Maple Syrup Urine Disease

MAPLE SYRUP URINE DISEASE
  • Maple syrup urine disease,an autosomal recessive metabolic disorder is caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex .
  • It is a mitochondrial, enzyme complex consisting of alpha-ketoacid decarboxylase ,Dihydrolipoyl dehydrogenase and Transacylase.
  • It leads to a build-up of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic byproducts in the blood and urine.
CLINICAL FEATURES OF MAPLE SYRUP URINE DISEASE:
  • The disease is characterized in an infant by the presence of sweet-smelling urine, with an odor similar to that of maple syrup. The sweet-smelling intermediates that accumulate in the urine give the disease its name.
  • Infants with this disease seem healthy at birth but if left untreated suffer severe brain damage, and eventually die.
  • From early infancy, symptoms of the condition include poor feeding, vomiting, dehydration, lethargy, hypotonia, seizures, ketoacidosis, opisthotonus, pancreatitis, coma and neurological decline.
DIAGNOSIS OF MAPLE SYRUP URINE DISEASE
  • Diagnosis is confirmed by amino acid analysis showing marked elevation in plasma level of leucine, isoleucine,valine and alloisoleucine (a steroisomer of isoleucine not normally found in blood) and depression of alanine.
  • Leucine levels are usually higher than those of other three amino acids.
  • Urine contain high levels of leucine, isoleucine and valine and their respective ketoacids.
  • The keto acids may be detected by adding a few drops 2-4 dinitrophenylhydrazine (DNPH) reagent which produces a yellow precipitate in positive test.
  • Ferric chloride gives navy blue colour with the patients urine.
Exam Question
  • An inherited deficiency of branched chain a keto acid dehydrogenase result in Maple syrup urine disease.
  • In maple syrup disease, the amino acids excreted in urine are Valine, Leucine ,Leucine.
  • Decarboxylation of valine, leucine and isolucine is defective in Maple syrup urine disease.
  • Enzyme deficient in maple syrup urine disease is α-ketoacid dehydrogenase.
  • In maple syrup urine disease FeCI3 test with urine gives blue color.

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