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Diseases Studied

The Rare Diseases Clinical Research Network is an NIH-funded research network of 20 active consortia or research groups working to advance treatment for diseases that are rare. Use the search tools on this page to find the diseases we currently study. You can reach out to the indicated consortia or research groups for more information on those diseases and studies underway.

This network focuses on clinical research and does not generally support clinical care outside of research activities. To learn about other rare diseases, please visit the Genetic and Rare Diseases Information Center (GARD), which is an NIH program that helps the public find reliable information about rare and genetic diseases. Their staff are specialists. Contact them at 1-888-205-2311 or email

All Diseases > Complex IV deficiency

Complex IV deficiency

Alternative Names: Mitochondrial Complex IV Deficiency (MC4DN); Complex 4 Mitochondrial Respiratory chain Deficiency; Cytochrome C Oxidase Deficiency (COX Deficiency)

Disease Category: Mitochondrial Disorders

An inherited, multisystemic, mitochondrial disorder characterized by protein complex IV deficiency. Shortage of this protein complex (structure made up of multiple proteins) disrupts the fourth step of oxidative phosphorylation, the process by which mitochondria (specialized cell structures) produce most of the body's energy. Signs include Leigh syndrome, encephalopathy (brain disease), lack of coordination, feeding difficulties, hypotonia (low muscle tone), muscle weakness, seizures, lactic acidosis (high blood lactate levels), intellectual disability, developmental regression (loss of acquired skills), heart disease, and kidney or liver problems.

Research groups studying this disease

Mitochondrial Disorders
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North American Mitochondrial Disease Consortium (NAMDC)

Improves quality of life for people affected by mitochondrial disease through education, outreach, advocacy, and clinical research initiatives.

Promotes research and education for the diagnosis, treatment, and cure of mitochondrial disorders while providing support to those affected.