To investigate the effect of loss of function of ephrin-A5 on medulloblastoma tumor growth in vivo, an ephrin-A5−/−Smo model was generated which lacks the ephrin-A5 gene and expresses a constitutively activated form of Smoothened (SmoA1) gene in cerebellar granule precursor cells. The gene discussed is EFNA5; the disease is medulloblastoma.