Three children with hypotonia, cardiac impairment, and defects of the mitochondrial respiratory chain complexes, but no ragged red fibers, are reported from the Hopital de la Timone, Chemin de l’Armee, d’Afrique, Marseille, France. Case 1 shared clinical and metabolic features with fatal infantile myopathy associated with cytochrome c oxidase deficiency as described by DiMauro: neonatal hypotonia and weakness, respiratory failure, and severe lactic acidosis. Post-mortem studies at age 7 weeks showed complex IV reduced in the liver but not in the heart and quantitative analysis of mtDNA showed depletion in muscle. Case 2 showed intractable cardiomyopathy, cyclic neutropenia, and 3-methylglutaconic aciduria. The boy died suddenly at age 27 months. Case 3 presented at age 16 months as an acute hypokinetic hypertrophic cardiomyopathy with transient hypotonia and mild lactic acidosis. After the acute episode the boy gradually improved and the neurological and cardiac examinations were normal at the age of 3 years. All cases showed lipid storage myopathy and decreased cytochrome c oxidase. Biochemical studies confirmed the cytochrome c oxidase deficiency in muscle in all cases. 
COMMENT. Histochemical staining of cytochrome c oxidase may be used for the diagnosis of mitochondrial myopathy when ragged red fibers are lacking. Schon EA et al. and Munnich A et al. review the mitochondrial myopathies and the clinical aspects of mitrochondrial disorders in the current issue of International Pediatrics 1992; 7:23-33. The diagnosis of mitochondrial disorder should be considered with (1) an unexplained association of symptoms; (2) an early onset and a rapidly progressive course; and (3) involvement of unrelated organs which share no common embryologic origin and no common biological functions. Determination of lactate/pyruvate and ketone body molar ratios in plasma may help to select patients at risk for further investigation. In a family with infantile mitrochondrial myopathy and cardiomyopathy reported from Rome, Italy, no correlation was found in the muscle between biochemistry and severity of the clinical intrafamilial phenotype.