JAK2 and acquired polycythemia vera: Thus, JAK2 V617F homozygote PV patients (around 30% depending on the cohorts) displayed a significantly higher hemoglobin level, increased incidence of pruritus, stimulated erythropoiesis and myelopoiesis, higher prevalence of splenomegaly, and increased progenitor cells in peripheral blood associated with a higher risk of fibrotic transformation in comparison with their heterozygote counterparts [5,29,30].