Polycythemia vera (PV) is a BCR-ABL1-negative myeloproliferative neoplasm (MPN) characterized by excessive proliferation of erythroid, myeloid, and megakaryocytic components in the bone marrow, mainly due to a Janus kinase 2 gene mutation (JAK2V617F). The gene discussed is JAK2; the disease is myeloproliferative neoplasm.