Janus kinase 2 (JAK2) is a cytoplasmic tyrosine kinase engaged with numerous intracellular signaling pathways involving receptors for erythropoetin, thrombopoetin, interleukin-3, granulocyte colony-stimulating factor and granulocyte–macrophage colony-stimulating factor.10 A single acquired somatic point mutation at V617F in JAK2 causes MPN in patients.11, 12 JAK2V617F is found in 95% polycythemia vera patients and detected in ~60% of ET and PMF patients.9 The JAK2V617F mutation affects the pseudokinase domain of JAK2 and makes JAK2 constitutively active.13 Here, JAK2 is linked to acquired polycythemia vera.