Curriculum · Gastroenterology
Familial adenomatous polyposis
What it is
Familial adenomatous polyposis (FAP) comes from autosomal dominant mutations of the APC gene, a tumor suppressor gene on chromosome 5q22. 20-25% of cases have a negative family history, so a quiet family does not rule it out.
How it presents
It is initially asymptomatic. Polyposis typically develops within the second or third decade of life.
How it is diagnosed
Flexible sigmoidoscopy or colonoscopy is what shows it. Polyps develop in the entire colon, always including the rectum, and more than 100 polyps are typically detected in classic FAP. Annual screening sigmoidoscopy or colonoscopy is the prevention arm; the age it starts is given as 10 years of age in one source and as age 12 in another.