PTCH1 and medulloblastoma: Deletion of the SHH-repressor Patched (PTCH1) in mice results in lethal medulloblastomas [127], and the deletion of AHR in PTCH1−/− granule cerebellar progenitor cells led to arrested differentiation, exacerbated tumorigenesis, and significantly reduced survival (median survival: 63.5 days for AHR+/+ versus 33 days for AHR−/−) [86].