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Genetic and Rare Diseases Information Center (GARD)

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Mitochondrial complex IV deficiency

Other Names for this Disease
  • Complex 4 mitochondrial respiratory chain deficiency
  • Complex IV deficiency
  • COX deficiency
  • Cytochrome C oxidase deficiency
  • Deficiency of mitochondrial respiratory chain complex4
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What are the signs and symptoms of cytochrome C oxidase (COX) deficiency?

There are currently 4 known forms of COX deficiency. The range and severity of signs and symptoms can vary widely from case to case.

In one form, referred to as the benign infantile mitochondrial myopathy type, symptoms may be limited to the skeletal muscles. Episodes of lactic acidosis may occur and can cause life-threatening complications if left untreated. However, with appropriate treatment, individuals with this form of the condition may spontaneously recover within the first few years of life.[1]

In the second form of the disorder, referred to as the infantile mitochondrial myopathy type, the skeletal muscles as well as several other tissues (such as the heart, kidney, liver, brain, and/or connective tissue) are affected. Symptoms associated with this form typically begin within the first few weeks of life and may include muscle weakness; heart problems; kidney dysfunction; failure to thrive; difficulties sucking, swallowing, and/or breathing; and/or hypotonia. Affected infants may also have episodes of lactic acidosis.[1]

The third form of COX deficiency is thought to be a systemic form of the condition and is referred to as Leigh's disease. This form is characterized by progressive degeneration of the brain as well as dysfunction of several other organs including the heart, kidneys, muscles, and/or liver. Symptoms of this form, which predominantly involve the central nervous system, may begin between three months and two years of age and may include loss of previously acquired motor skills and/or head control; poor sucking ability; loss of appetite; vomiting; irritability; and possible seizures. Intellectual disability may also occur.[1]

In the fourth form of COX deficiency, the French-Canadian type, the brain (as in Leigh's disease) and liver are particularly affected in addition to the skeletal muscles and connective tissues. However, in this form, the kidneys and heart appear to have near-normal enzyme activity. Individuals with this form may have developmental delay; hypotonia; slight facial abnormalities; Leigh's disease; strabismus; ataxia; liver degeneration; and/or episodes of lactic acidosis.[1]

Although some mildly affected individuals survive into adolescence or adulthood, this condition is often fatal in childhood.[2]
Last updated: 4/22/2013

  1. Cytochrome C Oxidase Deficiency. NORD. January 5, 2012; Accessed 4/17/2013.
  2. Cytochrome c oxidase deficiency. Genetics Home Reference. October 2012; Accessed 4/17/2013.