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Serrated adenoma and APC gene mutation

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Stained histological section of a serrated adenoma.

A small study suggests that serrated adenoma may be a form of familial adenomatous polyposis (FAP) and not a separate type of colorectal cancer.

Three serrated adenomas were found separately in three out of 11 Japanese patients from three families with FAP. Colorectal polyps numbered <100 in each of the three, and all serrated adenomas were found in the rectum. All three patients with serrated adenomas had mutations in the adenomatous polyposis coli (APC) gene—two proximal to the site of the gene, at codon 161, 332 and the third at the most distal site, codon 1556. Mutations in the other patients were located between codons 554 and 1324.

The rate of occurrence of serrated adenoma in the study was 30 times that in the general population so APC mutation may influence pathogenesis of serrated adenoma. The genetic results are compatible with a recent report describing colonic polyposis of <100 polyps as attenuated FAP, so serrated adenoma may actually be a phenotype of FAP.

All 11 patients had a total colonoscopy and multiple biopsies of polyps with a convoluted surface appearance suggesting serrated adenoma and confirmed as such by their characteristic appearance in histological stained sections.

The APC gene was screened by PCR of DNA from blood leucocytes and the protein truncation test. Complementary DNA was synthesised by reverse transcription of mRNA from blood leucocytes, amplified by PCR with APC gene primers, and the PCR products translated in vitro and determined as full or truncated proteins by gel electrophoresis.