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Mappings

MONDO

MONDO:0014668 cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 4

Primary MONDO disease identifier for this COA6 entry.

ICD-10-CM

ICD10CM:E88.49 Other mitochondrial metabolism disorders

ICD-10-CM has no code for COA6-related disease or for nuclear-type Complex IV deficiency. E88.49 is the residual code in the E88.4 mitochondrial metabolism block, so it is a broad rather than exact match. This follows the mapping already used by the sibling COA5 entry.

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Inheritance

1

Autosomal recessive HP:0000007

Biallelic COA6 variants were reported in compound heterozygosity or homozygosity, consistent with autosomal recessive inheritance. The small number of described families does not establish penetrance or a genotype-based severity ranking.

Autosomal recessive inheritance Penetrance: UNKNOWN Expressivity: UNKNOWN

Show evidence (1 reference)

PMID:31851937 SUPPORT DIRECT BACKGROUND Human Clinical

"Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X) (Calvo et al., 2012) and the other with a homozygous missense mutation (W66R) (Baertling et al., 2015)."

Reports biallelic genotypes in two unrelated families.

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Discussions and Knowledge Gaps

3

The disease is named a cardioencephalomyopathy. Is there documented central nervous system involvement in COA6 deficiency?

KNOWLEDGE GAP OPEN coa6_encephalopathy_not_documented

Attached to

phenotypes# pathophysiology#Myocardial Hypertrophic Remodeling

The cited foundational cases support a predominantly cardiac disorder, with hypotonia in one patient. They do not establish a specific encephalopathy phenotype. Sparse clinical ascertainment and infantile death leave the neurological spectrum uncertain; the disease name is not evidence for a particular CNS manifestation.

Does COA6 act purely as a disulfide reductase on the copper relay, or does it also carry copper itself?

OPEN QUESTION OPEN coa6_reductase_versus_metallochaperone

Attached to

pathophysiology#COA6 Reductase Dysfunction pathophysiology#Impaired CuA Metallation of COX2

Purified COA6 can bind copper under selected in-vitro conditions, but direct physiological copper transfer from COA6 to a client protein has not been demonstrated in the studies assessed by the 2022 review. Reductase activity has stronger experimental support. Its electron source, substrate specificity and the identity of the redox-active disulfide remain incompletely resolved.

Show evidence (5 references)

PMID:35053273 SUPPORT DIRECT REVIEW SYNTHESIS Other

"While two decades of studies have provided a clearer picture regarding the biochemical roles of SCO1 and SCO2 proteins, some discrepancy exists regarding the function of COA6, the new member of this pathway."

A critical review of the pathway stating that the question is open, which is the basis for recording it rather than asserting one side.

PMID:35053273 SUPPORT DIRECT REVIEW SYNTHESIS Other

"Its role as a copper metallochaperone has also been proposed."

Names the competing reading directly.

PMID:26160915 SUPPORT DIRECT PRIMARY RESULT In Vitro

"COA6 has the capacity to bind copper"

Direct experimental support for the copper-binding side, from a paper this entry also cites for the reductase-dependent assembly defect.

+ 2 more references

What explains variation in complex I involvement across COA6 patient tissues and experimental cell lines?

OPEN QUESTION OPEN coa6_isolated_versus_combined_complex_deficiency

Attached to

pathophysiology#Cytochrome c Oxidase Deficiency biochemical#Cytochrome c oxidase (Complex IV) activity

The original patient had combined complex I/IV deficiency in heart and normal fibroblast activities, whereas the W66R patient had isolated complex IV deficiency. Engineered human cell studies also differ in complex I involvement. These observations establish heterogeneity; they do not make combined deficiency incompatible with COA6 disease. Genotype, tissue and culture conditions are candidate explanations, but their contributions have not been resolved.

Show evidence (2 references)

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

PMID:32061935 SUPPORT DIRECT PRIMARY RESULT In Vitro

"However, at this point, the question as to how a loss of COA6 affects complex I remain open as no link between copper chaperone activity and complex I biogenesis has been observed."

The 2020 investigators explicitly leave the mechanism of complex I involvement unresolved.

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Pathophysiology

7

COA6 Reductase Dysfunction

Disease-associated COA6 variants impair protein abundance or function. Biochemical studies support a role for COA6 in reducing copper-coordinating cysteines of SCO1, SCO2 and COX2. Patient-derived fibroblasts showed a shift toward oxidized SCO1, whereas SCO2 oxidation differed between those cells and an engineered knockout model. W59C retains partial function in human complementation assays. A physiological copper-carrier role remains debated.

COA6 hgnc:18025

mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED

protein-disulfide reductase activity GO:0015035 ↓ DECREASED

mitochondrial intermembrane space GO:0005758

Downstream

Impaired CuA Metallation of COX2 Reduced availability of appropriately reduced copper-coordinating cysteines compromises CuA biogenesis.

Show evidence (4 references)

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT In Vitro

"we have solved the solution structure of COA6, which reveals a coiled-coil-helix-coiled-coil-helix domain typical of redox-active proteins found in the mitochondrial inter-membrane space"

Establishes the redox-active CHCH fold and intermembrane-space character that define this node's molecular lesion.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT In Vitro

"we demonstrate that COA6 can reduce the copper-coordinating disulfides of its client proteins, SCO1 and COX2, allowing for copper binding"

States the specific catalytic activity lost in this disorder, and names the two client proteins whose cysteines go unreduced.

PMID:32061935 SUPPORT DIRECT PRIMARY RESULT In Vitro

"We demonstrate that COA6 acts as a thiol-reductase to reduce disulfide bridges of critical cysteine residues in SCO1 and SCO2."

Independent confirmation of the thiol-reductase assignment, adding SCO2 to the client set.

+ 1 more reference

Impaired CuA Metallation of COX2

COA6 dysfunction compromises maturation of the binuclear CuA centre of COX2. COA6 interacts with newly synthesized COX2 and copper-delivery proteins. Reconstitution studies support transfer of Cu(I) from SCO1 to reduced COX2; the degree of failed metallation has not been directly quantified in the reported patient myocardium.

copper ion binding GO:0005507 ↓ DECREASED

Downstream

COX2 Destabilization Defective maturation is associated with reduced COX2 stability in experimental systems; the kinetics vary with the model and assay.

Show evidence (3 references)

PMID:25959673 SUPPORT DIRECT PRIMARY RESULT In Vitro

"COA6 interacts transiently with the copper-containing catalytic domain of newly synthesized COX2."

Places COA6 physically at the COX2 copper domain, which is the site this node describes.

PMID:25959673 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Our analyses define COA6 as a constituent of the mitochondrial copper relay system, linking defects in COX2 metallation to cardiac cytochrome c oxidase deficiency."

Connects failed COX2 metallation to the cardiac COX deficiency that this entry's downstream nodes describe.

PMID:26160915 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Our data reveal that COA6 is intricately involved in the copper-dependent biogenesis of COX2."

Independent statement that COX2 biogenesis is copper-dependent and COA6-dependent.

COX2 Destabilization

COA6 loss compromises the stability of newly synthesized COX2 in yeast. Patient fibroblast experiments also identify abnormal turnover of mitochondrially encoded complex IV subunits. Pulse-chase profiles differ between studies, so reduced COX2 abundance should not be equated with a single universal degradation rate or with a primary translation defect.

mitochondrial respiratory chain complex IV GO:0045277

Downstream

Complex IV Assembly Arrest Loss of mature COX2 limits its incorporation into the assembled enzyme.

Show evidence (2 references)

PMID:25959673 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Absence of COA6 leads to fast turnover of newly synthesized COX2 and a concomitant reduction in cytochrome c oxidase levels."

The source full text identifies the turnover experiment as coa6-null yeast.

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Using pulse-chase experiments, we demonstrate an increased turnover of mitochondrial encoded complex IV subunits."

Abnormal subunit turnover in cultured patient fibroblasts.

Complex IV Assembly Arrest

COA6 deficiency reduces assembly of mature complex IV and permits accumulation of COX1-containing assembly intermediates. In the W66R patient fibroblasts, monomeric complex IV was decreased while the measured CI/CIII2/CIVn supercomplexes were preserved; the assembly phenotype is therefore not uniform across all enzyme pools.

mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED

Experimental models

W66R patient-derived fibroblasts PRIMARY CELL CULTURE Patient cells carry the causative genotype and directly display the accumulated COX1 intermediate and accelerated subunit turnover.

Animal models

coa6-deleted budding yeast Saccharomyces cerevisiae partially recapitulates Respiratory growth, Cox2 abundance and assembled CcO provide measurable consequences of coa6 loss.

Downstream

Cytochrome c Oxidase Deficiency Reduced mature enzyme abundance limits complex IV activity.

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"The monomeric COX1 assembly intermediate accumulates."

Patient fibroblasts accumulate an early assembly intermediate.

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Although monomeric complex IV is decreased in patient fibroblasts, the CI/CIII2 /CIVn -supercomplexes remain unaffected."

The same culture experiments distinguish monomeric complex IV from supercomplex-associated pools.

Cytochrome c Oxidase Deficiency

Reduced cytochrome c oxidase activity limits terminal electron transfer and coupled oxidative phosphorylation. Both isolated complex IV deficiency and combined complex I/IV deficiency occur among the foundational clinical reports. The original compound-heterozygous patient had cardiac enzyme defects despite normal fibroblast assays; the W66R patient had a fibroblast complex IV defect.

mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED oxidative phosphorylation GO:0006119 ↓ DECREASED

cytochrome-c oxidase activity GO:0004129 ↓ DECREASED

Experimental models

COA6 knockout human cell line CELL LINE Engineered human cells demonstrate complex IV deficiency after COA6 loss. Additional complex I involvement and protein-import consequences depend on the model.

Downstream

Systemic Lactate Accumulation Respiratory dysfunction provides a plausible route to systemic lactate accumulation; tissue-specific metabolic flux was not measured in the clinical reports.

Hypotonia Hypotonia accompanies the biochemical disorder in the W66R patient, but its neural versus muscular origin and intervening mechanism have not been established.

Myocardial Hypertrophic Remodeling Cardiac respiratory-chain deficiency accompanies hypertrophic cardiomyopathy; the intervening remodeling mechanisms remain incompletely defined.

Decreased activity of mitochondrial complex IV

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

Myocardial Hypertrophic Remodeling

Hypertrophic cardiomyopathy is the dominant cardiac manifestation in the foundational COA6 reports. Respiratory-chain defects measured in affected heart support an association with myocardial bioenergetic dysfunction, but do not directly measure the sequence from ATP deficit to hypertrophic remodeling.

cardiac muscle cell CL:0000746

myocardium UBERON:0002349

Animal models

coa6 morphant zebrafish Zebrafish partially recapitulates Demonstrates cardiac dysfunction after coa6 knockdown, with a developmental phenotype that only partially models human hypertrophic remodeling.

Downstream

Hypertrophic cardiomyopathy

Show evidence (1 reference)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

Systemic Lactate Accumulation

Lactic acidosis was reported in the W66R patient. Impaired oxidative metabolism is a plausible explanation, but the clinical observation does not directly demonstrate increased glycolytic flux or identify the tissue producing excess lactate.

Downstream

Lactic acidosis

Show evidence (1 reference)

PMID:31515291 SUPPORT DIRECT BACKGROUND Human Clinical

"An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts"

Summarizes the W66R clinical report; this is background clinical evidence.

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Pathograph

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Phenotypes

4

Cardiovascular 1

Hypertrophic cardiomyopathy HP:0001639

Onset: NEONATAL

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

Metabolism 1

Lactic acidosis HP:0003128

Show evidence (1 reference)

PMID:31515291 SUPPORT DIRECT BACKGROUND Human Clinical

"An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts"

Summarizes the W66R clinical report; this is background clinical evidence.

Musculoskeletal 1

Hypotonia HP:0001252

Show evidence (1 reference)

PMID:31515291 SUPPORT DIRECT BACKGROUND Human Clinical

"An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts"

Summarizes the W66R clinical report; this is background clinical evidence.

Cellular 1

Decreased activity of mitochondrial complex IV HP:0008347

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

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Genetic Associations

1

COA6

Gene: COA6 hgnc:18025 relationship_type: CAUSATIVE

Show evidence (5 references)

PMID:24549041 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Using yeast coa6Δ cells, we show that conserved residues in the motif, including the residue mutated in a patient with mitochondrial disease, are essential for COA6 function, thus confirming the pathogenicity of the patient mutation."

Functional confirmation of variant pathogenicity by yeast complementation, which is the evidence that makes this gene causal rather than candidate.

PMID:26669719 SUPPORT DIRECT PRIMARY RESULT Model Organism

"we show that patient mutations in Coa6 disrupt Coa6-Cox2 interaction, providing the biochemical basis for disease pathogenesis"

Gives the biochemical mechanism by which the patient alleles are pathogenic - loss of the COA6-COX2 interaction - rather than only that they fail to complement in yeast.

PMID:31515291 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Disulfide-mediated oligomerization of the W59CCoa6 protein provides a structural explanation for the loss-of-function mutation."

A crystal structure of a patient allele, explaining at the protein level why the variant is loss-of-function.

+ 2 more references

Variants (3)

W59C Pathogenic

Gene: COA6 hgnc:18025 missense variant

W59C is a missense allele reported in compound heterozygosity with E87*. Expression partially restored CcO activity and COX2 levels in human complementation assays, whereas chimeric yeast experiments did not restore respiratory growth. The purified mutant forms disulfide-linked oligomers. Matrix mislocalization was reported in transfected U2OS cells, while other models retain intermembrane-space localization; these observations should not be generalized to every patient tissue.

Show evidence (4 references)

PMID:31851937 SUPPORT DIRECT BACKGROUND Human Clinical

"Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X)"

Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result in this mechanistic study.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT In Vitro

"expression of the W59C mutant leads to a partial recovery of CcO activity and COX2 levels"

Partial recovery demonstrates residual function in this human cell assay; it does not rank clinical severity.

PMID:31515291 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Disulfide-mediated oligomerization of the W59CCoa6 protein provides a structural explanation for the loss-of-function mutation."

The structural basis of loss of function for this specific allele.

+ 1 more reference

E87* Pathogenic

Gene: COA6 hgnc:18025 nonsense variant

Nonsense variant carried in compound heterozygosity with W59C in the same patient. Written E87X in one of the cited sources; the entry uses each source's own notation inside the sentence it quotes.

Show evidence (2 references)

PMID:31851937 SUPPORT DIRECT BACKGROUND Human Clinical

"one with compound heterozygous mutations (W59C and E87X)"

Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result in this mechanistic study.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT Computational

"The truncation mutation (E87X) clearly disrupts the CHCH domain by removing a large portion of the protein from helix 2 onward (Figures 2A and 2B)."

Mapping the patient truncation onto the experimentally determined protein structure predicts loss of a substantial part of the CHCH fold.

W66R Pathogenic

Gene: COA6 hgnc:18025 missense variant

Homozygous W66R was reported in the patient with neonatal hypertrophic cardiomyopathy, hypotonia and lactic acidosis. COA6 protein was undetectable in the original fibroblast study, and W66R failed to rescue CcO activity in later overexpression experiments.

Show evidence (2 references)

PMID:31851937 SUPPORT DIRECT BACKGROUND Human Clinical

"the other with a homozygous missense mutation (W66R)"

Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result in this mechanistic study.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT In Vitro

"we overexpressed the wild-type (WT) and mutant alleles of COA6 in control and COA6 patient fibroblasts and found that the W66R variant fails to rescue CcO activity"

Failure to rescue in this assay contrasts with partial W59C complementation, without establishing an all-allele clinical severity ranking.

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Medical Actions

4

Copper Supplementation

Action: Pharmacotherapy NCIT:C15986

Agent: copper CHEBI:28694

Platform: Small molecule

Copper supplementation is an experimental lead supported by complete rescue of respiratory and assembly defects in coa6-null yeast and partial rescue of complex IV deficiency in patient fibroblasts. These experiments do not establish clinical efficacy or an appropriate regimen for people with COA6 deficiency.

Mechanism Target:

MODULATES Cytochrome c Oxidase Deficiency — Partially improves the complex IV deficit in cultured patient fibroblasts; restoration of CuA metallation was not directly quantified.

Show evidence (1 reference)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Copper supplementation shows a partial rescue of complex IV deficiency in patient fibroblasts."

Partial recovery in cultured patient cells; no clinical treatment outcome is established.

Show evidence (2 references)

PMID:24549041 SUPPORT DIRECT PRIMARY RESULT Model Organism

"we show that exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells"

The yeast result. Complete rescue here, in contrast with the partial rescue reported in patient fibroblasts.

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Copper supplementation shows a partial rescue of complex IV deficiency in patient fibroblasts."

Partial recovery in cultured patient cells; no clinical treatment outcome is established.

Elesclomol (experimental)

Action: Experimental elesclomol pharmacotherapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: elesclomol CHEBI:79369

Platform: Small molecule

Elesclomol restored mitochondrial copper, respiration and CcO activity in coa6-deficient yeast, including yeast expressing pathogenic human-yeast COA6 chimeras. It also reduced pericardial edema and improved heart rate in COA6 morphant zebrafish. This is preclinical evidence: the mammalian patient fibroblasts in the same study carried SCO2 variants, not COA6 variants. Toxicity depended on experimental conditions; combined elesclomol and copper at 100 nM each was lethal in zebrafish.

Mechanism Target:

RESTORES Cytochrome c Oxidase Deficiency — Restored CcO activity in coa6-deficient yeast; this relationship is restricted to that experimental model.

Show evidence (1 reference)

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity."

Direct COA6 yeast rescue result; human efficacy is untested in this study.

Show evidence (3 references)

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity."

Direct COA6 yeast rescue result; human efficacy is untested in this study.

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Indeed, 100 nM ES treatment prevented pericardial edema and significantly increased the heart rate of Coa6-knockdown zebrafish embryos at 72 and 96 hpf without altering the heart rate of control embryos (SI Appendix, Fig. S8 E and F)."

COA6 morphant fish showed functional and morphological rescue.

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Consistent with the mechanism of action of ES, we observed that cosupplementation of 100 nM ES with 100 nM of copper resulted in 100% lethality (SI Appendix, Fig. S8B)."

The experimental zebrafish combination was lethal; efficacy at one dose does not establish safety of copper coadministration.

Supportive and Palliative Care

Action: Supportive Care NCIT:C15747

Platform: Other

Cardiac and metabolic support are general management considerations for severe mitochondrial cardiomyopathy. The cited COA6 reports do not establish an evidence-based disease-specific supportive or palliative protocol.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Platform: Other

For parents who each carry a pathogenic COA6 allele, standard autosomal recessive inheritance gives a 25 percent probability of a child inheriting both alleles in each pregnancy. Identification of familial variants permits discussion of carrier and reproductive testing.

Show evidence (1 reference)

PMID:31851937 SUPPORT INDIRECT BACKGROUND Human Clinical

"Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X) (Calvo et al., 2012) and the other with a homozygous missense mutation (W66R) (Baertling et al., 2015)."

Biallelic genotypes support the inheritance model underlying counseling; the quoted study does not itself measure recurrence or test prenatal diagnosis.

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Biochemical Markers

2

Cytochrome c oxidase (Complex IV) activity (DECREASED)

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

Complex IV subunit abundance (DECREASED)

Show evidence (1 reference)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"COA6 protein is undetectable and steady-state levels of complex IV and several of its subunits are reduced."

Reduced abundance in cultured fibroblasts from the W66R patient.

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Diagnosis

2

Molecular genetic testing and allele phasing

Identification of biallelic COA6 variants supports the molecular diagnosis in a compatible cardiac and biochemical presentation. The original discovery used targeted mitochondrial-gene sequencing, followed by Sanger confirmation and phasing of C1orf31 variants using cloned DNA. A particular trio or whole-exome workflow is not a required diagnostic criterion.

Genetic Testing NCIT:C15709

Show evidence (2 references)

PMID:22277967 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We performed "MitoExome" sequencing of the mitochondrial DNA (mtDNA) and exons of ~1000 nuclear genes encoding mitochondrial proteins and prioritized rare mutations predicted to disrupt function."

Describes the discovery sequencing method for the cohort containing the original COA6/C1orf31 case.

PMID:22277967 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"All prioritized variants detected in patients were independently validated by Sanger sequencing (48/49 variants validated), and compound heterozygous variants were phased through sequencing cDNA (GFM1), cloned DNA (BCS1L, C1orf31, TYMP, MTHFD1L), familial DNA (GFM1, AGK, EARS2), or by a..."

Specifically identifies cloned-DNA phasing for C1orf31 in the discovery study.

Respiratory-chain enzymology and assembly studies

Complex IV activity and assembly studies support biochemical characterization. Isolated IV deficiency is not mandatory, because combined I/IV deficiency was present in the original cardiac sample. Normal fibroblast assays did not exclude disease in that family. Pulse-chase and assembly-intermediate studies are research characterization, not universal diagnostic requirements.

Show evidence (2 references)

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

PMID:26160915 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Here, we demonstrate that the complex IV defect correlates with a severe loss in complex IV assembly in patient heart but not fibroblasts."

Direct tissue-versus-culture comparison showing why a normal fibroblast result cannot exclude the reported genotype.

📈

Progression

2

Infantile cardiac presentation

Age: Neonatal period or infancy

The W66R patient presented with neonatal hypertrophic cardiomyopathy. The original sequencing cohort records onset before one year for the compound-heterozygous patient; a uniform onset within the first days of life is not established.

Show evidence (2 references)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency."

Clinical presentation of the second reported patient.

PMID:22277967 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"| P31 | M | <1yr | hypertrophic cardiomyopathy | | hea fib | ↓↓ nl | | | ↓↓ nl | nd | C1orf31 |"

Table 1 records onset before one year, heart complex I/IV deficiency, and normal fibroblast activities in P31.

Fatal cardiac disease

Age: Infancy in the foundational reports

The original patient died before one year of age. These sparse reports do not establish a uniform time from birth to decompensation or the outcome of every possible COA6 genotype.

Show evidence (2 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4049311/ SUPPORT DIRECT BACKGROUND Human Clinical

"The patient died of hypertrophic cardiomyopathy at a young age (<1 year old) and his heart tissue exhibited a reduction in CcO enzyme activity"

Reports infantile cardiac death in the original compound-heterozygous patient.

PMID:32061935 SUPPORT DIRECT BACKGROUND Human Clinical

"Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity"

The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.

🧫

Experimental Models

2

W66R patient-derived fibroblasts PRIMARY_CELL_CULTURE

Fibroblasts from the homozygous W66R patient show absent detectable COA6, reduced complex IV, abnormal subunit turnover and accumulation of a COX1 intermediate. Copper produced partial rescue. Later complementation and redox work used immortalized derivatives, so culture context matters.

Pathograph links

Complex IV Assembly Arrest recapitulates fidelity: high observes: cellular Patient cells carry the causative genotype and directly display the accumulated COX1 intermediate and accelerated subunit turnover.

Limitations: This genotype shows a fibroblast defect, whereas the original W59C/E87* family had normal fibroblast enzyme assays despite affected heart tissue. The culture system does not establish cardiac severity.

Show evidence (1 reference)

PMID:25339201 SUPPORT DIRECT PRIMARY RESULT In Vitro

"For the first time, clinical details about a COA6-deficient patient are given and patient fibroblasts are functionally characterized"

Establishes patient fibroblasts as the characterized human cellular model.

COA6 knockout human cell line CELL_LINE

Engineered COA6-null HEK293T lines test complete loss of the protein. The 2015 study reported a prominent complex IV defect; the 2020 line had combined I/IV deficiency, reduced membrane potential and impaired potential-dependent protein import. These lines should not be assumed to have identical downstream phenotypes.

Pathograph links

Cytochrome c Oxidase Deficiency partially recapitulates fidelity: moderate observes: cellular Engineered human cells demonstrate complex IV deficiency after COA6 loss. Additional complex I involvement and protein-import consequences depend on the model.

Limitations: The kidney-derived transformed line does not model cardiac tissue. Engineered null alleles differ from the reported missense/truncating combinations, and residual protein or function is allele-dependent.

Divergences from the human mechanism

cause unrepresented qualifying

Engineered gene deletion does not recreate the specific biallelic patient variants or their allele-dependent residual function.

Show evidence (3 references)

PMID:26160915 SUPPORT DIRECT PRIMARY RESULT In Vitro

"Complete loss of COA6 activity using gene editing in HEK293T cells resulted in a profound growth defect due to complex IV deficiency"

Establishes the knockout line and its Complex IV growth phenotype.

PMID:32061935 SUPPORT DIRECT PRIMARY RESULT In Vitro

"In summary, in the absence of COA6, the import routes that depend on the inner membrane potential are affected. However, the membrane potential independent import into the intermembrane space via MIA40 was not reduced but rather stimulated."

The 2020 knockout distinguishes potential-dependent import defects from preserved or increased MIA40 import.

PMID:32061935 SUPPORT DIRECT PRIMARY RESULT In Vitro

"However, an increase in ROS production was not apparent in mutant cells, nor did we detect alterations in the mitochondrial glutathione redox potential."

Limits interpretation of the knockout phenotype: generalized oxidative stress was not established.

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Animal Models

2

coa6 morphant zebrafish

Transient coa6 morpholino knockdown produces reduced heart rate, failed cardiac looping, thin-walled enlarged chambers and pericardial edema. These developmental cardiac findings are not equivalent to measured human myocardial hypertrophy. Elesclomol improved edema and heart rate in this model.

Species

Zebrafish

Genotype

zfcoa6 morpholino knockdown

Publication

PMID:24549041

Pathograph links

Myocardial Hypertrophic Remodeling partially recapitulates fidelity: moderate observes: organism Demonstrates cardiac dysfunction after coa6 knockdown, with a developmental phenotype that only partially models human hypertrophic remodeling.

Limitations: Transient morpholino knockdown rather than a stable genetic mutant, so off-target and incomplete-knockdown effects cannot be excluded and only embryonic stages are assessed. The readouts are heart rate and gross cardiac development, not the hypertrophic remodelling of the human phenotype, so the match is to cardiac involvement rather than to hypertrophic cardiomyopathy specifically.

Divergences from the human mechanism

proxy quantity qualifying

The model's measured quantities are embryonic heart rate and gross cardiac morphogenesis. The node's quantity is hypertrophic remodelling of a formed neonatal myocardium. These are different cardiac readouts at different developmental stages.

Show evidence (1 reference)

PMID:24549041 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Furthermore, we show that zebrafish embryos with zfcoa6 knockdown display reduced heart rate and cardiac developmental defects, recapitulating the observed pathology in the human mitochondrial disease patient who died of neonatal hypertrophic cardiomyopathy."

Reports vertebrate cardiac defects after coa6 knockdown; the human death clause is background.

Show evidence (2 references)

PMID:24549041 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Furthermore, we show that zebrafish embryos with zfcoa6 knockdown display reduced heart rate and cardiac developmental defects, recapitulating the observed pathology in the human mitochondrial disease patient who died of neonatal hypertrophic cardiomyopathy."

Reports vertebrate cardiac defects after coa6 knockdown; the human death clause is background.

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Indeed, 100 nM ES treatment prevented pericardial edema and significantly increased the heart rate of Coa6-knockdown zebrafish embryos at 72 and 96 hpf without altering the heart rate of control embryos (SI Appendix, Fig. S8 E and F)."

COA6 morphant fish showed functional and morphological rescue.

coa6-deleted budding yeast

Deletion causes respiratory growth and CcO assembly defects. Copper and elesclomol rescue these defects under tested conditions. Hypoxia and reduced glutathione also suppress the growth phenotype, supporting a redox role. Loss of Sco2 or Cox12 in addition to Coa6 prevents copper rescue. Lowering cytochrome c improved Cox2 accumulation and complex IV assembly in a 2026 study; the proposed coordination of cofactor maturation remains a model-level hypothesis.

Species

Saccharomyces cerevisiae

Genotype

coa6Δ

Publication

PMID:24549041

Pathograph links

Complex IV Assembly Arrest partially recapitulates fidelity: moderate observes: cellular Respiratory growth, Cox2 abundance and assembled CcO provide measurable consequences of coa6 loss.

Limitations: Yeast lacks human cardiac tissue and does not model the clinical course. Null strains and chimeric overexpression assays do not reproduce a complete human biallelic genotype in its native tissue.

Show evidence (1 reference)

PMID:30038027 SUPPORT DIRECT PRIMARY RESULT Model Organism

"By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity."

Direct COA6 yeast rescue result; human efficacy is untested in this study.

Show evidence (5 references)

PMID:24549041 SUPPORT DIRECT PRIMARY RESULT Model Organism

"we show that exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells"

The yeast result. Complete rescue here, in contrast with the partial rescue reported in patient fibroblasts.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT Model Organism

"The respiratory growth of coa6Δ was almost fully rescued in hypoxic yeast, while that of yeast strains lacking proteins with established Cu metallochaperone activity (sco1Δ, cox17Δ, and cox11Δ) was not (Figure 5E)."

Hypoxic suppression is a mechanistic experiment, not a human treatment result.

PMID:31851937 SUPPORT DIRECT PRIMARY RESULT Model Organism

"Moreover, exogenous supplementation of a normoxic culture with reduced glutathione (GSH) also partially rescued respiratory growth of coa6Δ cells (Figure 5G), further supporting a redox role for Coa6 in the Cu delivery process."

Reducing conditions partially bypass the growth defect in yeast.

+ 2 more references

{ }

Source YAML

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name: COA6-Related Fatal Infantile Cardioencephalomyopathy
category: Mendelian
creation_date: "2026-09-10T00:00:00Z"
synonyms:
- Cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 4
- CEMCOX4
- Mitochondrial complex IV deficiency, nuclear type 13
- MC4DN13
- COA6 deficiency
description: >-
  COA6-related fatal infantile cardioencephalomyopathy (CEMCOX4 / MC4DN13) is an autosomal recessive mitochondrial
  disorder caused by biallelic COA6 variants. COA6 is an intermembrane-space assembly factor with experimentally
  demonstrated thiol-disulfide reductase activity that supports formation of the copper-containing CuA centre of
  COX2. Impaired COA6 function compromises COX2 maturation and cytochrome c oxidase assembly. The two foundational
  clinical reports describe severe hypertrophic cardiomyopathy with either combined complex I/IV deficiency or isolated
  complex IV deficiency; muscular hypotonia and lactic acidosis were reported in the W66R patient. The original
  compound-heterozygous patient died before one year of age. Residual function and tissue-specific biochemical findings
  vary, and the disease name alone does not establish encephalopathy. Copper binding by COA6 has been demonstrated
  in vitro, but its physiological role as a metallochaperone remains unresolved.
disease_term:
  preferred_term: COA6-related fatal infantile cardioencephalomyopathy (CEMCOX4/MC4DN13)
  term:
    id: MONDO:0014668
    label: cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 4
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0014668
      label: cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 4
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: Primary MONDO disease identifier for this COA6 entry.
  icd10cm_mappings:
  - term:
      id: ICD10CM:E88.49
      label: Other mitochondrial metabolism disorders
    mapping_predicate: skos:broadMatch
    mapping_source: ICD-10-CM
    mapping_justification: >-
      ICD-10-CM has no code for COA6-related disease or for nuclear-type Complex
      IV deficiency. E88.49 is the residual code in the E88.4 mitochondrial
      metabolism block, so it is a broad rather than exact match. This follows
      the mapping already used by the sibling COA5 entry.
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  penetrance: UNKNOWN
  expressivity: UNKNOWN
  description: >-
    Biallelic COA6 variants were reported in compound heterozygosity or homozygosity, consistent with autosomal
    recessive inheritance. The small number of described families does not establish penetrance or a genotype-based
    severity ranking.
  evidence:
  - reference: PMID:31851937
    reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X) (Calvo et al., 2012) and the other with a homozygous missense mutation (W66R) (Baertling et al., 2015).'
    explanation: Reports biallelic genotypes in two unrelated families.
    quote_role: BACKGROUND
    directness: DIRECT
progression:
- phase: Infantile cardiac presentation
  age_range: Neonatal period or infancy
  notes: The W66R patient presented with neonatal hypertrophic cardiomyopathy. The original sequencing cohort records onset before one year for the compound-heterozygous patient; a uniform onset within the first days of life is not established.
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:22277967
    reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: '| P31 | M | <1yr | hypertrophic cardiomyopathy |  | hea fib | ↓↓ nl |  |  | ↓↓ nl | nd | C1orf31 |'
    explanation: Table 1 records onset before one year, heart complex I/IV deficiency, and normal fibroblast activities in P31.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- phase: Fatal cardiac disease
  age_range: Infancy in the foundational reports
  notes: The original patient died before one year of age. These sparse reports do not establish a uniform time from birth to decompensation or the outcome of every possible COA6 genotype.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4049311/
    reference_title: Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The patient died of hypertrophic cardiomyopathy at a young age (&lt;1 year old) and his heart tissue exhibited a reduction in CcO enzyme activity
    explanation: Reports infantile cardiac death in the original compound-heterozygous patient.
    quote_role: BACKGROUND
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
pathophysiology:
- name: COA6 Reductase Dysfunction
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  biological_scale: MOLECULAR
  description: >-
    Disease-associated COA6 variants impair protein abundance or function. Biochemical studies support a role for
    COA6 in reducing copper-coordinating cysteines of SCO1, SCO2 and COX2. Patient-derived fibroblasts showed a
    shift toward oxidized SCO1, whereas SCO2 oxidation differed between those cells and an engineered knockout model.
    W59C retains partial function in human complementation assays. A physiological copper-carrier role remains debated.
  genes:
  - preferred_term: COA6
    term:
      id: hgnc:18025
      label: COA6
  cellular_components:
  - preferred_term: mitochondrial intermembrane space
    term:
      id: GO:0005758
      label: mitochondrial intermembrane space
  molecular_functions:
  - preferred_term: protein-disulfide reductase activity
    modifier: DECREASED
    term:
      id: GO:0015035
      label: protein-disulfide reductase activity
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
  evidence:
  - reference: PMID:31851937
    reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we have solved the solution structure of COA6, which reveals a coiled-coil-helix-coiled-coil-helix domain typical of redox-active proteins found in the mitochondrial inter-membrane space"
    explanation: >-
      Establishes the redox-active CHCH fold and intermembrane-space character
      that define this node's molecular lesion.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31851937
    reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we demonstrate that COA6 can reduce the copper-coordinating disulfides of its client proteins, SCO1 and COX2, allowing for copper binding"
    explanation: >-
      States the specific catalytic activity lost in this disorder, and names the
      two client proteins whose cysteines go unreduced.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: "COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We demonstrate that COA6 acts as a thiol-reductase to reduce disulfide bridges of critical cysteine residues in SCO1 and SCO2."
    explanation: >-
      Independent confirmation of the thiol-reductase assignment, adding SCO2 to
      the client set.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31851937
    reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Strikingly, mutations in COA6 significantly skew the relative ratio of reduced to oxidized cysteinyl sulfurs of SCO1, with the oxidized species predominating (Figure 6F).
    explanation: The redox defect is measured in COA6 patient-derived fibroblasts.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Impaired CuA Metallation of COX2
    causal_link_type: DIRECT
    description: >-
      Reduced availability of appropriately reduced copper-coordinating cysteines compromises CuA biogenesis.
    evidence:
    - reference: PMID:32061935
      reference_title: "COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Our analyses define COA6 as thiol-reductase, which is essential for CuA biogenesis."
      explanation: Asserts the causal step from COA6 reductase activity to CuA centre formation.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
- name: Impaired CuA Metallation of COX2
  biological_scale: MOLECULAR
  description: >-
    COA6 dysfunction compromises maturation of the binuclear CuA centre of COX2. COA6 interacts with newly synthesized
    COX2 and copper-delivery proteins. Reconstitution studies support transfer of Cu(I) from SCO1 to reduced COX2;
    the degree of failed metallation has not been directly quantified in the reported patient myocardium.
  molecular_functions:
  - preferred_term: copper ion binding
    modifier: DECREASED
    term:
      id: GO:0005507
      label: copper ion binding
  evidence:
  - reference: PMID:25959673
    reference_title: "Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "COA6 interacts transiently with the copper-containing catalytic domain of newly synthesized COX2."
    explanation: Places COA6 physically at the COX2 copper domain, which is the site this node describes.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:25959673
    reference_title: "Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our analyses define COA6 as a constituent of the mitochondrial copper relay system, linking defects in COX2 metallation to cardiac cytochrome c oxidase deficiency."
    explanation: >-
      Connects failed COX2 metallation to the cardiac COX deficiency that this
      entry's downstream nodes describe.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:26160915
    reference_title: "COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our data reveal that COA6 is intricately involved in the copper-dependent biogenesis of COX2."
    explanation: Independent statement that COX2 biogenesis is copper-dependent and COA6-dependent.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: COX2 Destabilization
    causal_link_type: DIRECT
    description: >-
      Defective maturation is associated with reduced COX2 stability in experimental systems; the kinetics vary
      with the model and assay.
    evidence:
    - reference: PMID:25959673
      reference_title: "Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Absence of COA6 leads to fast turnover of newly synthesized COX2 and a concomitant reduction in cytochrome c oxidase levels."
      explanation: The 2015 full text measures rapid turnover of newly synthesized Cox2 in coa6-deleted yeast. It supports this mechanism without establishing identical turnover kinetics in every patient cell line.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  chemical_entities:
  - preferred_term: copper(1+)
    term:
      id: CHEBI:49552
      label: copper(1+)
- name: COX2 Destabilization
  biological_scale: CELLULAR
  description: >-
    COA6 loss compromises the stability of newly synthesized COX2 in yeast. Patient fibroblast experiments also
    identify abnormal turnover of mitochondrially encoded complex IV subunits. Pulse-chase profiles differ between
    studies, so reduced COX2 abundance should not be equated with a single universal degradation rate or with a
    primary translation defect.
  cellular_components:
  - preferred_term: mitochondrial respiratory chain complex IV
    term:
      id: GO:0045277
      label: respiratory chain complex IV
  evidence:
  - reference: PMID:25959673
    reference_title: Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Absence of COA6 leads to fast turnover of newly synthesized COX2 and a concomitant reduction in cytochrome c oxidase levels.
    explanation: The source full text identifies the turnover experiment as coa6-null yeast.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Using pulse-chase experiments, we demonstrate an increased turnover of mitochondrial encoded complex IV subunits.
    explanation: Abnormal subunit turnover in cultured patient fibroblasts.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Complex IV Assembly Arrest
    causal_link_type: DIRECT
    description: Loss of mature COX2 limits its incorporation into the assembled enzyme.
    evidence:
    - reference: PMID:26160915
      reference_title: COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: caused by impaired biogenesis of the copper-bound mitochondrial DNA-encoded subunit COX2 and subsequent accumulation of complex IV assembly intermediates
      explanation: Gene-edited human cells connect impaired COX2 biogenesis to accumulation of assembly intermediates.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
- name: Complex IV Assembly Arrest
  biological_scale: CELLULAR
  description: >-
    COA6 deficiency reduces assembly of mature complex IV and permits accumulation of COX1-containing assembly intermediates.
    In the W66R patient fibroblasts, monomeric complex IV was decreased while the measured CI/CIII2/CIVn supercomplexes
    were preserved; the assembly phenotype is therefore not uniform across all enzyme pools.
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: The monomeric COX1 assembly intermediate accumulates.
    explanation: Patient fibroblasts accumulate an early assembly intermediate.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Although monomeric complex IV is decreased in patient fibroblasts, the CI/CIII2 /CIVn -supercomplexes remain unaffected.
    explanation: The same culture experiments distinguish monomeric complex IV from supercomplex-associated pools.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Cytochrome c Oxidase Deficiency
    causal_link_type: DIRECT
    description: Reduced mature enzyme abundance limits complex IV activity.
    evidence:
    - reference: PMID:26160915
      reference_title: COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Complete loss of COA6 activity using gene editing in HEK293T cells resulted in a profound growth defect due to complex IV deficiency
      explanation: Links COA6 loss to complex IV deficiency in a human cell model.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
- name: Cytochrome c Oxidase Deficiency
  conforms_to: "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"
  biological_scale: CELLULAR
  description: >-
    Reduced cytochrome c oxidase activity limits terminal electron transfer and coupled oxidative phosphorylation.
    Both isolated complex IV deficiency and combined complex I/IV deficiency occur among the foundational clinical
    reports. The original compound-heterozygous patient had cardiac enzyme defects despite normal fibroblast assays;
    the W66R patient had a fibroblast complex IV defect.
  molecular_functions:
  - preferred_term: cytochrome-c oxidase activity
    modifier: DECREASED
    term:
      id: GO:0004129
      label: cytochrome-c oxidase activity
  biological_processes:
  - preferred_term: mitochondrial electron transport, cytochrome c to oxygen
    modifier: DECREASED
    term:
      id: GO:0006123
      label: mitochondrial electron transport, cytochrome c to oxygen
  - preferred_term: oxidative phosphorylation
    modifier: DECREASED
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
  downstream:
  - target: Systemic Lactate Accumulation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Respiratory dysfunction provides a plausible route to systemic lactate accumulation; tissue-specific metabolic
      flux was not measured in the clinical reports.
  - target: Hypotonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Hypotonia accompanies the biochemical disorder in the W66R patient, but its neural versus muscular origin
      and intervening mechanism have not been established.
  - target: Myocardial Hypertrophic Remodeling
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cardiac respiratory-chain deficiency accompanies hypertrophic cardiomyopathy; the intervening remodeling mechanisms
      remain incompletely defined.
    evidence:
    - reference: PMID:26160915
      reference_title: "COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A pathogenic mutation in COA6, leading to substitution of a conserved tryptophan for a cysteine residue, results in a loss of complex IV activity and cardiomyopathy."
      explanation: >-
        Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result
        in this mechanistic study.
      quote_role: BACKGROUND
      directness: DIRECT
  - target: Decreased activity of mitochondrial complex IV
    causal_link_type: DIRECT
- name: Myocardial Hypertrophic Remodeling
  conforms_to: "complex_iv_assembly_deficiency#High-Energy Tissue Dysfunction"
  biological_scale: TISSUE
  description: >-
    Hypertrophic cardiomyopathy is the dominant cardiac manifestation in the foundational COA6 reports. Respiratory-chain
    defects measured in affected heart support an association with myocardial bioenergetic dysfunction, but do not
    directly measure the sequence from ATP deficit to hypertrophic remodeling.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  locations:
  - preferred_term: myocardium
    term:
      id: UBERON:0002349
      label: myocardium
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Hypertrophic cardiomyopathy
    causal_link_type: DIRECT
- name: Systemic Lactate Accumulation
  conforms_to: "complex_iv_assembly_deficiency#Lactic Acidosis and Metabolic Decompensation"
  biological_scale: ORGANISM
  description: >-
    Lactic acidosis was reported in the W66R patient. Impaired oxidative metabolism is a plausible explanation,
    but the clinical observation does not directly demonstrate increased glycolytic flux or identify the tissue
    producing excess lactate.
  downstream:
  - target: Lactic acidosis
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:31515291
    reference_title: Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts
    explanation: Summarizes the W66R clinical report; this is background clinical evidence.
    quote_role: BACKGROUND
    directness: DIRECT
phenotypes:
- category: Cardiovascular
  name: Hypertrophic cardiomyopathy
  description: >-
    Hypertrophic cardiomyopathy is reported in both foundational cases. Neonatal onset is specifically documented
    in the W66R patient.
  phenotype_term:
    preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
    onset:
      onset_category: NEONATAL
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
- category: Metabolic
  name: Lactic acidosis
  description: >-
    Lactic acidosis was described in the W66R patient. The available cases do not establish a population frequency.
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:31515291
    reference_title: Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts
    explanation: Summarizes the W66R clinical report; this is background clinical evidence.
    quote_role: BACKGROUND
    directness: DIRECT
- category: Neuromuscular
  name: Hypotonia
  description: >-
    Muscular hypotonia was described in the W66R patient. This finding alone does not establish encephalopathy or
    a primary skeletal myopathy.
  phenotype_term:
    preferred_term: Muscular hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:31515291
    reference_title: Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts
    explanation: Summarizes the W66R clinical report; this is background clinical evidence.
    quote_role: BACKGROUND
    directness: DIRECT
- name: Decreased activity of mitochondrial complex IV
  category: Metabolic
  description: Complex IV deficiency was found in both foundational reports, with tissue-dependent expression and variable involvement of complex I.
  phenotype_term:
    preferred_term: Decreased activity of mitochondrial complex IV
    term:
      id: HP:0008347
      label: Decreased activity of mitochondrial complex IV
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
biochemical:
- name: Cytochrome c oxidase (Complex IV) activity
  presence: DECREASED
  notes: >-
    Reduced complex IV activity is the shared biochemical finding. The original compound-heterozygous patient had
    combined complex I/IV deficiency in heart with normal fibroblast activities; the W66R patient had isolated complex
    IV deficiency in fibroblasts. Normal fibroblast results therefore did not exclude disease in the first family.
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency.
    explanation: Clinical presentation of the second reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
- name: Complex IV subunit abundance
  presence: DECREASED
  notes: Immunoblot findings in patient fibroblasts measure protein abundance, which is distinct from catalytic activity.
  evidence:
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: COA6 protein is undetectable and steady-state levels of complex IV and several of its subunits are reduced.
    explanation: Reduced abundance in cultured fibroblasts from the W66R patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
genetic:
- name: COA6
  relationship_type: CAUSATIVE
  gene_term:
    preferred_term: COA6
    term:
      id: hgnc:18025
      label: COA6
  notes: >-
    COA6, formerly C1orf31, encodes an intermembrane-space assembly factor. The foundational cases carry W59C/E87*
    in compound heterozygosity or homozygous W66R. Variant names here follow the original full-length protein numbering;
    effects in overexpression or chimeric yeast assays do not establish a clinical severity ranking.
  variants:
  - name: W59C
    description: >-
      W59C is a missense allele reported in compound heterozygosity with E87*. Expression partially restored CcO
      activity and COX2 levels in human complementation assays, whereas chimeric yeast experiments did not restore
      respiratory growth. The purified mutant forms disulfide-linked oligomers. Matrix mislocalization was reported
      in transfected U2OS cells, while other models retain intermembrane-space localization; these observations
      should not be generalized to every patient tissue.
    gene:
      preferred_term: COA6
      term:
        id: hgnc:18025
        label: COA6
    clinical_significance: PATHOGENIC
    type: missense_variant
    evidence:
    - reference: PMID:31851937
      reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X)"
      explanation: >-
        Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result
        in this mechanistic study.
      quote_role: BACKGROUND
      directness: DIRECT
    - reference: PMID:31851937
      reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "expression of the W59C mutant leads to a partial recovery of CcO activity and COX2 levels"
      explanation: >-
        Partial recovery demonstrates residual function in this human cell assay; it does not rank clinical severity.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
    - reference: PMID:31515291
      reference_title: "Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Disulfide-mediated oligomerization of the W59CCoa6 protein provides a structural explanation for the loss-of-function mutation."
      explanation: >-
        The structural basis of loss of function for this specific allele.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
    - reference: PMID:31515291
      reference_title: Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: 'Characterizations of the W59CCoa6-mutant protein in yeast (W26CyCoa6) and human cells by other groups have suggested differing localizations of the mature protein: to the IMS (51) and mislocalization to the matrix (in U2OS cells (21)).'
      explanation: Summarizes differing localization results across model systems.
      quote_role: BACKGROUND
      directness: DIRECT
  - name: E87*
    description: >-
      Nonsense variant carried in compound heterozygosity with W59C in the same
      patient. Written E87X in one of the cited sources; the entry uses each
      source's own notation inside the sentence it quotes.
    gene:
      preferred_term: COA6
      term:
        id: hgnc:18025
        label: COA6
    clinical_significance: PATHOGENIC
    type: nonsense_variant
    evidence:
    - reference: PMID:31851937
      reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "one with compound heterozygous mutations (W59C and E87X)"
      explanation: >-
        Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result
        in this mechanistic study.
      quote_role: BACKGROUND
      directness: DIRECT
    - reference: PMID:31851937
      reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: The truncation mutation (E87X) clearly disrupts the CHCH domain by removing a large portion of the protein from helix 2 onward (Figures 2A and 2B).
      explanation: Mapping the patient truncation onto the experimentally determined protein structure predicts loss of a substantial part of the CHCH fold.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  - name: W66R
    description: >-
      Homozygous W66R was reported in the patient with neonatal hypertrophic cardiomyopathy, hypotonia and lactic
      acidosis. COA6 protein was undetectable in the original fibroblast study, and W66R failed to rescue CcO activity
      in later overexpression experiments.
    gene:
      preferred_term: COA6
      term:
        id: hgnc:18025
        label: COA6
    clinical_significance: PATHOGENIC
    type: missense_variant
    evidence:
    - reference: PMID:31851937
      reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the other with a homozygous missense mutation (W66R)"
      explanation: >-
        Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result
        in this mechanistic study.
      quote_role: BACKGROUND
      directness: DIRECT
    - reference: PMID:31851937
      reference_title: "COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "we overexpressed the wild-type (WT) and mutant alleles of COA6 in control and COA6 patient fibroblasts and found that the W66R variant fails to rescue CcO activity"
      explanation: >-
        Failure to rescue in this assay contrasts with partial W59C complementation, without establishing an all-allele
        clinical severity ranking.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  evidence:
  - reference: PMID:24549041
    reference_title: "Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Using yeast coa6Δ cells, we show that conserved residues in the motif, including the residue mutated in a patient with mitochondrial disease, are essential for COA6 function, thus confirming the pathogenicity of the patient mutation."
    explanation: >-
      Functional confirmation of variant pathogenicity by yeast complementation,
      which is the evidence that makes this gene causal rather than candidate.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:26669719
    reference_title: "Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we show that patient mutations in Coa6 disrupt Coa6-Cox2 interaction, providing the biochemical basis for disease pathogenesis"
    explanation: >-
      Gives the biochemical mechanism by which the patient alleles are
      pathogenic - loss of the COA6-COX2 interaction - rather than only that they
      fail to complement in yeast.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31515291
    reference_title: "Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Disulfide-mediated oligomerization of the W59CCoa6 protein provides a structural explanation for the loss-of-function mutation."
    explanation: >-
      A crystal structure of a patient allele, explaining at the protein level
      why the variant is loss-of-function.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31515291
    reference_title: "Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An additional patient with a W66R mutation in Coa6 suffered from neonatal hypertrophic cardiomyopathy, muscular hypotonia, and lactic acidosis with a COX defect in the fibroblasts"
    explanation: >-
      Clinical or genetic observation summarized from the foundational patient reports; not a new clinical result
      in this mechanistic study.
    quote_role: BACKGROUND
    directness: DIRECT
  - reference: PMID:25339201
    reference_title: "Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "COA6/C1ORF31 is involved in cytochrome c oxidase (complex IV) biogenesis."
    explanation: >-
      Establishes the gene identity and its former alias C1orf31. Graded OTHER
      rather than HUMAN_CLINICAL: this is the abstract's opening sentence
      restating prior work, immediately before the paper presents its own
      patient, so it is background rather than this study's clinical finding.
    quote_role: BACKGROUND
    directness: DIRECT
treatments:
- name: Copper Supplementation
  description: >-
    Copper supplementation is an experimental lead supported by complete rescue of respiratory and assembly defects
    in coa6-null yeast and partial rescue of complex IV deficiency in patient fibroblasts. These experiments do
    not establish clinical efficacy or an appropriate regimen for people with COA6 deficiency.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: copper
      term:
        id: CHEBI:28694
        label: copper atom
  target_mechanisms:
  - target: Cytochrome c Oxidase Deficiency
    treatment_effect: MODULATES
    description: Partially improves the complex IV deficit in cultured patient fibroblasts; restoration of CuA metallation was not directly quantified.
    evidence:
    - reference: PMID:25339201
      reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Copper supplementation shows a partial rescue of complex IV deficiency in patient fibroblasts.
      explanation: Partial recovery in cultured patient cells; no clinical treatment outcome is established.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  evidence:
  - reference: PMID:24549041
    reference_title: "Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we show that exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells"
    explanation: >-
      The yeast result. Complete rescue here, in contrast with the partial rescue
      reported in patient fibroblasts.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:25339201
    reference_title: Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Copper supplementation shows a partial rescue of complex IV deficiency in patient fibroblasts.
    explanation: Partial recovery in cultured patient cells; no clinical treatment outcome is established.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Elesclomol (experimental)
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Elesclomol restored mitochondrial copper, respiration and CcO activity in coa6-deficient yeast, including yeast
    expressing pathogenic human-yeast COA6 chimeras. It also reduced pericardial edema and improved heart rate in
    COA6 morphant zebrafish. This is preclinical evidence: the mammalian patient fibroblasts in the same study carried
    SCO2 variants, not COA6 variants. Toxicity depended on experimental conditions; combined elesclomol and copper
    at 100 nM each was lethal in zebrafish.
  treatment_term:
    preferred_term: Experimental elesclomol pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: elesclomol
      term:
        id: CHEBI:79369
        label: elesclomol
  target_mechanisms:
  - target: Cytochrome c Oxidase Deficiency
    treatment_effect: RESTORES
    description: Restored CcO activity in coa6-deficient yeast; this relationship is restricted to that experimental model.
    evidence:
    - reference: PMID:30038027
      reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity.
      explanation: Direct COA6 yeast rescue result; human efficacy is untested in this study.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  evidence:
  - reference: PMID:30038027
    reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity.
    explanation: Direct COA6 yeast rescue result; human efficacy is untested in this study.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30038027
    reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Indeed, 100 nM ES treatment prevented pericardial edema and significantly increased the heart rate of Coa6-knockdown zebrafish embryos at 72 and 96 hpf without altering the heart rate of control embryos (SI Appendix, Fig. S8 E and F).
    explanation: COA6 morphant fish showed functional and morphological rescue.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30038027
    reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Consistent with the mechanism of action of ES, we observed that cosupplementation of 100 nM ES with 100 nM of copper resulted in 100% lethality (SI Appendix, Fig. S8B).
    explanation: The experimental zebrafish combination was lethal; efficacy at one dose does not establish safety of copper coadministration.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Supportive and Palliative Care
  description: >-
    Cardiac and metabolic support are general management considerations for severe mitochondrial cardiomyopathy.
    The cited COA6 reports do not establish an evidence-based disease-specific supportive or palliative protocol.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    This is a general supportive strategy, not a documented treatment-response claim from the two COA6 cases.
- name: Genetic Counseling
  description: >-
    For parents who each carry a pathogenic COA6 allele, standard autosomal recessive inheritance gives a 25 percent
    probability of a child inheriting both alleles in each pregnancy. Identification of familial variants permits
    discussion of carrier and reproductive testing.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    The recurrence probability is Mendelian reasoning under the two-carrier-parent assumption, not an observed rate
    from these small case reports. COA6-specific prenatal testing outcomes are not established by the cited studies.
  evidence:
  - reference: PMID:31851937
    reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'Mutations in COA6 have been reported in two unrelated human mitochondrial disease patients: one with compound heterozygous mutations (W59C and E87X) (Calvo et al., 2012) and the other with a homozygous missense mutation (W66R) (Baertling et al., 2015).'
    explanation: Biallelic genotypes support the inheritance model underlying counseling; the quoted study does not itself measure recurrence or test prenatal diagnosis.
    quote_role: BACKGROUND
    directness: INDIRECT
animal_models:
- name: coa6 morphant zebrafish
  species: Zebrafish
  genotype: zfcoa6 morpholino knockdown
  publication: PMID:24549041
  description: >-
    Transient coa6 morpholino knockdown produces reduced heart rate, failed cardiac looping, thin-walled enlarged
    chambers and pericardial edema. These developmental cardiac findings are not equivalent to measured human myocardial
    hypertrophy. Elesclomol improved edema and heart rate in this model.
  evidence:
  - reference: PMID:24549041
    reference_title: Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Furthermore, we show that zebrafish embryos with zfcoa6 knockdown display reduced heart rate and cardiac developmental defects, recapitulating the observed pathology in the human mitochondrial disease patient who died of neonatal hypertrophic cardiomyopathy.
    explanation: Reports vertebrate cardiac defects after coa6 knockdown; the human death clause is background.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:30038027
    reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Indeed, 100 nM ES treatment prevented pericardial edema and significantly increased the heart rate of Coa6-knockdown zebrafish embryos at 72 and 96 hpf without altering the heart rate of control embryos (SI Appendix, Fig. S8 E and F).
    explanation: COA6 morphant fish showed functional and morphological rescue.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  modeled_mechanisms:
  - target: Myocardial Hypertrophic Remodeling
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Demonstrates cardiac dysfunction after coa6 knockdown, with a developmental phenotype that only partially
      models human hypertrophic remodeling.
    limitations: >-
      Transient morpholino knockdown rather than a stable genetic mutant, so
      off-target and incomplete-knockdown effects cannot be excluded and only
      embryonic stages are assessed. The readouts are heart rate and gross
      cardiac development, not the hypertrophic remodelling of the human
      phenotype, so the match is to cardiac involvement rather than to
      hypertrophic cardiomyopathy specifically.
    divergences:
    - divergence_type: PROXY_QUANTITY
      materiality: QUALIFYING
      description: >-
        The model's measured quantities are embryonic heart rate and gross
        cardiac morphogenesis. The node's quantity is hypertrophic remodelling of
        a formed neonatal myocardium. These are different cardiac readouts at
        different developmental stages.
    evidence:
    - reference: PMID:24549041
      reference_title: Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Furthermore, we show that zebrafish embryos with zfcoa6 knockdown display reduced heart rate and cardiac developmental defects, recapitulating the observed pathology in the human mitochondrial disease patient who died of neonatal hypertrophic cardiomyopathy.
      explanation: Reports vertebrate cardiac defects after coa6 knockdown; the human death clause is background.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
- name: coa6-deleted budding yeast
  species: Saccharomyces cerevisiae
  genotype: coa6Δ
  publication: PMID:24549041
  description: >-
    Deletion causes respiratory growth and CcO assembly defects. Copper and elesclomol rescue these defects under
    tested conditions. Hypoxia and reduced glutathione also suppress the growth phenotype, supporting a redox role.
    Loss of Sco2 or Cox12 in addition to Coa6 prevents copper rescue. Lowering cytochrome c improved Cox2 accumulation
    and complex IV assembly in a 2026 study; the proposed coordination of cofactor maturation remains a model-level
    hypothesis.
  evidence:
  - reference: PMID:24549041
    reference_title: "Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we show that exogenous copper supplementation completely rescues respiratory and complex IV assembly defects in yeast coa6Δ cells"
    explanation: >-
      The yeast result. Complete rescue here, in contrast with the partial rescue
      reported in patient fibroblasts.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31851937
    reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The respiratory growth of coa6Δ was almost fully rescued in hypoxic yeast, while that of yeast strains lacking proteins with established Cu metallochaperone activity (sco1Δ, cox17Δ, and cox11Δ) was not (Figure 5E).
    explanation: Hypoxic suppression is a mechanistic experiment, not a human treatment result.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31851937
    reference_title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Moreover, exogenous supplementation of a normoxic culture with reduced glutathione (GSH) also partially rescued respiratory growth of coa6Δ cells (Figure 5G), further supporting a redox role for Coa6 in the Cu delivery process.
    explanation: Reducing conditions partially bypass the growth defect in yeast.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:26669719
    reference_title: Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Unlike Coa6 deficient cells, copper supplementation fails to rescue Cox2 levels of these double mutants.
    explanation: Double deletion of coa6 with sco2 or cox12 limits the copper rescue mechanism.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:42551500
    reference_title: Role of Coa6 in coordinating Cox2 and cytochrome c maturation in yeast mitochondria.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: We show that decreasing the level of the mobile electron transporter cytochrome c improves both Cox2 accumulation and complex IV assembly in the budding yeast coa6-null mutant.
    explanation: Recent yeast evidence links cytochrome c availability to Cox2/CIV maturation; human consequences have not been demonstrated.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  modeled_mechanisms:
  - target: Complex IV Assembly Arrest
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: Respiratory growth, Cox2 abundance and assembled CcO provide measurable consequences of coa6 loss.
    limitations: Yeast lacks human cardiac tissue and does not model the clinical course. Null strains and chimeric overexpression assays do not reproduce a complete human biallelic genotype in its native tissue.
    evidence:
    - reference: PMID:30038027
      reference_title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: By using a candidate-based approach, we identified an investigational anticancer drug, elesclomol (ES), that rescues respiratory defects of COA6-deficient yeast cells by increasing mitochondrial copper content and restoring CcO activity.
      explanation: Direct COA6 yeast rescue result; human efficacy is untested in this study.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
experimental_models:
- name: W66R patient-derived fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    Fibroblasts from the homozygous W66R patient show absent detectable COA6, reduced complex IV, abnormal subunit
    turnover and accumulation of a COX1 intermediate. Copper produced partial rescue. Later complementation and
    redox work used immortalized derivatives, so culture context matters.
  evidence:
  - reference: PMID:25339201
    reference_title: "Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "For the first time, clinical details about a COA6-deficient patient are given and patient fibroblasts are functionally characterized"
    explanation: Establishes patient fibroblasts as the characterized human cellular model.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  modeled_mechanisms:
  - target: Complex IV Assembly Arrest
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: CELLULAR
    description: >-
      Patient cells carry the causative genotype and directly display the
      accumulated COX1 intermediate and accelerated subunit turnover.
    limitations: >-
      This genotype shows a fibroblast defect, whereas the original W59C/E87* family had normal fibroblast enzyme
      assays despite affected heart tissue. The culture system does not establish cardiac severity.
- name: COA6 knockout human cell line
  experimental_model_type: CELL_LINE
  description: >-
    Engineered COA6-null HEK293T lines test complete loss of the protein. The 2015 study reported a prominent complex
    IV defect; the 2020 line had combined I/IV deficiency, reduced membrane potential and impaired potential-dependent
    protein import. These lines should not be assumed to have identical downstream phenotypes.
  evidence:
  - reference: PMID:26160915
    reference_title: "COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Complete loss of COA6 activity using gene editing in HEK293T cells resulted in a profound growth defect due to complex IV deficiency"
    explanation: Establishes the knockout line and its Complex IV growth phenotype.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In summary, in the absence of COA6, the import routes that depend on the inner membrane potential are affected. However, the membrane potential independent import into the intermembrane space via MIA40 was not reduced but rather stimulated.
    explanation: The 2020 knockout distinguishes potential-dependent import defects from preserved or increased MIA40 import.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: However, an increase in ROS production was not apparent in mutant cells, nor did we detect alterations in the mitochondrial glutathione redox potential.
    explanation: 'Limits interpretation of the knockout phenotype: generalized oxidative stress was not established.'
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  modeled_mechanisms:
  - target: Cytochrome c Oxidase Deficiency
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Engineered human cells demonstrate complex IV deficiency after COA6 loss. Additional complex I involvement
      and protein-import consequences depend on the model.
    limitations: >-
      The kidney-derived transformed line does not model cardiac tissue. Engineered null alleles differ from the
      reported missense/truncating combinations, and residual protein or function is allele-dependent.
    divergences:
    - divergence_type: CAUSE_UNREPRESENTED
      materiality: QUALIFYING
      description: >-
        Engineered gene deletion does not recreate the specific biallelic patient variants or their allele-dependent
        residual function.
discussions:
- discussion_id: coa6_encephalopathy_not_documented
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - "phenotypes#"
  - "pathophysiology#Myocardial Hypertrophic Remodeling"
  prompt: >-
    The disease is named a cardioencephalomyopathy. Is there documented central
    nervous system involvement in COA6 deficiency?
  rationale: >-
    The cited foundational cases support a predominantly cardiac disorder, with hypotonia in one patient. They do
    not establish a specific encephalopathy phenotype. Sparse clinical ascertainment and infantile death leave the
    neurological spectrum uncertain; the disease name is not evidence for a particular CNS manifestation.
- discussion_id: coa6_reductase_versus_metallochaperone
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - "pathophysiology#COA6 Reductase Dysfunction"
  - "pathophysiology#Impaired CuA Metallation of COX2"
  prompt: >-
    Does COA6 act purely as a disulfide reductase on the copper relay, or does it
    also carry copper itself?
  rationale: >-
    Purified COA6 can bind copper under selected in-vitro conditions, but direct physiological copper transfer from
    COA6 to a client protein has not been demonstrated in the studies assessed by the 2022 review. Reductase activity
    has stronger experimental support. Its electron source, substrate specificity and the identity of the redox-active
    disulfide remain incompletely resolved.
  evidence:
  - reference: PMID:35053273
    reference_title: "The Role of COA6 in the Mitochondrial Copper Delivery Pathway to Cytochrome c Oxidase."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "While two decades of studies have provided a clearer picture regarding the biochemical roles of SCO1 and SCO2 proteins, some discrepancy exists regarding the function of COA6, the new member of this pathway."
    explanation: >-
      A critical review of the pathway stating that the question is open, which
      is the basis for recording it rather than asserting one side.
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
  - reference: PMID:35053273
    reference_title: "The Role of COA6 in the Mitochondrial Copper Delivery Pathway to Cytochrome c Oxidase."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Its role as a copper metallochaperone has also been proposed."
    explanation: Names the competing reading directly.
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
  - reference: PMID:26160915
    reference_title: "COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "COA6 has the capacity to bind copper"
    explanation: >-
      Direct experimental support for the copper-binding side, from a paper this
      entry also cites for the reductase-dependent assembly defect.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:31515291
    reference_title: "Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the first 2 helices tethered by disulfide bonds, one of which likely provides the copper-binding site"
    explanation: >-
      The crystal structure assigns a likely copper-binding site, which is the
      structural basis for the metallochaperone proposal.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:35053273
    reference_title: The Role of COA6 in the Mitochondrial Copper Delivery Pathway to Cytochrome c Oxidase.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Importantly, the source of electrons used by COA6 for its disulfide reductase activity is unknown.
    explanation: The review identifies an unresolved component of the reductase model.
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
- discussion_id: coa6_isolated_versus_combined_complex_deficiency
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - "pathophysiology#Cytochrome c Oxidase Deficiency"
  - "biochemical#Cytochrome c oxidase (Complex IV) activity"
  prompt: >-
    What explains variation in complex I involvement across COA6 patient tissues and experimental cell lines?
  rationale: >-
    The original patient had combined complex I/IV deficiency in heart and normal fibroblast activities, whereas
    the W66R patient had isolated complex IV deficiency. Engineered human cell studies also differ in complex I
    involvement. These observations establish heterogeneity; they do not make combined deficiency incompatible with
    COA6 disease. Genotype, tissue and culture conditions are candidate explanations, but their contributions have
    not been resolved.
  evidence:
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: However, at this point, the question as to how a loss of COA6 affects complex I remain open as no link between copper chaperone activity and complex I biogenesis has been observed.
    explanation: The 2020 investigators explicitly leave the mechanism of complex I involvement unresolved.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
notes: >-
  This entry covers COA6 deficiency. Findings from SCO1, SCO2, COA5 or other copper-handling disorders are not assumed
  to apply to COA6 patients. The two foundational families and experimental models support a severe cardiac phenotype,
  but do not define the complete phenotypic range, population frequency, or response to treatment.
diagnosis:
- name: Molecular genetic testing and allele phasing
  description: >-
    Identification of biallelic COA6 variants supports the molecular diagnosis in a compatible cardiac and biochemical
    presentation. The original discovery used targeted mitochondrial-gene sequencing, followed by Sanger confirmation
    and phasing of C1orf31 variants using cloned DNA. A particular trio or whole-exome workflow is not a required
    diagnostic criterion.
  evidence:
  - reference: PMID:22277967
    reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We performed "MitoExome" sequencing of the mitochondrial DNA (mtDNA) and exons of ~1000 nuclear genes encoding mitochondrial proteins and prioritized rare mutations predicted to disrupt function.
    explanation: Describes the discovery sequencing method for the cohort containing the original COA6/C1orf31 case.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:22277967
    reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All prioritized variants detected in patients were independently validated by Sanger sequencing (48/49 variants validated), and compound heterozygous variants were phased through sequencing cDNA (GFM1), cloned DNA (BCS1L, C1orf31, TYMP, MTHFD1L), familial DNA (GFM1, AGK, EARS2), or by a molecular haplotyping approach(31) (ACAD9, AARS2, POLG) described in Supplementary Methods.
    explanation: Specifically identifies cloned-DNA phasing for C1orf31 in the discovery study.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
- name: Respiratory-chain enzymology and assembly studies
  description: >-
    Complex IV activity and assembly studies support biochemical characterization. Isolated IV deficiency is not
    mandatory, because combined I/IV deficiency was present in the original cardiac sample. Normal fibroblast assays
    did not exclude disease in that family. Pulse-chase and assembly-intermediate studies are research characterization,
    not universal diagnostic requirements.
  evidence:
  - reference: PMID:32061935
    reference_title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Remarkably, only one of the patients described with COA6 mutations showed a decreased complex I activity
    explanation: The discussion summarizes variable complex I involvement in the two foundational COA6 cases; both have complex IV deficiency.
    quote_role: BACKGROUND
    directness: DIRECT
  - reference: PMID:26160915
    reference_title: COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here, we demonstrate that the complex IV defect correlates with a severe loss in complex IV assembly in patient heart but not fibroblasts.
    explanation: Direct tissue-versus-culture comparison showing why a normal fibroblast result cannot exclude the reported genotype.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
references:
- reference: PMID:22277967
  title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
- reference: PMID:24549041
  title: "Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency."
- reference: PMID:25339201
  title: "Mutations in COA6 cause cytochrome c oxidase deficiency and neonatal hypertrophic cardiomyopathy."
- reference: PMID:25959673
  title: Cooperation between COA6 and SCO2 in COX2 maturation during cytochrome c oxidase assembly links two mitochondrial cardiomyopathies.
- reference: PMID:26160915
  title: COA6 is a mitochondrial complex IV assembly factor critical for biogenesis of mtDNA-encoded COX2.
- reference: PMID:26669719
  title: Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.
- reference: PMID:30038027
  title: Elesclomol restores mitochondrial function in genetic models of copper deficiency.
- reference: PMID:31515291
  title: "Structural and functional characterization of the mitochondrial complex IV assembly factor Coa6."
- reference: PMID:31851937
  title: COA6 Is Structurally Tuned to Function as a Thiol-Disulfide Oxidoreductase in Copper Delivery to Mitochondrial Cytochrome c Oxidase.
- reference: PMID:32061935
  title: COA6 Facilitates Cytochrome c Oxidase Biogenesis as Thiol-reductase for Copper Metallochaperones in Mitochondria.
- reference: PMID:35053273
  title: The Role of COA6 in the Mitochondrial Copper Delivery Pathway to Cytochrome c Oxidase.
- reference: PMID:42551500
  title: Role of Coa6 in coordinating Cox2 and cytochrome c maturation in yeast mitochondria.
- reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4049311/
  title: Copper supplementation restores cytochrome c oxidase assembly defect in a mitochondrial disease model of COA6 deficiency - PMC

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References & Deep Research