Cytochromec oxidase deficiency in infancy

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Abstract
Five children with early onset of muscle weakness, lactic acidosis and deficient cytochromec oxidase staining in the muscle biopsy were studied. By oximetric assay of the respiratory chain of isolated mitochondria, cytochromec oxidase deficiency was confirmed in four of the cases, while one case showed only a slight decrease of cytochromec oxidase activity but considerably reduced activity when assayed spectrophotometrically. The muscle biopsies exhibited mitochondrial structural abnormalities and lipid storage in the four cases with oximetrically confirmed cytochromec oxidase deficiency, while the biopsy of the case with markedly reduced activity of cytochromec oxidase only in the enzyme-histochemical and spectrophotometrical assays had normal morphology. The light microscopical staining of cytochromec oxidase in the four cases with oximetrically confirmed deficiency showed deficient staining of the enzyme in all extrafusal fibres in three cases but one of the cases had normal enzyme-histochemical activity of cytochromec oxidase in about 25% of the fibres. In two cases muscle spindles were included in the biopsy. The intrafusal fibres showed normal enzyme-histochemical activity of cytochromec oxidase. Ultrastructural examination of the enzyme distribution in two of the cases revealed great heterogeneity of the mitochondria. The structurally abnormal mitochondria were usually deficient of enzyme activity. The mitochondria of endothelial cells appeared to have normal activity. Immunohistochemical staining with polyclonal antibodies to cytochromec oxidase revealed presence of immunoreactive material corresponding to the localisation of mitochondria in all cases. The results show that enzyme-histochemical staining of cytochromec oxidase is a useful technique to reveal deficiency of the enzyme and to study the distribution of the deficiency within the tissue both at the light microscopical and ultrastructural levels. However, the results of one of the cases show that deficiency revealed by the enzyme-histochemical technique is not completely reliable. Oximetric studies on isolated mitochondria are necessary to confirm the suspected deficiency and to reveal combined defects of the respiratory chain.