Trait Document

Juvenile polyposis is the presence of certain types of polyps (i.e., abnormal growths) called “juvenile” polyps that can grow along the gastrointestinal (GI) tract (i.e., the stomach, small intestine (i.e., bowel), large intestine (i.e., bowel or colon), and rectum). Juvenile polyposis syndrome is a condition in which individuals have an increased risk to develop many juvenile polyps along the GI tract. Most juvenile polyps are benign (i.e., do not turn into cancer), but some juvenile polyps are malignant (i.e., do turn into cancer). The risk for having cancer in this syndrome is between 9% and 68%. The most common cancer seen in people with juvenile polyposis syndrome is colon cancer, but there are risks for cancer along the rest of the GI tract too (including stomach, pancreatic, and small intestine cancers). The average age of colon cancer diagnosis in people with juvenile polyposis syndrome is age 42 years.

Most people with juvenile polyposis syndrome are diagnosed by way of clinical exam and history by having one of three findings: five or more juvenile polyps in the colon; many juvenile polyps spread throughout the entire GI tract; or any number of juvenile polyps when they also have family members with juvenile polyps. Genetic testing is then ordered to confirm this clinical diagnosis.

About 20% of people with juvenile polyposis syndrome have a change or mutation in the SMAD4 gene, and another 20% have a mutation in the BMPR1A gene. The SMAD4 and BMPR1A genes make proteins that help to send chemical signals from the cell membrane (i.e., barrier or wall) to the nucleus (i.e., the center of the cell where the DNA is stored). By doing this, these two proteins work together to help control the activity of other genes and how the cells grow and divide. Mutations in the SMAD4 and BMPR1A genes are thought to stop the cell signals that control cell growth. This allows cells to grow and divide in an uncontrolled way, which can cause polyps to grow.

Management of juvenile polyposis syndrome often includes ways to screen for polyps and prevent cancers from growing, and ways to treat polyps or cancers that are already present. The best way to prevent cancers from growing is to screen for polyps on a regular basis. Screening for juvenile polyps begins at age 15 years with a colonoscopy and an upper endoscopy. If polyps are found, these screens are repeated every year. If no polyps are found, then these screens are repeated in two to three years. People with juvenile polyposis syndrome should also be watched closely for rectal bleeding, stomach pain, constipation, and diarrhea. They also have routine screening by complete blood counts (CBCs) (i.e., a test that looks at the kinds and numbers of cells in the blood).

When polyps are found on either colonoscopy or upper endoscopy, they are usually removed immediately through a process called a “polypectomy.” Removing the polyps as soon as they are found helps to lessen the risk of bleeding, prevents a blockage in the intestines, and can prevent any malignant polyps from growing into cancers. If there are too many polyps found, then surgery to remove part or all of the colon or stomach may be needed. If colon cancer is diagnosed, people refer to their surgeon and oncologist for treatment recommendations.

Juvenile polyposis syndrome is inherited in an autosomal dominant pattern. This means inheriting one SMAD4 or one BMPR1A mutation is enough for an individual to be affected and show signs of juvenile polyposis syndrome. The mutation can be inherited from an affected parent or it can occur brand new (de novo) in an affected child.

The risk to family members depends on whether or not the individual with juvenile polyposis syndrome has a parent affected with juvenile polyposis syndrome. If a parent also has juvenile polyposis syndrome, the risk of having a child with the condition is 50% with each pregnancy. If a parent does not have juvenile polyposis syndrome, the risk of other siblings being affected is very low.

People who have juvenile polyposis syndrome because of a mutation in the SMAD4 gene sometimes also have a disease called “Hereditary Hemorrhagic Telangiectasia” (see “Hereditary Hemorrhagic Telangiectasia” trait profile).