Leigh syndrome (LS), or subacute necrotizing encephalomyelopathy, having relatively homogeneous clinical symptomatology and pattern of neuropathological changes, shows remarkable heterogeneity in biochemical and molecular background. G8363A mitochondrial DNA mutation typical for MERRF syndrome and progressive cardiomyopathy may also be associated with LS. Clinical, biochemical and pathological findings in a boy aged 28 months who died with classical

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... edindetail.Hyperlactataemia,LCHAD-like organic acids profile and respiratory alkalosis(pH7.47,pCO2 4.9 mmHg, HCO3 3.0 mmol/l) were observed. Spectrophotometric assay showed deficit of respiratory chain complexes IVand I. Skeletal muscle biopsy revealed mosaic cytochrome oxidase deficit,lipid accumulation and ultrastructural abnormalities of mitochondria. Postmortem examination confirmed the presence of typical LS central nervous system lesions as well as hypertrophy of the left ventricle of the heart.