Overview

Familial adenomatous polyposis (FAP) is a rare, inherited condition caused by a defect in the adenomatous polyposis coli (APC) gene. Most people inherit the gene from a parent. But for 25 to 30 percent of people, the genetic mutation occurs spontaneously.

FAP 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 when you are 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 by removing polyps regularly.

Some people have a milder form of the condition, called attenuated familial adenomatous polyposis (AFAP). People with AFAP usually have fewer colon polyps (an average of 30) and develop cancer later in life.