Familial Adenomatous Polyposis

Diagnosis

Screening and Diagnosis

If you inherited the genetic defect that causes FAP, you're likely to begin developing polyps in your colon by your mid-teens. Once polyps start to appear, they often emerge rapidly, sometimes blanketing the entire colon. Mayo Clinic physicians usually start screening children known to be at risk in their early teens or even sooner. At-risk children are those with a parent with FAP or a family history of early-onset colon polyps or colorectal cancer. Screening exams are often performed every year, but the frequency may change, depending on the number and size of polyps found.

Endoscopic tests

At Mayo Clinic, endoscopic tests used to detect FAP include flexible sigmoidoscopy and colonoscopy — visual examinations of the colon using an endoscope, a thin, flexible tube with a miniature camera at the tip. Mayo Clinic gastroenterologists also use an endoscope to examine the upper part of the gastrointestinal tract for polyps or tumors in the duodenum, stomach and ampulla of Vater — the juncture where the liver and pancreatic ducts enter your small intestine. If you have a few small polyps, your doctor can remove them during the endoscopic exam. Eventually, though, polyps become too numerous to remove individually. Mayo Clinic specialists may recommend additional tests, such as thyroid exams and abdominal ultrasounds, to help detect other medical problems that can occur in people with FAP.

Genetic testing

Mayo Clinic has one of the most distinguished medical genetics programs in the country as well as state-of-the-art cytogenics, biochemical and molecular laboratories.

Genetic testing plays a key role in FAP. Performed on a small blood sample, a genetic test can help Mayo physicians establish a diagnosis in people who have some, but not all, of the signs of FAP. It can identify which members of affected families carry the abnormal gene so that they can receive prompt evaluation. High-risk children who are found not to have FAP are spared years of invasive exams and emotional distress.

For children who do carry the gene, appropriate screening and treatment greatly reduce the risk of cancer. Depending on where the genetic mutations occur, testing may also help determine whether you have a milder form of FAP or are at risk of certain complications of the disease.

You are not obligated to undergo genetic testing, and it should never be undertaken without careful consideration. Before you make a decision, a Mayo Clinic genetics counselor will discuss all the ramifications of testing with you, including the accuracy, medical usefulness and limitations of genetics tests; the psychological and medical implications for you and your family; and confidentiality issues. All patients who choose testing discuss the test results with their counselor.

Types of genetic tests

The Mayo Molecular Genetics Laboratory uses an innovative technique called multiplex ligation probe amplification to detect large deletions and alterations in genetic DNA. Mayo scientists also use DNA sequencing — a way of determining the order of nucleotides in a strand of DNA — to locate specific mutations within the APC gene. The APC gene is large and usually requires the expertise of several technologists for an accurate and timely analysis.

People with symptoms of classic FAP whose APC test is negative may have mutations on another gene called MYH. In such cases, Mayo Clinic scientists may sequence this gene a well. Patients with MYH abnormalities tend to have fewer cancers outside the colon and usually develop symptoms later than do people with classic FAP.