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Cytochrome C Oxidase Deficiency


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NORD is very grateful to George T Griffing, MD, Professor of Medicine, St Louis University School of Medicine, for assistance in the preparation of this report.

Synonyms of Cytochrome C Oxidase Deficiency

  • complex IV deficiency
  • COX deficiency
  • deficiency of mitochondrial respiratory chain complex IV

Disorder Subdivisions

  • COX deficiency, benign infantile mitochondrial myopathy type
  • COX deficiency French-Canadian type
  • COX deficiency, infantile mitochondrial myopathy type
  • Leigh's syndrome (subacute necrotizing encephalomyelopathy)

General Discussion

Cytochrome C Oxidase deficiency is a very rare inherited metabolic disorder characterized by deficiency of the enzyme cytochrome C oxidase (COX), or Complex IV, an essential enzyme that is active in the subcellular structures that help to regulate energy production (mitochondria). Deficiency of COX may be limited (localized) to the tissues of the skeletal muscles or may affect several tissues, such as the heart, kidney, liver, brain, and/or connective tissue (fibroblasts); in other cases, the COX deficiency may be generalized (systemic).

Four distinct forms of Cytochrome C Oxidase deficiency have been identifed. The first form of this disorder is known as COX deficiency, benign infantile mitochondrial myopathy. Affected infants exhibit many of the same symptoms as those with the more severe infantile form of the disease; however, because the COX deficiency is limited (localized) to tissues of the skeletal muscles, they typically do not have heart or kidney dysfunction.

In the second type of the disease, known as COX deficiency, infantile mitochondrial myopathy, because the COX deficiency affects tissues of the skeletal muscles as well as several other tissues, the disorder may be characterized by a generalized weakness of skeletal muscles (myotonia), abnormalities of the heart and kidneys, and/or abnormally high levels of lactic acid in the blood (lactic acidosis). De Toni-Fanconi-Debre syndrome may also be present and may include excessive thirst, excessive urination, and excessive excretion of glucose, phosphates, amino acids, bicarbonate, calcium and water in the urine.

The third form of COX deficiency, known as Leigh's disease (subacute necrotizing encephalomyelopathy), is thought to be a generalized (systemic) form of COX deficiency. Leigh's disease is characterized by progressive degeneration of the brain and dysfunction of other organs of the body including the heart, kidneys, muscles, and liver. Symptoms may include loss of previously acquired motor skills, loss of appetite, vomiting, irritability, and/or seizure activity. As Leigh's disease progresses, symptoms may also include generalized weakness; loss of muscle tone (hypotonia); and/or episodes of lactic acidosis.

In the fourth form of COX deficiency, known as COX deficiency French-Canadian type, the COX deficiency affects tissues of the skeletal muscles, connective tissue, and, in particular, the brain (Leigh's disease) and the liver. Affected infants and children may demonstrate developmental delays, diminished muscle tone (hypotonia), crossing of the eyes (strabismus), Leigh's disease, and/or episodes of lactic acidosis.

Most cases of COX deficiency are inherited as autosomal recessive genetic diseases. Rarely, COX deficiency occurs as the result of a new or inherited abnormality (mutation) in a mitochondrial gene.

Cytochrome C Oxidase Deficiency Resources

(Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder [e.g., lactic acidosis].)

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at

Other Organizations:

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