Sporadic gastric juvenile polyposis with a novel SMAD4 nonsense mutation in a mosaic pattern

A 50-year-old female was diagnosed with gastric hyperplastic polyps 7 years before and was followed up at another hospital. She was referred to our hospital because of the growth of gastric polyps and progression of anemia. She had no family history of polyposis. The polyps were observed only in the stomach, increased in size and number, and the erythematous edema got worse. Endoscopic mucosal resection (EMR) of the gastric polyp was performed. Pathologically, the gastric polyp was hamartomatous polyp, and the intervening mucosa between polyps showed no atypical structure without inflammation. Given that gastric juvenile polyposis (GJP) was clinically suspected, a genetic test using peripheral blood was performed. Target resequencing and Sanger sequencing analysis revealed a nonsense mutation in the SMAD4 gene at codon 169. The mutation was detected at a low frequency of 11%, and considered a mosaic mutation. Therefore, she was diagnosed with a sporadic GJP, and total gastrectomy was performed. Immunostaining of SMAD4 for the resected specimen showed a mixture of stained and unstained area in the epithelium of the polyp, indicating partial loss of SMAD4 expression. To our knowledge, this is the first reported case of GJP with a nonsense SMAD4 mutation at codon 169 in a mosaic pattern.