# Familial Adenomatous Polyposis and Polyposis Syndromes

> FAP and polyposis syndromes for NEET-PG Medicine: APC mutation, Peutz-Jeghers, Gardner and Turcot syndromes, extracolonic features and surgical planning.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/familial-adenomatous-polyposis-and-polyposis-syndromes
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; Sleisenger and Fordtran's Gastrointestinal and Liver Disease; Bailey and Love's Short Practice of Surgery
- How to cite: "Familial Adenomatous Polyposis and Polyposis Syndromes", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/familial-adenomatous-polyposis-and-polyposis-syndromes

## Direct answer

Familial adenomatous polyposis is an autosomal dominant condition caused by a germline APC mutation, producing more than 100 colorectal adenomas, usually from adolescence onward, and colorectal cancer is very likely if it is left untreated. Gardner and Turcot syndromes are named variants with extracolonic features. Peutz-Jeghers syndrome and juvenile polyposis are hamartomatous conditions with different genes and different risks.

## What you must remember

- **APC gene:** Located on chromosome 5q21; a germline tumour suppressor mutation that activates the Wnt signalling pathway.
- **Attenuated FAP:** Fewer adenomas, typically under about 100, with later onset and a somewhat lower cancer risk.
- **Gardner syndrome:** Adenomas with jaw and skull osteomas, epidermoid cysts, desmoid tumours and dental anomalies.
- **Turcot syndrome:** Polyposis with central nervous system tumours, typically medulloblastoma or glioma.
- **Peutz-Jeghers syndrome:** STK11 (LKB1) mutation, hamartomatous polyps mainly in the small bowel, and perioral and buccal pigmentation.
- **Juvenile polyposis:** SMAD4 or BMPR1A mutation, with juvenile polyps and increased gastrointestinal cancer risk.

## A worked case: a 22-year-old with hundreds of polyps

A 22-year-old presents with rectal bleeding, and his sister died of colorectal cancer at 35. Colonoscopy shows several hundred adenomatous polyps throughout the colon and rectum. The diagnosis of FAP is supported by the polyp burden and confirmed by APC germline testing, and first-degree relatives are offered cascade testing. The next step is upper gastrointestinal endoscopy, which may reveal duodenal and periampullary adenomas, staged by the Spigelman classification to guide surveillance. Thyroid ultrasonography is performed because papillary thyroid cancer is associated with FAP, and desmoid tumours are sought on imaging because they are a leading cause of morbidity after surgery.

Prophylactic colectomy is then planned, usually with ileal pouch-anal anastomosis, because the cancer risk is very high and endoscopic surveillance alone cannot control it. Had the patient instead had a jaw osteoma on X-ray, epidermoid cysts and a desmoid, the picture would point to Gardner syndrome, which is still managed as FAP with added extracolonic surveillance. Recognising the extracolonic features is the key to naming the variant correctly in an exam.

## Where the exam tries to catch you

The classic trap is pigmentation. A patient with polyps and perioral pigmentation has Peutz-Jeghers syndrome, whose polyps are hamartomatous rather than adenomatous, and whose cancer risks include breast, pancreas and gynaecological sites. Another trap is confusing juvenile polyposis with FAP, because both produce polyps in young patients, but juvenile polyps are hamartomatous and the gene is different. A desmoid tumour in a patient with polyposis points to Gardner syndrome or FAP, and brain tumours with polyposis point to Turcot syndrome. Finally, examiners test surgical planning: once adenomas are present in FAP, the answer is prophylactic colectomy, not repeated polypectomy.

## Frequently asked questions

### Which gene is mutated in familial adenomatous polyposis?

The APC gene, located on chromosome 5q21, is mutated in familial adenomatous polyposis. It acts as a tumour suppressor in the Wnt signalling pathway, and germline mutation is inherited in an autosomal dominant pattern.

### Which syndrome shows perioral pigmentation with small bowel hamartomatous polyps?

Peutz-Jeghers syndrome shows mucocutaneous pigmentation on the lips and buccal mucosa, with hamartomatous polyps mainly in the small intestine. It is caused by an STK11 (LKB1) mutation and raises cancer risk at several sites.

### What distinguishes Gardner syndrome from classic familial adenomatous polyposis?

Gardner syndrome combines FAP with extracolonic features such as jaw and skull osteomas, epidermoid cysts, desmoid tumours and dental abnormalities. Classic FAP is defined by colonic adenomas, with extracolonic features as additional clues to the variant.

### When is prophylactic colectomy recommended in familial adenomatous polyposis?

Prophylactic colectomy is recommended in FAP once adenomas appear, usually in adolescence or early adulthood, because colorectal cancer is very likely if the colon is left in place. Duodenal and thyroid surveillance continue after surgery.

### Which polyposis syndrome is caused by SMAD4 or BMPR1A mutation?

Juvenile polyposis syndrome is caused by SMAD4 or BMPR1A mutations, with juvenile polyps and increased gastrointestinal cancer risk. It differs from FAP because its polyps are hamartomatous rather than adenomatous.