Mutational abrogation of the PTEN/MMAC1 gene in gastrointestinal polyps in patients with Cowden disease

Background & Aims: To understand the molecular etiology of Cowden disease-associated gastrointestinal polyps, we analyzed the mutational status of PTEN/ MMAC1, a recently identified Cowden disease gene located at 10q23, in gastric hamartomas, colonic adenoma, and juvenile polyps of 3 patients with Cowden disease. Methods: Messenger RNA expression, gene deletion, and sequence alteration of PTEN/MMAC1 were evaluated by quantitative polymerease chain reaction (PCR), PCR-single-strand conformation polymorphism, and sequencing analysis. Results: Germline missense mutation at codon 289 (AAA to GAA, Lys to Glu) and deletion of the wild-type allele were detected in the polyps of 2 patients with Cowden disease in the same family. Germline allelic deletion and transcriptional silencing of the remaining allele, probably caused by abnormal methylation, were also observed in a gastric hamartoma of 1 patient. Conclusions: The germline mutation and alteration of the remaining allele observed in this study strongly support that PTEN/MMAC1 functions as a tumor suppressor in Cowden disease. This study is the first to show that the mutational abrogation of PTEN/MMAC1 plays a causal role in the genesis of gastrointestinal polyps in Cowden disease, providing molecular genetic evidence that colonic adenoma, juvenile polyp, and gastric hamartoma could be included in the manifestations of Cowden disease.