In the Ptch1+/− mouse model, higher spontaneous MB incidence is shown in a C57BL/6 background compared with a CD1 background (40.9% vs. 7.7%) [11,12], suggesting that a larger proportion of dividing cells may acquire tumor-initiating mutations in the early postnatal cerebellum depending on the genetic background [11]. The gene discussed is PTCH1; the disease is neoplasm.