Mitochondrial myopathy with lactic acidaemia, Fanconi-De Toni-Debré syndrome and a disturbed succinate: cytochrome c oxidoreductase activity.

A patient with severe muscular hypotonia, failure to thrive, a metabolic acidosis and a renal tubular dysfunction is presented. The disease followed a fatal course. Blood lactate and pyruvate levels as well as lactate/pyruvate ratios were strongly elevated. There were a massive excretion of lactate in urine, a generalized hyperaminoaciduria, a proteinuria and a mellituria. The carnitine concentration was diminished in blood and muscle tissue. Biochemical investigations of skeletal muscle and liver tissue revealed a defect in the respiratory chain at the level of succinate: cytochrome c oxidoreductase. The defect could not be demonstrated in cultured fibroblasts.