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COX20
cytochrome c oxidase assembly factor COX20
The COX20 gene provides instructions for a protein critical in the proper assembly and function of cytochrome c oxidase, a vital enzyme within the cell's mitochondria. The COX20 gene encodes the cytochrome c oxidase assembly factor COX20, a protein essential for the biogenesis of mitochondrial complex IV.
COX20 is located on the long (q) arm of chromosome 1, at band 1q44. Arm ratio per GRCh38 - banding schematic.
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Clinical tests that include this
Overview
The COX20 gene is responsible for producing the COX20 protein, which plays a crucial role in the biogenesis of cytochrome c oxidase, also known as mitochondrial complex IV. This complex is a key component of the electron transport chain, a cellular process vital for generating most of the cell's energy in the form of adenosine triphosphate (ATP).
Dysfunction of the COX20 protein can impair the assembly or activity of complex IV, leading to insufficient energy production. This can affect various tissues and organs, particularly those with high energy demands, such as the brain and muscles. Consequently, variants in the COX20 gene are associated with a range of rare inherited conditions, predominantly impacting neurological and metabolic functions.
What the gene does
The COX20 protein acts as a chaperone specifically involved in the assembly pathway of mitochondrial complex IV. Within the mitochondria, complex IV is the final enzyme in the electron transport chain, responsible for transferring electrons to oxygen, leading to the production of water and the generation of a proton gradient that drives ATP synthesis. The assembly of this large, multi-subunit complex is a highly intricate process requiring the coordinated action of numerous assembly factors, including COX20.
COX20 is thought to specifically facilitate the incorporation of subunit I (COXI) into the nascent complex IV. Without adequate COX20 activity, the proper formation of a functional complex IV is compromised, leading to a deficiency in its enzymatic activity. This defect in mitochondrial respiration results in a significant reduction in ATP production, which can have profound effects on cellular metabolism and overall physiological function throughout the body.
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Chromosome location
The COX20 gene is located on chromosome 1, specifically at position 1q44. This designation indicates its precise address on the long arm (q) of chromosome 1, within region 44. The human genome is organised into 23 pairs of chromosomes, with chromosome 1 being the largest.
Protein structure
The COX20 protein consists of 118 amino acids. Domain architecture has not been experimentally characterised in detail for this protein.
Key variants
Genetic variations within the COX20 gene can alter the protein's structure or function, impairing its ability to correctly facilitate the assembly of mitochondrial complex IV. These variants can range from single nucleotide changes to larger deletions or insertions within the gene sequence. The inheritance pattern associated with pathogenic COX20 variants is varied, reflecting the diverse clinical presentations.
Sample of pathogenic variants
5 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.157+3G>C | - | Pathogenic/Likely pathogenic | ★★☆☆ | COX20-related disorders |
c.222G>T | p.Trp74Cys | Pathogenic | ★☆☆☆ | Mitochondrial complex IV deficiency, nuclear type 11 |
c.154A>C | p.Thr52Pro | Pathogenic | - | Mitochondrial complex IV deficiency, nuclear type 11 |
c.157+7A>G | - | Pathogenic | - | Mitochondrial complex IV deficiency, nuclear type 11 |
c.98C>T | p.Ser33Leu | Pathogenic | - | Mitochondrial complex IV deficiency, nuclear type 11 |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the COX20 gene are linked to rare inherited conditions primarily characterised by mitochondrial dysfunction and impaired complex IV activity. These conditions often manifest with neurological symptoms, including ataxia, dystonia, and developmental delay, reflecting the high energy demands of brain tissue. Metabolic abnormalities may also be observed due to systemic energy deficits. The specific symptoms and severity can vary significantly among affected individuals, even within the same family.
No disease links recorded for this gene in our reference set.
UK clinical status
The COX20 gene is included in several NHS Genomic Medicine Service national test panels, reflecting its clinical significance in the UK. It is screened on panels related to Ataxia and cerebellar anomalies, Childhood onset dystonia, chorea or related movement disorder, Hereditary ataxia (both adult and childhood onset), Hereditary neuropathy or pain disorder, Likely inborn error of metabolism, and various Mitochondrial disorders, including Mitochondrial disorder with complex IV deficiency and Possible mitochondrial disorder - nuclear genes. These inclusions highlight its role in diagnosing a range of complex neurological and metabolic conditions.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What happens if there is a variant in the COX20 gene?
Pathogenic variants in the COX20 gene can impair the proper assembly and function of mitochondrial complex IV. This leads to a deficiency in cellular energy production, which can cause a range of symptoms, particularly affecting the brain and muscles, manifesting as neurological and metabolic disorders.
How is a condition related to COX20 diagnosed?
Diagnosis of a COX20-related condition typically involves genetic testing to identify pathogenic variants in the gene. This may be complemented by biochemical tests to assess mitochondrial complex IV activity and clinical evaluation of symptoms, often in specialist clinics.