Non-CML MPNs such as polycythemia vera (PV), essential thrombocythemia (ET), or idiopathic myelofibrosis (IMF) display recurrent anomalies in the JAK2 tyrosine kinase that plays a critical role in mediating hematopoietic cytokine receptor signaling through the JAK/STAT pathway [80]. The gene discussed is JAK2; the disease is essential thrombocythemia.