XRCC2 and medulloblastoma: In this study, loss of either non-homologous end joining (NHEJ) gene DNA Ligase IV (Lig4), or genes involved in homologous recombination (HR) like X-ray cross complementation 2 (XRCC2), and breast cancer growth suppressor protein 2 (BRCA2), or (Lig4/XRCC2) in combination with p53 deficiency resulted in PTCH1 downregulation, GLI1 activation and rapid development of medulloblastoma [37].