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Familial adenomatous polyposis

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Related Terms
  • Adenomatous polyposis coli, APC gene, APC protein, colon cancer, cyst, desmoid tumor, FAP, hereditary polyposis of the colon, inherited genetic condition, intestinal cancer, MUTYH gene, MYH glycosylase, polyp, rectal cancer.

Background
  • Familial adenomatous polyposis (FAP) is an inherited genetic condition that causes the growth of hundreds to thousands of polyps (abnormal mushroom-shaped growths of tissue) in a patient's lower intestine (including the colon and rectum). Polyps may be seen in a patient's upper intestine as well. About one in 30,000 people is affected with FAP.
  • Polyps usually begin to grow in patients at about age 10 to 12. Initially, these polyps do not cause symptoms in most patients. However, they greatly increase the risk of colon cancer, in which cells in the colon divide uncontrollably and develop into tumors. Almost all patients with FAP develop colon cancer by age 40.
  • FAP is known to be caused by mutations in a gene called adenomatous polyposis coli or APC (APC). This gene contains the genetic code for making the APC protein, which regulates growth in normally functioning cells. Mutations in the APC gene can result in an abnormal APC protein that cannot properly control cell growth. This leads to the formation of polyps in patients with FAP.
  • If the polyps are removed before cancer develops, patients may greatly reduce their risk of developing cancer. If colon cancer does develop, it can be life-threatening. However, it can be treated in a number of ways, including surgery, radiation therapy, and chemotherapy.

Diagnosis
  • Familial adenomatous polyposis (FAP) is usually diagnosed by checking for the presence of polyps in a patient's colon. There are several methods that can be used to screen for polyps. Patients who have a family history of FAP are encouraged to undergo screening early on (in their teens) so that polyps can be detected before cancer has a chance to develop.
  • Colonoscopy: Doctors may perform a colonoscopy to check for polyps in the colon. In a colonoscopy, a flexible tube with a light attached (called an endoscope) is inserted through a patient's anus. The endoscope can transmit images of the patient's colon to the doctor so that any polyps can be observed.
  • Barium enema: To visualize the entire large intestine, a liquid dye called barium may be used to fill and coat a patient's intestine. Then, a doctor uses X-rays to take pictures of the patient's intestine. The barium will cause any polyps along the lining of the intestine to appear as dark areas on the X-ray image, allowing the polyps to be observed.
  • Computed tomography: An imaging technique called a computed tomography (CT) scan may be used to observe polyps in a patient's colon. A CT scan is a noninvasive imaging technique that uses a series of X-rays to create detailed three-dimensional images of the inside of a patient's body. Polyps can then be detected in these images.
  • Genetic testing: Mutations in the APC gene or MUTYH gene are known to cause FAP. Genetic tests can be used to check for these mutations and diagnose FAP. These tests may confirm a diagnosis if there is a family history of FAP or if symptoms of FAP are present.

Complications
  • Colon cancer: The most common complication in patients with familial adenomatous polyposis (FAP) is colon cancer. About one percent of all cases of colon cancer are due to FAP, and all patients with FAP develop colon cancer by the time they are 40. Colon cancer is a disease in which the growth of cells in the colon has become deregulated, such that they divide uncontrollably and develop tumors. Colon cancer is a potentially life-threatening condition, and further complications may result when tumor cells metastasize (spread) to other tissues. Prognosis is worst in cases where the tumor has metastasized to other areas of the body such as the liver.
  • Desmoid tumors: Some patients with FAP develop tumors that are not cancerous, called desmoid tumors. These fibrous tumors are similar to scar tissue, and they often develop in the abdomen. Even though they are not cancerous, they may cause pain if they grow large enough to block a blood vessel or the bowel. Desmoid tumors may be surgically removed but usually grow back after removal.

Treatment
  • If polyps are found at an early stage before cancer has a chance to develop, they can be surgically removed. Patients with familial adenomatous polyposis (FAP) who have polyps removed early in the disease have a very high chance of not developing cancer (near 100%).
  • There are often too many polyps present to remove each one individually. Depending on the extent of the disease, a patient will need to have the entire colon removed (a colectomy) or the colon, rectum, and in some cases the anus removed (a proctocolectomy).
  • In a colectomy, the colon is removed, and the small intestine is surgically connected directly to the anus. In a proctocolectomy in which the colon and rectum are removed, a small pouch is inserted to connect the small intestine to the anus and allow the passage of waste. In a proctocolectomy in which the colon, rectum, and anus have been removed, a portion of the intestine may be brought out through a hole in the abdominal wall, so waste can be directly delivered to an external bag.
  • Patients who undergo surgery need to have frequent checkups (every three to twelve months) to ensure that polyps do not begin to form in other parts of the digestive tract, such as the stomach, upper third of the small intestine (duodenum), or rectum (if it was not initially removed). If new polyps are observed, patients may need to undergo additional surgeries.
  • In patients who do not have polyps removed promptly and as a result develop cancer, a number of treatments are available to help to control the tumor growth. Tumors may be removed surgically or cancer cells may be killed with radiation or with drugs (such as irinotecan, oxaliplatin, and 5-fluorouracil). Patients who develop cancer should consult with a physician to determine the best therapy. If treated at an early stage, patients who develop colon cancer have a good chance of surviving.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
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Causes
  • General: Familial adenomatous polyposis coli (FAP) is known to be caused by mutations in a gene called adenomatous polyposis coli or APC. This gene contains the genetic code for making the APC protein, which normally functions in cells to regulate cell growth. Mutations in the APC gene can result in an abnormal APC protein that cannot properly control cell growth. This leads to the formation of polyps in patients with FAP.
  • More than 700 different mutations in the APC gene may lead to FAP. The most common disease-causing mutations in the APC gene result in the production of a shortened version of the APC protein that is unable to function normally. Some mutations in the APC gene lead to more severe forms of FAP (more polyps and faster onset) than other mutations.
  • Inheritance: Most cases of familial adenomatous polyposis (FAP) are inherited, meaning that a defective gene was transmitted from a parent to the child. Patients with FAP may have a mutation, or genetic error, in a gene called adenomatous polyposis coli or APC. Individuals receive two copies of most genes (one from the mother and one from the father). In patients with FAP, at least one copy of the APC gene appears to be defective.
  • If an individual has a parent with one mutant APC gene, that individual has a 50% chance of inheriting a mutant APC gene and developing the disease. Because only one defective gene is needed for FAP to develop, the disease is considered to follow an autosomal dominant inheritance pattern.
  • Some cases of FAP follow an autosomal recessive inheritance pattern, meaning two abnormal copies of a gene are needed for the condition to develop. The recessive form of FAP (also called MYH-associated polyposis) is caused by mutations in the MUTYH gene. This gene makes a protein called MYH glycosylase, which is an enzyme that repairs mistakes in DNA.
  • Random occurrence: About a third of cases of FAP are not inherited, but instead result from a spontaneously arising mutation in the APC gene in the egg, sperm, or in early embryonic development.
  • Other: FAP may also be caused by mutations in the MUTYH gene. This gene makes a protein called MYH glycosylase, which is an enzyme that repairs mistakes in DNA. Mistakes may occur in DNA during cell division and these mistakes may cause other genes to undergo mutations and to function incorrectly. In individuals with MUTYH mutations, mistakes may accumulate in the DNA because they are not properly repaired. Over time, these mutations may cause cells to grow abnormally, which could eventually lead to cancer.
  • About two-thirds of patients with Turcot syndrome have mutations in the APC gene. Turcot syndrome is a condition that is related to FAP. Patients with Turcot syndrome develop colorectal cancer along with brain cancer.

Risk factors
  • Because familial adenomatous polyposis (FAP) is inherited, a family history of the disease is the main risk factor.
  • About 6% of people with Ashkenazi Jewish Heritage have a mutant variant of the APC gene (an amino acid substitution at one position in the gene) that may increase the risk of developing colon cancer by 10-20%.

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