Coeliac disease is caused by an immune reaction to gluten, a protein found in wheat, barley, and rye. But eating gluten alone isn’t enough to trigger the disease. It takes a specific genetic setup, an immune system that misidentifies gluten as a threat, and often an environmental push to tip the balance. Roughly 1.4% of the global population tests positive for coeliac antibodies, though only about 0.7% have biopsy-confirmed damage to the small intestine, meaning many cases go undiagnosed.
The Genetic Foundation
Coeliac disease starts with your genes. More than 90% of people with the condition carry a specific immune gene variant called HLA-DQ2, and most of the remainder carry a related variant called HLA-DQ8. These genes code for molecules on the surface of immune cells that present fragments of food proteins to the rest of the immune system. In people with DQ2 or DQ8, these molecules happen to bind gluten fragments especially well, which sets the stage for an overreaction.
Carrying these genes is necessary but far from sufficient. Between 30% and 40% of the general population has DQ2 or DQ8, yet only about 3% of carriers ever develop coeliac disease. That gap tells us genetics loads the gun, but something else pulls the trigger.
Beyond the HLA genes, researchers have identified up to 57 additional genetic variations that contribute to susceptibility. Some of these affect signaling pathways involved in inflammation and immune regulation. Each one adds a small amount of risk on its own, but together they help explain why some DQ2/DQ8 carriers develop the disease while most don’t.
How Gluten Provokes the Immune System
When you eat gluten, your digestive system breaks it into smaller protein fragments called peptides. In most people, these peptides pass through without incident. In someone genetically predisposed to coeliac disease, the process goes wrong at a very specific step.
An enzyme naturally present in the gut lining modifies certain gluten peptides by swapping out one building block for another. This tiny chemical edit introduces a negative electrical charge into the peptide. That charge dramatically increases how tightly the peptide locks into the DQ2 or DQ8 molecule on immune cells. X-ray crystal imaging has confirmed this: the modified gluten peptide fits into the immune molecule’s binding groove like a key into a lock.
Once locked in, the immune cell displays the modified gluten fragment to T cells, a type of white blood cell that coordinates immune attacks. These T cells recognize the gluten fragment as dangerous and launch an inflammatory response. Over time, that inflammation destroys the tiny, finger-like projections (villi) lining the small intestine. Since villi are responsible for absorbing nutrients, their destruction leads to the malabsorption, fatigue, digestive symptoms, and nutritional deficiencies that characterize coeliac disease.
Viral Infections as a Trigger
If genetics and gluten were the whole story, most people with coeliac disease would develop it in early childhood, shortly after their first exposure to wheat. Instead, the disease can appear at any age, suggesting that something disrupts the immune system’s tolerance to gluten at a particular moment. Viral infections are one of the strongest candidates.
Research published in The BMJ tracked children from birth and found that certain gut viruses, particularly enteroviruses, may damage the intestinal lining enough to let gluten peptides slip deeper into the gut wall than they normally would. Once there, the peptides encounter immune cells in an environment primed for a defensive response. The virus essentially provides a “danger signal” that activates immune cells already in the presence of modified gluten fragments. The child may not even show obvious symptoms of the viral infection for this process to begin.
This mechanism helps explain why coeliac disease sometimes appears after a period of illness, stress, or surgery. Anything that temporarily compromises the gut barrier could, in a genetically susceptible person, be the event that breaks tolerance to gluten for good.
The Role of Gut Bacteria
The trillions of bacteria living in your intestines also appear to influence whether coeliac disease develops. A large prospective study published in PNAS followed at-risk children over time and found distinct microbial shifts before the disease appeared. Children who went on to develop coeliac disease had higher levels of bacterial species previously linked to inflammation, and lower levels of species known for anti-inflammatory effects.
Specifically, children who later developed the disease had reduced levels of bacteria that help maintain gut barrier integrity and regulate immune responses. When one key species dropped, it was associated with increased production of a bacterial toxin that impairs immune function. Similar microbial patterns have been observed in children who go on to develop type 1 diabetes, suggesting a shared pathway between autoimmune conditions.
Whether these microbial changes are a cause of coeliac disease or an early consequence of the immune process already underway isn’t fully settled. But the shifts appear before any clinical signs of the disease, which suggests the microbiome plays an active role rather than simply responding to damage already done.
Family Risk and Heredity
Coeliac disease runs strongly in families. Parents, siblings, and children of someone with the condition are at substantially elevated risk. A Mayo Clinic study found that 44% of first-degree relatives who were screened tested positive for coeliac disease. That’s a striking number, and it’s the reason most gastroenterology guidelines recommend screening close family members even if they have no symptoms.
The high family risk reflects both shared HLA genes and shared non-HLA genetic variants. But families also share environments, diets, and early-life exposures, including similar gut microbiomes passed from parent to child during birth and early feeding. Disentangling genetic from environmental contributions in families remains difficult, but the practical takeaway is clear: if one person in a family is diagnosed, others should be tested.
When Gluten Is Introduced in Infancy
For parents of at-risk infants, timing of gluten introduction has been a source of anxiety. A meta-analysis in The Journal of Pediatrics found no evidence that introducing gluten before six months increases risk. However, delaying gluten past six months was associated with a 25% increase in the likelihood of developing coeliac disease compared to introduction between four and six months.
Current guidelines recommend introducing gluten between four and twelve months of age, while avoiding large quantities in the first weeks after introduction. Breastfeeding, once thought to be protective, has not been shown to prevent coeliac disease in randomized trials, though it offers other health benefits. The key message is that neither very early nor very late introduction appears to help, and moderate timing within the recommended window is the best current approach.
Connection to Other Autoimmune Conditions
Coeliac disease rarely exists in isolation. About 21% of people with coeliac disease also have at least one other autoimmune condition. The most common is autoimmune thyroid disease, affecting roughly 41% of those with a coeliac-associated autoimmune condition. Type 1 diabetes is the next most frequent, appearing in about 14% of that group.
This overlap likely stems from shared genetic risk factors. Many of the immune-regulating genes involved in coeliac disease also play roles in other autoimmune conditions. Having coeliac disease doesn’t cause thyroid disease or diabetes directly, but the same underlying immune wiring that makes someone susceptible to one often makes them vulnerable to others. This is why people diagnosed with coeliac disease are often monitored for thyroid function and blood sugar over time.
Putting It Together
Coeliac disease isn’t caused by a single factor. It requires a genetic predisposition (HLA-DQ2 or DQ8), exposure to gluten, and typically one or more additional triggers: a viral infection that breaches the gut barrier, shifts in gut bacteria that tilt the immune environment toward inflammation, or other stressors that disrupt oral tolerance. The enzyme that modifies gluten peptides in the gut wall is the molecular bridge that connects the genetic susceptibility to the immune attack. Without that modification step, the immune system’s DQ2 and DQ8 molecules wouldn’t grip gluten tightly enough to start the cascade.
This layered causation explains why the disease is so variable in its timing and presentation. Two siblings can carry the same genes, eat the same diet, and yet one develops coeliac disease at age three while the other is diagnosed at forty, or never at all. The combination of triggers matters, and we’re still learning which combinations are most dangerous and how they interact.