Peutz Jeghers Syndrome (1971) is a rare autosomal dominant genetic disorder, first described by Peutz in 1921. The condition is characterized by the presence of hammartomas in the gastrointestinal tract; predominantly in the small intestine. These hammartomatous polyps are typified by extensive smooth cell arborization throughout, and are associated with mucocutaneous melanocytic macules. Although these hammartomas are benign per se, patients with PJS have an increased risk of developing gastrointestinal cancer, as well as cancers of extra-intestinal sites. The polyps by themselves can cause intussusception, which may require surgical intervention. Other symptoms of PJS include appearance of melanin spots on several parts of the body, which usually fade during teenage years, diarrhea and constipation, gastrointestinal bleeding, bloating of the belly, anemia, and nausea.

PJS can be diagnosed based on the symptoms, X-ray of the abdomen, and biopsy of the polyps. A genetic test is now available, which can confirm the presence of the defective gene responsible for PJS. The test is especially important for families at risk, in order to ensure early surveillance of possible cancer development.

Treatment involves removal of large polyps by endoscopy and resection for repeated intussusceptions, intestinal obstructions, or bleedings. Most of the cases can be treated conservatively, by blood transfusion, iron therapy, or anticholinergic drugs.

PJS is caused due to defects in the Serine/Threonine Protein Kinase 11 (STK11) gene, located on chromosome 19. Although the exact function of STK11 is not known, it has been purported to function as a tumor suppressor gene, whereby its expression could cause a growth arrest of the cell at the G1 phase. Inactivation of the STK11 gene has also been suggested to interfere with the APC/beta-catenin and the p53 pathways. The penetrance of the gene is varied.