To time the developmental origin of medulloblastoma with this approach, we quantified clonal SNV densities from the allele frequency distribution of somatic variants in 181 primary medulloblastomas of all subgroups (Extended Data Fig. 6a,b; comprising 108 group 3/4 medulloblastomas, 21 infant Sonic Hedgehog (SHH)-medulloblastomas, 35 childhood/adulthood SHH-medulloblastomas and 17 WNT-medulloblastomas). The gene discussed is SHH; the disease is medulloblastoma.