Juvenile polyposis syndrome (JPS) is a polyp predisposition syndrome, where there is a higher risk to develop polyps in your digestive tract running in the family. The name juvenile describes the specific types of polyps that develop, not the age when you develop them. This type starts with many small growths, or polyps, in your colon that can cause bleeding and anemia and may eventually develop into cancer if not removed. A specialized doctor called a gastroenterologist can go in and remove these growths before they turn into cancer.
Pathogenic (or harmful) variants in one of two genes cause JPS: BMPR1A and SMAD4. It is inherited in an autosomal dominant pattern, meaning that children of someone who carries a pathogenic variant each have a 50% risk to inherit the variant and associated cancer risks. Notably, women and men both have the BMPR1A and SMAD4 genes and have the same chances to inherit and pass down variants in these genes. Therefore, both sides of the family are important when assessing inherited risk. About 33% (or 1 in 3 people) with this condition will have a parent with polyps. The other 2 in 3 (or 67%) of people have no family history and will be the first ones in their family with this condition.
Genetic testing is available for this condition. There are different ways to complete this testing. This can include:
The risk that someone with JPS will get cancer over their lifetime is between 9 and 50%, including cancer of the colon, rectum, small intestine, and pancreas. The chance of stomach cancer is 21% in those who have gastric polyps. One study showed the risk for colon cancer may be as high as 68%.
There is also a risk for an increased number of polyps, from 4 or 5 to more than 100. These are not cancerous and many of them will stay benign, but they have the potential to develop into cancer. They can be anywhere in your digestive tract: stomach, small intestine, colon, or rectum.
The chance to develop colon cancer partly depends on if you get regular colonoscopies. A colonoscopy can reduce the risk of colon cancer by removing the polyps before they have a chance to develop into cancer.
Another thing to know about JPS is that people with a SMAD4 pathogenic gene variant have a higher chance of also having another condition called hereditary hemorrhagic telangiectasia (HHT). Our genes are very complex, and sometimes different changes in the same gene can cause different health issues. Some variants in the SMAD4 gene only cause JPS, while different variants in the same SMAD4 gene can cause JPS and HHT. This result may come up while doing testing for another, unrelated condition as part of general genetic screening. HHT can cause nose bleeds and an increased risk for aneurysms and arteriovenous malformations (groups of abnormal blood vessels connecting arteries and veins in the brain and lungs). There is treatment available for people with HHT.
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