What condition is signified by a sweet odor in the urine, especially in infants?

The condition characterized by a sweet odor in the urine, particularly in infants, is indicative of maple syrup urine disease. This metabolic disorder arises from a deficiency of certain enzymes required to break down branched-chain amino acids: leucine, isoleucine, and valine. As a result, these amino acids and their corresponding keto acids accumulate in the body, leading to a distinctive sweet or maple syrup-like smell in the urine.

This odor serves as a key clinical clue for diagnosis, especially in neonates and young infants, who may present with feeding difficulties, lethargy, or neurological problems if the condition goes untreated. Early identification and management are critical to prevent severe complications, including developmental delays and life-threatening metabolic crises.

In contrast, the other conditions listed do not typically present with a sweet smell in the urine. Isovaleric acidemia, for example, is associated with a "sweaty feet" odor due to the accumulation of isovaleric acid, while phenylketonuria presents with a mousy or musty odor due to phenylalanine accumulation. Tyrosinemia might result in a rancid smell, reflecting different metabolic disturbances. Each of these conditions has unique metabolic implications and clinical presentations but does not