What is celiac disease?
Celiac disease is a disease of the small intestine. The small intestine is a 22 foot long tube that begins at the stomach and ends at the large intestine (colon). The first 10 inches (25cm) of the small intestine (the part that is attached to the stomach) is called the duodenum, the middle part is called the jejunum, and the last part (the part that is attached to the colon) is called the ileum. Food empties from the stomach into the small intestine where it is digested and absorbed into the body. While food is being digested and absorbed, it is transported by the small intestine to the colon. What enters the colon is primarily undigested food. In celiac disease, there is an immunological (allergic) reaction within the inner lining of the small intestine to proteins (gluten) that are present in wheat, rye, barley and, to a lesser extent, in oats. The immunological reaction causes inflammation that destroys the lining of the small intestine. This reduces the absorption of the dietary nutrients and can lead to symptoms and signs of nutritional, vitamin, and mineral deficiencies.
The other terms used forceliac disease include sprue, nontropical sprue, gluten enteropathy, and adult celiac disease. (Tropical sprue is another disease of the small intestine that occurs in tropical climates. Although tropical sprue may cause symptoms that are similar to celiac disease, the two diseases are not related.)
Celiac disease is common in European countries, particularly in Ireland, Italy, Sweden, and Austria. In Northern Ireland, for example, one in every 300 people has celiac disease. In Finland, the prevalence may be as high as one in every 100 persons. Celiac disease also occurs in North America where the prevalence has been estimated to be one in every 3000 people. Unfortunately, most population studies underestimate the prevalence of celiac disease because many individuals who develop celiac disease have few or no symptoms until later in life. Moreover, a study suggests that the prevalence of celiac disease in the United States is similar to that in Europe.
What causes celiac disease?
The destruction of the inner lining of the small intestine in celiac disease is caused by an immunological (allergic) reaction to gluten in the diet that inflames and destroys the inner lining of the small intestine. There is evidence that this reaction is partially genetic and partially inherited. Thus, approximately 10% of the first-degree relatives (parents, siblings or children) of individuals with celiac disease also will have celiac disease. In addition, in approximately 30% of fraternal twins and 70% of identical twins, both twins will have celiac disease. Finally, certain genes have been found to be more common in individuals with celiac disease than in those without celiac disease.
Gluten is a family of proteins present in wheat. Some of the proteins that make up gluten (the ones that are dissolved by alcohol) are called gliadin. It is the gliadin in gluten that causes the immunological reaction in celiac disease. The mechanism whereby gliadin becomes toxic (damaging) is not clear; however, much scientific study is being done, and we are beginning to understand the mechanism.
Proteins, including gliadin, are long chains of amino acids--up to several hundred--attached to each other. Normally during digestion, the digestive enzymes within the small intestine break-up proteins into single amino acids and smaller chains of amino acids. This is necessary because the intestine can only absorb single amino acids or, at most, chains of 3-4 amino acids. Single amino acids and chains of several amino acids do not cause problems for the intestine. It appears, however, that gliadin is not completely broken-up by intestinal enzymes. Several longer chains of amino acids remain intact. Somehow these larger chains enter the cells lining the intestine, perhaps because the cells are abnormally permeable (leaky) to longer chains of amino acids. Some of these longer chains are toxic (damaging) to the intestinal cells. One of the longer chains attaches to an enzyme (tissue transglutaminase) inside the cells. In individuals with celiac disease, the complex of the longer chain of amino acids and tissue transglutaminase sets off an immune reaction that attacks the complex and at the same time damages the intestinal cells.
Barley and rye contain gliadin-like proteins and can cause celiac disease in genetically-predisposed individuals. Oats also contain gliadin-like proteins, but unlike barley and rye, the gliadin-like proteins in oats cause only a mild inflammation and that too in only a few individuals who are predisposed to develop celiac disease. Rice and corn do not cause celiac disease because they do not contain gliadin-like proteins.
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Diagnosis of Celiac Disease