JAK2 and acquired polycythemia vera: The vast majority of PV patients are the result of acquired JAK2 mutations in their stem cells, namely JAK2V617F on exon 14 (95% of PV patients) or mutations in exon 12 of the JAK2 gene (2–3% of PV patients) (Pardanani et al., 2007; Scott et al., 2007).