PTCH1 and medulloblastoma: Several reports have illuminated aspects of PTCH1 epigenetic regulation: no methylation has been reported in the proximal promoter region 1B of the PTCH1 promoter in primary medulloblastomas, suggesting the possibility of methylation of its distal region, 1C [31]; a knockout mouse tumor model has documented changes in PTCH1 expression after treatment with demethylating agents [32].