Attenuated Familial Adenomatous Polyposis: Diagnosis, Management, and Future Prognosis

Abstract

Attenuated familial adenomatous polyposis is a variant of familial adenomatous polyposis (FAP) in which patients present with 99 or fewer cumulative polyps in the colon and/or rectum, with a tendency toward more proximal colonic polyps [1,2]. The average age of adenoma development and of colon cancer occurrence is clearly older than in typical FAP. However, there is a wide variation in the age of onset of these lesions and a wide variation in the numbers of adenomas in individuals within attenuated FAP families, with some individuals presenting with more than 100 lifetime polyps. Therefore, it is difficult and often impossible to distinguish attenuated FAP from typical FAP in single individuals. The most suggestive cases initially are patients over the age of 50 who exhibit 50-100 adenomas. Younger patients with fewer adenomas and older patients with greater than 100 adenomas are difficult to categorize. This means that examination of multiple family members is often needed to distinguish FAP and attenuated FAP in a family. Genetic testing is now also helpful in this regard, as mutations giving rise to attenuated FAP preferentially occur in localized regions of the APC gene.