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USMLE Step 1

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Metabolic Disorders

Maple Syrup Urine Disease

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Maple Syrup Urine Disease (MSUD) is an autosomal recessive metabolic disorder that leads to the accumulation of branched-chain amino acids.

Maple Syrup Urine Disease is caused by a defect in branched-chain ketoacid dehydrogenase, a Vitamin B1 (Thiamine)-dependent enzyme, which leads to the accumulation of the branched-chain amino acids:isoleucine, leucine, and valine.

Infants affected have urine with a distinctive sweet odor that is reminiscent of maple syrup. Accumulation of branched-chain amino acids leads to a number of CNS problems: developmental delay, lethargy, and posturing (decorticate or decerebrate). If untreated, patients usually die in infancy.

Since thiamine pyrophosphate (TPP) is a cofactor for branched-chain ketoacid dehydrogenase, some forms of maple syrup urine disease may improve and be treated with thiamine.

Find Maple Syrup Urine Disease and other Metabolic Disorders among Pixorize's visual mnemonics for the USMLE Step 1 and NBME Exams.