APC and Familial adenomatous polyposis: It is valuable to estimate the prevalence in the general population of benign clinical features associated with cancer predisposition syndromes to help distinguish those suggestive of a diagnosis, such as bilaterality, CHRPE, or multiple osteomas in FAP, and LLD, oral mucosa papules, and acral/palmoplantar keratosis in PHTS, from those that may only support the suspected diagnosis, such as macrocephaly and mental retardation (in PHTS) or oligodontia (in syndromes due to mutated genes associated with Wnt1 (APC, AXIN2).