Liver phosphorylase deficiency (glycogen storage disease VI, Hers disease)
- William J Craigen, MD, PhD
William J Craigen, MD, PhD
- Professor of Molecular and Human Genetics
- Baylor College of Medicine
There are a number of inborn errors of glycogen metabolism that result from mutations in genes for virtually all of the proteins involved in glycogen synthesis, degradation, or regulation. Those disorders that result in abnormal storage of glycogen are known as glycogen storage diseases (GSDs). They have largely been categorized by number according to the chronology of recognition of the responsible enzyme defect (table 1). Liver phosphorylase deficiency (GSD VI, MIM #232700), also known as Hers disease, is usually a mild form of glycogenosis; however, severe hepatomegaly and recurrent severe hypoglycemia have been described . It is due to deficiency of the liver isoform of phosphorylase.
Liver phosphorylase deficiency is reviewed here. Other GSDs are reviewed separately.
Glycogen is the stored form of glucose and serves as a buffer for glucose needs. Glycogen is formed in periods of dietary carbohydrate loading and broken down when glucose demand is high or dietary availability is low (figure 1).
Glycogen is most abundant in liver and muscle, which are most affected by disorders of glycogen metabolism. The physiologic importance of a given enzyme in liver and muscle determines the clinical manifestations of the disease. The main role of glycogen in the liver is to store glucose for release to tissues that are unable to synthesize significant amounts during fasting. The major manifestations of disorders of glycogen metabolism affecting the liver are hypoglycemia and hepatomegaly. (See "Physiologic response to hypoglycemia in normal subjects and patients with diabetes mellitus".)
A more extensive overview of GSD is presented separately. (See "Overview of inherited disorders of glucose and glycogen metabolism".)
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