The present study showed that mutations associated with CTNNB1 Syndrome are also found in exon 3, although mutations in this region are usually associated with cancer, because exon 3 bears important amino-acid residues for β-catenin degradation, such as the CK1-α phosphorylation site (S45), GSK3-β phosphorylation sites (S33, S37, and T41), and Fbw1 (D32 and G34). Here, CTNNB1 is linked to cancer.