Laboratory Studies
Serum glucose levels are measured to document the degree of hypoglycemia. Serum electrolytes calculate the anion gap to determine presence of metabolic acidosis; typically, patients with glycogen-storage disease type 0 (GSD-0) have an anion gap in the reference range and no acidosis. See the Anion Gap calculator.
Serum lipids (including triglyceride and total cholesterol) may be measured. In patients with glycogen-storage disease type 0, hyperlipidemia is absent or mild and proportional to the degree of fasting.
Urine (first voided specimen with dipstick test for ketones and reducing substances) may be analyzed. In patients with glycogen-storage disease type 0, urine ketones findings are positive, and urine-reducing substance findings are negative. However, urine-reducing substance findings are positive (fructosuria) in those with fructose 1-phosphate aldolase deficiency (fructose intolerance).
Serum lactate is in reference ranges in fasting patients with glycogen-storage disease type 0. Serum lactate is elevated in the postprandial state of patients with glycogen-storage disease type 0.
Liver function studies provide evidence of mild hepatocellular damage in patients with mild elevations of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels.
Plasma amino-acid analysis shows plasma alanine levels as in reference ranges or low during a fast.
Imaging Studies
Skeletal radiography may reveal osteopenia.
Other Tests
Evaluation of a patient with suspected glycogen-storage disease type 0 requires monitored assessment of fasting adaptation in an inpatient setting.
Patients typically have hypoglycemia and ketosis, with lactate and alanine levels in the low or normal part of the reference range approximately 5-7 hours after fasting.
A glucagon challenge test may be needed if the fast fails to elicit the expected rise in plasma glucose. Lactate and alanine levels are in the reference range.
By contrast, a glucagon challenge test after a meal causes hyperglycemia, with increased levels of plasma lactate and alanine.
Oral loading of glucose, galactose, or fructose results in a marked rise in blood lactate levels.
Procedures
Liver biopsy for microscopic analysis and enzyme assay confirms the diagnosis. Liver biopsy may show low but not absent glycogen content and low or absent glycogen synthase activity. [6] Diagnosis may include linkage analysis in families with affected members and sequencing of the entire coding region of the GSY2 gene for mutations. Genetic testing may help avoid the need for a liver biopsy.
Histologic Findings
Histologic analysis of liver tissue demonstrates moderately decreased amounts of periodic acid-Schiff (PAS)–positive, diastase-sensitive glycogen stores.
Evidence of increased fat accumulation in the liver may be observed, as in other glycogen-storage diseases.
Electron microscopic analysis of liver sections shows normal glycogen structure.
Muscle glycogen stores are normal.
