Cytochrome C oxidase deficiency in two siblings with Leigh encephalomyelopathy.

Two siblings with cytochrome c oxidase deficiency are described. One of them died of subacute necrotizing encephalomyelopathy which was proven by autopsy. The other was also suspected of having Leigh encephalomyelopathy by the findings on brain CT scans. The former, a younger brother, was in good health until the age of 10 months when progressive dysphagia, muscular hypotonia and abnormal eye movements became apparent. Six months later he suddenly died due to respiratory insufficiency. The latter, an elder brother, started to show nystagmus, abnormal eye movements and ataxia at the age of 5 years. A deficiency of cytochrome c oxidase in the younger brother was demonstrated in autopsied liver and brain, while such a deficiency in the elder brother was shown in biopsied peripheral muscle tissue and in cultured skin fibroblasts. Both patients showed a marked heat lability of cytochrome c oxidase. These results suggest that the biochemical defect observed in the siblings is due to a genetic defect. This seems to be the first case of a generalized defect in cytochrome c oxidase.