The occurrence of somatic activation mutation (valine to phenylalanine) in the pseudokinase domain (V617F) of JAK2 has been implicated in myeloproliferative neoplasms (MPNs) like polycythemia vera (PV: 90% of patients), essential thrombocythemia (ET: 50% of patients) and primary myelofibrosis (PMF: 50% of patients) (3–6). Here, JAK2 is linked to primary myelofibrosis.