Juvenile polyposis syndrome (JPS) is an autosomal dominant predisposition to the 
occurrence of hamartomatous polyps in the gastrointestinal tract. Diagnosis of 
JPS is based on the occurrence of numerous colon and rectum polyps or any number 
of polyps with family history and, in the case of juvenile polyps, their 
occurrence also outside the large intestine. The JPS is caused by mutations in 
SMAD4 and BMPR1A. Products of the SMAD4 gene are involved in signal transduction 
in the transforming growth factor β pathway and BMPR1A protein is a receptor 
belonging to the family of transmembrane serine/threonine kinases. Both proteins 
are responsible for processes determining appropriate development of colonic 
mucosa. The JPS belongs to the group of hamartomatous polyposes. The 
hamartomatous polyposis syndromes constitute a group of diseases in which 
manifestations differ slightly and only molecular diagnostics gives the 
possibility of verifying the clinical diagnosis.