PTCH1 and medulloblastoma: The first study was carried out in a mouse model of medulloblastoma based on Ptc gene inactivation (tc is an antagonist of the Sonic Hedgehog (SHH) signaling pathway that acts as a regulator of stem cells and progenitors in the central nervous system): particularly, it was used a model that allows Ptc gene inactivation either in neural stem cells or GNPs.