Thus, mutations in the third nucleotide within the binding domainof the 5′-splice site in U1 were detected in medulloblastoma cells.Alternative splicing results in inactivation of tumor-suppressor genes(PTCH1) and activation of oncogenes (GLI2and CCND2) in medulloblastoma cells with mutant U1sn- RNA [98]. The gene discussed is PTCH1; the disease is medulloblastoma.