CHEK1 and medulloblastoma: Finally, using the radiosensitive Patched-1+/- (Ptch1+/-) mouse model system that has a defect in radiation-induced activation of the ATR-Chk1 checkpoint signaling pathway, Mancuso et al. reported induction of medulloblastoma in the non-irradiated brain tissues after partial irradiation of the lower half of the animal with a 3 Gy dose of X-rays[10].