To determine the effects of the enhanced ISR on medulloblastoma development, Ptch1+/− mice were crossed with Gadd34−/− mice, and then the resulting progeny were intercrossed to obtain Ptch1+/−; Gadd34 wild type (Gadd34+/+) mice, Ptch1+/−; Gadd34+/− mice, and Ptch1+/−; Gadd34−/− mice. The gene discussed is PPP1R15A; the disease is medulloblastoma.