It is important for the cells to be able to break down carbohydrates, because this provides the energy the cells need for most of their reactions. Thus, the breakdown of glucose and glycogen, the storage form of glucose, is vital. There are several glycogen metabolism disorders; however, that involve problems with the breakdown of glycogen. Four of these disorders result in hypoglycemia.
Type I Glycogen Storage Disease
Type I glycogen storage disease is caused by someone not having enough of an enzyme called glucose-6-phosphatase in the lining of the intestines, kidneys and liver, as explained in "Harrison's Principles of Internal Medicine" by Dr. Yuan-Tsong Chen, director of the Institute of Biomedical Sciences. Enzymes are merely proteins that the cells use to speed up the time of a reaction and, without the glucose-6-phosphatase enzyme, people with this disorder cannot break down a substance called glucose-6-phosphate to form glucose. As a result, infants have hypoglycemia, or a low amount of glucose in the bloodstream.
Type III Glycogen Storage Disease
A deficiency of an enzyme called amyloglucosidase and/or oligoglucanotransferase results in Type III glycogen storage disease. Chen explains in "Harrison's Principles of Internal Medicine" that these enzymes are needed to completely break down glycogen, the stored form of glucose. Not having enough of either one or both of these enzymes leads to abnormal glycogen. Similar to Type I, children may have a large liver, a high amount of lipids in the bloodstream and a low amount of blood glucose. The treatment of types I and III involves keeping a normal level of glucose in the bloodstream.
Type VI Glycogen Storage Disease
Dr. Aditi Dagli of the Glycogen Storage Disease Program writes in the April 23, 2009, issue of "Gene Reviews" that this glycogen metabolism disorder is due to a deficiency of an enzyme that is normally found in the liver, called glycogen phosphorylase. This type of glycogen storage disease is fairly mild, but people with this disorder do have a large liver and a low amount of blood glucose because without this enzyme, glycogen accumulates in the liver. Because this type is so mild, most adults do not have any symptoms at all, but pregnant women can become hypoglycemic.
Type IX Glycogen Storage Disease
A deficiency in one part of the structure of the phosphorylase kinase enzyme located in the muscle and liver leads to Type IX. While Type VI is a rare disorder, type IX is common, Chen says in "Harrison's Principles of Internal Medicine." The cells in the muscles and liver use the phosphorylase kinase enzyme to activate the glycogen phosphorylase enzyme. Thus, having a problem within the structure of phosphorylase kinase means glycogen is not broken down and the liver cannot release glucose into the bloodstream. As a result, people have a large liver and a low blood glucose level.
References
- Gene Reviews: Glycogen Storage Disease Type VI
- "Harrison's Principles of Internal Medicine"; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
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