Celiac Disease (cont.)
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
inherited. Thus, approximately 10% of 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 among individuals with
celiac disease than among individuals 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 gliaden becomes toxic (damaging) is not clear; however, much scientific study is being done, and we are beginning to understand the mechanism.
Proteins, including gliaden, are long chains of amino acids-up to several hundred--attached to each other. Normally during digestion, 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 only can 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 gliaden 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 within the cells, tissue transglutaminase. In individuals with celiac disease, the complex of the longer chain of amino acids and tissue tranglutaminase 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 inflammation weakly and 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.
Next: What does celiac disease do to the small intestine? »
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