Juvenile polyposis syndrome: An autosomal dominant disorder in which polyps develop throughout the gastrointestinal tract in the first decade or two of life. People with the disease are at increased risk for developing gastrointestinal cancers. Abbreviated JPS. There can also be diarrhea, GI bleeding, and protein-losing from the intestinal wall. JPS is clearly heterogeneous (more than one entity) as regards causation. Some cases of JPS appear sporadic with no family history of juvenile polyposis, while other cases are due to mutations in the MADH4 gene on chromosome 18 or the BMPR1A gene on chromosome 10. Also known as juvenile intestinal polyposis (JIP), juvenile polyposis coli (JPC).