familial adenomatous polyposis
Meaning of familial adenomatous polyposis: It runs through families on a single dominant gene, yet a sizeable share of cases begin with a brand new mutation.
Definition of familial adenomatous polyposis
Familial adenomatous polyposis is an inherited condition in which hundreds to thousands of polyps, small growths, develop on the lining of the colon and rectum, usually starting in the teenage years. It follows a fault in a gene called APC. Any single polyp may turn cancerous, and with so many present the risk of colorectal cancer becomes near certain without intervention.
How is it inherited?
The APC gene normally restrains growth in the lining of the bowel. A person inherits one faulty copy, and each child of an affected parent has an even chance of inheriting it in turn. Polyps form where the remaining working copy is lost in an individual cell, which happens often enough across the vast surface of the colon that growths appear in large numbers. A substantial minority of people have no affected relative at all, because the fault arose new in the egg or sperm that formed them; a first case in a family therefore does not rule the diagnosis out.
How does it differ from ordinary colon polyps?
| Familial adenomatous polyposis | Sporadic polyps | |
|---|---|---|
| Number | Hundreds to thousands | One to a handful |
| Age at appearance | Adolescence onward | Middle age onward |
| Cause | An inherited gene fault | Chance changes accumulated with age |
| Lifetime cancer risk | Near certain without intervention | Small for any single polyp |
| Approach | Removal of the colon, since individual removal is impractical | Removal of the individual polyp |
Each polyp carries roughly the same modest chance of becoming colorectal cancer as any other adenoma. The near certainty comes from the sheer number, not from any single growth being especially dangerous. A milder version exists, sometimes called attenuated, with fewer polyps appearing later and more of them on the right side.
What happens outside the colon?
The gene acts throughout the body, so the condition is not confined to the bowel. Polyps commonly form in the stomach and in the duodenum, the first stretch of small intestine, and duodenal growths matter enough to be followed in their own right. Desmoid tumors, dense fibrous growths that do not spread but invade locally, occur more often than in the general population, particularly after abdominal surgery. Bony growths of the jaw and skull, extra or missing teeth, skin cysts and a harmless pigmented patch in the retina also occur. Older names such as Gardner syndrome described these combinations before they were understood as one condition, now sometimes recorded as familial polyposis.
Also known as
Used in a sentence
Genetic counseling was recommended for family members after the patient's diagnosis of familial adenomatous polyposis.
Good to know
Familial adenomatous polyposis differs from sporadic colon polyps in both its inherited cause and the number of polyps involved, and the near universal cancer risk follows from that number rather than from any single polyp being unusually dangerous.
Word origin
Where “familial adenomatous polyposis” comes from
Formed from adenoma, from Greek aden, meaning gland, and -oma, meaning tumor, combined with polyposis, from Greek polys, meaning many, and -osis, meaning a condition, describing the numerous glandular growths characteristic of the disease.