The WHO (World Health Organization) diagnostic criteria for MPNs include the driver mutations; therefore in PV the JAK2 mutation frequency is 98%; in ET the JAK2, CALR, and MPL mutation frequency is 60%, 22%, and 3%, while in PMF the frequency of JAK2, CALR, and MPL mutation is 58%, 25%, and 7% [8]. The gene discussed is JAK2; the disease is essential thrombocythemia.