Attenuated Familial Adenomatous Polyposis (AFAP) Results from an international collaborative study

Abstract Aim. The study aimed to describe genetical and clinical features of Attenuated Familial Adenomatous Polyposis (AFAP) and to propose clinical criteria and guidelines for treatment and surveillance. Method. A questionnaire study was carried out of polyposis registries with data on patients with presumed AFAP, defined as having /= 25. Results. One hundred and ninety six patients were included. The median number of adenomas was 25 (0-100) with a uniform distribution of colorectal adenomas and carcinomas (CRC). Age at CRC diagnosis was delayed by 15 years compared with classic FAP. Eighty two patients had a colectomy and an ileorectal anastomosis (IRA) and 5/82 (6%) had a secondary proctectomy. The location of the mutation in the APC gene was known in 69/171 (40%) tested patients. Only 15/29 (52%) of mutations in APC were found in parts of the gene usually associated with AFAP (the 5' end, exon 9 and 3' end). Conclusions. A subset of FAP patients with a milder phenotype does exist and treatment and surveillance should be modified accordingly. The mutation detection rate is lower than in classic FAP and mutations in AFAP patients are located throughout the APC gene. We propose the following clinical diagnostic criteria for AFAP: A dominant mode of inheritance of colorectal adenomatosis and <100 colorectal adenomas at age 25 or older. Colonoscopy should be preferred to sigmoidoscopy and surveillance should be life-long. In the majority of patients prophylactic colectomy and ileorectal anastomosis is recommended at the age of 20-25 years.