Mice with activation of NRasG12D+/− alone (Mx1-Cre+;NRasG12D+/−, hereafter G12D) developed chronic myeloproliferation with long latency (median survival >365 days), consistent with an MPN-like phenotype13, whereas mice deficient for EZH2 alone (Mx1-Cre+;Ezh2f/f, hereafter E2-KO) had little effect on hematopoiesis. The gene discussed is EZH2; the disease is myeloproliferative neoplasm.