source: Colorectal disease

year: 2010

authors: Knudsen A L ,Bülow S, Tomlinson I, Möslein G, Christensen I J, Heinimann K

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 ≤ 100 colorectal adenomas at age ≥ 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 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 had to 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