Fatal infantile mitochondrial encephalomyopathy with complex I and IV deficiencies.

A 4-month-old male infant had a fatal infantile mitochondrial disease associated with cardiomyopathy. He had elevated lactate concentrations in blood and cerebrospinal fluid and an increased lactate/pyruvate ratio. Histochemical analysis of muscle biopsy revealed several ragged-red fibers on modified Gomori trichrome stain and mildly decreased cytochrome c oxidase (complex IV) activity. Complex I and IV activities of the respiratory chain in muscle were decreased to about 35% of normal values biochemically; subunits of the two complexes were decreased nonselectively on immunoblotting. Mitochondrial DNA analysis failed to detect any mutation. Complex I and IV deficiencies should be considered as one of the causes of fatal infantile mitochondrial disease.