What enzyme is deficient in maple syrup disease?

Maple syrup disease (MSUD) is a genetic disorder characterized by a deficiency in branched-chain alpha-keto acid dehydrogenase. This enzyme is crucial for the metabolism of branched-chain amino acids: leucine, isoleucine, and valine. When this enzyme is deficient, these amino acids and their corresponding keto acids accumulate in the body, leading to the clinical manifestations of MSUD, which can be severe and life-threatening if not managed appropriately.

The buildup of these substances is what gives the urine its characteristic sweet odor, reminiscent of maple syrup, hence the name of the condition. Diagnosis is typically confirmed through biochemical tests, including elevated levels of these amino acids in the plasma and urine.

The other enzymes listed are associated with different metabolic disorders. Phenylalanine hydroxylase is related to phenylketonuria (PKU), homogentisic acid oxidase is linked to alkaptonuria, and tyrosinase is involved in albinism. Each plays a unique role in specific amino acid metabolism, but none of these are connected to the metabolic pathways affected in maple syrup disease.