MPN, including polycythemia vera, essential thrombocythemia, and primary myelofibrosis are clonal diseases of hematopoietic progenitor cells associated with common mutations in the Janus kinase 2 (JAK2) gene, the gene encoding the thrombopoietin receptor (MPL), and the calreticulin (CALR) gene [48,49,50,51,52]. The gene discussed is JAK2; the disease is acquired polycythemia vera.