PTCH1 and nevoid basal cell carcinoma syndrome: To determine whether PTCH1 loss also generates medulloblastoma in a human stem cell system, we isolated keratinocytes from a healthy control (KTM1, referred as control) and from two different patients with Gorlin syndrome (KAS537 and KAS573 referred as Gorlin 1 and Gorlin 2, respectively; Figures S3A and S3B), both of whom were predisposed to medulloblastoma due to heterozygous germline mutations in PTCH1 (Cowan et al., 1997, Hahn et al., 1996, Johnson et al., 1996, Wu et al., 2017).