EPAS1 and pulmonary arterial hypertension: Chuvash polycythemia patients and a corresponding mouse model with a VHLR200W mutation develop polycythemia and pulmonary hypertension, and the pulmonary hypertension of the mouse model is improved by deletion of one allele of Hif2α, suggesting that there is a pathogenic role of HIF2α in this disease (Bushuev et al., 2006; Hickey et al., 2010; Formenti et al., 2011).