It has been demonstrated that the JAK2 V617F point mutation, a common molecular genetic abnormality, occurs in polycythemia vera (PV), essential thrombocythemia histiocytosis (ET) and primary myelofibrosis (PMF); therefore, the JAK2 mutation may be an important diagnostic tool for the detection of myeloproliferative neoplasms (MPNs) (2). The gene discussed is JAK2; the disease is primary myelofibrosis.