Juvenile Polyposis Syndrome-Hereditary Hemorrhagic Telangiectasia (JPS-HHT)

Juvenile polyps are hamartomatous lesions in the gastrointestinal (GI) tract with a distinct histological appearance of normal epithlium with cystic glands embedded in hyperplastic stroma and inflammatory infiltrate. Juvenile polyps are typically benign, but in individuals with juvenile polyposis syndrome (JPS), there is a 9-68% risk for malignant transformation (Howe et al., 1998). JPS is defined by either the presence of more than five juvenile polyps in the colorectum, or multiple juvenile polyps throughout the GI tract, or any number of juvenile polyps and a positive family history. Clinical features associated with other hamartomatous polyposis syndromes (i.e. PTEN-related disorders, Gorlin syndrome) are not present in JPS. Mutations in both the BMPR1A and SMAD4 genes are known to be causative of JPS. There are no strong genotype-phenotype correlations, although gastric polyps are more frequently observed in patients with SMAD4 gene mutations. Mutations in the SMAD4 gene are also associated with a juvenile polyposis syndrome-hereditary hemorrhagic telangiectasia (JPS-HHT) phenotype. Once again, the genotype alone can not predict the phenotype as the same SMAD4 mutations have been reported in patients with isolated JPS as well as JPS-HHT (Gallione et al., 2010). A contiguous gene deletion syndrome including the BMPR1A gene and the neighboring PTEN gene on chromosome 10q has been reported in association with juvenile polyposis of infancy, characterized by its early onset and presence of polyps throughout the GI tract. Additionally, macrocephaly, digital clubbing, and hypotonia have been observed in these patients. Prognosis is generally poor.