Overview

Familial adenomatous polyposis (FAP) is a rare, inherited condition that causes extra tissue (polyps) to form in your large intestine (colon) and rectum. Polyps can also occur in the upper gastrointestinal tract, especially the upper part of your small intestine (duodenum). If untreated, the polyps in the colon and rectum are likely to become cancerous in your 40s.

Most people with familial adenomatous polyposis eventually need surgery to remove the large intestine to prevent cancer. The polyps in the duodenum also can develop cancer, but they can usually be managed by careful monitoring and removing polyps regularly.

About

Familial adenomatous polyposis is caused by a defect in the adenomatous polyposis coli (APC) gene. Most people inherit the genetic abnormality from a parent. But in about 25 percent of cases, the genetic mutation occurs spontaneously.

The abnormal gene causes hundreds or even thousands of polyps to grow in your colon and rectum, usually starting by your mid-teens. The polyps are nearly 100 percent certain to develop into colon cancer or rectal cancer by the time you're in your 40s.

Familial adenomatous polyposis can cause other complications:

• Duodenal polyps. These polyps grow in the upper part of your small intestine and may become cancerous. But with careful monitoring, duodenal polyps can often be detected and removed before cancer develops.
• Periampullary polyps. These polyps occur where the bile and pancreas ducts enter the duodenum (ampulla). Periampullary polyps might become cancerous but can often be detected and removed before cancer develops.
• Desmoids. These noncancerous masses can arise anywhere in the body but often develop in the stomach area (abdomen). Desmoids can cause serious problems if they grow into nerves or blood vessels or exert pressure on other organs in your body.
• Other cancers. Rarely, FAP can cause cancer to develop in your thyroid gland, central nervous system, adrenal glands, liver or other organs.
• Noncancerous skin tumors.
• Noncancerous bone tumors.
• Pigment changes in the retina of your eye.
• Dental abnormalities.

Diagnosis

Diagnosis at Mayo Clinic

You're at risk of familial adenomatous polyposis if you have a parent, child, brother or sister with the condition.

If you're at risk, it's important to be screened frequently, starting in childhood. Annual exams can detect the growth of polyps before they become cancerous. At Mayo Clinic, at-risk children who have the defective gene or whose genetic status isn't known are screened every year starting at age 10. At-risk children who don't have the defective gene are screened periodically starting at age 15.

Mayo Clinic specialists use these screening tests for FAP and its complications:

• Sigmoidoscopy. A flexible tube is inserted into your rectum to inspect the rectum and sigmoid — the last two feet of the colon. At Mayo, sigmoidoscopy is used to screen at-risk children who haven't yet developed polyps.
• Colonoscopy. A flexible tube is inserted into your rectum to inspect the entire colon. At Mayo, colonoscopy is used after polyps start growing and after age 18, and if attenuated FAP is suspected or already diagnosed.
• Esophagogastroduodenoscopy (EGD) and side-viewing duodenoscopy. Two types of scopes are used to inspect your esophagus, stomach and upper part of the small intestine (duodenum and ampulla). The doctor may remove a small tissue sample (biopsy) for further study.
• CT or MRI. Imaging of the abdomen and pelvis may be used, especially to evaluate desmoid tumors.

Genetic testing

A simple blood test can determine if you carry the abnormal gene that causes FAP. Genetic testing may also detect whether you're at risk of complications of FAP.

Mayo Clinic specialists may suggest genetic testing if:

• You have family members with FAP
• You have some, but not all, of the signs of FAP

Ruling out FAP spares at-risk children years of screening and emotional distress. For children who do carry the gene, appropriate screening and treatment greatly reduce the risk of cancer.

At Mayo Clinic, genetics counselors discuss the pros and cons of testing with you, including the psychological and medical implications and confidentiality issues. If you choose genetic testing, your counselor and your doctor discuss the results with you.

The Molecular Genetics Laboratory uses the latest techniques to detect specific mutations in the APC gene associated with FAP. If the initial genetic test is negative, Mayo scientists can sequence the MUTYH gene to determine if you have MUTYH-associated polyposis.

Additional tests

Mayo Clinic specialists may recommend thyroid exams and other testing to detect other medical problems that can occur if you have FAP.

Source: http://www.mayoclinic.com