Celiac disease is linked to heredity, meaning you only can develop celiac if you carry the genes that predispose you to it. Therefore, physicians increasingly are using celiac disease genetic testing to determine if someone has the predisposition to develop the condition.
Almost everybody eats gluten, a protein found in the grains wheat, barley and rye. However, in people who have the right genes, gluten ingestion may eventually lead to celiac disease, an autoimmune condition that causes your own disease-fighting white blood cells to attack the lining of your small intestine.
Not everyone who carries celiac disease genes ultimately will develop celiac disease — in fact, while up to 40% of the population has one or both of the necessary genes, only 1% of the population actually has celiac disease. So having the genetic potential doesn't mean you'll be diagnosed with celiac disease and need to give up gluten; in fact, the odds are stacked against it.
However, genetic testing for celiac disease can provide another piece to the diagnostic puzzle, especially in cases where your diagnosis isn't clear-cut or where you're trying to determine future testing needs.
Celiac Disease Genetic Testing Looks for Two Genes
Bear with me — this gets complicated.
The genes that predispose you to celiac disease are located on the HLA-class II complex of our DNA, and they're known as the DQ genes. Everyone has two copies of a DQ gene — one from their mother and one from their father. There are numerous types of DQ genes, but there are two that are involved in the vast majority of celiac disease cases: HLA-DQ2 and HLA-DQ8.
Of these, HLA-DQ2 is by far the most common in the general population, especially among people with European heritage — some 30% or more of people whose ancestors hailed from that part of the world carry HLA-DQ2. HLA-DQ8 is considered more rare, appearing in about 10% of the overall population, although it's extremely common in people from Central and South America.
Studies have shown that about 96% of the people diagnosed by biopsy with celiac disease carry DQ2, DQ8 or some combination of the two. Since you get one DQ gene from your mother and one from your father, it's possible for you to have two copies of DQ2, two copies of DQ8, one copy of DQ2 and one of DQ8, or one copy of either DQ2 or DQ8 combined with another DQ gene.
In any event, if you carry one copy of either DQ2 or DQ8, you're considered to have a much higher risk of celiac disease. There's some evidence that carrying two copies of one of the genes (either DQ2 or DQ8) may increase your risk even more.
At least one study has shown that another specific gene, HLA-DQ7, also predisposes individuals to celiac disease. In fact, in that study, 2% of people with biopsy-proven celiac disease carried HLA-DQ7, but not DQ2 or DQ8. However, there's some controversy over whether having DQ7 actually predisposes you to celiac disease, and genetic testing in the U.S. does not currently recognize DQ7 as a "celiac disease gene."
In addition, new research indicates you don't need to carry HLA-DQ2 or HLA-DQ8 in order to develop non-celiac gluten sensitivity. There may be additional HLA-DQ genes involved in gluten sensitivity; read more in Do you need specific genes to develop gluten sensitivity?
Celiac Gene Test Involves Simple Screen
Testing for the celiac disease genes isn't invasive at all. You'll either provide a laboratory with a sample of your blood, use a swab to collect a few of the cells from inside your cheek, or use a syringe to gather some of your saliva. Your blood, cheek cells or saliva then are analyzed by a laboratory; any of these methods produces equally accurate results.
Although most people have genetic testing performed in conjunction with other tests ordered by their physician, it's easy (although expensive) to obtain the test without a physician being involved.
For example, Enterolab, which provides testing for gluten sensitivity, offers a celiac gene test for $149. Other direct-to-consumer genetic testing services (including MyCeliacID, a saliva-based test that retails for $329) offer celiac disease testing. However, if you decide to go the direct-to-consumer route, be aware that your health insurance most likely won't cover the cost.
Genetic Testing Doesn't Equal Diagnosis
Since not everyone who carries a celiac gene winds up being diagnosed with celiac disease, a positive genetic test does not equal a diagnosis. (See: I tested positive in my celiac gene test. Should I go gluten-free?)
All your positive celiac disease genetic test does is place you in what physicians consider a "high-risk" group for celiac disease. Therefore, the celiac disease gene tests are mainly useful to rule out celiac disease in cases where celiac symptoms are present. In some cases, a person might have celiac test results that aren't clear-cut, and a gene test can help a physician make the proper diagnosis.
Gene tests also are helpful to rule out celiac disease in family members of diagnosed celiacs. Celiac disease testing for relatives is recommended once someone in your family is diagnosed, but if you know you carry the celiac disease gene, you should be followed more closely.
Finally, it's possible to use the gene tests to see if celiac disease is a possibility in someone who's already consuming a gluten-free diet.
You need to be eating gluten for conventional celiac disease testing to be accurate. However, some people realize that eating gluten-free makes them feel better, and remove the gluten protein from their diets before undergoing testing for celiac disease. If they later decide they want a diagnosis, they have two choices: attempt a gluten challenge, or undergo genetic testing.
You don't need to be eating gluten for the celiac disease gene test — again, the test only determines if you have the potential to develop celiac disease, not if you actually have it. Therefore, although genetic testing can't provide absolute answers about whether you actually have celiac disease, many people prefer it to a gluten challenge because it doesn't require them to go back on gluten to obtain more information about their condition.
There's much we don't yet know about celiac disease, and it's not clear why some people with celiac disease genes develop it while others do not. However, celiac disease genetic testing can help to determine risk for the condition in family members, and in cases that aren't completely clear-cut.
Celiac Disease Center at Columbia University. Serologic and Genetic Testing. Accessed Jan. 5, 2012.
National Institutes of Health. NIH Consensus Development Conference on Celiac Disease. Accessed Jan. 5, 2012.
Sacchetti L. et al. Discrimination between Celiac and Other Gastrointestinal Disorders in Childhood by Rapid Human Lymphocyte Antigen Typing. Clinical Chemistry. Aug. 1998, Vol. 44, No. 8, p. 1755-1757.
University of Chicago Celiac Disease Center. Genetic Testing. Accessed Jan. 5, 2012.