TP53 and microcephaly: Using a well-characterized Mcph1 knockout mouse model of microcephaly (Liang et al, 2010; Liu et al, 2021), we show here for the first time that loss of Mcph1 results in impaired terminal differentiation of erythroid progenitors due to a p53-independent acytokinetic mitosis, leading to severe congenital anemia.