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HomePediatrics: Genetics and Metabolic DiseaseGlycogen-Storage Disease Type 0 (GSD-0) (Glycogen Synthetase Deficiency)

Glycogen-Storage Disease Type 0 (GSD-0) (Glycogen Synthetase Deficiency)

Background

Glycogen-storage disease type 0 (GSD-0), or glycogen synthetase deficiency, commonly appears in infancy and early childhood with fasting hypoglycemia accompanied by ketosis and low normal reference range blood levels of lactate and alanine. Although feeding relieves symptoms, it results in postprandial hyperglycemia and hyperlacticacidemia. Unlike other forms of glycogen-storage disease, glycogen-storage disease type 0 does not involve the storage of excessive or abnormal glycogen and is characterized by moderately decreased glycogen stores in the liver. Recent reports suggest that patients with glycogen-storage disease type 0 present with symptoms that range from asymptomatic hyperglycemia to recurrent hypoglycemic seizures.

Glycogen is most abundant in the liver and muscle. In the liver, glycogen is a storage form of glucose. During periods of fasting, when little to no glucose is taken in enterally, glycogen releases glucose to be used by tissues that need them to function. In the muscle, glycogen is the source of energy for muscle activity. Thus, glycogen storage disorders can manifest as hypoglycemia, ketosis, lethargy, fatigue, weakness, muscle cramping, and exercise intolerance.

There are two isoforms of the glycogen synthase enzyme. GYS1 is expressed in the skeletal and cardiac muscle. GYS2 is expressed in the liver. GSD-0 is caused by a defect in the gene that encodes for the liver GYS2. It is an autosomal-recessive condition.

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