CTNNB1 and Familial adenomatous polyposis: The majority of cases are sporadic and develop due to mutations in the Catenin Beta 1 (CTNNB1) gene, while the rest (approximately 10%) are associated with the familial adenomatous polyposis (FAP) syndrome caused by germline inactivating mutations in the adenomatous polyposis coli (APC) gene involved in the downregulation of β-catenin.