Npm1 heterozygous mice develop erythroid dysplasia with elevated mean corpuscular volume and red cell distribution width, normal red blood cell counts and hemoglobin (Hb) levels, and dysplastic megakaryocytes.15 However, the role of NPM1 in the pathogenesis of MDS/AML is unclear, since NPM1 is not deleted in most patients with a del(5q), nor have NPM1 mutations been identified in patients with a del(5q).23 Here, NPM1 is linked to acute myeloid leukemia.