31st December 2024

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP, <1%) is an autosomal dominant condition due to mutations in the APC tumour suppressor gene located on chromosome 5. It is associated with multiple colorectal adenomas, which are initially benign but likely to undergo malignant transformation. Those with FAP are also at an increased risk of developing duodenal tumours.

Diagnosis is through genetic testing of suspected individuals. Surveillance sigmoidoscopy is advised from 12 years, with prophylactic surgery usually undertaken before the age of 25 depending on the number and size of polyps and degree of dysplasia.

Gardner’s syndrome is a variant of FAP characterised by retinal pigmentation, osteomas of the skull and mandible, thyroid carcinoma, and epidermoid cysts on the skin.