Juvenile Polyposis Syndrome (JPS)
JPS is characterized by predisposition to hamartomatous polyps in the gastrointestinal (GI) tract, specifically in the stomach, small intestine, colon, and rectum. "Generalized juvenile polyposis" refers to polyps of the upper and lower GI tract. "Juvenile polyposis coli" refers to polyps of the colon only.
The polyps vary in size and shape: some are flat (sessile), whereas others have a stalk (pedunculated). The number of polyps in individuals with JPS varies. Some individuals may have only four or five polyps over their lifetime; others in the same family may have more than 100.
Bleeding may result from sloughing of the polyp or its surface epithelium with the passage of stool. If the polyps are left untreated, they may cause bleeding and anemia.
Juvenile polyps develop from infancy through adulthood. Most individuals with JPS have some polyps by age 20 years.
In juvenile polyposis of infancy, associated with a contiguous deletion of BMPR1A and PTEN, polyps develop within the first few years of life and are accompanied by hypoproteinemia, protein-losing enteropathy, diarrhea, anemia, anasarca, and failure to thrive [Taylor et al 2021].
Cancer risks associated with JPS. Most juvenile polyps are benign; however, malignant transformation can occur. Lifetime estimates of developing GI cancers in families with JPS range from 11% to 86%, with variability by region, time period included, and associated gene [Latchford et al 2012, Aytac et al 2015, Ishida et al 2018, Blatter et al 2020, MacFarland et al 2021]. In the largest study thus far of individuals with JPS caused by SMAD4/BMPR1A pathogenic variants, 15% of individuals developed cancer, which is consistent with other more recent studies [Blatter et al 2020]. Of individuals treated surgically and followed with surveillance, four of 27 individuals with SMAD4 pathogenic variants and none of eight individuals with BMPR1A pathogenic variants developed cancer [Aytac et al 2015]. Most of the increased risk is attributed to colorectal cancer; cancers of the stomach, upper GI tract, and pancreas have also been reported:
The incidence of colorectal cancer is 17%-22% by age 35 years and approaches 68% by age 60 years. The median age at diagnosis is 42 years.
The incidence of gastric cancer is 21% in those with gastric polyps.
The relative risk for colorectal cancer was 34.0% in individuals with JPS. The mean age of diagnosis of colorectal cancer was 43.9 years, with a cumulative lifetime risk of 38.7% [
Brosens et al 2007].
Historically, the cancer incidence in one large family with a germline SMAD4 pathogenic variant suggested a lifetime risk for colorectal cancer of approximately 40%, and a lifetime risk for upper GI cancers of 20% [Howe et al 1998]. However, these cancer rates may change over time with the implementation of screening of young at-risk individuals and the removal of polyps before cancer develops.
Juvenile Polyposis Syndrome / Hereditary Hemorrhagic Telangiectasia (JPS/HHT)
Individuals with JPS/HHT have variable findings of juvenile polyposis and HHT (see Table 2). Most individuals with JPS who have an SMAD4 germline pathogenic variant have one or more clinical features of HHT. The findings of HHT may manifest in early childhood. A high frequency of pulmonary arteriovenous malformations (with digital clubbing) and epistaxis has been consistently noted in individuals with SMAD4-related HHT. Conversely, telangiectases do not appear to be a constant feature. Additional complications reported in individuals with JPS/HHT include anemia, migraine headaches, and exercise intolerance.
Thoracic aortic disease (e.g., aortic root dilatation, aneurysm, and aortic dissection) and mitral valve dysfunction have been reported in individuals with SMAD4 pathogenic variants [Heald et al 2015].
Expanding phenotype. There are reports of individuals with an SMAD4 pathogenic variant who also presented with retinitis pigmentosa, retinal detachment, joint laxity, and/or a marfanoid habitus. Data for these findings is limited and it is unclear if these are features of the SMAD4-related JPS/HHT phenotype. More work is needed to assess the frequency of these findings to determine medical management recommendations. Providers may wish to be aware of these reports and evaluate individuals on a case-by-case basis.