High p53 expression induces apoptosis in fetal liver erythroblasts, and erythroid-specific inactivation of the mouse Mdm2 gene, a key negative regulator of p53, leads to increased apoptosis in erythroblasts and embryonic lethality due to a severe anemia (Mdm2lox/loxEpoRcre+) [26]. The gene discussed is MDM2; the disease is anemia.