The therapeutic importance of JAK2 accelerates the development of its inhibitors, and a number of ATP competitive (Type-I) inhibitors with good efficacy have even been pushed into preclinical and clinical stages12–16, such as the FDA approved JAK2 inhibitor Ruxolitinib (Fig. 1A) for the treatment of myelofibrosis and hydroxyurea-resistant polycythemia vera (PV)17–21. The gene discussed is JAK2; the disease is acquired polycythemia vera.