SHH and Mobius syndrome: CCANs linked to ATOH1 are identified in SHH clusters, which is consistent with previous reports that ATOH1+ cerebellar granule cell progenitors (GNPs), which express SOX2 in the developing external granule layer, are particularly vulnerable to SHH‐driven tumorigenesis (Figures 1F and 2D).[28, 29] Group 3 tumors account for ≈25–30% of MBs and have the worst prognosis.