JAK2 and essential thrombocythemia: A single point JAK2 V617F mutation was identified in 23 (88.5%) of 26 patients with PV, 24 (57.1%) of 42 with ET, six (85.7%) of seven with MF and two (66.7%) of three with unclassifiable MPN detected by at least one method with positive result (Table 2).