JAK2 and acquired polycythemia vera: An increasing need for phlebotomy means either that the PV erythrocytes have too much iron available to them [110], or that conversion by 9pUPD to JAK2 V617F homozygosity has occurred; rarely are PV patients also heterozygous for the HFE gene mutation, C282Y, which further promotes iron absorption and enhances erythropoiesis.