JAK2 and myeloproliferative disorder: The more indolent and frequent JAK2V617F point mutations which induce myeloproliferative neoplasms occur within exons 12–15 of the pseudokinase domain of JAK2 (Fig. 1A), and require the N-terminal FERM domain for binding homodimeric type-I cytokine receptors [5], unlike JAK2 translocation proteins where it is invariably lost.