A single somatic mutation, V617F (exon 14) in the JH2 domain of JAK2, which disrupts the JH1-JH2 autoinhibitory interaction, leading to JAK2 hyperactivation40–42, is a common hallmark of the BCR::ABL1-negative myeloproliferative neoplasms. The gene discussed is JAK2; the disease is myeloproliferative disorder.