A 2-week-old neonate presents with vomiting, lethargy, and odour of burned caramel/maple syrup from the urine. A urine DNPH (dinitrophenylhydrazine) test is positive. Plasma amino acids show elevated leucine, isoleucine, and valine. Which enzyme is deficient in this disorder?
- A Propionyl-CoA carboxylase
- B Methylmalonyl-CoA mutase
- C Branched-chain alpha-ketoacid dehydrogenase (BCKAD) complex ✓
- D Isovaleryl-CoA dehydrogenase
Correct answer: C. Branched-chain alpha-ketoacid dehydrogenase (BCKAD) complex
Explanation
Maple syrup urine disease (MSUD) results from deficiency of the branched-chain alpha-ketoacid dehydrogenase (BCKAD) complex, which decarboxylates the alpha-keto acids derived from leucine, isoleucine, and valine. Accumulation of these keto acids gives urine a maple syrup/burned caramel odour. Positive DNPH test indicates alpha-keto acids. Propionyl-CoA carboxylase deficiency causes propionic acidaemia; methylmalonyl-CoA mutase deficiency causes methylmalonic aciduria; isovaleryl-CoA dehydrogenase deficiency causes isovaleric acidaemia (sweaty feet odour).
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.