When PTCH1−/− iPSCs were subcutaneously injected into immunodeficient mice, the resulting teratomas almost exclusively contained immature ectodermal lineage cells expressing medulloblastoma markers, and the percentages of the area occupied by medulloblastoma-like tissue were larger in PTCH1−/− teratomas than in PTCH1+/− teratomas. The gene discussed is PTCH1; the disease is medulloblastoma.