A Novel Germline Mutation of the APC Gene: A Case Report of Familial Adenomatous Polyposis Requiring Repeated Endoscopic Resections for Gastroduodenal Polyps

Familial adenomatous polyposis (FAP) is a precancerous clinical entity, which is characterized by the development of numerous adenomatous polyps throughout the colon and rectum. The majority of FAP are associated with mutations of the adenomatous polyposis coli (APC) gene. Until now, more than 1,000 different APC mutations have been reported and some mutations express attenuated phenotypes which are milder forms with 10∼100 colorectal polyps. We identified a novel mutation of APC gene which expressed an attenuated FAP but caused large gastroduodenal tubular adenomas requiring repeated endoscopic resections. A 16-year-old girl was referred to Incheon St. Mary’s Hospital for evaluation of gastric polyposis. Initial esophagogastroduodenoscopy (EGD) showed numerous gastric polyps in the fundus and upper body and a few polyps in the duodenum. Pathologic examination confirmed gastric polyps as fundic gland polyps and duodenal polyps as tubular adenomas. Only a few colonic polyps of 2 to 5 mm in size were found on colonoscopy. Genetic analysis using polymerase chain reaction and direct sequencing revealed a novel stop codon mutation at codon 1522 in exon 16 of APC gene. At 12-month, 18-month, and 35-month follow-up EGD, large duodenal polyp and gastric polyps were removed endoscopically.