We report the case of a boy who developed a motor neuropathy during infectious episodes at 18 mo and 3 y of age. When he was 7 y old, he suffered persistent weakness and areflexia; his resting lactate and pyruvate values were 3. 65 mM and 398 microM, respectively (controls: 1. 1 +/- 0. 3 mM and 90 +/- 22 microM), and an exercise test demonstrated a lactic acidosis (13. 6 mM; controls: 6. 4 +/- 1. 3 mM) with a high pyruvate level (537 microM; controls: 176 +/- 15 microM) and a low lactate/pyruvate ratio (24. 2; controls: 35 +/- 2). The results of polarographic studies on muscle mitochondria suggested a defect in pyruvate oxidation (pyruvate 17 ng atom O/min/mg protein; controls: 115 +/- 42), whereas glutamate, palmitoylcarnitine, and succinate were good respiratory substrates. The activity of total pyruvate dehydrogenase complex (PDHC) in muscle mitochondria and in fresh mononuclear cells was markedly decreased (9. 7 and 0. 054 nmol 14CO2/min/mg protein, respectively; controls: 123 +/- 4. 5 and 0. 733 +/- 0 VSports手机版. 03, respectively). Immunochemical analysis in muscle mitochondria demonstrated an absence of the alpha and beta E1 PDHC subunits. After 2 y of treatment with 500 mg/d thiamine, the patient was clinically improved. A genetic study of the main regions of mutations (exon 10 and 11) in the X chromosome encoding for the E1 alpha subunit of PDHC did not show any mutation. These data indicate that, although genetically different, this case enters in a very rare category of patients with PDHC deficiency without cerebral dysfunction and improved by thiamine + L-carnitine therapy. .