Attenuated familial adenomatous polyposis (AFAP): a review of the literature

Abstract

Over the last decade, a subset of familial adenomatous polyposis(FAP) patients with a milder course of disease termed attenuated familial adenomatous polyposis (AFAP) has been described. AFAP is not well-defined as a disease entity – the reports on AFAP are largely casuistic or only deal with a few kindreds – and the diagnostic criteria and methods of investigation differ markedly. The true incidence and frequency of AFAP is not known. The mutations in APC associated with AFAP have mainly been detected in three parts of the gene: in the 5′ end (the first five exons), in exon 9 and in the distal 3′ end. The main features of AFAP are 100 or less colorectal adenomas with a tendency to rectal sparing, a delay in onset of adenomatosis and bowel symptoms of 20–25 years, a delay in onset of colorectal cancer (CRC) of 10–20 years and death from CRC of 15–20 years, and although the lifetime penetrance of CRC appears to be high, CRC does not seem to develop in nearly all affected patients. A more limited expression of the extracolonic features is seen, but gastric and duodenal adenomas are frequently encountered. Colonoscopy is preferred to sigmoidoscopy, should begin at the age of 20–25 years and no upper age limit of stopping surveillance is justified. Regular esophago-gastro-duodenoscopy (EGD) is recommended. Until further research has provided us with a more substantiated knowledge about AFAP changes in current surveillance and treatment are not recommended. Prophylactic colectomy with ileorectal anastomosis (IRA) is recommended in most patients.