Hamartomatous polyposis syndromes are characterized by an overgrowth of cells or tissues native to the area in which they normally occur. Peutz-Jeghers syndrome and juvenile polyposis are both characterized by the presence of hamartomatous polyps and increased risk of malignancy in the gastrointestinal tract. Cowden's disease is associated with germ-line mutations in the PTEN gene (10q22-23) and an increased risk of breast and thyroid malignancies. Ruvalcaba-Myhre-Smith syndrome is less common; controversy suggests that it may represent a variant of Cowden's disease.