2025 – PAGE 354 – INBORN ERRORS OF METABOLISM & MISCELLANEOUS METABOLIC DISORDERS

GLYCOGEN STORAGE DISEASES

NOTE: GLYCOGEN STORAGE DISEASES (GSD) include von Gierke’s disease, Pompe’s disease, Cori’s disease and McArdle’s disease. We’ll focus on the two most commonly tested. Since these are storage diseases, they do not present in the first week of life.

MNEMONIC: If you can remember VoPoCoMc, then you now have a mnemonic for the four GSDs. Also, McArdle’s = M = Mitochondrial = Muscle problems. Having said that, they seem to be getting away from the eponyms for these particular disorders.

GSD I (AKA VON GIERKE’S DISEASE)

GSD I (AKA VON GIERKE’S DISEASE) is the most commonly tested of the glycogen storage diseases. There is a glucose-6-phosphatase deficiency, which results in an inability to break down glycogen. Glycogen then deposits in the liver, kidneys, and pancreas, resulting in hepatomegaly. Some patients have a “doll-like” face. It only presents when there is hypoglycemia (when meals are spread), so will not present in the first week of life. Labs show a fasting hypoglycemia, ketoacidosis (from fat breakdown), lactic acidosis, and hyperuricemia. Treat inpatients with continuous feedings. Treat outpatients with a LOW-carb diet and frequent complex carbohydrates such as cornstarch (since they break down slowly and thus prevent hypoglycemia). A high-carb diet would be wrong because it would just result in MORE GLYCOGEN being made and deposited!

• PEARL: Glycogen stores cannot be broken down, so glucagon is useless for hypoglycemia.

GSD II (AKA POMPE or POMPE’S DISEASE)

GSD II (AKA Pompe’s Disease is NOT a mitochondrial disorder; it is a LYSOSOMAL disorder in which cellular breakdown of glycogen cannot occur. Deposition occurs in the liver, muscles, and heart, so look for organomegaly. Symptoms can begin at less than one month of age, or not until many years later as a teen. For babies, look for a floppy/HYPOTONIC baby with FTT and macroglossia. Death can occur due to respiratory failure. There is NO hypoglycemia in GSD II because other glycogen stores CAN be broken down. The problems in this disease arise due to the deposition. A key finding in this disease is CARDIOMEGALY from deposition in the heart. Look for left axis deviation (LAD) on an EKG.

• MNEMONIC: PUMP-LAY’s disease! PUMP = HEART, and LAY should remind you that this is a LYsosomal disease!
• MNEMONIC: Have you heard of Pompe’s restaurant? Well, imagine being at POMPE’s restaurant (or PUMP-LAY’s restaurant), where there’s so much food that you have to roll out your HUGE TONGUE to put all of the food on it. After that, you end up completely HYPOTONIC/FLOPPY because of a food coma!