Plasma amino acid analyses in two cases of maple syrup urine disease.

Maple syrup urine disease is a rare inborn error of metabolism, characterized by elevated plasma levels of branched chain amino acids and urinary excretion of branched chain keto acids. Plasma amino acid levels in two subjects were followed by deproteinizing plasma, derivatizing the free amino acids with phenylisothiocyanate, and analysis by HPLC. The results indicate that valine, leucine and isoleucine are elevated in Maple syrup urine disease, and that leucine remains high even after dietary treatment.