Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an inherited, autosomal dominant condition in which numerous adenomatous polyps form mainly in the lining of the large intestine. The polyps begin benign but, if untreated, one or more will eventually turn malignant, so colon cancer is close to certain; the cited risk rises from 7 percent by age 21 to 87 percent by age 45 and 93 percent by age 50. Three variants are described: classic FAP and attenuated FAP, both caused by defects in the APC gene on chromosome 5, and an autosomal recessive form, MUTYH-associated polyposis, caused by MUTYH defects on chromosome 1. Attenuated FAP produces far fewer polyps and appears later. A blood test can detect the APC change, at-risk people are offered routine bowel surveillance, and colon resection is recommended when many polyps are found.