Derepression of the shared target HIF2α most likely causes the polycythemia and pulmonary hypertension of Irp1-/- mice (Anderson et al., 2013; Ghosh et al., 2013; Wilkinson and Pantopoulos, 2013), and dysregulation of the shared targets ferritin, TfR1, and eALAS likely lead to the diseases of Irp2-/- mice (LaVaute et al., 2001; Cooperman et al., 2005; Galy et al., 2005; Ferring-Appel et al., 2009; Jeong et al., 2011; Ghosh et al., 2013). This evidence concerns the gene IREB2 and polycythemia.