These phenotypes bear a remarkable similarity to an aggregate phenotype for Gfi1−/− mice (which exhibit severe neutropenia, a monocytosis, and normal numbers of red cells and platelets; Karsunky et al., 2002) and Gfi1b−/− mice (which die in utero with arrested erythroid and megakaryocytic development; Saleque et al., 2002). Here, GFI1B is linked to neutropenia.