19th July 2023

Familial Adenomatous Polyposis (FAP)

FAP is a rare autosomal dominant condition characterised by the development of hundreds to thousands of colonic polyps by aged 30-40 years. FAP results from a mutation in the APC tumour suppressor gene on chromosome 5. 80% of cases are familial. Without definitive treatment, almost all FAP patients will develop CRC by the age of 40. Those with FAP may be identified through family genetic screening or by presenting with symptoms such as abdominal pain, PR bleeding or symptoms of bowel obstruction. These patients should undergo colonoscopy at the time of diagnosis and then regularly to assess the polyp burden. Patients invariably require total colectomy or proctocolectomy to reduce their CRC risk. Gardner’s syndrome is a variant of FAP where, in addition to colonic polyps, patients are prone to develop extra-intestinal tumours, including desmoid tumours, osteomas, thyroid and skin tumours (lipomas, fibromas and epidermoid cysts).