In these mutants, endogenous or gamma irradiation-induced DNA damage and p53-dependent apoptosis were shown to occur non-selectively in all progenitors that undergo active proliferation; abrogating p53 ameliorated the microcephaly but made little improvement to the structure of the mutant brain, which agree well with the wide-spread loss-of-function defects of these genes in many other organs. Here, TP53 is linked to microcephaly.