no study to date measuring the serum and endothelial levels of potential biomarkers simultaneously particularly in the context of PAH related to CHD18–20. Here, ACE is linked to pulmonary arterial hypertension.