Over 99% of people affected by coeliac disease have the HLA DQ2, HLA DQ8, or parts of these genes. Interestingly, 20-30% of the population carry one or both of these genes. However, only 3% of the people who carry one or both genes will actually develop coeliac disease.
Genetic testing, also known as DNA testing, can be done to find out if a person is a carrier of these genes. It is performed by a blood test or buccal (inside cheek) scraping and the sample is sent to a lab to be analysed. Since not everybody who possesses the coeliac gene/s will go on to develop the condition, a genetic test is useful to rule out, and not confirm coeliac disease. In other words, if a person does not have either of these 2 genes, there is virtually no chance of ever developing coeliac disease in their lifetime.
Genetic testing can also be useful when a person has started a gluten free diet before getting tested for coeliac disease. To diagnose coeliac disease, gluten must be eaten for 6-8 weeks before testing. This is known as taking a gluten challenge. If this gluten challenge is not possible for various reasons, a genetic test can be done to rule out coeliac disease (or to know if there is a possibility of having coeliac disease). Gluten does not have to be eaten for a genetic test to be done. Another good use for genetic testing is when an endoscopy is difficult. Similarly, in this case, a negative genetic test will rule out coeliac disease.
The gold standard for diagnosing coeliac disease in adults is an antibody blood test followed by confirmation by endoscopy and biopsy. A positive genetic test alone does not confirm coeliac disease. However, in children, genetic testing may be useful in diagnosing coeliac disease. New guidelines in the UK, published by the British Society of Paediatric Gastroenterology, Hepatology and Nutrition (BSPGHAN) and Coeliac UK in February 2013 state that a biopsy may not be necessary in every case. These new guidelines state that children with symptoms of coeliac disease, who have a high level of antibodies by blood test, and have the gene/s for coeliac disease do not need confirmation by biopsy.
Personally, as a mother, I feel that genetic testing is useful for children of parents with coeliac disease. It is always a relief to know if your child does not carry the genetic makeup that makes them vulnerable to this condition. On the other hand, it is useful to know if your child does possess HLA DQ2/8, so that regular monitoring for symptoms and testing can be done.
What do you think about this?
“Diagnosis Guidelines.” Coeliac UK. N.p., n.d. Web. 07 May 2014. <https://www.coeliac.org.uk/healthcare-professionals/diagnosis/diagnosis-guidelines/>.
Jenkins R (2010) Gene tests for coeliac disease used inappropriately: experts. Australian doctor.