CTNNB1 and Familial adenomatous polyposis: Approximately 85–90% of DT cases are sporadic, associated with mutations in the CTNNB1 gene that encodes β-catenin, while 5–10% of cases arise in the context of familial adenomatous polyposis (FAP) in which there is a germline mutation in the adenomatous polyposis coli gene (APC)1.