Amino-acid disorders including phenylketonuria and MSUD — formative SAQs

SAQ 1 (10 marks)

A term male neonate is well at birth and on breast and formula feeds. At 72 hours of age he becomes lethargic, feeds poorly, vomits, and is found with opisthotonic posturing and intermittent dystonia. The nursing staff note a sweet, caramel-like smell to his urine. A blood gas shows a high anion-gap metabolic acidosis with ketosis; the ammonia is normal. ^{[7] [8]}

a) Explain why this picture of a well neonate deteriorating 48 to 120 hours into feeds with ketoacidosis and an odour is classic for maple syrup urine disease, and name the single most specific confirmatory metabolite. (3 marks) ^[7]

b) Outline the acute management, naming the four moves of the shared metabolic protocol and the rationale for supplementing isoleucine and valine while restricting leucine. (4 marks) ^{[7] [8]}

c) Describe the role of extracorporeal removal, including the leucine threshold or trajectory that would trigger it, and explain why outcome tracks time on the toxic metabolite. ^[7] (3 marks) ^[7]