Familial adenomatous polyposis (FAP) is a disease caused by a malfunction of a single gene; as a result, genetic tests can be very useful in diagnosing and treating FAP. These tests can also help predict the particular symptoms that may develop in an individual as well as the severity of colorectal disease. A genetic workup starts with a visit to a genetic counselor, who takes a detailed family history, explains the genetics of FAP, and discusses the usefulness and implications of pursuing genetic testing. After the initial consultation, patients can opt to have their blood drawn and sent out for genetic testing.

In addition to helping diagnose affected patients, genetic tests can also have the benefit of helping reduce anxiety among asymptomatic family members who are not sure if they are affected. A positive genetic test result in one family member can help direct his or her care and can ensure that he or she receives appropriate surveillance and treatment; in addition, once a family mutation has been identified, other family members can pursue the testing at a lower cost and can be definitively diagnosed or excluded from having FAP without having to undergo screening endoscopy exams.

In the case of a “negative” test, or one that does not find a mutation, the results can serve as a family benchmark and alert other affected family members that a familial mutation cannot be identified. Presently, only 80 percent of FAP families have a mutation that can be identified with current testing technology. In the case of an unidentifiable mutation, all at-risk family members (as determined by a detailed family history) still need to undergo regular endoscopy screening.