Coeliac disease (), also spelled celiac disease, is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy. Symptoms include chronic diarrhoea, failure to thrive (in children), and fatigue, but these may be absent and symptoms in all other organ systems have been described. It is estimated to affect about 1% of all Indo-European populations, but is thought to be significantly underdiagnosed. A growing portion of diagnoses are being made in asymptomatic persons as a result of increased screening.

Coeliac disease is caused by a reaction to gliadin, a gluten protein found in wheat (and similar proteins of the tribe Triticeae which includes other cultivars such as barley and rye). Upon exposure to gliadin, the enzyme tissue transglutaminase modifies the protein, and the immune system cross-reacts with the bowel tissue, causing an inflammatory reaction. That leads to flattening of the lining of the small intestine (called villous atrophy). This interferes with the absorption of nutrients because the intestinal villi are responsible for absorption. The only effective treatment is a lifelong gluten-free diet. While the disease is caused by a reaction to wheat proteins, it is not the same as wheat allergy.

This condition has several other names, including: cœliac disease (with "œ" ligature), c(o)eliac sprue, non-tropical sprue, endemic sprue, gluten enteropathy or gluten-sensitive enteropathy, and gluten intolerance. The term coeliac derives from the Greek κοιλιακός (koiliakόs, abdominal), and was introduced in the 19th century in a translation of what is generally regarded as an ancient Greek description of the disease by Aretaeus of Cappadocia.

Signs and symptoms

Classic symptoms of coeliac disease include diarrhea, weight loss (or stunted growth in children), and fatigue, but while coeliac disease is primarily a bowel disease, bowel symptoms may also be limited or even absent. Some patients are diagnosed with symptoms related to the decreased absorption of nutrients or with various symptoms which, although statistically linked, have no clear relationship with the malfunctioning bowel. Given this wide range of possible symptoms, the classic triad is no longer a requirement for diagnosis.

Children between 9 and 24 months tend to present with bowel symptoms and growth problems shortly after first exposure to gluten-containing products. Older children may have more malabsorption-related problems and psychosocial problems, while adults generally have malabsorptive problems. Many adults with subtle disease only have fatigue or anaemia. may be present. As the bowel becomes more damaged, a degree of lactose intolerance may develop. However, the variety of gastrointestinal symptoms that may be present in patients with coeliac disease is great, and some may have a normal bowel habit or even tend towards constipation. Frequently the symptoms are ascribed to irritable bowel syndrome (IBS), only later to be recognised as coeliac disease; a small proportion of patients with symptoms of IBS have underlying coeliac disease, and screening may be justified.

Coeliac disease leads to an increased risk of both adenocarcinoma and lymphoma of the small bowel, which returns to baseline with diet. Longstanding disease may lead to other complications, such as ulcerative jejunitis (ulcer formation of the small bowel) and stricturing (narrowing as a result of scarring).

Malabsorption-related

The changes in the bowel make it less able to absorb nutrients, minerals and the fat-soluble vitamins A, D, E, and K.

Miscellaneous

Coeliac disease has been linked with a number of conditions. In many cases it is unclear whether the gluten-induced bowel disease is a causative factor or whether these conditions share a common predisposition.

IgA deficiency is present in 2% of patients with coeliac disease, and in turn this condition features a tenfold increased risk of coeliac disease. Other features of this condition are an increased risk of infections and autoimmune disease.
Dermatitis herpetiformis; this itchy cutaneous condition has been linked to a transglutaminase enzyme in the skin, features small bowel changes identical to those in coeliac disease and occurs more often (in 2%) in patients with coeliac disease. have all been linked with coeliac disease, but the strength of these associations and the causality are still subject to debate.
Growth failure and/or pubertal delay in later childhood can occur even without obvious bowel symptoms or severe malnutrition. Evaluation of growth failure often includes coeliac screening.
Miscarriage and infertility.
Hyposplenism (a small and underactive spleen) - it is unclear whether this actually increases infection risk in the same way as in other people without a functioning spleen.
Other auto-immune disorders: diabetes mellitus type 1, autoimmune thyroiditis, primary biliary cirrhosis, and microscopic colitis.

Role of other grains

Wheat varieties or subspecies containing gluten such as spelt and Kamut, and the rye/wheat hybrid triticale, also trigger symptoms.

Barley and rye also induce symptoms of coeliac disease. It is most probable that oats produce symptoms due to cross contamination with other grains in the fields or in the distribution channels.. Another vendor (McCann's), while not claiming to produce a gluten-free product, points out that the risk of contamination from their oats product is low due to the processes they use. Other cereals, such as maize (corn), quinoa, millet, sorghum, and rice are safe for patients to consume. Non-cereal carbohydrate-rich foods such as potatoes and bananas do not contain gluten and do not trigger symptoms.

Diagnosis

There are several tests that can be used to assist in diagnosis. The level of symptoms may determine the order of the tests, but all tests lose their usefulness if the patient is already taking a gluten-free diet. Intestinal damage begins to heal within weeks of gluten being removed from the diet, and antibody levels decline over months. For those who have already started on a gluten-free diet, it may be necessary to perform a re-challenge with 10 g of gluten (four slices of bread) per day over 2–6 weeks before repeating the investigations. Those who experience severe symptoms (e.g. diarrhoea) earlier can be regarded as sufficiently challenged and can be tested earlier.

Blood tests

Antibody testing

Serology by blood test is useful both in diagnosing coeliac disease (high sensitivity of about 98%, i.e. it misses 2 in 100 cases) and in excluding it (high specificity of over 95%, i.e. a positive test is most likely confirmative of coeliac disease rather than another condition). Because of the major implications of a diagnosis of coeliac disease, professional guidelines recommend that a positive blood test is still followed by an endoscopy. A negative test may still prompt a biopsy if the suspicion remains very high; this would pick up the remaining 2% undiagnosed cases, as well as offering alternative explanations for the symptoms. As such, endoscopy with biopsy is still considered the gold standard in the diagnosis of coeliac disease. Serology tests are based on indirect immunofluorescence (reticulin, gliadin and endomysium) or ELISA (gliadin or tissue transglutaminase).

Guidelines recommend that a total serum IgA level is checked in parallel, as coeliac patients with IgA deficiency may be unable to produce the antibodies on which these tests depend ("false negative"). In those patients, IgG antibodies against transglutaminase (IgG-TTG) may be diagnostic.

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