Ancestry type testing for celiac genes

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Melinda Dennis MS, RDN, LDN

Q:  My daughter was diagnosed with celiac disease by biopsy over 20 years ago with symptoms that resolved on a gluten-free diet. She recently found out through one of the “ancestry-type” site’s testing that she doesn’t even have the gene for celiac disease. How can this be? She’s now trying a bit of gluten and not experiencing any side effects. Are these non-medical gene tests reliable? They are testing her genome and found no gene, so I’m thinking that she must not have celiac disease after all. Is it possible for her to still have celiac disease without the gene?

I really would like an understanding of the reliability of these offline genetic tests as they relate to celiac disease and what to do if one of these tests says that you don’t have celiac disease after all. Thank you!

Answer


The short answer: We (the Celiac Center at Beth Israel Deaconess Medical Center) recommend that patients do not use the ancestry testing programs to rule out celiac disease since these tests may not reliably capture the full genetic profile for celiac disease.  Instead, we recommend following up with a clinician skilled in celiac disease who will provide formal celiac genetic testing.

The gold standard for celiac disease diagnosis is endoscopy with small bowel biopsy. We recommend that patients who have a secure diagnosis of celiac disease remain on a strict gluten-free diet for health purposes.  For those with a questionable diagnosis a formal gluten challenge study can be performed, supervised by an expert celiac physician.

Here’s a little background on the genes for celiac disease:

The Human Leukocyte Antigen (HLA) genes are linked to many autoimmune diseases, including celiac disease. Everyone has a copy from their mother and a copy from their father.  These copies can come in different versions called alleles. The HLA gene alleles that predispose to celiac disease are called DQ2 and DQ8.

Almost all people with CD have at least one copy of DQ2 or DQ8. People with only one copy of DQ2 or DQ8 have a ~3% risk of having CD, whereas people who have two copies of either have a ~10% risk.1

If you DO have one of these genetic markers, it is possible that you have or may develop CD. Your doctor will need to perform more tests. Since 30-40% of the general population has at least one copy of DQ2 or DQ8 but do not go on to develop celiac disease, hence the gene test is not a good test to confirm celiac disease.2

If you do NOT have one of these two genetic markers, your doctor can rule out celiac disease with almost 100% certainty.

Rarely, people with only 1/2 of the DQ2 gene (ie. DQ2.2, DQ2.5 or DR5) will get celiac disease but this occurs in <5% of people with celiac disease.1 If the genetic test used does not have the ability to “look for” and identify all of these possible variations,  the consumer may receive inaccurate test results. For this reason, we recommend having celiac gene testing done by your doctor in the clinical setting. You do not need to eat gluten in order to have the gene testing.

References

  1. CeliacNow. FAQ: Diagnosing Celiac Disease https://www.bidmc.org/-/media/files/beth-israel-org/centers-and-departments/digestive-disease-center/celiac-center/_faq-diagnosing-celiac-disease-feb-2016.pdf?la=en. Accessed May 24, 2019.
  2. Rubio-Tapia A, Hill ID, Kelly CP, et al. ACG clinical guidelines: diagnosis and management of celiac disease. Am J Gastroenterol 2013;108:656-76; quiz677.
  3. Pietzak MM, Schofield TC, McGinniss MJ, Nakamura RM. Stratifying risk for celiac disease in a large at-risk United States population by using HLA alleles. Clin Gastroenterol Hepatol. 2009 Sep;7(9):966-71.

Disclosure
Melinda Dennis, MS, RDN, LD is the Nutrition Coordinator of the Celiac Center at Beth Israel Deaconess Medical Center in Boston, MA. She is currently the Senior Nutrition Advisor to NCA and has been a paid consultant of NCA.

Note: This information is provided by NCA and Melinda Dennis, NCA's Senior Consulting Dietitian. This information is meant for educational purposes and is not intended to substitute for personalized medical advice or replace any medical advice provided directly to you by your health care provider. This information can be printed and used in consultation with your physician or dietitian. No liability is assumed by NCA, Ms. Dennis or her nutrition consulting service Delete the Wheat, LLC. by providing this information.

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About Melinda Dennis MS, RDN, LDN

Melinda Dennis, Senior Nutrition Consultant for NCA, is an expert celiac dietitian and and Nutrition Coordinator for the Celiac Center at Beth Israel Deaconess Medical Center in Boston, MA. Diagnosed with celiac disease in 1990, she specializes in the nutritional treatment of patients with celiac disease and gluten-related disorders.

Melinda lectures internationally and has written extensively on the nutritional management of celiac disease including the award-winning book Real Life with Celiac Disease. Melinda was the original founder of NCA in 1993 and so it is only fitting that she comes back to us in this capacity. We are truly honored to have her on our team.