XRCC4 and medulloblastoma: This study demonstrates that ablation of XRCC4 in combination with p53 in neural stem/progenitors efficiently induces brain tumours at 100% penetrance, in which a heterogeneous population of NS is targeted that arise in medulloblastomas in young mice, whereas only GBMs and not other glioma subtypes arise in advanced aged adult mice, with the latter more highly represented in other p53 knockout5 and mutant models6.