Fatal infantile cytochrome C oxidase deficiency

Fatal infantile cytochrome C oxidase deficiency, also known as fatal infantile cardioencephalomyopathy due to cytochrome c oxidase (complex IV) deficiency, is a severe mitochondrial disorder characterized by a profound deficiency of cytochrome c oxidase (COX), the terminal enzyme (complex IV) of the mitochondrial respiratory chain. This enzyme is essential for cellular energy production, and its deficiency leads to devastating multi-system failure, predominantly affecting tissues with high energy demands such as skeletal muscle, heart, and brain. The condition typically presents in the neonatal or early infantile period with severe lactic acidosis, progressive hypertrophic cardiomyopathy, encephalopathy, and profound skeletal myopathy with hypotonia and weakness. Affected infants may also develop respiratory failure, feeding difficulties, and failure to thrive. Muscle biopsy characteristically shows reduced or absent COX activity, and ragged-red fibers may be observed. The clinical course is rapidly progressive, and the prognosis is extremely poor, with most affected infants dying within the first year of life due to cardiorespiratory failure. The disorder is caused by mutations in nuclear genes encoding structural subunits or assembly factors of the cytochrome c oxidase complex, including SCO2, COX10, COX15, and others. Inheritance is autosomal recessive in most cases, though mitochondrial DNA mutations affecting COX subunits can also be responsible. There is currently no curative treatment available. Management is supportive and may include nutritional support, management of lactic acidosis, and palliative care. Cofactor supplementation (such as copper in SCO2-related cases) has been explored but has not demonstrated consistent clinical benefit.

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