No major predisposition gene for familial myeloproliferative neoplasms (MPN) has been identified. Here we demonstrate that the autosomal dominant transmission of a 700-kb duplication in four genetically related families predisposes to myeloid malignancies, including MPN, frequently progressing to leukemia. Using induced pluripotent stem cells and primary cells, we demonstrate that overexpression of ATG2B and GSKIP enhances hematopoietic progenitor differentiation, including of megakaryocytes, by increasing progenitor sensitivity to thrombopoietin (TPO). ATG2B and GSKIP cooperate with acquired JAK2, MPL and CALR mutations during MPN development. Thus, the germline duplication may change the fitness of cells harboring signaling pathway mutations and increases the probability of disease development.

JAK2V617F is the predominant mutation in myeloproliferative neoplasms (MPN). Modeling MPN in a human context might be helpful for the screening of molecules targeting JAK2 and its intracellular signaling. We describe here the derivation of induced pluripotent stem (iPS) cell lines from 2 polycythemia vera patients carrying a heterozygous and a homozygous mutated JAK2V617F, respectively. In the patient with homozygous JAK2V617F, additional ASXL1 mutation and chromosome 20 allowed partial delineation of the clonal architecture and assignation of the cellular origin of the derived iPS cell lines. The marked difference in the response to erythropoietin (EPO) between homozygous and heterozygous cell lines correlated with the constitutive activation level of signaling pathways. Strikingly, heterozygous iPS cells showed thrombopoietin (TPO)-independent formation of megakaryocytic colonies, but not EPO-independent erythroid colony formation. JAK2, PI3K and HSP90 inhibitors were able to block spontaneous and EPO-induced growth of erythroid colonies from GPA+CD41+ cells derived from iPS cells. Altogether, this study brings the proof of concept that iPS can be used for studying MPN pathogenesis, clonal architecture, and drug efficacy.