The polycythemia and pulmonary hypertension phenotype of Irp1-/- mice and the anemia and neurodegeneration phenotype of Irp2-/- mice likely support a unique functions of IRP1 and IRP2 in erythropoiesis/cardiovascular regulation and erythroblasts/nervous system, respectively. The gene discussed is ACO1; the disease is pulmonary arterial hypertension.