SHH and medulloblastoma: This unique postnatal expansion of neuronal precursors is driven in large part by the mitogen Sonic Hedgehog (SHH) [1], and deregulation of the SHH signaling pathway in GCPs gives rise to a subset of medulloblastoma [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24], which is the most prevalent metastatic brain tumor of childhood [5,8].