A 6-day-old newborn is brought to the neonatal intensive care unit due to poor feeding, lethargy, and episodes of vomiting. The infant's parents report that the urine has a distinctive sweet, maple syrup-like odor. Laboratory evaluation reveals metabolic acidosis along with elevated levels of branched-chain amino acids and their corresponding ketoacids in the blood. Which enzyme deficiency is most consistent with this patient's clinical presentation?

Vital Signs:

• Temperature: 36.8°C (98.2°F)
• Heart Rate: 140/min
• Respiratory Rate: 45/min

Laboratory Findings:

• Metabolic acidosis with an increased anion gap
• Elevated branched-chain amino acids (leucine, isoleucine, valine)
• Accumulation of corresponding α-ketoacids