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Synonyms:
Liver Phosphorylase Deficiency, Hers Disease
In Type VI Glycogen Storage Disease (GSD VI), the most frequent first symptoms include an enlarged liver and low blood sugar (hypoglycemia). After we eat, excess glucose is stored as glycogen mostly in the liver to be used later when we are fasting (not eating for 3-4 hours) to maintain normal glucose levels in our body. The phosphorylase enzyme plays a vital role in the breakdown of glycogen into glucose. With a deficiency of the liver phosphorylase enzyme, glycogen cannot be broken down to glucose (sugar), and the accumulating glycogen results in an enlarged liver.) Patients with Type VI GSD actually have only partial deficiency of the enzyme and milder forms of glycogen storage disease.
Clinically, this form of glycogen storage disease appears to be similar to, but is usually considerably milder than glucose-6-phosphatase deficiency GSD (type I GSD). These patients present with hepatomegaly and growth retardation early in childhood. Since people with Type VI GSD are able to store glucose as glycogen but not able to release it normally, with time the stores of glycogen build up in the liver causing the liver to swell (hepatomegaly). This is much like being able to place groceries from the store into your kitchen cabinets, but not being able to get the food out of the cabinets when needed. Hypoglycemia (low blood sugars), hyperlipidemia (elevated cholesterol and fats in the blood), and hyperketosis (increased ketones in the urine and blood) are usually mild if present. Lactic acid and uric acid are normal. The heart and skeletal muscles are not involved. The hepatomegaly improves with age and usually disappears around puberty.
The diagnosis of this disease is based on liver biopsy material; assays must be done for glycogen content (which is increased) as well as for phosphorylase activity. Phosphorylase activity in the liver tissue is present but reduced. The liver does its many other functions normally, and there is not usually any evidence of liver failure.
Due to the mildness of the clinical findings, treatment is usually not required. The continued presence of low blood sugar can eventually leads to delayed growth. Should hypoglycemia and growth failure be a major problem, these patients should receive the same nutritional management that has been effective in Type I GSD and Type III GSD.
Links:
Hers Disease from National Organization for Rare Disorders [NORD]
OMIM GSD Type VI info on Online Mendelian Inheritance in Man searchable database
Type VI GSD info from eMedicine
Hers Disease from Madisons Foundation
This page was created in September 2008.
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