A study involving 34 mountaineers revealed that marked increase in plasma ET-1 level was associated with elevated sPAP after ascent (Fig. 3, middle).234 Another research also delineated that PAP was positively correlated with increased plasma ET-1, indicating the contribution of elevated ET-1 to exaggerated pulmonary hypertension at high altitude.233 However, how ET-1 affects HAPE development remains to be further investigated. The gene discussed is EDN1; the disease is pulmonary arterial hypertension.