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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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Your Question

I am a healthcare provider for a 4-year-old girl with cytochrome C oxidase deficiency. How does this condition manifest? What is the life expectancy for a child with this diagnosis? She continues to gain new skills, but will she at some point show a regression in skills? She is diagnosed as having cortical visual impairment, though she continues to rely on her vision to gain information about her environment. Will she eventually go completely blind?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is cytochrome C oxidase (COX) deficiency?

Cytochrome C oxidase deficiency (COX deficiency) is a condition that can affect several parts of the body including the skeletal muscles, heart, brain and liver. The range and severity of signs and symptoms can vary widely among affected individuals (even within the same family) and depend on the form of the condition present. Features in mildly affected individuals may include muscle weakness and hypotonia; in more severely affected individuals, brain dysfunction; heart problems; an enlarged liver; lactic acidosis; and/or a specific group of features known as Leigh syndrome may also be present. COX deficiency is caused by mutations in any of at least 14 genes; the inheritance pattern depends on the gene involved. The condition is frequently fatal in childhood, but mildly affected individuals may survive into adolescence or adulthood.[1]
Last updated: 4/22/2013

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.[2]

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.[2]

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.[2]

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.[2]

Although some mildly affected individuals survive into adolescence or adulthood, this condition is often fatal in childhood.[1]
Last updated: 4/22/2013

What is the life expectancy for cytochrome C oxidase (COX) deficiency?

There are varying degrees of severity in COX deficiency. Individuals with more severe cases may die during infancy, while those with less severe cases have lived into adulthood.[3] We cannot predict the life expectancy for a particular child.
Last updated: 11/16/2012

Do children with cytochrome C oxidase (COX) deficiency typically lose previously acquired skills?

Loss of skills, also known as developmental regression, can occur in individuals with COX deficiency associated with Leigh disease.[4] Individuals may have developmental delay or mental retardation, but regression is not present in all individuals with this disorder.[3] It is impossible to determine if a particular child will experience future regression.
Last updated: 5/20/2008

Can visual impairment progress to blindness in people with cytochrome C oxidase (COX) deficiency?

Some individuals with COX deficiency develop optic atrophy, which can affect their vision.[3] We cannot comment on whether this particular child will eventually lose her vision.
Last updated: 5/20/2008