Myeloproliferative neoplasms (MPNs) are clonal hematopoietic disorders characterized by an overproduction of erythrocytes, thrombocytes and/or leukocytes driven by mutations in Janus kinase 2 (JAK2), calreticulin, or myeloproliferative leukemia-related protein-encoding genes that induce constitutive activation of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway1,2. The gene discussed is JAK2; the disease is myeloproliferative neoplasm.