What is familial adenomatous polyposis (FAP)?
Familial adenomatous polyposis (FAP) is a rare genetic condition that can have a high risk of causing bowel cancer if not treated. It used to be called Gardner syndrome.
FAP causes lots of small growths called polyps to grow in the large bowel. If they are left untreated, at least one of them is highly likely to turn into bowel cancer, usually by the age of 40.
How does FAP occur?
Cells contain genes, which are the instructions that cells need to work properly. A change in a gene, called a variant or mutation, means these instructions may not be correct anymore. People with FAP have a variant in their APC gene.
How is FAP inherited?
Genes are passed from parents to children, and everyone has two copies of each gene – one from our mother and one from our father. If one parent has FAP, the child has a 50% chance of also inheriting it.
How is FAP diagnosed?
FAP is usually diagnosed through genetic testing, which involves having a blood test to check for the APC gene variant. A test for FAP is usually offered around the age of ten or twelve for children whose parents or siblings have FAP. You may also be offered genetic testing if a high number of polyps are found during a colonoscopy or bowel cancer treatment.
How is FAP treated?
If you have FAP, you may be offered screening tests to find cancer at an early stage, and to find and treat any changes that are likely to develop into cancer later. This screening may include a colonoscopy to look at the lining of your bowel, and an upper endoscopy to look for signs of cancer in the stomach or small bowel.
You may also choose to have surgery to remove the large bowel, and potentially also the rectum. This is a personal decision and your doctor can talk to you about the best time to do this depending on your age, risk, genes, bowel screening results, and feelings about surgery.
*Statistics from https://www.bowelcanceruk.org.uk/about-bowel-cancer/risk-factors/family-history/map-and-fap/ Accessed 19.05.26