Overview of inherited disorders of glucose and glycogen metabolism
- William J Craigen, MD, PhD
William J Craigen, MD, PhD
- Professor of Molecular and Human Genetics
- Baylor College of Medicine
- Basil T Darras, MD
Basil T Darras, MD
- Professor of Neurology
- Harvard Medical School
There are a number of inborn errors of glucose and glycogen metabolism that result from mutations in genes for virtually all of the proteins involved in glycogen synthesis, degradation (glycogenosis), or regulation. Those disorders that result in abnormal storage of glycogen are known as glycogen storage diseases (GSDs). They are largely categorized by number according to the chronology of recognition of the responsible enzyme defect (table 1). The age of onset varies from in utero to adulthood.
This topic review provides a brief overview of the inherited disorders of glucose and glycogen metabolism (glycogenoses). The individual disorders are discussed separately in the appropriate topic reviews.
Glycogen is the stored form of glucose and serves as a buffer for glucose needs. It is composed of long polymers of a 1-4 linked glucose, interrupted by a 1-6 linked branch point every 4 to 10 residues. Glycogen is formed during 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 the liver and muscle and plays the following roles:
●The main role of glycogen in the liver is to maintain glucose homeostasis. The liver stores glucose for release to tissues that are unable to synthesize significant amounts during fasting.
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- Tegtmeyer LC, Rust S, van Scherpenzeel M, et al. Multiple phenotypes in phosphoglucomutase 1 deficiency. N Engl J Med 2014; 370:533.