In contrast to cells from ATR-, CtIP-, CEP152- and PCNT-Seckel syndrome patients, we have shown that MEFs from Cenpj-deficient mice are not impaired in ATR-dependent DNA damage signaling but instead show an elevated frequency of extra centrioles, multipolar spindles, and near tetraploid karyotypes. Here, RBBP8 is linked to microcephalic primordial dwarfism.