An infant presents to OPD with a history of vomiting and poor feeding. The burnt sugar odor is present in baby's urine. Lab examination reveals elevated levels of leucine,  isoleucine and valine. The most likely diagnosis is ?
The odor of urine in maple syrup urine disease (branched-chain ketonuria, or MSUD) suggests maple syrup or burnt sugar.
The biochemical defect in MSUD  involves the α-keto acid decarboxylase complex. Plasma and urinary levels of  leucine, isoleucine, valine and their α-keto acids and α-hydroxy acids (reduced α-keto acids) are elevated, but the urinary keto acids derive principally from leucine. Signs and symptoms of MSUD include often fatal ketoacidosis, neurological derangements, mental retardation, and a maple syrup odor of urine. The mechanism of toxicity is unknown. Early diagnosis by enzymatic analysis is essential to avoid brain damage and early mortality by replacing dietary protein by an amino acid mixture that lacks  leucine, isoleucine, and valine.
Reference- Harper’s illustrated biochemistry. 30th edition page -304
Phenylketonuria
Alkaptonuria
Tyrosinemia
Maple syrup urine disease