An infant brought to the hospital with chief complaints of distended a

An infant brought to the hospital with chief complaints of distended abdomen and short stature .on examination liver and kidneys were enlarged.laboratory finding shows low plasma glucose,uric acid-10%,serum cholesterol -278mg% What is the probable diagnosis

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Probable Diagnosis: Von Gierke Disease (Glycogen Storage Disease Type I)

This presentation is classic for GSD Type Ia (Von Gierke disease) - caused by a deficiency of the enzyme glucose-6-phosphatase.

Matching the Clinical Features

Finding in the Case	Explanation in Von Gierke Disease
Distended abdomen	Massive hepatomegaly from glycogen accumulation in the liver
Short stature	Growth retardation - a hallmark feature
Enlarged liver	Primary site of glycogen storage
Enlarged kidneys	Glycogen also deposits in renal tubular cells causing nephromegaly
Low plasma glucose	Glucose-6-phosphatase is needed for the final step of both glycogenolysis and gluconeogenesis; its absence causes severe fasting hypoglycemia
Uric acid elevated (10%)	Hyperuricemia - caused by competitive inhibition by lactate of renal tubular urate secretion, plus increased uric acid production
Serum cholesterol 278 mg%	Hyperlipidemia - from increased lipolysis secondary to decreased glucose availability, causing hypertriglyceridemia and hypercholesterolemia

Pathophysiology

Glucose-6-phosphatase catalyzes the last step of both gluconeogenesis and glycogenolysis in the liver:

Glucose-6-phosphate → Glucose (requires glucose-6-phosphatase)

Without this enzyme:

Glycogen cannot be converted to free glucose → hypoglycemia
Glucose-6-phosphate builds up → excess glycolysis → lactic acidosis
Lactate competes with urate for renal tubular secretion → hyperuricemia
Hypoglycemia stimulates lipolysis → hyperlipidemia (high cholesterol + triglycerides)
Glycogen accumulates in hepatocytes and renal tubular cells → hepato-nephromegaly

Inheritance and Subtypes

Autosomal recessive inheritance
Type Ia (~80%): defect in glucose-6-phosphatase catalytic subunit (G6PC gene)
Type Ib (~20%): defect in the glucose-6-phosphate translocase (transport system)

Key Diagnostic Tests

Failure to raise blood glucose after galactose loading (galactose is normally converted to glucose via glucose-6-phosphate, but this last step is blocked)
Epinephrine/glucagon tolerance test: no rise in blood glucose (but lactate rises instead)
Liver biopsy with direct assay of glucose-6-phosphatase activity - confirmatory
Genetic testing for G6PC mutations

Treatment

Frequent meals and nocturnal nasogastric feeding with uncooked cornstarch to maintain blood glucose
Avoidance of prolonged fasting
Allopurinol for hyperuricemia
Dietary management of hyperlipidemia

Sources: Tietz Textbook of Laboratory Medicine, 7th ed.; Robbins & Kumar Basic Pathology; Lippincott Illustrated Reviews Biochemistry, 8th ed.

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All 4 Clinical Cases - Glycogen Storage Diseases (GSD)

Clinical Case 1 - ✅ Already Discussed

Diagnosis: Von Gierke Disease (GSD Type Ia)

Deficient enzyme: Glucose-6-phosphatase
Key features: Hepato-nephromegaly, short stature, hypoglycemia, hyperuricemia, hypercholesterolemia

Clinical Case 2

Diagnosis: Pompe Disease (GSD Type II)

Deficient enzyme: Acid α-glucosidase (Acid maltase)

Feature in Case	Explanation
Neonate with hepatomegaly	Glycogen accumulates in liver
Cardiac hypertrophy on echo	Massive glycogen deposition in cardiac muscle - cardiomegaly is the dominant feature
Floppy baby, diminished muscle tone	Skeletal muscle glycogen accumulation → muscle weakness
Low α-glucosidase in leukocytes, muscle, liver	Confirms the enzyme deficiency (diagnostic)

This is the infantile form - presents in first few months of life, patients usually die within 1 year from cardiac failure
It is the only GSD that is also a lysosomal storage disease (the enzyme is lysosomal)
Blood glucose is normal (unlike Von Gierke) since glucose-6-phosphatase is intact
Treatment: Enzyme replacement therapy with recombinant human acid α-glucosidase (approved 2006)

Clinical Case 3

Diagnosis: McArdle Disease (GSD Type V)

Deficient enzyme: Muscle glycogen phosphorylase (myophosphorylase)

Feature in Case	Explanation
Fatigability worsened on exertion	Muscle cannot break down glycogen for energy during exercise
Lags behind friends on walking	Exercise intolerance - typical presentation in young adults
Muscle biopsy: subsarcolemmal "lakes" of glycogen	Pathognomonic - glycogen accumulates just beneath the muscle cell membrane

Characteristic sign: "Second wind phenomenon" - symptoms improve after ~10 min of moderate exercise as fatty acid metabolism kicks in
Forearm ischemic test: flat venous lactate curve with exaggerated ammonia rise (because the glycolytic block prevents lactate production)
Serum CK is elevated even at rest
No cardiac or liver involvement
Blood glucose and lactate are low after exercise (as seen in Case 4, which is the same disease)

Clinical Case 4 - ✅ Answered in Notes

Diagnosis: McArdle Disease (GSD Type V)

Deficient enzyme: Muscle glycogen phosphorylase
Post-exercise: low plasma glucose + low lactate + high muscle glycogen = classic McArdle picture
The glycolytic block means lactate cannot be produced from muscle glycogen

Quick Reference Summary Table

Case	Disease	GSD Type	Deficient Enzyme	Key Clue
1	Von Gierke	Type I	Glucose-6-phosphatase	Hepato-nephromegaly + hypoglycemia + hyperuricemia
2	Pompe	Type II	Acid α-glucosidase	Floppy neonate + cardiomegaly + normal glucose
3 & 4	McArdle	Type V	Muscle glycogen phosphorylase	Exercise intolerance + subsarcolemmal glycogen + flat lactate on ischemic test

Sources: Tietz Textbook of Laboratory Medicine 7th ed.; Robbins & Kumar Basic Pathology; Lippincott Biochemistry 8th ed.; Rheumatology 2022 Elsevier

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