Classic familial adenomatous polyposis (FAP) is a genetic condition that is passed from one generation to another in a family. FAP is uncommon; and an estimated number of people who have FAP vary from one in 22,000 to one in 7,000. About 30% of people with FAP have no family history of this condition.
FAP is caused by mutations in a gene called adenomatous polyposis coli (APC), which is responsible for making protein that regulates growth in normally functioning cells. Mutations in APC result in abnormal APC protein that cannot properly control cell growth. This causes the formation of polyps.
Polyps are abnormal mushroom-shaped growths of tissue that can grow in a patient’s lower intestine, including the colon and rectum. Polyps may also be seen in the upper intestine (duodenum). Approximately 80% of people with FAP can also form polyps in the stomach and small intestine. Polyps in the stomach are usually located in the upper portion and are not usually cancerous. Polyps in the duodenum can develop cancer but can usually be managed by regularly removing them.
People with FAP may begin to develop multiple noncancerous polyps in the colon as early as mid-teens. If untreated, polyps in the colon almost always become cancerous. Most people with FAP eventually need surgery to remove the colon and prevent cancer.
Not all symptoms of FAP are cancer-related. Some additional features of FAB may include:
- Noncancerous bony growths, usually found on the jaw.
- Extra, missing, or teeth that have not come in.
- A congenital eye condition (CHRPE).
- Noncancerous skin changes.
- Desmoid tumors
- Adrenal masses
Signs and Symptoms
Family history is one of the largest and most common sign of FAP. Other signs and symptoms of FAP include:
- Rectal bleeding
- Change in bowel habits
- Abdominal pain, cramping, and/or bloating
- Unexplained weight loss
- Thin stools
- Unexplained diarrhea and/or constipation
Note: people without a family history many not know they have this disorder until they begin to have major symptoms from the polyps or cancer develops.
Family members can have a blood analysis if they are at risk for FAP. The APC mutation can be detected in over 80% of people with FAP. In 20% of people with FAP, the gene abnormality cannot be detected.
There are two widely used methods for detecting mutations: a protein truncation test, and direct DNA sequencing. Gene testing should first be done on a family member who has FAP. If the mutation is found, the other family members can then be tested.
A colonoscopy and possibly an upper endoscopy of the stomach may also be performed to detect the polyps, which are the classic signs of FAP. A capsule endoscopy might be considered to evaluate the small bowel for polyps not detected by routine endoscopies.
People with FAP have too many polyps for them to be removed one at a time. The only long-term treatment for FAP is surgery to remove the colon and any other affected areas. The type of colon surgery depends on what area of the colon is infected with the polyps. A gastroenterologist and surgeon work together to determine the most appropriate surgery.
The most common surgical treatments include:
- Total colectomy and ileorectal anastamosis (IRA)
- Colectomy with ileoanal pouch
- Proctocoletomy and ileostomy.
People and children who discover they have the FAP or AFAP gene mutation should:
- At 12 years of age: begin colon checks with either a colonoscopy or flexible sigmoidoscopy. These procedures are usually performed every year, although the timing may be different depending on the size and number of polyps found.
- At 20 years of age: begin stomach and duodenum checks every year with an upper endoscopy (EGD).
- Parent’s with AFAP: have your children checked for polyps at 18 years of age, sooner if they exhibit any of the signs and symptoms of FAP.
For more information on FAP or AFAP, please check the follow website links: