[Intermittent branched--chain ketoacidurie in ketotic hypoglycemia: investigations to localize the biochemical defect (author's transl)].

We are reporting a girl aged eight years with ketotic hypoglycemia, mental deficiency and retarded motor and somatic development. Investigation of plasma amino acid concentrations during a spontaneous hypoglycemia revealed an increase in the branched-chain amino acids valine (4.1), leucine (7.8) and isoleucine (1.7 mg/100 ml), while alanine was decreased (1.2 mg/100 ml) and ketonuria was present. The determination of the branched-chain ketoacid decarboxylase in leukocytes showed a decrease of approximately 50% of normal for alpha-ketoisocaproic acid (KIC) as substrate, whereas values for alpha-ketoisovaleric acid (KIVA) and alpha-keto-beta-methylvaleric acid (MEVA) were normal. In fibroblasts activities for all three substrates were in the normal range. Intermittend maple-syrup-urine disease was excluded by oral loading tests with the branched-chain amino acids and with an isocaloric, high-protein diet. Impairment of oxydative decarboxylation of leucine, valine, and isoleucine secondary to increased ketogenesis may play an etiologic role in ketotic hypoglycemia, since we observed, by gaschromatographic analysis, an increase in the urinary excretion of KIVA (5.5 mumol/h), KIC (29.4), and MEVA (47.9) after a provocative test with an isocaloric ketogenic diet for 36 hrs. The significance of branched-chain hyperaminoacidemia and branched chain alpha-ketoaciduria is discussed in this context.