Glycogen Storage Disorders - Pediatrics

Snapshot
- A 16-year-old boy presents to his primary care physician with a complaint of fatigue and muscle cramps. He recently tried out for his high school basketball team and found himself exhausted and unable to run after performing a set of high intensity sprints. He notes that after resting briefly, he is able to get a “second wind.” After practice, he noticed that his urine was a brown color. Laboratory results are significant for an elevated creatine kinase level of 1,423 U/L (normal < 200 U/L). There was no elevation of lactate levels on forearm nonischemic testing. (McArdle disease)

Introduction

Glycogen Storage Diseases
GSD	Defective Enzyme	Characteristics
Von Gierke disease (type 1)	Hepatic glucose-6-phosphatase	Autosomal recessive Usually presenting at 3-6 months of age Hepatomegaly Signs of hypoglycemia seizure "Doll-like" face Poor growth ↑ uric acid due to impaired renal clearance and increased production gout ↑ lactic acid ↑ triglycerides xanthomas pancreatitis
Pompe disease (type 2)	Lysosomal α(1,4)-glucosidase	Autosomal recessive Infantile form cardiomegaly generalized muscle hypotonia respiratory distress Juvenile and adult form skeletal myopathy delayed-gross motor development limb-girdle weakness respiratory issues
Cori disease (type 3)	Glycogen debranching enzyme	Autosomal recessive Most cases involve the muscle and liver Hepatomegaly Mild hypoglycemia intact gluconeogenesis
McArdle disease (type 5)	Muscle glycogen phosphorylase	Autosomal recessive Affects theskeletal muscle No elevation of blood lactate during forearm exercise test ↑ creatine kinase Muscle cramp, fatigue, myalgias, and myoglobinuria "Second wind" phenomenom rapid relief of fatigue and myalgia secondary to increase blood flow, improved free fatty acid delivery, and liver glucose utilization

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