In MBs lacking the Btg1 gene, we observed a two-fold increase of the percentage of CD15-positive cells with respect to Ptch1+/−/Btg1WT tumors (p < 0.0001; Mann–Whitney U-test; Figures 7C,D), with a greater tendency of CD15+ cells to aggregate into clusters. Here, FUT4 is linked to Mobius syndrome.