Maple syrup urine disease (MSUD) or branched-chain ketoaciduria
- It is an inborn error of metabolism of branched-chain amino acids valine, leucine and isoleucine.
- It is due to deficiency of an enzyme that catalyzes the second reaction in these amino acids metabolism i.e. branched chain-alpha keto acid dehydrogenase which catalyzes the decarboxylation of branched-chain amino acids.
- As a result, the branched-chain amino acids, leucine, isoleucine and valine, and their a-keto acids accumulate in the blood, urine, and CSF.
- There is a characteristic maple syrup odor to the urine.
In maple syrup urine disease there is the excretion of branched-chain amino acids (isoleucine, leucine, valine) and their keto acids (α-keto β-methyl valerate, α-ketoisocaproate, α-ketoisovalerate) in the urine.