The importance of JAK2 in hematological malignancies became apparent in 2005 after four research groups identified a single missense mutation within the pseudokinase domain of JAK2; JAK2 p. V617F, as the primary driving alteration underlying most MPNs (Baxter et al., 2005; James et al., 2005; Kralovics et al., 2005; Levine et al., 2005; Silvennoinen and Hubbard, 2015a; Hubbard, 2018). The gene discussed is JAK2; the disease is hematologic disorder.