Maple syrup urine disease (MSUD) was first described as a rapid onset of Menkes' neurodegenerative disease in 1954. It is a defect of metabolism due to abnormal activity of the branched-chain alpha-ketoacid dehydrogenase (BCKAD) complex. This complex is responsible for the breakdown of branched-chain amino acids:
Leucine
Isoleucine
Valine
The underlying defect in the BCKAD complex disrupts the metabolism of branched-chain amino acids, which leads to an accumulation of branched-chain amino acids (BCAAs) in the plasma and their respective branched-chain ketoacids in the urine. It classically manifests in the neonatal period with failure to thrive, delayed developmental milestones, feeding difficulties, and a maple syrup odor in the urine or cerumen. Treatment consists of close metabolic monitoring and dietary restriction of branched-chain amino acids. If left untreated, irreversible neurological damage and metabolic catastrophe ensue. Good clinical outcomes can be expected if management is initiated early.
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