JAK2 and acquired polycythemia vera: According to the World Health Organization (WHO) classification, four variants of myeloproliferative neoplasms (MPNs), associated with JAK2, CALR, and MPL gene mutations were identified: Polycythemia vera (PV), essential thrombocytopenia (ET), primary myelofibrosis (PMF), and prefibrotic PMF (pre-PMF) [64].