Familial adenomatous polyposis

Diagnosis and Testing

How do I get tested for familial adenomatous polyposis?

Testing for familial adenomatous polyposis can be done through a simple blood test. The type of tests to be ordered by your doctor is called sequencing of the APC gene which is when the "spelling" of the APC gene is checked for errors. They may also order a deletion/duplication analysis of the APC gene that looks for big chunks of the gene that are missing or added that could be missed with sequencing.

For MUTYH-associated polyposis, there are typically two changes in the MUTYH gene that cause this colon polyp predisposition, called c.536A>G (p.Tyr179Cys) and c.1187G>A (p.Gly396Asp). These mutations are carried by approximately 1%-2% of the general population and account for at least 90% of all MUTYH pathogenic variants in northern European populations. Genetic testing would check for these two mutations first to see if the changes are present or not. If that testing is normal, then your doctor may order sequencing of the MUTYH gene where the "spelling" of the MUTYH gene is checked for errors. Deletion/duplication analysis of the MUTYH gene is also available, though there have been very few mutations of this type reported.

These tests are usually ordered by a genetics health provider after genetic counseling which will examine an individual's personal and family history to determine if genetic testing for the APC and/or MUTYH gene makes sense as opposed to testing for another genetic condition. A genetic counselor focused on cancer in your area can be found at www.nsgc.org website.

References
  • Jasperson, K. W. (2017, February 2). APC-Associated Polyposis Conditions. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK1345/.
  • Nielsen, M. (2019, October 10). MUTYH Polyposis. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK107219/.
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More Diagnosis and Testing Content

Is there newborn testing for familial adenomatous polyposis?

Is there more than one type of test for familial adenomatous polyposis?

Who else in my family should I test for familial adenomatous polyposis?

Does it matter if you test blood versus saliva versus a biopsy for familial adenomatous polyposis?

Is there newborn testing for familial adenomatous polyposis?

There is not newborn testing for familial adenomatous polyposis at this time.

References
  • Jasperson, K. W. (2017, February 2). APC-Associated Polyposis Conditions. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK1345/.
  • Nielsen, M. (2019, October 10). MUTYH Polyposis. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK107219/.
Is there more than one type of test for familial adenomatous polyposis?

There are different options for genetic testing. A meeting with a genetics health provider for genetic counseling can help determine which option of genetic testing makes the most sense for you based on your personal or family history. An individual may be only tested for the APC gene. An individual may be tested for the APC gene along with multiple other genes that can also cause an increased risk for colon polyps, including the MUTYH gene which causes MUTYH-associated polyposis. Testing multiple genes at once is called a cancer gene panel. A genetic counselor focused on cancer in your area can be found at www.nsgc.org website.

References
  • Jasperson, K. W. (2017, February 2). APC-Associated Polyposis Conditions. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK1345/.
  • Nielsen, M. (2019, October 10). MUTYH Polyposis. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK107219/.
Who else in my family should I test for familial adenomatous polyposis?

An individual who has a mutation in the APC gene has a 50% chance to pass the mutation on to each of their children. The siblings of an individual who has a mutation have a 50% chance to inherit the mutation. Most often, the mother or father of an individual who carries a mutation also carries the mutation, but this is not always true with FAP. Sometimes a mutation in the APC gene happens for the first time in an individual and was not inherited from their mother or father.

For MUTYH-associated polyposis, if an individual has two mutations in the MUTYH gene, each of their siblings has a 25% chance of also having two mutations. It is recommended that the partner of an individual who has MUTYH-associated polyposis receives genetic testing of the MUTYH gene to determine the risk for their future children to have MUTYH-associated polyposis.

Since screening for colon polyps begins at a young age with this condition, a discussion with a genetics provider and your child's doctor is recommended to determine the best time to perform genetic testing. Genetic testing for a hereditary cancer condition is an individual's choice, and is an option available, but not mandatory, for other family members.

References
  • Jasperson, K. W. (2017, February 2). APC-Associated Polyposis Conditions. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK1345/.
  • Nielsen, M. (2019, October 10). MUTYH Polyposis. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK107219/.
Does it matter if you test blood versus saliva versus a biopsy for familial adenomatous polyposis?

Blood is the preferred specimen, but saliva can be used as an alternative as your APC and/or MUTYH genes are most often the same in blood or saliva. Testing is not recommended on a biopsy sample as we would be testing the genetic makeup of the tumor, rather than the cells that are representative of the person's inherited genetic makeup (germline). Different labs have different specimens that are or are not willing to accept. A genetic counselor focused on cancer who can help with laboratory requirements in your area can be found at www.nsgc.org website.

References
  • MUTYH mutY DNA glycosylase. (2019, October 19). Retrieved from https://www.ncbi.nlm.nih.gov/gtr/genes/4595/.

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