Here is a Crash course on Celiac disease with the most relevant information related to the Celiac disease gene (DQ2 and DQ8) test.
What is Celiac Disease?
Celiac disease is an autoimmune disorder triggered in some people after eating gluten. The intolerance to gluten causes inflammation in the small intestine and, over time, damages the intestinal lining that is responsible for absorbing nutrients from food. Celiac also affects other parts of the body, such as skin and bones [1].
Prevalence of Celiac Disease
Gluten intolerance is more common than one would think. Almost one percent of the population in western countries is at risk of celiac disease [2], based on data from the US [3], Ireland [4], Italy [5], and Sweden [6]. However, the prevalence varies across countries and ethnic groups. For example, it is rare in Japan [7], but one in twenty people is gluten intolerant in Algeria’s Saharawi tribe [8].
The majority of celiac cases remain undiagnosed or have been misdiagnosed [9]. For example, a study of Italian children discovered that 6 out of 7 were previously undiagnosed [5].
This lack of correct diagnosis or not testing for celiac disease for DQ2 and DQ8 gene tests is mostly because symptoms of celiac often differ among patients and may overlap with other health conditions. Hence, it is important to test for celiac disease.
After living without any symptoms for years, skin rashes, vomiting, diarrhea, and abdominal pain may appear out of nowhere [2] until a diagnosis confirms the disease.
Celiac Disease Symptoms
Symptoms of celiac show up when it becomes difficult to absorb nutrients, after damage to the lining of the small intestine.
They vary from person to person, but the most commonly observed symptoms include:
- Chronic diarrhea
- Weight loss
- Bloating, which occurs in almost half of the cases
- Chronic fatigue
- Iron deficiency (sometimes with anemia) due to improper absorption of nutrients
- Recurring abdomen pain
- Low vitamin D levels
- Reduced bone mineral density
- Canker sores (aphthous stomatitis) – benign and non-infectious mouth sores
- Short stature
- High levels of aminotransferase enzymes
Untreated celiac disease can lead to serious complications in the long term, such as:
- Osteoporosis
- Reduced spleen function
- Infertility or Frequent miscarriages
- Neurological disorders
- Ulcers in the intestine
Genetic Component of Celiac Disease - DQ2 and DQ8 gene is responsible
Celiac is basically a disease caused by our genes. So, what is the celiac disease gene, and whether we can get tested for the celiac disease gene?
People with celiac disease gene and their family members are at higher risk. That’s because the antibodies fighting gluten can only be produced by very specific genes.
On chromosome 6, regions called human leukocyte antigen (HLA) complexes carry DQ2 and DQ8 gene, which is found in almost all celiac patients [1]. These DQ2 and DQ8 genes produce the antibodies responsible for fighting gluten.
Although many celiac disease genes are known today, 90 percent of cases involve celiac disease gene DQ2 and almost all remaining ones involve celiac disease gene DQ8. Ironically, even those carrying both celiac disease genes, i.e. DQ2 and DQ8, aren’t guaranteed to have celiac and can be completely healthy, without any symptoms. In fact, only about 3% of people carrying the celiac disease gene will ever develop celiac in their lifetime [10]. We still don’t understand why.
However, this much is understood: people who do not carry the celiac disease gene almost never have celiac disease. Because families share many genes, celiac is more common in families with a gluten allergy history.
While the general population has about a one percent chance of the disease, it is almost twice as common among second-degree relatives (e.g., in cousins) of celiac patients.
Among first-degree relatives (parents, children, siblings), the risk increases to 7.5 percent. The risk is high among siblings of celiac patients, at almost ten percent. The risk for children of positive parents is 7.9 percent but for parents of positive children is only about three percent [11].
Among siblings, an identical twin of a celiac patient is at the highest risk of the disease: studies show 3 out of 4 such cases show celiac in both twins since identical twins share all the celiac disease genes [12]. That is more than any other autoimmune disease, including Type 1 diabetes (36%), Crohn’s disease (33%), and multiple sclerosis (25%).
Diagnosing/ Testing For Celiac Disease for DQ2 and DQ8 Gene Test
Diagnosis of celiac disease or celiac disease testing for DQ2 and DQ8 gene tests can be a long arduous process, requiring multiple tests and careful monitoring of symptoms.
A patient needs to meet four out of five diagnostic criteria [13] listed below:
- Typical symptoms of celiac disease include chronic diarrhea, weight loss, anemia (low oxygen in the blood), and fatigue.
- A positive test for tTG antibodies for celiac; these are the antibodies that attack gluten and cause inflammation in the small intestine.
- Presence of celiac disease gene – either DQ2 or DQ8 genes; these genes code the information that makes the antibodies for celiac disease.
- Damage to the small intestinal wall is checked by performing a biopsy.
- Benefit from a gluten-free diet, which should relieve the symptoms over time.
There is no cure for celiac disease.
However, after the proper test for celiac disease including a celiac disease gene test and confirmation of the disease, it is possible to live a normal life by avoiding gluten.
Many gluten-free options are available due to increased awareness in the past few years.
References
[1] Green, Peter H. R., and Christophe Cellier. “Celiac Disease.” New England Journal of Medicine, vol. 357, no. 17, 2007, pp. 1731–43. Crossref, https://doi.org/10.1056/nejmra071600.
[2] Kumar, Anil. “RxHomeTest – At Home Health Tests | Saliva and Dry Blood Tests.” RxHomeTest, Dec. 2020, rxhometest.com/article/celiac-gluten-intolerance.
[3] Fasano, A. (1996), Where have all the American celiacs gone?. Acta Pædiatrica, 85: 20-24. https://doi.org/10.1111/j.1651-2227.1996.tb14242.x
[4] S D Johnston, R G Watson, S A McMillan, J Sloan, A H Love, Coeliac disease detected by screening is not silent–simply unrecognized., QJM: An International Journal of Medicine, Volume 91, Issue 12, Dec 1998, Pages 853–860, https://doi.org/10.1093/qjmed/91.12.853
[5] Catassi, C., et al. (1996), The coeliac iceberg in Italy. A multicentre antigliadin antibodies screening for coeliac disease in school-age subjects. Acta Pædiatrica, 85: 29-35. https://doi.org/10.1111/j.1651-2227.1996.tb14244.x
[6] Grodzinsky E, Franzen L, Hed J, Ström M. High prevalence of celiac disease in healthy adults revealed by antigliadin antibodies. Annals of Allergy. 1992 Jul;69(1):66-70. PMID: 1626762.
[7] Makishima et. al.” Intestinal Diffuse Large B-Cell Lymphoma Associated with Celiac Disease: A Japanese Case.” International Journal of Hematology, vol 83, 2006.
[8] Catassi, C et al. “Why is coeliac disease endemic in the people of the Sahara?.” Lancet (London, England) vol. 354,9179 (1999): 647-8. doi:10.1016/s0140-6736(99)02609-4
[9] “20 Things You Might Not Know About Celiac Disease.” Celiac Disease Foundation, 15 Jan. 2022, celiac.org/about-the-foundation/featured-news/2016/08/20-things-you-might-not-know-about-celi ac-disease.
[10] Massachusetts General Hospital. “Genetic Testing for Celiac Disease.” Massachusetts General Hospital, www.massgeneral.org/children/celiac-disease/genetic-testing-for-celiac-disease. Accessed 12 Feb. 2022.
[11] Singh, Prashant, et al. “Risk of Celiac Disease in the First- and Second-Degree Relatives of Patients with Celiac Disease: A Systematic Review and Meta-Analysis.” American Journal of Gastroenterology, vol. 110, no. 11, 2015, pp. 1539–48. Crossref, https://doi.org/10.1038/ajg.2015.296.
[12] Polanco, Isabel, et al. “Gluten-Sensitive Enteropathy in Spain: Genetic and Environmental Factors.” The Genetics of Coeliac Disease, 1981, pp. 211–34. Crossref, https://doi.org/10.1007/978-94-011-8114-3_27.
[13] Catassi, Carlo, and Alessio Fasano. “Celiac Disease Diagnosis: Simple Rules Are Better Than Complicated Algorithms.” The American Journal of Medicine, vol. 123, no. 8, 2010, pp. 691–93. Crossref, https://doi.org/10.1016/j.amjmed.2010.02.019
Emily Pond
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