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TOPIC: Celiac and Gluten Sensitivity Genes
Celiac and Gluten Sensitivity Genes 11 Sep 2008 18:38 #549
What do the Genetic Markers Mean ....
This article appeared in the Spring 2008 edition of Celiac.com's Scott-Free Newsletter .
Celiac.com 08/17/2008 - Are you confused about genetic testing for celiac disease or Gluten sensitivity? Do you want to know what tests you should request and which laboratory to use? Have you already had celiac DQ genetic testing but are not sure what the results mean or what your risk is of developing celiac disease or gluten sensitivity? These are the questions I will answer in the next few pages.
What does it mean to be homozygous or heterozygous for celiac genes?
Homozygous means that you have two copies e.g. DQ2/DQ2, DQ8/DQ8 whereas heterozygous means you have one copy of DQ2 or DQ8. Some people have one copy of DQ2 and one of DQ8 (DQ2/DQ8) and they have a greater risk for celiac disease than someone with only one copy of either DQ2 or DQ8 but not as great a risk as someone with two copies of DQ2 (DQ2/DQ2). Since DQ2 is associated with a greater risk of celiac disease than DQ8, then one copy of DQ2 plus a DQ8 (DQ2/DQ8) indicates a higher risk than having two copies of DQ8 (DQ8/DQ8). Hopefully, I have not lost you yet but if I have please continue to read on because the information that follows will still be helpful to you.
What is this alpha and beta subunit typing and why is it important?
The beta subunit is the most important component of the DQ molecule, but the alpha subunit has also been shown to carry an increased risk for celiac disease. Unfortunately, since testing for both is more complicated and expensive it is not always done.
Also, some think that since the beta subunit carries most of the risk and the alpha unit only minor risk, testing for only the beta subunit is adequate. Several clinical laboratories have chosen this approach. They only test for, and report on, DQ2 and DQ8 based on beta subunit types, so their results typically look like this: HLA DQB1*02 detected, DQ2 positive, etc. This is the policy of the laboratory at Bonfils, who also does testing for Quest Diagnostics and Enterolab as well as many hospitals. However, the alpha subunit of DQ2 also carries some risk for celiac disease.
What if you are positive for the beta subunit of DQ2 or DQ8 by testing from Bonfils, Enterolab or Quest?
If the beta subunit is present then Bonfils, Enterolab and Quest tests will report DQ2 and/or DQ8 positive. Sometimes the report will just report DQ2 negative and DQ8 negative, especially when a hospital is reporting the results obtained from Bonfils. However, when the beta subunit is not present and they report DQ2 negative and/or DQ8 negative, it is still possible that an alpha subunit could be present. Results reported in this manner are, in my opinion, potentially misleading. I believe they can lead a doctor to assume that an individual is not at increased risk for, or cannot have celiac disease, when this may or may not be true. Unfortunately, the patient in such circumstances may be told that they can not have celiac disease, yet they may not only be at risk for the disease, they may well have it while being told it is impossible or extremely improbable.
What does Prometheus do and how do they report their results?
Prometheus, like Kimball and LabCorp, includes alpha and beta subunit typing. In the past they did not indicate whether there was one or two copies of DQ2 or DQ8 if someone was positive. If a patient was DQ2 and DQ8 positive then these labs reported their full genetic DQ type. However, if one or the other was negative, their exact genotype was not reported. Recently, not only has Prometheus started reporting the full DQ2 and DQ8 genotype, but they are now reporting whether someone is homozygous or heterozygous as well. They are also reporting the relative risk for celiac disease based on the pattern shown by testing. However, they are still not reporting the other DQ types.
What is the advantage of the new Prometheus reporting?
Since Prometheus results now include a calculation of the individualâ€™s risk of celiac disease, compared with the general population, the patient can see how high their risk of celiac disease is, as well as being able to estimate the risk for their parents and their children.
As you can see, the risk of celiac disease has a wide range of possibilities, which depend on the individualâ€™s DQ results. This risk can be below 0.1% if you do not have any portion of the high-risk genes DQ2 and DQ8. On the other hand, the risk may be very high (more than 31 times the risk of the general population) if you have two copies of the full complement of DQ2 molecule. Again, I would like to point out that if you have DQ2/DQ2, DQ2/DQ8, or DQ8/DQ8, then both of your parents and all of your children have to have at least one copy of an at-risk celiac gene. Your childâ€™s complete type will depend on the DQ contribution from their other parent.
What other laboratories do both alpha and beta subunit testing?
What if you do not have DQ2 or DQ8?
What if your genetic testing was done by Enterolab, Quest, Bonfils or a hospital that utilized Bonfils, and it indicated that you were DQ2 and DQ8 negative?
What if you have not yet had celiac DQ genetic testing?
I recommend that everyone have the testing. I realize that most insurance companies and doctors, including some celiac experts, would disagree with me. However, the value of DQ testing is that it can provide a great deal of information about your risk, especially if you have testing done for both alpha and beta subunits. I recommend that you have testing done by Kimball Genetics, LabCorp or Prometheus if you have not yet had genetic testing done. If your insurance or budget does not allow for this more expensive testing, but does cover testing by Quest or Bonfils or you can afford the $159 that Enterolab charges, then I still recommend that you get DQ testing using one of these laboratories. You just need to be aware of the limitations of the results as I have reviewed them here.
What are the advantages of DQ testing through Kimball Genetics?
Kimball can perform testing on either blood or mouth swab samples. The tests can be ordered without a doctorâ€™s order. You can purchase testing on mouth swab sample for $345. The advantages of Kimballâ€™s tests include alpha and beta subunit testing and full DQ typing to determine if you carry the other gluten sensitive DQ patterns besides DQ2 and DQ8.
What about LabCorp?
LabCorp also provides both alpha and beta subunit testing and they report the other DQ types. They only provide testing on blood samples, a doctor must order the testing, and preauthorization is required.
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