Of the many progenitor populations, the most prominently expanded population in Runx1+/− mice, namely GMPs, have been regarded as candidate targets for oncogenic transformation in leukemia.37 Furthermore, GMPs were efficiently transformed into leukemia-initiating cells by retroviral transduction of MLL-AF9.38 Therefore, the sustained expansion of preleukemic GMPs in FPD patients may greatly elevate the likelihood of acquiring cooperating mutations to develop full-blown leukemia. The gene discussed is MLLT3; the disease is leukemia.