OBSOLETE: APC-related attenuated familial adenomatous polyposis

APC-related attenuated familial adenomatous polyposis (AFAP) is a hereditary colorectal cancer predisposition syndrome caused by pathogenic variants in the APC (adenomatous polyposis coli) gene. This entry in Orphanet is marked as OBSOLETE, meaning it has been retired and its content has been merged into or replaced by a broader or updated classification. AFAP is now generally classified under the broader entity of familial adenomatous polyposis (FAP) or APC-associated polyposis conditions. In its clinical presentation, AFAP is characterized by the development of fewer colorectal adenomatous polyps than classic FAP — typically between 10 and 100 cumulative adenomas, compared to hundreds or thousands in classic FAP. Polyps tend to appear later in life, often in the third to fourth decade, and are frequently located in the proximal (right-sided) colon. Despite the reduced polyp burden, individuals with AFAP still carry a significantly elevated lifetime risk of colorectal cancer if left unmonitored, with cancer typically developing approximately 10–15 years later than in classic FAP. Upper gastrointestinal polyps, particularly duodenal adenomas and fundic gland polyps of the stomach, may also occur. Extraintestinal manifestations such as desmoid tumors and osteomas are less common than in classic FAP but can occur. Management of AFAP involves regular colonoscopic surveillance beginning in the late teenage years or early twenties, with polypectomy of detected adenomas. When polyp burden becomes too great for endoscopic management, surgical options including colectomy with ileorectal anastomosis may be recommended. Upper gastrointestinal endoscopy is also advised for duodenal polyp surveillance. Genetic counseling is recommended for affected individuals and at-risk family members. Patients are encouraged to consult current Orphanet and clinical guidelines, as this specific entry has been retired in favor of updated disease classifications.

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