Immunoblot analyses of glycogen debranching enzyme in different subtypes of glycogen storage disease type III

Glycogen storage disease type III is the failure to metabolize the sugar glycogen adequately as a result of a debranching enzyme deficiency. The disease is marked by abnormal deposits of glycogen in the liver, heart and muscles. Neural involvement, disorders of the spleen and cardiac enlargement often occur with glycogen storage disease. Among the categories of the disease are: type IIIA in which the enzyme deficiency is in both the liver and muscle; type IIIB in which the deficiency is in the liver only; and type IIID in which there is a transferase deficiency, or deficiency of an enzyme that serves as a catalyst in glycogen processing. A study was conducted to determine the presence of the debranching enzyme in several types of tissues from 41 patients with glycogen storage disease type III. An immunoblot analysis of the tissue was conducted. Three patients with type IIID disease were found to have normal amounts of the debranching enzyme in the tissues studied. In tissues from the remaining patients with types IIIA, B, and D glycogen storage disease, the debranching enzyme was either absent or greatly reduced. The immunoblot test was found to have value as a predictor of whether a fetus will be born with the disease. It is believed that the type III disease has a genetic origin. Parents of two patients with type IIIA disease had intermediate levels of the debranching enzyme. Immunoblot tests performed on amniotic fluid cells, from one type III patient who was pregnant, indicated that the fetus would not be affected. The prediction was confirmed after the birth of the child. The immunoblot analysis may be a reliable method for prenatal diagnosis of some forms of glycogen storage disease. (Consumer Summary produced by Reliance Medical Information, Inc.)