Attenuated Familial Adenomatous Polyposis: An Evolving and Poorly Understood Entity

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PURPOSE:Familial adenomatous polyposis is a well-described, autosomal dominant, inherited syndrome characterized by diffuse polyposis of the colon and rectum as well as various upper gastrointestinal and extraintestinal manifestations. A subset of patients present with fewer colorectal polyps, later age of onset of polyps and cancer, and a predilection toward involvement of the proximal colon. This variant of familial adenomatous polyposis is known as attenuated familial adenomatous polyposis. The purpose of this review is to summarize current knowledge regarding this poorly understood entity and propose guidelines for diagnosis, surveillance, and surgical management.METHODS:The MEDLINE database was searched from 1985 onward using the keywords, “attenuated familial adenomatous polyposis,” “AFAP,” “adenomatous polyposis coli gene,” and “APCgene.” Additional articles were identified through the reference sections of retrieved papers. All papers that pertained to attenuated familial adenomatous polyposis or mutations in theAPCgene producing an attenuated phenotype were included.RESULTS:Attenuated familial adenomatous polyposis is transmitted in an autosomal dominant fashion. Several distinct mutations within theAPCgene have been associated with an attenuated phenotype, but variability of disease expression within kindreds possessing identical mutations makes classification difficult. Polyps are diagnosed at a mean age of 44 years, with cancer diagnosed at a mean of 56 years of age. Frequent involvement of the proximal colon necessitates the use of colonoscopy for surveillance, and infrequent involvement of the rectum supports the role of a total abdominal colectomy and ileorectal anastomosis.CONCLUSIONS:Although currently recognized as a distinct clinical entity, attenuated familial adenomatous polyposis may be part of a spectrum of disease that includes familial adenomatous polyposis and is caused by different mutations within theAPCgene. Because of its unique characteristics, yet apparent overlap with familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, increased awareness of attenuated familial adenomatous polyposis should improve diagnosis, surveillance, and treatment strategies in this unique subset of familial polyposis syndromes.

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