Familial adenomatous polyposis (FAP) is a genetic condition that causes growths of tissue (polyps) to develop in the large intestine (colon) and rectum. If these polyps are not removed, the polyps will become cancerous with time. There are three forms of FAP: classic, attenuated (milder), and autosomal recessive FAP. In the classic form, a person can have thousands of polyps and usually develops colon cancer in their 30s. In attenuated FAP, colon cancer usually does not develop until a person is in their 50s. In autosomal recessive FAP, a person usually develops less than 100 polyps. In addition to polyps and colon cancer, FAP can also cause noncancerous growths in the intestines (desmoid tumors) as well as cancerous and noncancerous growths in other parts of the body, including part of the small intestine (duodenum), stomach, bones, and skin.
Both classic and attenuated FAP are caused by a change (mutation) in the APC gene, while autosomal recessive FAP is caused by mutations in the MUTYH gene. The APC and MUTYH genes help to keep cell growth under control. Mutations in these genes can cause uncontrolled cell growth, leading to polyp formation in the colon and rectum. FAP caused by mutations in the APC gene is inherited in an autosomal dominant manner, which means a mutation in only one of the two copies a person has is enough to cause the condition. FAP caused by mutations in the MUTYH gene is inherited in an autosomal recessive manner, which means a mutation in both copies of the gene a person has is needed to cause the condition.
FAP is considered as a possible diagnosis in a person with multiple polyps in their colon. The diagnosis can be officially confirmed with genetic testing. Treatments include removal of the polyps and removal of the colon. If you or your child has been diagnosed with FAP, talk to a doctor about all treatment options. Support groups are also available to connect with others who are affected by FAP.