Familial Adenomatous Polyposis (FAP): Symptoms, Causes, Treatment & Genetic Testing
Overview
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Familial adenomatous polyposis (FAP) is an inherited condition linked mainly to disease-causing variants in the APC gene, leading to numerous adenomatous polyps in the colon and rectum.
- Polyps can develop before symptoms appear, sometimes from a young age, making appropriate screening important for people with increased risk.
- FAP can run in families, with each child of a parent carrying a disease-causing APC variant having a 50% chance of inheriting it.
- Genetic testing can help identify APC variants and may be recommended when multiple adenomatous polyps, a relevant family history, or other findings raise suspicion of FAP.
- Early identification and ongoing management can reduce health risks, with treatment and surveillance tailored to the person's polyp burden, genetic findings, age, and overall health.
FAP, or familial adenomatous polyposis, is a medical condition most often discovered when a family member is diagnosed, when colonoscopy reveals multiple polyps, or when a genetic test raises an alarm. Such unfamiliar information can make the situation seem personal.
FAP is an inherited condition that leads to the occurrence of numerous adenomatous polyps in the patient's colon and rectum. The important part is that these polyps can be present before any clear symptoms appear, which is why family history and relevant screening contribute to more accurate screening for people at higher risk of having this condition.
So, what exactly causes FAP? How is it passed from parents to children? What are the early signs, and what is the genetic test for familial polyposis? This guide covers the answers, along with diagnosis, treatment, family screening, and the role of APC gene testing.
What Is Familial Adenomatous Polyposis (FAP)?
Familial adenomatous polyposis (FAP) is a hereditary condition that causes many adenomatous polyps to develop in the colon and rectum. These polyps are usually benign when they first appear, but without appropriate monitoring and management, they can progress toward colorectal cancer.
FAP is typically associated with a pathogenic variant in the APC gene. It is uncommon, but important to recognize because polyps can begin developing at a young age, sometimes before a person notices any symptoms.
There is a wide range of APC-related polyposis types, such as classic FAP and attenuated FAP (AFAP), which can differ in their symptoms and levels of risk for colorectal cancer.
In layperson's terms, FAP means more than just having some polyps in the colon. FAP is a genetic disorder that requires monitoring over time, so appropriate genetic evaluation and treatment can be introduced when necessary.
What Causes Familial Adenomatous Polyposis?
FAP is generally caused by a mutation in the APC gene, which is involved in regulating cell growth and division.
1. APC Gene Variant
The APC gene helps regulate cell growth. A disease-causing variant in this gene can disrupt normal cell-growth control and contribute to the development of adenomatous polyps.
2. Abnormal polyp development
When APC-related growth regulation is disrupted, adenomatous polyps can develop throughout the colon and rectum. In classic FAP, hundreds or even thousands of polyps may eventually develop.
3. Different APC-related forms
The seriousness of this condition can vary greatly from person to person. Classic FAP often leads to the formation of hundreds or even thousands of polyps, whereas AFAP is characterized by a smaller number of polyps, which usually appear later in life.
4. Family history is an important clue
A family history of FAP, numerous colorectal polyps, or colorectal cancer in a young person are all factors that may contribute to a recommendation for genetic counseling.
How Is FAP Inherited?
The inheritance mode of FAP is autosomal dominant, which means that only one genetic variant of the APC gene is enough to present the condition.
- If one of the parents is a carrier of an APC mutation, each child has a chance of inheriting the mutation (50%).
- In case of genetic mutation inheritance, another child may develop FAP due to genetic predisposition and requires proper medical follow-up.
- In case of genetic mutation non-inheritance, the child is not a carrier of the familial APC mutation and does not pass it on to their offspring.
- Having no family history is not always an indication that FAP will not occur. In some instances, a person may have a new mutation of the APC gene that was not present in any of their parents.
- Testing family members can be helpful, as genetic counseling and testing can help identify which people are at risk and therefore warrant further screening.
What Are the Symptoms of Familial Adenomatous Polyposis?
Usually, FAP is detected fairly late because the early symptoms are not evident. Polyps can begin forming in childhood/or adolescence without any symptoms observed.
If a person gets more polyps or their size increases, the following symptoms might appear:
- Blood in stool/rectal bleeding
- Lasting diarrhea/various changes in bowel activity
- Abdominal pains or cramps
- Sudden weight loss
- Weakness due to anemia
FAP might manifest itself in forms other than colon manifestations, such as some pathological dental, skin, bone, and eye disorders.
Note: These symptoms do not confirm FAP. They can occur with several other conditions. A family history of FAP, multiple colorectal adenomatous polyps, or early-onset colorectal cancer is more significant when assessing whether FAP should be investigated.
When Should You Consider Genetic Testing for FAP?
Genetic testing for FAP may be advised if there are signs of a hereditary polyposis syndrome in your or your family's medical history.
Your doctor or a genetic counselor may suggest it if:
- You have multiple colorectal adenomatous polyps, particularly when the number of polyps is high, or they are diagnosed at a young age.
- A close relative of yours has been diagnosed with FAP or an APC-causing disease.
- You were diagnosed with colorectal cancer at an unusually young age.
- You or your family members had a history of many adenomatous polyps or relevant cancers.
- The number and the species of your polyps raise a suspicion of a hereditary syndrome.
- Your doctor suspects FAP based on colonoscopy even if no one in the family has been diagnosed before, since new cases of APC mutations may originate in individuals who do not have a family history of the disease.
What does APC testing look for?
The test for familial polyposis uses DNA to identify genetic alterations that lead to polyposis disorders. In the case of familial adenomatous polyposis (FAP), a mutation of the APC gene is typically present.
- The tests performed will usually include analysis of the APC gene for mutations that cause the disease.
- Analyses could include DNA sequencing, which looks for small mutations, as well as deletion or duplication analyses, which look for large mutations that are not easily detected by sequencing.
- A physician or genetic counselor may recommend using a broader hereditary polyposis panel depending on how the patient presents clinically.
- The test can be ordered when the physician suspects FAP as a result of clinical symptoms such as multiple adenomatous polyps, family history, and many other findings.
- The test result has to be evaluated along with the clinical picture of the patient and medical history to be interpreted properly.
If APC testing has been recommended, Redcliffe Labs offers an Adenomatous Polyposis Coli (APC) Gene Analysis Test. The test is specifically designed to look for genetic changes in the APC gene associated with familial adenomatous polyposis.
APC Gene Analysis Test at Redcliffe Labs
- Test: Adenomatous Polyposis Coli (APC) Gene Analysis
- Parameters: 1
- Sample: DNA/fluids
- Fasting: Not required
How Is Familial Adenomatous Polyposis Diagnosed?
FAP is diagnosed by putting together colonoscopy findings, personal and family history, and genetic testing. No single test is used in every case.
1. Colonoscopy
When many adenomatous polyps are observed in the colon and rectum, this is one of the first signs of FAP. The characteristics of the structure and configuration of the polyps will help differentiate between FAP and other polyposis syndromes.
2. Genetic Testing
Genetic testing can identify a disease-causing germline variant in the APC gene and can help confirm an APC-associated polyposis condition when the clinical findings support FAP.
3. Examination of Polyps
Tissue removed during colonoscopy can be examined to determine the type and characteristics of the polyps.
4. Family History
The family history helps to identify FAP. When the patient knows that FAP runs in his family or there are many cases of colorectal polyposis in relatives, the family's findings may suggest that the disease may be inherited.
5. Additional Evaluation
If the findings do not help establish a diagnosis of FAP, doctors may consider other hereditary polyposis syndromes and broader genetic testing.
Importantly, not finding an APC variant does not automatically rule out FAP. When the clinical findings strongly suggest the condition, doctors may continue management and surveillance based on the overall clinical picture.
What Is the Treatment for Familial Adenomatous Polyposis?
Treatment for FAP focuses on reducing colorectal cancer risk, controlling polyp growth, and monitoring for complications inside and outside the colon. The approach depends on the type of FAP, polyp burden, age, symptoms, and overall health.
1. Ongoing Monitoring
People have to undergo constant investigations of the colon and rectum as part of a check-up to track polyp progression and to catch any alarming changes as soon as possible.
2. Polyp Extraction
If necessary, polyp extraction can be performed using an endoscopic technique. It works well when the quantity and dimensions of polyps allow this procedure to be effective.
3. Preventive Operation
Because the classic form of FAP results in many structural changes in the colon, surgical intervention for colon removal becomes an essential step in the long-term management of the disease. A specialized doctor makes conclusions about when to operate and what type of operation to perform based on the individual's health condition.
4. Management of Upper-GI Polyps
FAP can lead to polyps in the duodenum and stomach as well; thus, monitoring of the upper gastrointestinal tract may be indicated.
5. Use of Medications in Certain Situations
Some medications, including non-steroidal anti-inflammatory medicines, may be used in certain cases to help manage polyps; however, they cannot replace the importance of monitoring and surgery when appropriate.
6. Management Out of The Bowel
FAP is linked with certain problems outside the colon; thus, management and monitoring can also address other problems if found.
The treatment is personalized according to each situation. Thus, a team involved in developing an optimal surveillance plan and treatment methods will consist of a gastroenterologist, colorectal surgeon, specialist in medical genetics, and other experts.
Can Familial Adenomatous Polyposis Be Prevented?
FAP cannot currently be prevented because it is caused by a genetic change that may be inherited or, in some cases, occur for the first time in a family. However, its health impact can be managed through early identification, planned care, and long-term follow-up.
- Know Your Genetic Risk: Knowing whether a person is carrying a variant of the APC gene will help determine who needs closer medical attention.
- Do Not Rely on Symptoms: FAP might progress for years without showing symptoms, so waiting for symptoms to appear is not a recommended strategy.
- Follow an Individual Care Plan: When to start investigation and treatment depends on such factors as type of FAP, polyp burden, age, and previous diagnoses.
- Keep Long-Term Follow-Up: The treatment doesn't necessarily stop after completing the treatment once. Regular follow-up can help doctors identify new or returning issues.
- Look Beyond Colorectal Health: FAP can lead to concerns in other parts of the body beyond the colon. Therefore, treatment may involve surveillance for additional potential complications.
- Discuss Family Planning: Consulting with a medical geneticist may be helpful for individuals harboring an APC mutation to comprehend the implications of existing health issues regarding the offspring.
The goal is not to prevent the genetic condition itself, but to identify it early and manage its consequences before they become more serious.
FAP vs Lynch Syndrome
Both FAP and Lynch syndrome are hereditary conditions that can increase the risk of colorectal cancer, but they develop in different ways and require different approaches to screening and management.
|
Feature |
FAP |
Lynch Syndrome |
|
Main genes involved |
Usually APC |
Commonly MLH1, MSH2, MSH6, PMS2, or EPCAM |
|
Typical colorectal finding |
Numerous adenomatous polyps |
Usually no large number of polyps |
|
Colorectal cancer risk |
Very high without appropriate management |
Increased, but the pattern differs from FAP |
|
Usual age of onset |
Polyps often begin at a young age |
Cancers can develop at a relatively young age |
|
Genetic testing |
Often focuses on APC when FAP is suspected |
Usually involves mismatch repair genes |
|
Management |
Intensive polyp surveillance and, when appropriate, preventive surgery |
Regular cancer surveillance based on the individual's genetic and family risk |
The key difference: FAP is characterized by the development of many adenomatous colorectal polyps, whereas Lynch syndrome primarily increases cancer risk through inherited defects in DNA mismatch repair without the characteristic polyposis seen in FAP.
FAQs
What are the first symptoms of familial adenomatous polyposis?
Familial adenomatous polyposis may initially not present any signs of its presence, even if many polyps are being formed. As the number and/or size of the polyps increases, some patients may experience rectal bleeding and changes in the function of the bowel, as well as abdominal pain, unexplained weight loss, and weakness caused by anemia. However, these symptoms can also occur with other digestive conditions, so they do not confirm FAP on their own.
What is the genetic test for familial polyposis?
The main test for familial adenomatous polyposis (FAP) involves finding mutations in the gene responsible for FAP, namely the APC gene. Based on the patients' symptoms and family background, a doctor may suggest genetic testing for the APC gene alone or as a part of a larger hereditary polyp testing. The results of genetic testing need to be considered alongside the medical and family history.
Can familial adenomatous polyposis be cured?
At this time, there are no treatment options that can eliminate the underlying genetic issue for FAP. The condition, however, is not left untreated, and medical surveillance and treatment that minimizes the chances of having colon cancer or other complications can be performed. The type of treatment used can depend on the quantity and features of the diagnosed polyps. Treatment may include endoscopic polyp removal, medication in some cases, or preventive colon surgery.
What is the best treatment for adenomatous polyps in FAP?
No treatment method can be said to be the best since not every single person diagnosed with FAP will benefit from the same approach. In fact, the approach taken depends on factors such as the amount and size of the polyps, their location, the rate of growth, and the person's health condition. Removal of single polyps can sometimes be carried out during endoscopy, whereas serious cases with extensive colorectal polyposis often require some surgical intervention. Most importantly, it is the specialist who decides on the most appropriate procedure depending on each case.
Can you have FAP without a family history?
Yes. Although FAP is usually inherited from a parent with an APC disease-causing variant, some people develop a new APC variant that was not inherited from either parent. These cases are sometimes referred to as de novo cases. Therefore, having no known family history of FAP does not completely rule out the condition, particularly when a person has numerous adenomatous polyps or other findings that raise suspicion of a hereditary polyposis syndrome.
What is the difference between FAP and Lynch syndrome?
Both FAP and Lynch syndrome are inherited disorders that increase the risk of colorectal cancer. Their differences are in causative genes and clinical manifestations. A mutation in the APC gene usually causes FAP. The development of numerous colorectal adenomas characterizes it. At the same time, Lynch syndrome is based on mutations in the genes responsible for DNA mismatch repair and does not produce the massive number of colorectal adenomas seen in FAP.
Where can I get an APC gene test for familial adenomatous polyposis?
If a healthcare professional has recommended APC genetic testing, Redcliffe Labs offers an Adenomatous Polyposis Coli (APC) Gene Analysis Test. The test looks for genetic changes in the APC gene associated with familial adenomatous polyposis. Before testing, it is helpful to discuss your personal and family history with a healthcare professional so that the appropriate genetic test can be selected, and the results can be interpreted in the right clinical context.
References
- Vasen HFA, et al. Guidelines for the clinical management of familial adenomatous polyposis (FAP). Gut. 2008;57(5):704–713.
https://doi.org/10.1136/gut.2007.136127 - Brosens LAA, et al. Clinical Practice Guidelines for the Management of Inherited Polyposis Syndromes. Gastroenterology.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5701653/
- Grover S, et al. ACMG technical standards and guidelines for genetic testing for inherited colorectal cancer (Lynch syndrome, familial adenomatous polyposis, and MYH-associated polyposis). Genetics in Medicine.
https://www.gimjournal.org/article/S1098-3600%2821%2904708-0/fulltext?utm_
- Jasperson KW, Patel SG, Ahnen DJ. APC-Associated Polyposis Conditions. GeneReviews®.
https://www.ncbi.nlm.nih.gov/sites/books/NBK1345/
- Hendren JR, Dabaghi E, Sommovilla J, Liska D. Review of Familial Adenomatous Polyposis: Current Understanding and Clinical Management. JCO Oncology Practice. 2026. DOI: 10.1200/OP-25-00553.
