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With Type III Glycogen Storage Disease, the debrancher enzyme deficiency causes the body to form glycogen molecules that have an abnormal structure. This abnormal structure also prevents the glycogen from being broken down into free glucose.
There have been observed a variety of subtypes of this disorder, and there appears to be considerable variation in the tissues affected by the defect (such as white blood cells, muscle, liver, and so forth). In GSD Type IIIa, the disease involves both liver and muscle tissues. The less commonly seen Type IIIb appears to involve only the liver.
Children with Type III Glycogen Storage Disease are often first diagnosed because they have been noticed to have a swollen abdomen due to a very large liver. Some children have problems with low blood sugars on fasting but this is not as common as in Type I GSD. Growth may be delayed during childhood but most reach a normal adult height. Muscle weakness is commonly present in childhood and can, at times, be severe. Often the liver returns to a normal size at puberty, although the enzyme defect persists.
Chemical analysis of the blood usually shows low blood sugar, elevated glycogen content in red blood cells, and elevated levels of fat. Uric acid and lactic acid levels are usually normal. Biopsy of the liver shows inflammatory changes, with great elevations of abnormal-structured glycogen content, and a deficiency of the debrancher enzyme. Biopsy of muscle shows an accumulation of abnormal-structured glycogen in GSD Type IIIa.
Treatment for Type III Glycogen Storage Disease consists of frequent feedings and a high protein diet. Continuous nasogastric feedings and the starch regimes similar to those used for Type I GSD are useful.
Persons with debrancher deficiency have lived well into late adulthood. Muscle disorders seem to be an increasing problem with age in those persons with GSD Type IIIa. The heart can be mildly enlarged, but the function is usually normal.
Links:
Forbes Disease from National Organization for Rare Disorders
OMIM GSD Type III info from Online Mendelian Inheritance in Man searchable database
Type III GSD info from e-medicine
Muscular Dystrophy Association [MDA] info on Type III GSD
Metabolic Diseases of Muscle from the Muscular Dystrophy Association [MDA]
“Keeping up with Metabolic Myopathies” from the MDA’s Quest Magazine
Glycogenosis Type III from NeuroHelp [The University of Oklahoma, College of Medicine]
GSD Type III from Madisons Foundation
This page was created in June 2001.
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