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Complex V (Adenosine triphosphate (ATP) synthase or ATPase) couples proton flow from the inter-membrane space back to the matrix by the conversion of ADP and inorganic phosphate to ATP. Mitochondrial ATPase is a multisubunit enzyme that catalyzes ATP synthesis during oxidative phosphorylation. The complete loss of the ATP synthase enzyme activity is probably not compatible with life. However, partial loss or complex V deficiency, reflected by a lower amount of functional ATP synthase, causes a medical condition characterized by progressive myopathy, hypertrophic cardiomyopathy, seizures, and severe lactic acidosis. It is often associated with evidence of brainstem degeneration leading to coma. The presence of methyl glutaconic aciduria can be a major clue in the diagnosis of Complex V deficiency in an infant. Only few cases have been described in the literature. The clinical features included craniofacial dysmorphism, micrognathia, and hypospadias. Progressive muscle hypotonia, severe lactic acidosis, hypertrophic cardiomyopathy, and hepatomegaly were also present. Heart failure is reported as the cause of death within the first week of life.

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ATPase Deficiency; TPAF2 Deficiency; ATP Synthase Deficiency.

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The incidence is unknown.

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It has been suggested that a mutation in the encoded assembly gene for the development of ATPase enzyme might be responsible for Complex V deficiency.

Kuwertz-Broking E, Koch HG, Marquardt T, et al: Renal Fanconi syndrome: First sign of partial respiratory chain complex IV deficiency. Pediatr Nephrol 14:495, 2000.  [PubMed: 10872193]
Thyagarajan D, Byrne E; Mitochondrial disorders of the nervous system: Clinical, biochemical, and molecular genetic features. Int Rev Neurobiol 53:93, 2002.  [PubMed: 12512338]

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