Summary: Celiac.com 09/24/2022 - When an individual is diagnosed with celiac disease, every family member is affected. Suddenly, the diagnosing physician or the helpful support group informs the new celiac that first and second degree relatives must be regularly tested for celiac disease. They learn that it is necessary because celiac disease is a genetic condition and could appear at any time in other family members. Antibody vs. Genetic Testing The blood tests that celiacs are more familiar with are the antibody tests. These tests, such as the tissue transglutaminase test, or the antiendomysial antibody test, measure the immune response to gluten that occurs at a point in time (think of it as a photograph). These are important tests because they characterize the extent to which the immune system is responding to a specific antibody created in response to gluten. More celiacs and their families are learning about genetic testing, which is also a blood test. Unlike antibody testing, the HLA gene testing for celiac disease measures the presence or absence of genetic material that is found on the surface of cells. Celiac disease is associated with the presence of HLA DQ2 and HLA DQ8. Genetics of Celiac Disease When the genetic predisposition for celiac disease was detected (on Chromosome 6) researchers noted that the genes were a necessary but not sufficient condition for the disease to develop. In fact, up to one third of the U.S. population has the genes for celiac disease, but it is thought that only 1-4% will actually develop the disease at some point during their lifetimes. This means that people with DQ2 or DQ8 can develop celiac disease, but aren’t destined to develop it. This is most evident in the case of identical twins, where only one of the twins is affected by celiac disease. Despite the fact that the twins have identical genes, the unaffected twin only has a 70% chance of developing the condition. How can this happen? Researchers and medical professionals use the term “environment” to refer to lifestyle factors, diet, or medical history that affect an individual’s chances of developing a disease. It is thought that environmental factors such as the duration of breast feeding and the presence of other autoimmune disorders can impact the development of celiac disease. Environmental factors can have a protective effect or a promotional effect with regard to the development of a genetic disease. Medical Knowledge and Celiac Genetics At the International Celiac Conference in Paris last summer, numerous presentations were made by researchers looking at the role that of other genes that could modify, protect, or directly lead to the development of celiac disease. Most of them, however, failed to establish a direct connection between a gene and the disease process. Since the Paris conference, however, researchers have published work that looks at subsets of HLA DQ2 and HLA DQ8 and have determined that some combinations of these subsets lead to a greater or lesser risk of developing celiac disease (called gene dosing). In addition, it is thought that a certain genetic typing (within DQ2 and DQ8) can identify people who will develop celiac disease later in life. Gene Testing Considerations The gene test for celiac disease is a blood test that looks to measure HLA DQ2 and HLA DQ8 positivity on the surface of cells. It does not diagnose celiac disease. It places an individual into an “at-risk” group for celiac disease, which indicates the individual should be closely monitored with antibody testing in the future. Celiac centers across the United States have different approaches towards the use of genetic testing with patients and families concerned about celiac disease. Be sure to talk to your doctor about his/her perspective on genetic testing for celiac disease. Rule Out Celiac Disease Given that two-thirds of the U.S. population does not have DQ2 or DQ8, which are necessary for celiac disease to occur, the gene test can “rule out” with a very high degree of certainty that person’s potential for becoming celiac (95% of celiacs are DQ2 positive, 5% are DQ8 positive). In families where the potential celiacs are children, many parents feel that genetic testing offers them additional information—the ability to know which of their children to monitor more closely. On the Diet before Diagnosis In individuals with symptoms who have been on the gluten-free diet for a significant period of time, the gene test is often the only way to determine if symptoms could possibly be related to celiac disease. For a person who faces this situation, a negative gene test would indicate that symptoms are not likely to be celiac disease. A positive gene test, however, does not diagnose the disease but increases the likelihood that it is present. The Blame Game Genetic testing provides very useful information for clinicians and families facing celiac disease. However, family members may joke about or comment that testing will determine whose side of the family is at fault for the presence of celiac disease. Genetic testing of any kind affects everyone in the family (close and distant relatives). Interpersonal relationships and potential problems should at least be considered before testing. In considering the genetic test, families have to realistically assess what they will do with the information if and when members test positive. If the family is planning to have a gluten-free household anyway, genetic testing will not offer information that will change the health outcome of each family member. In this circumstance, the family is probably not a good candidate for genetic testing. The Cost of Genetic Testing Genetic testing can be very expensive, and this can vary by geography and the type of medical center where the testing is done. Costs include the cost of the actual test, the hospital laboratory fees, equipment/supplies, and processing. Ask your doctor’s office about the cost of the test before you have it done. In addition, you should take steps to insure that your insurance company will cover the test before the blood is drawn, unless you plan to pay for the test yourself.
