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Glycogen Storage Diseases

By

Matt Demczko

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
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Glycogen storage diseases are carbohydrate metabolism disorders Overview of Carbohydrate Metabolism Disorders Carbohydrate metabolism disorders are errors of metabolism that affect the catabolism and anabolism of carbohydrates. The inability to effectively use metabolites of carbohydrates accounts for... read more . There are many numbered and named types, all of which are caused by deficiencies of enzymes involved in glycogen synthesis or breakdown; the deficiencies may occur in the liver or muscles and cause hypoglycemia or deposition of abnormal amounts or types of glycogen (or its intermediate metabolites) in tissues.

Age of onset, clinical manifestations, and severity vary by type, but symptoms and signs are most commonly those of hypoglycemia and myopathy.

Diagnosis of glycogen storage diseases is suspected by history, examination, and detection of glycogen and intermediate metabolites in tissues by MRI or biopsy. Diagnosis is confirmed by DNA analysis or less commonly by detecting a significant decrease of enzyme activity in liver (types I, III, VI, and VIII/IX), muscle (types IIb, III, VII, and VIII/IX), skin fibroblasts (types IIa and IV), or red blood cells (type VII) or by lack of an increase in venous lactate with forearm activity/ischemia (types V and VII). (See also testing for suspected inherited disorders of metabolism Initial testing Most inherited disorders of metabolism (inborn errors of metabolism) are rare, and therefore their diagnosis requires a high index of suspicion. Timely diagnosis leads to early treatment and... read more .)

Prognosis and treatment of glycogen storage diseases vary by type, but treatment typically includes dietary supplementation with cornstarch to provide a sustained source of glucose for the hepatic forms of GSD and exercise avoidance for the muscle forms.

Defects in glycolysis (rare) may cause syndromes similar to GSDs. Deficiencies of phosphoglycerate kinase, phosphoglycerate mutase, and lactate dehydrogenase mimic the myopathies of GSD types V and VII; deficiencies of glucose transport protein 2 (Fanconi-Bickel syndrome) mimic the hepatopathy of other GSD types (eg, I, III, IV, VI).

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