Clinical studies found that several gain-of-function mutations that occurred in the primary hydroxylation site (Pro531) at EPAS1 caused erythroctosis and pulmonary hypertension [51].While, the unique EPAS1 mutation in the Tibetan people were associated with lower hemoglobin concentrations [52, 53], suggesting that it played a loss-of-function role to high blood viscosity and cardiovascular disorders. Here, EPAS1 is linked to pulmonary arterial hypertension.