Mono-allelic deletions, point mutations and translocations of one or more of these transcription factors often occur in pediatric B-ALL.9, 22 Reduced levels of factors encoded by Ikzf1, Runx1, Tcf3, Pax5 and Ebf1 may each be important individually for predisposing EB mice to tumor development, while concerted loss of these factors, particularly in combination, would potently induce loss of differentiation. The gene discussed is TCF3; the disease is precursor B-cell acute lymphoblastic leukemia.