APC and Familial adenomatous polyposis: The standard clinical diagnosis of FAP is based on the identification of >100 colorectal adenomatous polyps.8 However, when a proband has no family history of an FAP phenotype, we should consider the following possibilities: (1) a de novo APC mutation, which is identified in 10–25% of FAP patients; (2) MAP, which is an autosomal recessive hereditary disease; or (3) somatic APC mosaicism.