Cytochrome-C-oxidase deficiency in muscles of a floppy infant without mitochondrial myopathy

Summary A 4-month-old girl had hypotonia, muscle weakness and cardiomyopathy at birth and died at the age of 8 months from heart failure. Muscle biopsy showed normal muscle fibers, normal mitochondria and type II hypotrophy, in agreement with clinical and neurophysiological signs consistent with a suprasegmental lesion. Cytochrome-C-oxidase was the only respiratory chain enzyme that was profoundly decreased in the patient's muscle, but not in her brain, heart and cultured fibroblasts. We suggest that cytochrome-C-oxidase deficiency in skeletal muscle is not always associated with mitochondrial abnormalities and may not always indicate primary muscle pathology.This work was carried out under a grant of the Muscular Dystrophy Association, USA and research grant CT 81.00146.04 from the Consiglio Nazionale delle Ricerche, Italy