Janus kinase 2 (JAK2) is a protein tyrosine kinase that transduces cellular signals through the Janus kinase signal transducer and an activator of transcription pathways (JAK-STAT), which mediates cell growth, differentiation, apoptosis, transformation, and other fundamental cell functions, and is active in both normal hematopoiesis and hematological malignancies. The gene discussed is JAK2; the disease is hematologic disorder.