, Volume 22, Issue 6, pp 706-722

Renal clearance of branched-chain L-amino and 2-oxo acids in maple syrup urine disease

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In maple syrup urine disease (MSUD), branched-chain L-amino (BCAA) and 2-oxo acids (BCOA) accumulate in body fluids owing to an inherited deficiency of branched-chain 2-oxo acid dehydrogenase complex activity. In MSUD, little information is available on the significance of urinary disposal of branched-chain compounds. We examined the renal clearance of leucine, valine, isoleucine and alloisoleucine, and their corresponding 2-oxo acids 4-methyl-2-oxopentanoate (KIC), 3-methyl-2-oxobutanoate (KIV), (S)- (S-KMV), and (R)-3-methyl-2-oxopentanoate (R-KMV), using pairs of plasma and urine samples (n=63) from 10 patients with classical MSUD. The fractional renal excretion of free BCAA was in the normal range (<0.5%) and indepen-dent of the plasma concentrations. The excretion of bound (N-acylated) BCAA was normal and not significantly dependent on the BCAA plasma concentrations. The fractional renal excretion of BCOA was in the order KIC≪KIV