A 2-year-old presents with hypotonia, hypoketotic hypoglycemia, elevated plasma C8 and C10 acylcarnitines, and sudden cardiac arrest during a febrile illness. The most likely deficient enzyme is:

• A Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD)
• B Short-chain acyl-CoA dehydrogenase (SCAD)
• C Carnitine palmitoyltransferase I (CPT-I)
• D Medium-chain acyl-CoA dehydrogenase (MCAD) ✓

Explanation

MCAD deficiency is the most common fatty acid oxidation disorder. It causes accumulation of medium-chain acylcarnitines (C6, C8, C10), detected on newborn screening. During fasting or illness, fatty acid oxidation is impaired, causing hypoketotic hypoglycemia (no ketones because beta-oxidation is blocked, yet glucose is depleted). Sudden death in previously healthy infants is characteristic. LCHAD produces C16/C18 species; CPT-I deficiency shows normal or elevated C0 with low acylcarnitines.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.