The understanding of the pathogenesis of PV vastly grew after activating mutations in the Janus kinase 2 (JAK2) gene were identified in most patients with PV, with the classical JAK2 V617F mutation present in approximately 96 % and JAK2 exon 12 mutations in approximately 3 % of patients with PV [11, 12]. The gene discussed is JAK2; the disease is acquired polycythemia vera.