When Brca2Δex3-4 was coupled with global Trp53 knockout, mice formed medulloblastomas with complete penetrance and exhibited a significant decrease in survival due to the tumor burden of double mutants (Fig. 1 F and G) in contrast to Brca2WT; Trp53−/− and Brca2Δex3-4; Trp53+/+ animals, which did not develop MBs. This evidence concerns the gene TP53 and Mobius syndrome.