PTCH1 and medulloblastoma: We then investigated the mutation status of PTCH1 and TP53, as both genes are frequently mutated in SHH medulloblastoma (Cavalli et al., 2017, Kool et al., 2014, Northcott et al., 2017), and dominant-negative mutations of TP53 are known to be acquired in vitro in human pluripotent stem cells (Merkle et al., 2017).