Juvenile polyposis syndrome

Inheritance

How is juvenile polyposis inherited?

Juvenile polyposis syndrome (JPS) is inherited in an autosomal dominant manner. This means that the condition is the result of a change in a person's genetic information. A change (called a mutation or pathogenic variant) in the BMPR1A or the SMAD4 gene has been shown to cause JPS. Humans have two copies of both the BMPR1A and the SMAD4 genes, one from their mother and one from their father. A person has JPS syndrome when a mutation on one copy of either the BMPR1A or the SMAD4 gene prevents it from working, even though the second copy of the BMPR1A or SMAD4 gene is working correctly. Men and women are equally likely to have JPS. A person with JPS syndrome has a 50% chance of passing the copy of the gene with the JPS causing mutation to each of their children and 50% to pass down the standard copy of the gene to each of their children.

About 33% of individuals with JPS syndrome have a parent who also has JPS syndrome, meaning it was inherited. However, approximately 67% of individuals with JPS syndrome did not inherit the genetic change from a parent. The genetic changes that cause JPS in these individuals are de novo, meaning they happened spontaneously or randomly only in that individual, likely around the time they were conceived.

References
  • Larsen Haidle J, Howe JR. Juvenile Polyposis Syndrome. 2003 May 13 [Updated 2017 Mar 9]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2019. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1469/[/link
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What is a variant or VUS in the SMAD4 gene?

Can you have juvenile polyposis syndrome without having a SMAD4 gene mutation?

My child has juvenile polyposis syndrome. Will others in the family have it?

What is a variant or VUS in the SMAD4 gene?

Sometimes genetic testing shows a change in the SMAD4 gene called a "variant of unknown significance" or a VUS. This means that a genetic change was found that we do not fully understand. In other words, this genetic change may cause juvenile polyposis or it may be normal variation. We need more data to be sure. A genetic counselor or geneticist can help explain what this result means. Over time, scientists may learn more about variants of unknown significance. If someone has a VUS in SMAD4, they should check with their healthcare provider on an annual basis for updates on the VUS.

References
  • Accessed on November 14, 2019: Joy Larsen Haidle, MS, CGC and James R Howe, MD; GeneReviews, Juvenile Polyposis Syndrome (https://www.ncbi.nlm.nih.gov/books/NBK1469/)
Can you have juvenile polyposis syndrome without having a SMAD4 gene mutation?

It is possible to develop juvenile polyps without having a mutation in the SMAD4 gene. However, having multiple juvenile polyps is a red flag that juvenile polyposis syndrome is likely the culprit. Having a genetic evaluation can help determine the genetic cause of the juvenile polyp development.

References
  • Accessed on November 14, 2019: Joy Larsen Haidle, MS, CGC and James R Howe, MD; GeneReviews, Juvenile Polyposis Syndrome (https://www.ncbi.nlm.nih.gov/books/NBK1469/)
My child has juvenile polyposis syndrome. Will others in the family have it?

Because juvenile polyposis syndrome is inherited in an autosomal dominant inheritance pattern, it means that every first degree relative of an affected individual has a 50% chance of also having it. First degree relatives are siblings, children, and parents. Second degree relatives should have testing after first degree relatives are all tested. in a specific example, let's say 27-year-old Andrea has been diagnosed with juvenile polyposis syndrome. Andrea has 3 children. EACH of her children has an individual 50% chance to also have it. Andrea has 2 siblings: one brother and one sister. EACH of her siblings has an individual 50% chance to also have it. Andrea's mother has testing and is negative. This means that Andrea's mothers side of the family does NOT need to have any more testing. Andrea's father has testing and is positive. Each of Andrea's father's siblings should have testing as well, because they have an individual 50% chance of being positive as well.

References
  • Accessed on November 14, 2019: Joy Larsen Haidle, MS, CGC and James R Howe, MD; GeneReviews, Juvenile Polyposis Syndrome (https://www.ncbi.nlm.nih.gov/books/NBK1469/)

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