Carnitine deficiency vs MCAD and LCHAD deficiencies
How to tell Carnitine deficiency and MCAD and LCHAD deficiencies apart when a board question makes them look alike.
Carnitine deficiency is transport failure with muscle/cardiac lipid buildup; MCAD is fasting hypoketotic hypoglycemia; LCHAD adds long-chain systemic disease and maternal HELLP association.
Side by side
Primary carnitine deficiency causes impaired carnitine uptake/reabsorption and reduced long-chain fatty acid transport into mitochondria, with muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, and muscle lipid accumulation.
MCAD deficiency causes hypoketotic hypoglycemia after fasting with dicarboxylic aciduria; LCHAD deficiency causes hypoketotic hypoglycemia plus cardiomyopathy, neuropathy, retinopathy, or maternal HELLP risk.
OCTN2 carnitine transporter dysfunction lowers intracellular carnitine, limiting long-chain acyl group entry into mitochondria for beta-oxidation.
Medium-chain or long-chain 3-hydroxyacyl-CoA dehydrogenase defects block beta-oxidation after fatty acids have entered mitochondrial metabolism.
Low carnitine, muscle lipid accumulation, weakness, and cardiomyopathy support carnitine deficiency.
Fasting-induced hypoketotic hypoglycemia, dicarboxylic aciduria, and acylcarnitine profile support MCAD/LCHAD patterns.
The trap
All impair fatty acid use and ketones, so transport clue, chain length, dicarboxylic acids, and maternal pregnancy clue separate them.
The repair move
For fatty acid oxidation disorders, locate the block at carnitine transport versus chain-specific beta-oxidation.
Try a free question
CoreA 9-month-old infant has progressive muscle weakness, dilated cardiomyopathy, and hypoketotic hypoglycemia after a 12-hour fast. Plasma free carnitine is markedly reduced. Muscle biopsy shows lipid droplets accumulating in myocytes. Which condition is most likely?
Show answer and explanation
Answer: A. Primary carnitine deficiency. Primary carnitine deficiency is OCTN2 carnitine transporter dysfunction; long-chain fatty acids cannot enter mitochondria for beta-oxidation, producing muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, and lipid accumulation in muscle. Treatment is carnitine supplementation.
Why the other choices are tempting
- B. MCAD deficiency causes hypoketotic hypoglycemia with normal carnitine and characteristic dicarboxylic aciduria; it does not classically cause cardiomyopathy.
- C. LCHAD deficiency causes hypoketotic hypoglycemia plus cardiomyopathy/neuropathy/retinopathy but carnitine levels are typically normal or only secondarily reduced.
- D. Von Gierke (G6P deficiency) causes severe fasting hypoglycemia with lactic acidosis and hepatomegaly, not cardiomyopathy with low carnitine.
- E. Pompe disease causes lysosomal glycogen accumulation in heart and muscle, not lipid accumulation with carnitine deficiency.
Flashcards
Tap a card to flip it.
What clue supports Carnitine deficiency?
Choose Carnitine deficiency when the stem gives this pattern: Carnitine deficiency causes impaired long-chain fatty acid transport into mitochondria, muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, and lipid accumulation in muscle.
What clue supports MCAD and LCHAD deficiencies?
Choose MCAD and LCHAD deficiencies when the stem gives this contrasting pattern: MCAD deficiency causes hypoketotic hypoglycemia after fasting with dicarboxylic aciduria; LCHAD deficiency causes hypoketotic hypoglycemia plus cardiomyopathy, neuropathy, retinopathy, or maternal HELLP risk.
Quick answers
What is the fastest way to tell Carnitine deficiency from MCAD and LCHAD deficiencies?
Carnitine deficiency is transport failure with muscle/cardiac lipid buildup; MCAD is fasting hypoketotic hypoglycemia; LCHAD adds long-chain systemic disease and maternal HELLP association.
What is the key clue for Carnitine deficiency?
Primary carnitine deficiency causes impaired carnitine uptake/reabsorption and reduced long-chain fatty acid transport into mitochondria, with muscle weakness, cardiomyopathy, hypoketotic hypoglycemia, and muscle lipid accumulation.
What is the key clue for MCAD and LCHAD deficiencies?
MCAD deficiency causes hypoketotic hypoglycemia after fasting with dicarboxylic aciduria; LCHAD deficiency causes hypoketotic hypoglycemia plus cardiomyopathy, neuropathy, retinopathy, or maternal HELLP risk.
What is the common trap with Carnitine deficiency vs MCAD and LCHAD deficiencies?
All impair fatty acid use and ketones, so transport clue, chain length, dicarboxylic acids, and maternal pregnancy clue separate them.