JAK2 and essential thrombocythemia: Several reports of the JAK2 V617F mutation frequency in MPN showed that there is a wide variation, ranging from 51.6 to 79% in all MPN, from 79.2 to 100% in PV, from 25 to 70% in ET, from 12.5 to 90% in PMF and from 25 to 67.5% in MPN-U.