The chronic myeloproliferative neoplasms (MPN), which include polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) [1], are characterized by a V617F point mutation in the exon 14 of Janus Kinase 2 (JAK2) that occurs in 95% of PV and 60% of ET or PMF patients [2], [3]. The gene discussed is JAK2; the disease is primary myelofibrosis.