Oral L-alloisoleucine loading studies in healthy subjects and in patients with maple syrup urine disease

Pediatr Res. 1991 Nov;30(5):430-4. doi: 10.1203/00006450-199111000-00007.


Total body and renal elimination of L-alloisoleucine was assessed after oral loads (0.57 mmol/kg body wt) in four healthy subjects and in five patients with maple syrup urine disease (MSUD) of different degrees of severity. As judged from the fictive initial concentration, L-alloisoleucine is distributed evenly in the total body water space. In the controls, estimated half-time of total elimination was 9.2 +/- 2.2 h (n = 4). In the MSUD patients, it ranged from 26 h (mild variant) to about 8 d (classical type). Because of its low renal clearance rate, L-alloisoleucine was cleared through ketomethylvalerate to greater than 99% in normals and to at least 73% in the MSUD patients. Assuming small variation in the losses of ketomethylvalerate through L-isoleucine formation and through renal excretion, this test allows ranking of MSUD patients with regard to their residual in vivo branched-chain oxo-acid dehydrogenase activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)
  • Administration, Oral
  • Adolescent
  • Child
  • Female
  • Half-Life
  • Humans
  • Isoleucine / administration & dosage
  • Isoleucine / blood
  • Isoleucine / pharmacokinetics*
  • Keto Acids / metabolism
  • Ketone Oxidoreductases / metabolism
  • Kidney / metabolism
  • Maple Syrup Urine Disease / metabolism*
  • Multienzyme Complexes / metabolism
  • Tissue Distribution


  • Keto Acids
  • Multienzyme Complexes
  • Isoleucine
  • alpha-keto-beta-methylvaleric acid
  • Ketone Oxidoreductases
  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)