Juvenile polyposis: 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. There can also be diarrhea, GI bleeding, and protein-losing from the intestinal wall.
The majority of cases of juvenile polyposis appear sporadic with no family history of juvenile polyposis. Other cases may be clearly inherited. The disorder shows reduced penetrance so that in some families there appear to be "skipped generations."
Juvenile polyposis syndrome is clearly heterogeneous (more than one entity) as regards causation. 15% to 20% of cases are due to germline mutations in the MADH4 gene (also known as SMAD4/DPC4) which is located on chromosome 18 in band 18q21 1. Mutations in the gene for bone morphogenic protein receptor 1A (BMPR1A), residing on chromosome 10 in band 10q22.3, account for 25% to 40% of cases. The cause(s) of the remaining cases of juvenile polyposis remain unknown.
Juvenile polyposis is also known as juvenile intestinal polyposis (JIP), juvenile polyposis coli (JPC), juvenile polyposis syndrome (JPS), juvenile polyposis of stomach, and familial polyposis of entire gastrointestinal tract (familial polyposis of entire GI tract).