Which amino acid is found in maple syrup urine disease?

Maple syrup urine disease (MSUD) is a metabolic disorder characterized by the body's inability to break down certain branched-chain amino acids due to a deficiency in specific enzyme complexes. The amino acids that are not properly metabolized in MSUD are isoleucine, leucine, and valine.

Leucine is particularly notable in the context of MSUD because its accumulation can lead to significant neurological problems and the distinctive smell of maple syrup in urine, which is a hallmark symptom of the disorder. The presence of elevated levels of leucine in the blood is a critical indication in the diagnosis of maple syrup urine disease.

While both isoleucine and valine are also involved in MSUD, the question specifically identifies the amino acid associated with the disease's clinical symptoms, making leucine the correct answer. Tyrosine is not directly related to MSUD, as it is not one of the branched-chain amino acids affected by this disorder.