A female infant with a biochemical defect of the respiratory chain and of β-oxidation and neuropathological changes typical for Leigh’s disease is reported from the Department of Neurology, University of Würzburg, Departments of Pediatrics and Pathology, University of Homburg, and Department of Pediatrics, University of Freiburg, Germany. The infant was seen at age 2 months because of hypotonia, delayed motor development and lactic acidosis. Decreased activities of both cytochrome c oxidase and long chain acyl coenzyme A dehydrogenase were found in a muscle specimen of 11 months and in a liver specimen obtained post mortem at 13 months. Myoclonic seizures accompanied by multifocal EEG epileptic discharges were treated with valproate. Seizures were controlled, but her general condition deteriorated within 2 months, respiratory insufficiency worsened and the acidosis became intractable. Post mortem examinations showed severe demyelination in the capsula interna, calcification in the brain stem ganglia, and gliosis in the pons and medulla. The liver was enlarged with centrolobular fatty infiltration. A rare occurrence of two independent mitochondrial enzyme defects is suggested. 
COMMENT. Valproate administration was not considered the cause but may have worsened the palmitoyl CoA dehydrogenase deficiency. Leigh’s syndrome, first described in 1951, appears to be non-specific biochemically as well as clinically. Consistent early clinical features in the infantile cases are a quiet immobility with lack of crying and hypotonia. In addition to the COX deficiency and dehydrogenase deficiency described above, defects of the pyruvate dehydrogenase multi-enzyme complex and pyruvate carboxylase have been reported.