Hyperactive signaling of the Janus-Associated Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) pathway is central to the pathogenesis of Philadelphia-chromosome-negative myeloproliferative neoplasms (MPN), i.e., polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) which are characterized by inherent biological and clinical heterogeneity. The gene discussed is SOAT1; the disease is acquired polycythemia vera.