A neonate presents on day 3 of life with encephalopathy, seizures, and a peculiar odour of 'maple syrup' in urine and cerumen. Plasma amino acids show markedly elevated leucine, isoleucine, and valine with elevated alloisoleucine. Which enzyme complex is deficient?
- A Propionyl-CoA carboxylase
- B 3-methylglutaconyl-CoA hydratase
- C Branched-chain alpha-keto acid dehydrogenase (BCKDH) complex ✓
- D Isovaleryl-CoA dehydrogenase
Explanation
Maple syrup urine disease (MSUD) results from deficiency of branched-chain alpha-keto acid dehydrogenase (BCKDH) complex — a multienzyme complex that decarboxylates the keto-acid products of leucine, isoleucine, and valine. Accumulation of leucine is primarily neurotoxic (excitotoxic, cerebral edema). Alloisoleucine is pathognomonic. The maple syrup odour is from sotolone (a ketoacid metabolite). Propionyl-CoA carboxylase deficiency causes propionic acidemia. Isovaleryl-CoA dehydrogenase deficiency causes isovaleric acidemia (sweaty feet odour). MSUD requires emergency management with protein-free fluids and BCAA-free formula.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.