Equally, venesection of Peruvian high-altitude residents suffering from chronic mountain sickness — a condition in which polycythemia, hypoxemia, and pulmonary hypertension are features (109) — brings about a very rapid fall in circulating hepcidin levels, consistent with an erythroid regulator signaling the tension between erythropoietic drive and iron supply (110). Here, HAMP is linked to pulmonary arterial hypertension.