The EGL hyperplasia and disrupted GNP migration that we observe in the vermis of Norrin-deficient Neurod2-SmoA1+/− mice are particularly noteworthy, as this region is reported to be protected from malignant progression31,32, and raises the possibility that the anti-tumour progression effects of Norrin/Fzd4 signalling in the stroma contribute to this regional barrier to tumourigenesis. Here, FZD4 is linked to neoplasm.