Short answer · Medically reviewed summary · Last updated: 2026-05-08
Familial Adenomatous Polyposis (FAP) is a hereditary condition characterized by the development of hundreds to thousands of precancerous polyps in the colon and rectum, which carry an extremely high risk of progressing to colorectal cancer if left untreated. Because it is a systemic genetic disorder, Familial Adenomatous Polyposis can also affect other parts of the digestive tract and various organ systems throughout the body. What causes Familial Adenomatous Polyposis? Familial Adenomatous Polyposis is caused by a germline mutation in the APC (adenomatous polyposis coli) gene, which provides instructions for making a protein that acts as a tumor suppressor.
1 people with Familial Adenomatous Polyposis have shared their first-person experience on this question at DiseaseMaps.
What is Familial Adenomatous Polyposis
What is Familial Adenomatous Polyposis? Plain-language, medically reviewed definition plus the lived reality told by patients.
Familial Adenomatous Polyposis (FAP) is a hereditary condition characterized by the development of hundreds to thousands of precancerous polyps in the colon and rectum, which carry an extremely high risk of progressing to colorectal cancer if left untreated. Because it is a systemic genetic disorder, Familial Adenomatous Polyposis can also affect other parts of the digestive tract and various organ systems throughout the body.
What causes Familial Adenomatous Polyposis?
Familial Adenomatous Polyposis is caused by a germline mutation in the APC (adenomatous polyposis coli) gene, which provides instructions for making a protein that acts as a tumor suppressor. When this gene is mutated, cells in the colon grow and divide uncontrollably, leading to the formation of numerous adenomas. Familial Adenomatous Polyposis is inherited in an autosomal dominant pattern, meaning each child of an affected parent has a 50% chance of inheriting the mutation.
Who is affected by Familial Adenomatous Polyposis?
The prevalence of Familial Adenomatous Polyposis is estimated to be between 1 in 7,000 and 1 in 22,000 individuals worldwide. While the condition affects both men and women equally, the clinical onset typically occurs during adolescence or early adulthood, with the average age of polyp detection around 16 years old. If untreated, the risk of developing colorectal cancer approaches 100% by age 40.
What are the clinical subtypes and features of FAP?
There are two primary classifications based on the number of polyps and clinical severity:
- Classic FAP: Characterized by the presence of 100 to thousands of colorectal adenomas, usually appearing in the teenage years.
- Attenuated FAP (AFAP): A milder form where patients typically develop fewer than 100 polyps, often appearing later in life, with a lower but still significant risk of cancer.
- Extraintestinal manifestations: Beyond the colon, Familial Adenomatous Polyposis may cause desmoid tumors, osteomas (bone growths), congenital hypertrophy of the retinal pigment epithelium (CHRPE), and dental abnormalities.
Next steps
- Consult a gastroenterologist or clinical geneticist to discuss genetic testing and personalized screening schedules.
- Join the 147 members of the Familial Adenomatous Polyposis community on DiseaseMaps.org to share experiences and find support.
- Ensure all first-degree relatives receive appropriate genetic counseling and surveillance.
Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician.
References
- NIH Genetic and Rare Diseases Information Center (GARD): Familial Adenomatous Polyposis
- Orphanet: Familial Adenomatous Polyposis (ORPHA733)
- OMIM (Online Mendelian Inheritance in Man): Adenomatous Polyposis of the Colon (#175100)
- The Polyposis Registry and patient advocacy groups like the Colon Cancer Foundation
Posted Mar 8, 2020 by Tracey 100
