Recently, Irp1−/− mice were documented to develop polycythemia and pathological iron metabolism due to stress erythropoiesis, as well as pulmonary hypertension and cardiac hypertrophy and fibrosis (Anderson et al., 2013; Ghosh et al., 2013; Wilkinson and Pantopoulos, 2013). The gene discussed is ACO1; the disease is pulmonary hypertension.