JAK2 and essential thrombocythemia: Lastly, we investigated the impact of JAK2 V617F allele burden on bone marrow hyperplasia, and found that BM granulopoiesis (%) increased with JAK2 V617F allele burden, other than BM erythropoiesis (%) in ET patients, but opposite results were obtained in PV patients, although not to a significant extent, as shown in Table 4.