JAK2 and essential thrombocythemia: The JAK2 V617F mutation is found in most patients with essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) [2]. This mutation results in constitutive activation of the JAK-STAT signalling pathway, leading to increased proliferation of hematopoietic cells independently of external cytokine signals [3].