Which branched-chain amino acids accumulate due to maple syrup urine disease?

Maple syrup urine disease (MSUD) is a metabolic disorder caused by a deficiency in the branched-chain alpha-keto acid dehydrogenase complex, which is essential for the breakdown of branched-chain amino acids. The primary amino acids that accumulate due to this deficiency are isoleucine, leucine, and valine.

In normal metabolism, these branched-chain amino acids are transaminated and subsequently decarboxylated into their respective keto acids. However, when the enzyme complex is dysfunctional, this process is impaired, leading to a toxic buildup of isoleucine, leucine, and valine in the bloodstream. The accumulation results in various symptoms, including a characteristic maple syrup odor of the urine, which is where the disease gets its name.

Understanding the specific amino acids involved is crucial not just for recognizing the disease but also for its management and dietary recommendations. Restricting dietary intake of isoleucine, leucine, and valine is a primary therapy for managing MSUD, allowing patients to avoid the toxic effects associated with their accumulation.