Glycogen Storage Diseases

  • At least 15 types have been identified, all resulting in abnormal glycogen metabolism and the accumulation of glycogen within cells.
  • Periodic acid–Schiff stain identifies glycogen and is useful in identifying these diseases.
  • Very Poor Carbohydrate Metabolism.
  • Types I, II, III, and V are autosomal recessive.
Von Gierke disease (type I) Severe fasting hypoglycemia, ↑↑ Glycogen in liver and kidneys, ↑ blood lactate, ↑ triglycerides, ↑ uric acid (Gout), and hepatomegaly, renomegaly. Liver does not regulate blood glucose. Glucose-6-phosphatase Treatment: frequent oral

glucose/cornstarch; avoidance of fructose and galactose

Impaired gluconeogenesis and glycogenolysis

Pompe disease (type II) Cardiomegaly, hypertrophic cardiomyopathy, hypotonia, exercise intolerance, and systemic findings lead to early death. Lysosomal acid α-1,4-glucosidase with α-1,6-glucosidase activity (acid maltase) PomPe trashes the PumP (1,4) (heart, liver, and muscle)
Cori disease (type III) Milder form of von Gierke (type I) with normal blood lactate levels. Accumulation of limit dextrin–like structures in cytosol. Debranching enzyme (α-1,6-glucosidase) Gluconeogenesis is intact
McArdle disease (type V) ↑ glycogen in muscle, but muscle cannot break it down → painful Muscle cramps, Myoglobinuria (red urine) with strenuous exercise, and arrhythmia from electrolyte abnormalities. Second-wind phenomenon noted during exercise due to ↑ muscular blood flow.

(Myophosphorylase)

Skeletal muscle glycogen phosphorylase

Hallmark is a flat venous lactate curve with normal rise in ammonia levels during exercise

 

Blood glucose levels typically unaffected

McArdle = Muscle

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