A 10-month-old infant is brought with vomiting, lethargy, and hypoglycemia after an upper respiratory illness. Urine organic acids show dicarboxylic acids and low ketones. Acylcarnitine profile shows elevated octanoylcarnitine (C8). Which enzyme is deficient?
- A Carnitine palmitoyltransferase I (CPT I)
- B Medium-chain acyl-CoA dehydrogenase (MCAD) ✓
- C Very long-chain acyl-CoA dehydrogenase (VLCAD)
- D Short-chain acyl-CoA dehydrogenase (SCAD)
Correct answer: B. Medium-chain acyl-CoA dehydrogenase (MCAD)
Explanation
MCAD deficiency is the most common fatty acid oxidation disorder, presenting with hypoketotic hypoglycemia during fasting or illness. Elevated B8 (octanoylcornitine) acylcarnitine is diagnostic. VLCAD shows elevated B14:1. CPT I deficiency causes hypoketotic hypoglycemia but with normal acylcarnitine profile and elevated free carnitine.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.