In characterizing a disease model for myeloproliferative neoplasms, Yeh and colleagues generated iPSC lines from CD34+ peripheral blood cells of two patients with JAK2-V617F defined myeloproliferative disorders (MPD), one evidencing polycythemia vera (PV) and the other with primary myelofibrosis (PMF). The gene discussed is JAK2; the disease is acquired polycythemia vera.