TP53 and Mobius syndrome: Yet, we also observed an increased p53 expression within the tumors lacking the Btg1 gene (Ptch1+/−/Btg1KO vs. Ptch1+/−/Btg1WTp = 0.0070; Student's t-test; Figure 7A), which, given the proapoptotic action of p53, may explain the lack of increase of proliferation in MBs.