During the monitoring period, more than one third of Ptch1Δ/+ mice developed medulloblastomas by week 30 (n = 23/58, 39%), while this frequency was reduced by ≥60% in Ptch1Δ/+Pn-1Δ/+ (n = 7/42, 16%) and Ptch1Δ/+Pn-1Δ/Δ mice (n = 1/11, 9%). Here, PTCH1 is linked to medulloblastoma.