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Clinical manifestations and diagnosis of familial adenomatous polyposis

Daniel C Chung, MD
Tomer Adar, MD
Section Editor
Paul Rutgeerts, MD, PhD, FRCP
Deputy Editor
Shilpa Grover, MD, MPH, AGAF


Familial adenomatous polyposis (FAP) is characterized by the presence of multiple colorectal adenomatous polyps (typically more than 100). Multiple colorectal adenomas may also be seen in individuals with MUTYH-associated polyposis (MAP). Other rare causes include the polymerase proofreading-associated polyposis (PPAP) syndrome or hereditary mixed polyposis [1].

This topic will review the genetics, clinical manifestations, and diagnosis of FAP. Surveillance strategies for FAP and the clinical features and diagnosis of MUTYH-associated polyposis and the hamartomatous polyposis syndromes are discussed separately. (See "Familial adenomatous polyposis: Screening and management of patients and families" and "MUTYH-associated polyposis" and "Peutz-Jeghers syndrome: Epidemiology, clinical manifestations, and diagnosis" and "Juvenile polyposis syndrome" and "PTEN hamartoma tumor syndrome, including Cowden syndrome".)


Familial adenomatous polyposis (FAP) has an estimated prevalence of three cases per 100,000 individuals and accounts for less than 1 percent of all colorectal cancers in the United States [2]. It affects both sexes equally and has a worldwide distribution [3].


Familial adenomatous polyposis (FAP) and its variants are caused by germline mutations in the tumor suppressor gene, Adenomatous Polyposis Coli (APC), located on chromosome 5q21-q22 [4].

FAP follows an autosomal dominant pattern of inheritance with nearly complete penetrance of colonic polyposis but variable penetrance of the extracolonic manifestations of the disease. Up to 25 percent of FAP cases are due to new or de novo APC mutations [5]. Such patients do not have a family history of FAP. (See "Genetics: Glossary of terms" and "Inheritance patterns of monogenic disorders (Mendelian and non-Mendelian)" and 'Clinical manifestations' below and "Inheritance patterns of monogenic disorders (Mendelian and non-Mendelian)", section on 'Incomplete or variable penetrance'.)

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Literature review current through: Sep 2017. | This topic last updated: May 24, 2017.
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