Abnormal activation of SHH signaling might predispose to occurrence of medulloblastoma by inducing the inhibition of the retinoblastoma tumor-suppressor gene and directly inducing mediators of cell mitosis such as the proto-oncogene N-myc, which amplification and overexpression can lead to tumorigenesis (Kenney et al., 2003; Oliver et al., 2003). Here, MYCN is linked to retinoblastoma.