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). This evidence concerns the gene HAMP and chronic mountain sickness.