⚡ Glycogen storage diseases (GSDs) can be divided into those affecting primarily muscle and those affecting the liver.
🔍 See also Von Gierke Disease entry.

🧬 Aetiology

Glycogen = a high molecular weight polymer of glucose residues.
🏋️‍♂️ Muscle and 🫀 liver contain significant glycogen stores.
🔧 Enzymes: Glycogen formed by glycogen synthase, broken down by glycogen phosphorylase.

🧑‍⚕️ Clinical

Most are autosomal recessive enzyme deficiencies.
🫀 Hepatomegaly is common (but ❌ no splenomegaly).
⚠️ Hypoglycaemia → drowsiness, seizures, failure to thrive.
📉 Lactic acidosis common in infancy presentations.
👶 Infants: poor growth, hypoglycaemia. 👦 Older children: hypotonia, muscle weakness, wasting.

⚠️ Complications (Long-Term)

Severe hypoglycaemia → cerebral oedema, coma, death.
🫁 Hepatic tumours (adenoma/adenocarcinoma).
🩸 Glomerular hyperfiltration & glomerulosclerosis.
🧠 Brain damage, severe anaemia, growth failure.

🔑 Commoner Forms of GSD

Type I – Von Gierke’s 🫀 Glucose-6-phosphatase deficiency → hepatomegaly, severe fasting hypoglycaemia, lactic acidosis. High mortality though some survive. Avoid fructose & galactose.
Type II – Pompe’s ❤️ Acid maltase (lysosomal α-1,4-glucosidase) deficiency. Cardiomyopathy, hypotonia, enlarged tongue. Death in infancy. 💡 Mnemonic: “Pompe trashes the pump” (heart, liver, muscle).
Type III – Cori’s 🧩 Debranching enzyme deficiency. Milder than Von Gierke’s, normal lactate, but risk of cardiomyopathy.
Type IV – Andersen’s 🧒 Branching enzyme deficiency → hepatosplenomegaly, cirrhosis, failure to thrive. Often fatal in childhood. Neuromuscular form may present later.
Type V – McArdle’s 🏃 Muscle glycogen phosphorylase deficiency. Painful muscle cramps, exercise intolerance, myoglobinuria (red urine), arrhythmias. “Second-wind phenomenon” during exercise. Normal life expectancy.

📌 Summary

GSDs are inherited disorders of glycogen metabolism → abnormal accumulation of glycogen in tissues. At least 15 types identified; Types I–V are the most important and are autosomal recessive. Diagnosis often via PAS stain of tissues to identify glycogen.

🧠 Mnemonic: “Vice President Can’t Accept Money” → Von Gierke (I), Pompe (II), Cori (III), Andersen (IV), McArdle (V).

Cases — Glycogen Storage Diseases (GSDs)

Case 1 — Von Gierke’s disease (Type I) 🍼: A 6-month-old infant presents with recurrent hypoglycaemic seizures, hepatomegaly, and failure to thrive. Bloods: hypoglycaemia, lactic acidosis, hyperuricaemia, hypertriglyceridaemia. Diagnosis: GSD Type I (glucose-6-phosphatase deficiency). Managed with frequent cornstarch feeds and avoidance of fasting.
Case 2 — Pompe disease (Type II) ❤️: A 3-month-old boy presents with severe hypotonia (“floppy baby”), feeding difficulties, cardiomegaly, and respiratory distress. ECG: short PR interval, large QRS complexes. Echo: hypertrophic cardiomyopathy. Diagnosis: GSD Type II (acid maltase deficiency). Managed with enzyme replacement therapy (alglucosidase alfa) and supportive care.
Case 3 — McArdle’s disease (Type V) 🏃: A 20-year-old man presents with exercise intolerance, painful muscle cramps, and episodes of myoglobinuria after strenuous activity. Exam: muscle hypertrophy, but no hepatomegaly. Labs: CK raised. Forearm exercise test: no rise in lactate. Diagnosis: GSD Type V (myophosphorylase deficiency). Managed with lifestyle modification (avoid intense exercise, take oral sucrose before exertion).

Teaching Point 🩺: Glycogen storage diseases are inherited metabolic disorders of glycogen synthesis/breakdown. - Type I (Von Gierke): liver — hypoglycaemia, hepatomegaly. - Type II (Pompe): muscle/heart — cardiomyopathy, hypotonia. - Type V (McArdle): muscle — exercise-induced cramps, myoglobinuria. Diagnosis: enzyme assay or genetic testing. Management is supportive, diet-based, and enzyme replacement in Pompe.

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Glycogen storage diseases

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