Coeliac disease or celiac disease is a long-term autoimmune disorder that primarily affects the small intestine. Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite and among children failure to grow normally. This often begins between six months and two years of age. Non-classic symptoms are more common, especially in people older than two years. There may be mild or absent gastrointestinal symptoms, a wide number of symptoms involving any part of the body or no obvious symptoms. Coeliac disease was first described in childhood; however, it may develop at any age. It is associated with other autoimmune diseases, such as diabetes mellitus type 1 and thyroiditis, among others.
Coeliac disease is caused by a reaction to gluten, a group of various proteins found in wheat and in other grains such as barley and rye. Moderate quantities of oats, free of contamination with other gluten-containing grains, are usually tolerated. The occurrence of problems may depend on the variety of oat. It occurs in people who are genetically predisposed. Upon exposure to gluten, an abnormal immune response may lead to the production of several different autoantibodies that can affect a number of different organs. In the small bowel, this causes an inflammatory reaction and may produce shortening of the villi lining the small intestine (villous atrophy). This affects the absorption of nutrients, frequently leading to anaemia.
Diagnosis is typically made by a combination of blood antibody tests and intestinal biopsies, helped by specific genetic testing. Making the diagnosis is not always straightforward. Frequently, the autoantibodies in the blood are negative, and many people have only minor intestinal changes with normal villi. People may have severe symptoms and be investigated for years before a diagnosis is achieved. Increasingly, the diagnosis is being made in people without symptoms, as a result of screening. Evidence regarding the effects of screening, however, is not sufficient to determine its usefulness. While the disease is caused by a permanent intolerance to gluten proteins, it is distinct from wheat allergy, which is much rarer.
The only known effective treatment is a strict lifelong gluten-free diet, which leads to recovery of the intestinal mucosa, improves symptoms and reduces risk of developing complications in most people. If untreated, it may result in cancers such as intestinal lymphoma and a slightly increased risk of early death. Rates vary between different regions of the world, from as few as 1 in 300 to as many as 1 in 40, with an average of between 1 in 100 and 1 in 170 people. It is estimated that 80% of cases remain undiagnosed, usually because of minimal or absent gastrointestinal complaints and lack of knowledge of symptoms and diagnostic criteria. Coeliac disease is slightly more common in women than in men. The term "coeliac" is from the Greek κοιλιακός (koiliakós, "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.