Familial Adenomatous Polyposis

Also known as: Adenomatous Polyposis Coli; Familial Multiple Polyposis; Familial Polyposis Coli; Hereditary Polyposis Coli; Polyposis Coli


Familial adenomatous polyposis (FAP) is a rare inherited condition that is caused by a mutation (spelling mistake) in the APC gene. The main feature of FAP is the formation of large numbers of adenomas (pre-cancerous polyps; see entry Cancer) in the large bowel.


Medical text written October 2018 and reviewed November 2020 by Professor Sue Clark, Consultant Colorectal Surgeon and Director, The Polyposis Registry, St Mark’s Hospital, London, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

People with FAP usually have no symptoms unless the condition is not picked up until they develop large polyps or even bowel cancer. These can cause:

  • blood in the faeces
  • change in bowel habit (usually towards looser and more frequent motions)
  • anaemia

There are some other features associated with FAP, including:

  • adenomas (polyps) in the duodenum (part of bowel immediately beyond the stomach)
  • osteomas (harmless bony lumps on the jaw or skull)
  • epidermoid (skin) cysts
  • desmoids (non-cancerous masses of scar-like tissue)

The large bowel polyps usually appear in adolescence, and grow very slowly. Left untreated they inevitably develop into bowel cancer, usually by the age of 40-50 years.

What are the causes?

FAP is caused by a mutation (spelling mistake) in the APC gene.

How is it diagnosed?

Most individuals with FAP are known to be at risk because they have an affected parent. In around 90% of families the genetic spelling mistake causing FAP in that family can be identified, so family members can have a blood test to see whether or not they have inherited it. This is usually offered at around 12-14 years of age. If the genetic mutation in a family cannot be found, colonoscopy (telescope test via the anus) is used to look for bowel polyps, again starting from 12-14 years of age.

Once someone is diagnosed with FAP by genetic testing, a colonoscopy is needed to see how many polyps they have and how large they are.

How is it treated?

The most important part of the management of FAP aims to prevent large bowel cancer by removing the pre-cancerous polyps. Usually this needs surgery to remove most or all of the large bowel. This is most commonly done in the late teens.

Follow-up is very important. Any remaining large bowel needs regular monitoring by endoscopy (flexible telescope), so that developing polyps can be removed. The duodenum (part of bowel immediately beyond the stomach) also needs to be examined regularly with a flexible endoscopy through the mouth, so that polyps there can be identified and treated.

Inheritance patterns and pre-natal diagnosis

Inheritance patterns
FAP is dominantly inherited. In about 80% of cases this is inherited from a parent. In the other 20% the affected person is the first in the family to have FAP, but can pass it on.

Prenatal diagnosis
Prenatal diagnosis by chorionic villus biopsy or amniocentesis is possible when a parent is affected and the gene mutation known. Pre-implantation genetic diagnosis is also available to allow an affected individual to have children free of the condition.

Is there support?

FAP Gene Support Group

Tel: 01664 566101
Email: enquiries@fapgene.com
Website: fapgene.com

Established in 2004, the FAP Gene Support Group provides support, information and education to those affected by Familial Adenomatous Polyposis and Gardner’s Syndrome (FAP), and aims to raise awareness of the condition. The Group also holds an annual, informal chat day.

Group details last reviewed November 2020.

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