Medulloblastoma consist of four predominant subgroups with distinct molecular characteristics: Group 1 tumors exhibit mutations in the sonic hedgehog (SHH) gene and its protein receptors; group 2 tumors are induced by changes in WNT signaling, generally through the main responsive gene, β-catenin; group 3 tumors occur due to alterations in transforming growth factor-β-orthodenticle homeobox 2 signaling; and group 4 tumors arise from MYC and MYCN mutations (4–7). The gene discussed is SHH; the disease is medulloblastoma.