TP53 and Mobius syndrome: Given homozygous loss of p53 dramatically increased the penetrance and accelerated Ptch1 loss-driven SHH-MB formation, we investigated whether p53R172P and p53WT alleles were, respectively, inactivated in SHH-MBs arising from Ptch1+/−p53R172P and Ptch1+/−p53WT models.