Coeliac disease: could gluten be the problem? Symptoms, genes and testing

The genetic foundation: HLA-DQ2 and HLA-DQ8

Coeliac disease does not develop without a specific genetic context. Almost all confirmed coeliac disease patients carry variants of the HLA-DQ2 or HLA-DQ8 genes. These genes are found in roughly 30% of the general UK population, yet only around 1% develop coeliac disease, which means the genes are necessary but not sufficient. A negative result for both HLA-DQ2 and HLA-DQ8 essentially rules out coeliac disease with a very high degree of certainty. A positive result indicates genetic susceptibility and warrants further investigation through antibody blood testing, particularly if symptoms are present. The HLA-DQ2.5 variant carries the highest risk, present in approximately 90% of coeliac disease patients, while HLA-DQ8 accounts for most of the remaining cases.

The gluten intolerance immune mechanism

When someone with the coeliac genetic profile is exposed to gluten, a protein found in wheat, barley, and rye, their immune system produces antibodies against tissue transglutaminase (tTG), an enzyme in the gut lining. Over time, this immune response causes villous atrophy, the flattening of the tiny finger-like projections lining the small intestine that are responsible for nutrient absorption. The result is impaired absorption of iron, B12, folate, vitamin D, calcium, and zinc. The gluten intolerance test UK most commonly used in primary care measures tTG-IgA antibody levels as the first screening step.

Non-coeliac gluten sensitivity

Not everyone who experiences symptoms after eating gluten has coeliac disease. Non-coeliac gluten sensitivity produces similar bloating, brain fog, fatigue, and digestive discomfort without the autoimmune antibody response or intestinal damage. It cannot be diagnosed through blood testing but is typically identified by symptom improvement on a gluten-free diet after coeliac disease and wheat allergy have been excluded. The distinction matters for management: coeliac disease requires a strict lifelong gluten-free diet and monitoring for complications, while non-coeliac sensitivity requires dietary management but carries different long-term risks.

Nutrient deficiencies as a consequence of undiagnosed coeliac disease

Because coeliac disease damages the small intestine before diagnosis, many people present with nutrient deficiencies rather than classic digestive symptoms. Iron deficiency anaemia that fails to respond to supplementation is one of the most common presentations. Low ferritin, low B12, low folate, and low vitamin D are all frequently found in newly diagnosed coeliac patients. In some cases, these nutrient consequences are the only visible signal for years. A coeliac blood test at home UK is particularly relevant for people with unexplained iron deficiency anaemia or persistent fatigue when other causes have not been found.

Associated conditions and higher-risk groups

Coeliac disease is more common in people with a first-degree relative who has been diagnosed, with risk approximately 10% in that group. It is also more prevalent in people with type 1 diabetes, Down syndrome, autoimmune thyroid disease, and other autoimmune conditions. Having one autoimmune condition increases the likelihood of others because the underlying immune dysregulation often affects multiple systems. Hashimoto's thyroiditis and coeliac disease, in particular, are found together more frequently than chance would predict. If you have one autoimmune diagnosis and unexplained gut symptoms, coeliac screening is a logical next step.

Dermatitis herpetiformis and extra-intestinal presentations

Coeliac disease does not always present with digestive symptoms. Dermatitis herpetiformis is a blistering itchy skin rash caused by the same immune mechanism as intestinal coeliac disease and responds to a gluten-free diet. Neurological symptoms including peripheral neuropathy and ataxia, as well as mouth ulcers, joint pain, and reproductive health issues, are all recognised extra-intestinal manifestations. These presentations make coeliac disease particularly easy to miss when clinicians focus only on gastrointestinal symptoms.

The current UK pathway for coeliac investigation involves antibody blood testing followed by intestinal biopsy in most adults to confirm the diagnosis. Genetic testing plays an important complementary role in specific situations.

tTG-IgA antibody testing is the primary blood screening test. Elevated tTG-IgA in someone eating a gluten-containing diet is highly specific to coeliac disease. It will not be elevated if you have already started a gluten-free diet, which means it is important to continue eating gluten before testing.

Total IgA is measured alongside tTG-IgA because approximately 2-3% of the population have IgA deficiency. In these individuals, tTG-IgA will appear normal even if coeliac disease is present, and an alternative antibody test is required.

Iron, Ferritin, Vitamin D, Vitamin B12, and Folate testing identifies the nutrient deficiencies that accompany undiagnosed coeliac disease and reveals how much damage has already occurred to absorptive capacity.

If a coeliac screen through blood testing is positive, the standard NHS pathway leads to referral for a gastroscopy and intestinal biopsy to confirm the diagnosis before a formal gluten-free diet is recommended. DNA genetic testing can guide this process by confirming whether the genetic predisposition is present, particularly if antibody results are borderline or testing is being done after dietary gluten has already been removed.

The gluten-free diet and what strict adherence means in practice

The only established treatment for coeliac disease is a lifelong gluten-free diet that excludes all wheat, barley, and rye. Even small amounts of gluten, below the threshold of noticeable symptoms, can trigger ongoing intestinal damage and perpetuate nutrient malabsorption. Cross-contamination in food preparation is a significant source of inadvertent gluten exposure. Strict adherence typically allows the intestinal lining to heal over 12 to 24 months, with nutrient levels normalising as absorption recovers. Tracking ferritin, B12, vitamin D, and folate through regular retesting is the most objective way to confirm that the gut is healing and absorption is improving.

Correcting nutrient deficiencies that accumulated before diagnosis

People newly diagnosed with coeliac disease often begin with significant deficits in iron, B12, folate, and vitamin D built up over years of impaired absorption. Dietary correction alone may be insufficient in the short term, and supplementation guided by blood test results is frequently required. B12 status is particularly important because deficiency can cause neurological symptoms that are reversible if addressed early but become harder to resolve the longer they persist. Tracking biomarker shifts over the first year of a gluten-free diet provides reassurance that absorption is recovering as it should.

Gut microbiome support during and after treatment

The intestinal damage caused by coeliac disease alters the composition of the gut microbiome, and some of this dysbiosis persists even after the gluten-free diet is established. Research suggests that the microbiome of people with coeliac disease differs from healthy controls even when the intestinal mucosa has healed. A varied, fibre-rich gluten-free diet that includes naturally gluten-free whole grains such as oats (for those who tolerate them), quinoa, and brown rice supports microbiome recovery. Fermented foods that introduce live cultures, where tolerated, contribute to bacterial diversity during the gut healing process.

Monitoring for associated conditions over time

Coeliac disease increases the long-term risk of osteoporosis because of calcium and vitamin D malabsorption, particularly when diagnosis is delayed. Bone density assessment, vitamin D tracking, and adequate dietary calcium are all relevant long-term management considerations. Fertility is also affected by undiagnosed coeliac disease, with improvement typically seen after diagnosis and dietary adherence. Annual blood testing that includes bone markers, nutrient status, and inflammatory markers gives the clearest picture of how the body is responding to treatment over time.