Genotype-Phenotype Associations of APC Mutations With Pouch Adenoma in Patients With Familial Adenomatous Polyposis.

Background: Patients with familial adenomatous polyposis (FAP) may carry various adenomatous polyposis coli (APC) mutations. However, genotype-phenotype correlation for APC mutations is still debated and is yet to be evaluated with regard to pouch polyp formation.

Objective: To evaluate the association between APC mutation type and exon location and the outcome of pouch adenoma.

Design Setting And Patients: Forty-five FAP patients with defined pathogenic APC mutations, who underwent total proctocolectomy and ileal pouch anal anastomosis were classified by mutation type and location. Analysis was conducted for clinical and endoscopic parameters.

Results: Twenty patients had either indel/deletion mutations and 25 had nonsense/missense mutations. The indel/deletion group was associated with higher prevalence of preoperative hundreds of colonic adenomas (66.7% vs. 30%; P=0.030), lower rates of stapled versus sewn anastomosis (46.7% vs. 76%; P=0.060), of single stage surgery (13.3% vs. 44%; P=0.045) and with higher pouch adenoma formation rate (50% vs. 8%; P=0.002). Twenty-seven were carriers of exons 1 to 14 mutations and 18 were carriers of exon 15 mutations. Carriers of exon 15 mutations had higher prevalence of preoperative hundreds of colonic adenomas (55.6% vs. 22.2%; P=0.003) and a higher tendency for pouch and cuff adenoma formation rate. Adjusted odds ratio for pouch adenoma formation was 8.32 (1.42-48.80; P=0.019) for the indel/deletion group versus nonsense/missense, but no significant independent association was noted with mutation location. The mean number of pouch and cuff adenoma formation (per endoscopy) was higher among carriers of exon 15 mutations, but no significant independent association was noted the with mutation type.

Conclusions: Type and location of APC mutation are associated with colonic polyp burden, surgical outcome and likelihood of developing pouch adenomas. These findings may contribute to surgical and endoscopic surveillance decisions for FAP patients.