COA5-Related Fatal Infantile Cardioencephalomyopathy

Mendelian MONDO:0014667 Pathograph 17 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COA5-related fatal infantile cardioencephalomyopathy (CEMCOX3; mitochondrial complex IV deficiency nuclear type 9, MC4DN9) is an ultra-rare autosomal recessive disorder of cytochrome c oxidase assembly caused by biallelic COA5 variants. Patient fibroblasts accumulate early MTCO1-containing assembly intermediates and have reduced mature complex IV. COA5 knockout cells localize the assembly defect between MTCO1 maturation and MTCO2 incorporation. The 2011 and 2025 clinical reports describe three affected children in two Turkish families, all homozygous for c.157G>C (p.Ala53Pro). Neonatal hypertrophic cardiomyopathy and infantile death dominate the reported course. The 2025 patient also had respiratory insufficiency, lactic acidosis, urinary lactate and ethylmalonic acid elevation, and hepatic abnormalities. Normal brain imaging in that patient does not exclude neurological involvement in the wider disorder. The small case series cannot establish penetrance, phenotype frequencies, or the full clinical spectrum.

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1
Mappings
1
Inheritance
7
Pathophys.
10
Phenotypes
3
Gaps
17
Pathograph
1
Genes
1
Variants
2
Medical Actions
4
Differentials
3
Models
6
References
1
Deep Research
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Mappings

ICD-10-CM
ICD10CM:E88.49 Other mitochondrial metabolism disorders
skos:broadMatch ICD-10-CM
ICD-10-CM has no code specific to COA5-related disease or to nuclear-type Complex IV deficiency. E88.49 is the residual code within the E88.4 mitochondrial metabolism block and is therefore a broad, not exact, match.
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Inheritance

1
Autosomal recessive HP:0000007
The homozygous COA5 p.Ala53Pro variant segregates with disease in the reported families, with heterozygous carrier parents in the 2025 family. Three affected children from two families do not establish population penetrance or the range of expressivity. The founding siblings died as neonates and the later patient at three months.
Autosomal recessive inheritance Penetrance: UNKNOWN Expressivity: UNKNOWN
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Trio whole-exome sequencing conducted at the Exeter Genomics Laboratory identified a previously reported COA5 variant (c.157G>C, p.Ala53Pro), confirming both parents to be heterozygous carriers"
Homozygosity in the affected child with both parents heterozygous carriers is the segregation pattern of autosomal recessive inheritance.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A female neonate born to second cousins of Turkish descent presented with tachypnoeic episodes on the first day of life"
Parental consanguinity is consistent with recessive inheritance; it does not establish a founder effect.
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Discussions and Knowledge Gaps

3
The disease is named a cardioencephalomyopathy, but is there any documented central nervous system involvement in COA5 deficiency?
KNOWLEDGE GAP OPEN coa5_encephalopathy_not_documented
Attached to
pathophysiology#Hypertrophic Myocardial Remodeling phenotypes#Hypertrophic Cardiomyopathy
The disease name includes encephalomyopathy, but the available clinical descriptions emphasize neonatal cardiomyopathy and the 2025 patient had normal brain imaging. Normal structural imaging does not exclude functional or later neurological involvement. The neurological spectrum remains unresolved in this small, early-lethal case series.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Neuroimaging of the brain was normal."
Documents normal brain imaging in one patient; it does not establish absence of encephalopathy in the disorder.
Where does human COA5 sit within the mitochondrion, and does it act purely as an assembly factor at the MTCO1-to-MTCO2 transition or also as a regulator of the copper and haem metallochaperone modules?
OPEN QUESTION OPEN coa5_submitochondrial_localisation_and_metallochaperone_role
Attached to
pathophysiology#Arrested Early Complex IV Assembly
COA5 knockout experiments implicate both early MTCO1-to-MTCO2 assembly and COX2 metallochaperone interactions. The 2022 study supports a dynamic apo-metallochaperone complex-stabilizing role in engineered human cells, while the 2025 study leaves the precise structural role and localization for further investigation. How p.Ala53Pro affects these interactions is unresolved; yeast import findings do not establish human import dependence.
Show evidence (3 references)
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"identified the twin CX9C protein PET191/COA5 as a key contributor in human cells"
Places COA5 in the copper-centre biogenesis machinery in human knockout cells, which is the alternative role this question is about.
PMID:18503002 SUPPORT DIRECT PRIMARY RESULT Model Organism
"The import of Pet191 differs from that of other twin-Cx(9)C motif class of proteins in being independent of the Mia40 pathway."
Evidence about the yeast orthologue Pet191, not about human COA5. It is cited only to substantiate why yeast import and localisation data cannot be read across to the human protein.
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191"
Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions. This has not been measured in patient cells.
Is COA5 c.157G>C (p.Ala53Pro) a Turkish founder allele, or has the same variant arisen independently?
OPEN QUESTION OPEN coa5_founder_allele_unverified
Attached to
genetic#COA5 pathogenic variants causing CEMCOX3 (MC4DN9) prevalence#Worldwide
The two reported Turkish families share homozygous p.Ala53Pro. The authors propose a founder effect but explicitly require haplotype analysis to establish it. Recurrence alone is insufficient.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"this could point towards the likelihood of the variant being a founder pathogenic variant within the Turkish population"
States the founder hypothesis as a possibility, in the authors' own hedged terms, which is exactly the epistemic status recorded here.
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Pathophysiology

7
Impaired COA5 Assembly-Factor Function
Homozygous COA5 p.Ala53Pro impairs assembly-factor function. Wild-type COA5 complementation restores complex IV activity in patient fibroblasts. This functional defect does not establish complete absence of the missense protein; the null cell models are distinct experimental perturbations.
COA5 hgnc:33848 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COA5 (hgnc:33848). hgnc:33848 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Arrested Early Complex IV Assembly Loss of functional COA5 impairs early complex IV assembly; patient-cell rescue attributes the defect to COA5.
Disrupted COX2 Metallochaperone Interactions Loss of COA5/PET191 disrupts COX2 assembly-factor interactions in engineered HEK293T cells. Transfer of this precise intermediate to p.Ala53Pro patient cells remains provisional.
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
Complementation with wild-type COA5 restores Complex IV activity in patient cells, establishing loss of COA5 function as the direct molecular lesion.
Disrupted COX2 Metallochaperone Interactions
Mechanism confidence: Provisional
In PET191/COA5 knockout HEK293T cells, newly synthesized COX2 fails to interact with SCO1, COA6 and COX16. These experiments support a COA5-dependent metallochaperone assembly function, but do not establish that p.Ala53Pro disrupts each interaction identically.
Experimental models
TALEN PET191/COA5 knockout HEK293T cells CELL LINE The knockout disrupts COX2 association with SCO1, COA6 and COX16.
Downstream
Arrested Early Complex IV Assembly Impaired recruitment of COX2 maturation factors provides a candidate explanation for failure to incorporate mature MTCO2. The exact connection to the patient missense assembly defect remains unresolved.
Show evidence (1 reference)
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191"
Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions. This has not been measured in patient cells.
Arrested Early Complex IV Assembly
Patient fibroblasts accumulate an early COX1/MTCO1-containing intermediate lacking COX2, COX4 and COX5b, with reduced mature complex IV. In COA5 knockout U2OS cells, complexome profiling places the block between MTCO1 maturation and MTCO2 incorporation. Complete loss of the holocomplex in knockout cells should not be equated with complete loss in patient fibroblasts.
mitochondrial respiratory chain complex IV assembly GO:0033617 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial respiratory chain complex IV assembly (GO:0033617). GO:0033617 is a biological process from the Gene Ontology. ↓ DECREASED
mitochondrial respiratory chain complex IV GO:0045277 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves mitochondrial respiratory chain complex IV, annotated with respiratory chain complex IV (GO:0045277). GO:0045277 is a cellular component from the Gene Ontology.
Experimental models
COA5 p.Ala53Pro patient-derived dermal fibroblasts PRIMARY CELL CULTURE Patient fibroblasts accumulate an early COX1-containing intermediate and have reduced mature complex IV. Wild-type COA5 restores complex IV activity.
CRISPR/Cas9 COA5 knockout U2OS cell line CELL LINE The knockout reproduces the patients' isolated Complex IV defect and resolves it further: MTCO1-containing subcomplexes accumulate, MTCO2 is absent, and the holoenzyme is lost, placing the COA5 step between MTCO1 maturation and MTCO2 incorporation.
Downstream
Reduced Complex IV Activity Impaired formation of mature complex IV reduces cytochrome c oxidase activity. Wild-type COA5 restores complex IV activity in patient fibroblasts.
Loss of Complex IV-Containing Supercomplexes Failure to assemble mature complex IV limits its incorporation into respiratory supercomplexes in COA5 knockout U2OS cells.
Show evidence (3 references)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Detailed analysis of complex IV assembly intermediates in patient fibroblasts by 2D-BN PAGE revealed the accumulation of a small assembly intermediate containing subunit COX1 but not the COX2, COX4, or COX5b subunits, indicating that C2orf64 is involved in an early step of the complex IV..."
Directly localizes the COA5/C2orf64 lesion to an early step of Complex IV assembly, with a COX1-containing intermediate that fails to acquire COX2.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Mitochondrial complexome profiling pinpointed a role of COA5 in early CIV assembly, more specifically, its involvement in the stage between MTCO1 maturation and the incorporation of MTCO2"
Complexome profiling of a CRISPR/Cas9 COA5 knockout cell line places the COA5-dependent step precisely between MTCO1 maturation and MTCO2 incorporation.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"CIV protein subunits exhibited a statistically significant decrease in protein abundance up to almost fourfold, whereas CI, CII, CIII, and CV protein abundance remained unchanged"
Proteomic profiling of immortalised patient fibroblasts supports selective reduction of CIV protein abundance.
Reduced Complex IV Activity
Cytochrome c oxidase activity is deficient in patient-derived fibroblasts and skeletal muscle. Reduced terminal oxidase function is expected to limit oxidative energy production, but the cited clinical studies do not directly measure myocardial ATP synthesis or prove its complete collapse.
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial electron transport, cytochrome c to oxygen (GO:0006123). GO:0006123 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Systemic Lactate Accumulation Reduced oxidative metabolism provides a plausible route to increased lactate production. Pyruvate flux and the intervening metabolic steps were not measured in COA5 patients.
Hypertrophic Myocardial Remodeling Impaired mitochondrial energy production plausibly contributes to myocardial remodeling. The tissue-specific steps from the assembly defect to hypertrophy have not been resolved.
Decreased Activity of Mitochondrial Complex IV The enzymatic defect is measured as reduced cytochrome c oxidase activity.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
The assembly block translates into measurably deficient Complex IV activity in patient muscle, the functional consequence asserted by this edge.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
Complementation with wild-type COA5 restores Complex IV activity in patient cells, establishing loss of COA5 function as the direct molecular lesion.
Loss of Complex IV-Containing Supercomplexes
Mechanism confidence: Provisional
COA5 knockout U2OS cells lose the III2+IV supercomplex and accumulate I+III2 assemblies. This respiratory-chain reorganization is an experimental consequence of COA5 deletion; its extent and functional contribution in patient myocardium are unknown.
Experimental models
CRISPR/Cas9 COA5 knockout U2OS cell line CELL LINE Complexome profiling resolves the loss of III2+IV and increase in I+III2 supercomplexes.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"When assessing complex III subunits, a complete loss of the supercomplexes III2+IV (Ss) was observed in the COA5KO cell line"
Directly documents loss of III2+IV in the engineered U2OS line.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"An increased abundance of respiratory supercomplexes containing complexes I and III2 (S0: I+III2) was observed in the COA5KO cell line"
Documents the corresponding increase in I+III2 assemblies.
Systemic Lactate Accumulation
The 2025 patient had fluctuating blood lactate elevation, urinary lactate elevation and severe lactic acidosis during terminal deterioration. Increased lactate production from impaired oxidative metabolism is a physiological interpretation; the study did not measure lactate production or clearance flux.
Downstream
Lactic Acidosis Lactate accumulation accompanies the documented severe lactic acidosis.
Lacticaciduria Systemic lactate accumulation is accompanied by increased urinary lactate.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
Documents fluctuating blood lactate elevation in the 2025 patient.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
Documents urinary lactate elevation; ethylmalonic acid was a concurrent finding with an unresolved causal route.
Hypertrophic Myocardial Remodeling
Hypertrophic cardiomyopathy is the dominant reported clinical manifestation. The 2025 patient had biventricular and septal hypertrophy, a non-compaction appearance, and subsequent poor cardiac function. The cellular remodeling response and the origin of the non-compaction morphology remain uncharacterized.
cardiac muscle cell CL:0000746 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves cardiac muscle cell (CL:0000746). CL:0000746 is a cell type from the Cell Ontology.
Downstream
Hypertrophic Cardiomyopathy The remodeling response is expressed as hypertrophic cardiomyopathy.
Ventricular Septal Hypertrophy Septal hypertrophy is a component of the hypertrophic remodeling.
Show evidence (2 references)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy"
The founding report establishes cardiomyopathy as the defining organ manifestation of COA5 deficiency.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
Characterizes the cardiac phenotype in the second reported family as biventricular hypertrophic cardiomyopathy with non-compaction morphology.
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Pathograph

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Pathograph: causal mechanism network for COA5-Related Fatal Infantile Cardioencephalomyopathy Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

10
Cardiovascular 3
Hypertrophic Cardiomyopathy HP:0001639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Biventricular hypertrophic cardiomyopathy, annotated with Hypertrophic cardiomyopathy (HP:0001639), qualified as neonatal onset. HP:0001639 is a phenotype from the Human Phenotype Ontology.
Onset: NEONATAL
Show evidence (3 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
Echocardiographic documentation of biventricular hypertrophic cardiomyopathy in the second reported family.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"C2orf64 mutational analysis should be considered for complex IV deficient patients, in particular those with hypertrophic cardiomyopathy"
The founding report's own conclusion identifies hypertrophic cardiomyopathy as the presentation that should prompt COA5 testing, supporting it as the characteristic phenotype.
PMID:39779219 SUPPORT DIRECT BACKGROUND Human Clinical
"two siblings affected by neonatal hypertrophic cardiomyopathy manifesting a rare, homozygous COA5 missense variant"
The 2025 abstract summarizes neonatal hypertrophic cardiomyopathy in the founding sibling pair.
Ventricular Septal Hypertrophy HP:0005144 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Septal hypertrophy, annotated with Ventricular septal hypertrophy (HP:0005144). HP:0005144 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"biventricular hypertrophic cardiomyopathy with septal hypertrophy"
Reports septal hypertrophy as a component of the echocardiographic cardiomyopathy phenotype.
Noncompaction Cardiomyopathy HP:0012817 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Non-compaction appearance of the myocardium, annotated with Noncompaction cardiomyopathy (HP:0012817). HP:0012817 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"non-compaction appearance of the myocardium"
Records the non-compaction morphology observed on echocardiography.
Digestive 1
Abnormal Hepatic Echogenicity HP:0031142 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased hepatic echogenicity, annotated with Abnormal hepatic echogenicity (HP:0031142). HP:0031142 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Liver function tests were abnormal with increased echogenicity of liver on ultrasound."
Reports the hepatic ultrasound and biochemical abnormality directly.
Genitourinary 2
Lacticaciduria HP:0003648 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated urinary lactate, annotated with Lacticaciduria (HP:0003648). HP:0003648 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
Reports elevated urinary lactate in the patient's organic-acid profile.
Ethylmalonic Aciduria HP:0003219 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ethylmalonic aciduria (HP:0003219). HP:0003219 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"elevated urinary lactate and ethylmalonic acid"
Records ethylmalonic aciduria in the metabolic profile of the reported patient.
Metabolism 1
Lactic Acidosis HP:0003128 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
Quantifies the lactate elevation underpinning the lactic acidosis phenotype.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"poor cardiac function, and severe lactic acidosis, and finally passed away at 3 mo of age"
Documents progression to severe lactic acidosis during the fatal decompensation.
Respiratory 2
Tachypnea HP:0002789 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tachypnoeic episodes, annotated with Tachypnea (HP:0002789). HP:0002789 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A female neonate born to second cousins of Turkish descent presented with tachypnoeic episodes on the first day of life"
Tachypnoea on day one of life was the presenting feature in this patient.
Respiratory Insufficiency HP:0002093 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Respiratory insufficiency (HP:0002093). HP:0002093 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
Documents respiratory insufficiency requiring intubation.
Cellular 1
Decreased Activity of Mitochondrial Complex IV HP:0008347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Isolated complex IV deficiency, annotated with Decreased activity of mitochondrial complex IV (HP:0008347). HP:0008347 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
Direct histochemical demonstration of reduced Complex IV activity in patient muscle.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
Complex IV activity in patient fibroblasts was deficient and rescuable, which both demonstrates the deficiency and attributes it to COA5.
🧬

Genetic Associations

1
COA5 pathogenic variants causing CEMCOX3 (MC4DN9)
Gene: COA5 hgnc:33848 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is COA5 (hgnc:33848). hgnc:33848 is a gene from the HUGO Gene Nomenclature Committee. variant_origin: GERMLINE
Autosomal recessive
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy"
Identifies COA5 (C2orf64) as the causal gene in the founding family.
Variants (1)
COA5 c.157G>C (p.Ala53Pro) Pathogenic
Gene: COA5 hgnc:33848 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COA5 (hgnc:33848). hgnc:33848 is a gene from the HUGO Gene Nomenclature Committee.
Homozygous missense variant in the twin-CX9C domain, shared by the two published families. The 2025 paper records a pathogenic ClinVar classification. A founder effect was proposed but requires haplotype verification.
Show evidence (3 references)
PMID:39779219 SUPPORT DIRECT BACKGROUND Other
"The homozygous COA5 missense variant has been recorded on ClinVar as a pathogenic variant associated with isolated COX deficiency"
Reports the ClinVar classification recorded by the 2025 authors.
PMID:39779219 NO_EVIDENCE DIRECT PRIMARY RESULT Computational
"the REVEL meta-predictor score was below the recommended threshold for this variant, necessitating further study"
A below-threshold REVEL result does not itself support the pathogenic classification; functional complementation is the relevant positive evidence.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
Complementation with wild-type COA5 restores Complex IV activity in patient cells, establishing loss of COA5 function as the direct molecular lesion.
💊

Medical Actions

2
Supportive and Metabolic Care
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
The 2025 case report describes symptomatic management, including intubation and inotropic support. It reports no disease-modifying treatment or controlled therapeutic trial.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Clinical care was directed to symptomatic management only when a presumptive diagnosis of mitochondrial disorder with hypertrophic cardiomyopathy was made"
Documents symptomatic management in this case.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
Describes the neonatal course, its severity, and the point at which intensive support was required.
Genetic Counseling and Carrier Testing
Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Platform: Other
For two heterozygous carrier parents, the Mendelian autosomal recessive recurrence risk is one in four per pregnancy, assuming segregation of the familial pathogenic allele. This is an inheritance-based calculation, not an observed recurrence-rate estimate. Identifying the familial variant permits targeted testing of relatives.
Show evidence (1 reference)
PMID:39779219 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"confirming both parents to be heterozygous carriers"
Both parents were carriers; the one-in-four risk follows from autosomal recessive segregation rather than a measured case-series rate.
🔬

Diagnosis

5
Skeletal muscle histochemistry and immunofluorescence
Skeletal-muscle COX histochemistry documented complex IV deficiency in the 2025 patient; immunofluorescence showed reduced MTCO1 with normal NDUFB8. These were investigations in the reported case, not a requirement to perform biopsy before molecular testing.
skeletal muscle biopsy for COX histochemistry and OXPHOS immunofluorescence NCIT:C51895 NCI Thesaurus (NCIT)
Markers: COX histochemical activity; MTCO1 and NDUFB8 immunoreactivity
Results: Moderate COX deficiency in all assessed muscle fibres; reduced MTCO1 immunoreactivity with normal NDUFB8 levels. Preserved protein abundance or assembly does not establish normal catalytic activity of every other complex.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
The muscle biopsy histochemistry is what demonstrated the Complex IV deficiency in the reported patient.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"This was corroborated by quadruple OXPHOS immunofluorescence assay, which showed a marked loss of MTCO1 immunoreactivity (Fig 2B), whereas NDUFB8 (complex I subunit) protein levels were normal"
Documents the muscle immunofluorescence findings separately from enzyme activity.
Blood and urine lactate measurement
Blood lactate and urinary organic-acid measurements documented metabolic abnormalities in the 2025 patient. These findings support investigation of mitochondrial disease but are not specific to COA5.
blood lactate measurement NCIT:C79450 NCI Thesaurus (NCIT)
Markers: Blood lactate concentration; urinary lactate and ethylmalonic acid
Results: Blood lactate elevated and fluctuating (2.5-11 mmol/L in the reported patient); urinary lactate and ethylmalonic acid elevated.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
Documents the magnitude and the variability of the lactate elevation that this diagnostic step detects.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
Documents urinary lactate elevation; ethylmalonic acid was a concurrent finding with an unresolved causal route.
Echocardiography
Echocardiography characterized hypertrophy and non-compaction morphology in the 2025 patient.
echocardiography NCIT:C16525 NCI Thesaurus (NCIT)
Markers: Ventricular wall thickness; myocardial trabeculation and compaction
Results: Biventricular hypertrophic cardiomyopathy with septal hypertrophy and a non-compaction appearance of the myocardium.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
Echocardiography is what established the cardiac phenotype in the reported patient.
Trio whole-exome sequencing with mitochondrial genome analysis
Trio exome sequencing identified homozygous COA5 p.Ala53Pro after mitochondrial genome analysis found no pathogenic mtDNA variant in the 2025 case. Molecular diagnosis requires interpretation of biallelic COA5 variants in the clinical and biochemical context; the sequence of tests in this case is not a universal testing algorithm.
trio whole-exome sequencing NCIT:C101295 NCI Thesaurus (NCIT)
Markers: COA5 genotype; mitochondrial DNA sequence
Results: Homozygous COA5 c.157G>C (p.Ala53Pro) with both parents heterozygous; no pathogenic mtDNA variant.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Molecular genetic testing eliminated pathogenic mitochondrial DNA (mtDNA) variants after a complete analysis of the mitochondrial genome."
Documents mitochondrial genome testing in this patient.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Trio whole-exome sequencing conducted at the Exeter Genomics Laboratory identified a previously reported COA5 variant (c.157G>C, p.Ala53Pro), confirming both parents to be heterozygous carriers"
Trio exome sequencing is the test that made the molecular diagnosis in the reported patient.
Complementation and knockout functional studies
Research functional studies support variant interpretation: wild-type COA5 complementation restored complex IV activity in patient fibroblasts and engineered knockout lines reproduced the assembly defect. These experiments complement clinical sequencing evidence; they are not established routine diagnostic tests.
functional molecular analysis NCIT:C19770 NCI Thesaurus (NCIT)
Markers: Complex IV activity and assembly after wild-type COA5 re-expression
Results: Complex IV activity restored by wild-type COA5 in patient fibroblasts; the isolated Complex IV assembly defect is reproduced in a COA5 knockout cell line.
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
The complementation experiment is the functional evidence that establishes variant pathogenicity for this gene.
📈

Progression

2
Neonatal presentation
Age: First days of life
Presentation is in the neonatal period. The 2025 patient had tachypnoeic episodes on day one with elevated blood lactate and was found on echocardiography to have biventricular hypertrophic cardiomyopathy; she required intubation and inotropic support at 11 days and was discharged at 6 weeks. The two siblings in the founding report had fatal neonatal cardiomyopathy.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
Describes the neonatal course, its severity, and the point at which intensive support was required.
Fatal decompensation
Age: First days to 3 months
The two siblings in the 2011 report died as neonates. The 2025 patient was discharged at six weeks, readmitted a month later with worsening respiratory distress concurrent with rhinovirus infection, poor cardiac function and severe lactic acidosis, and died at three months. These reports do not establish outcomes for other genotypes or longer-term survivors.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A month later, she was readmitted with further deterioration of respiratory distress concurrent with a rhinovirus infection, poor cardiac function, and severe lactic acidosis, and finally passed away at 3 mo of age."
Readmission occurred a month after the preceding discharge at six weeks; the infection was concurrent with terminal deterioration.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"two siblings affected by fatal neonatal cardiomyopathy"
Establishes the fatal neonatal course in the founding family.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
The 2011 and 2025 reports together describe three affected individuals from two families: a sibling pair with fatal neonatal cardiomyopathy and one unrelated child. Both families are of Turkish descent and carry homozygous COA5 c.157G>C (p.Ala53Pro). These reports do not provide a population prevalence estimate.
Show evidence (3 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"the rare c.157G>C, p.Ala53Pro variant was found only in two incidences where both patients were of Turkish ethnicity"
Establishes that as of 2025 the causal allele had been observed in only two independent instances, both in patients of Turkish ethnicity, which is the basis for the ultra-rare, case-count-only occurrence record.
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In this report, a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy."
The first report contributes two affected siblings.
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Here, we present an unrelated family in which a clinically affected child harbours the identical COA5 missense variant"
The second report contributes one unrelated affected child; together the reports describe three children.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from COA5-Related Fatal Infantile Cardioencephalomyopathy:

Other nuclear-type mitochondrial complex IV deficiencies
Overlapping Features Other nuclear complex IV assembly disorders can produce overlapping biochemical defects. The abnormal complex IV assay alone does not identify COA5.
Distinguishing Features
  • A molecular result identifying biallelic COA5 variants distinguishes the gene-defined disorder; clinical features alone do not establish the causal assembly factor.
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT BACKGROUND Other
"To date, pathogenic mutations leading to a mitochondrial disorder have been identified in only seven of the corresponding human genes."
The 2011 introduction describes multiple nuclear assembly-factor causes; its historical gene count is not used as a current count.
Ethylmalonic encephalopathy (ETHE1)
Overlapping Features Ethylmalonic encephalopathy overlaps in ethylmalonic acid elevation and reduced muscle cytochrome c oxidase activity.
Distinguishing Features
  • ETHE1-related disease prominently affects brain, gastrointestinal tract and peripheral vessels. The reported COA5 cases are dominated by neonatal cardiomyopathy; gene testing resolves the etiologic distinction.
Show evidence (1 reference)
PMID:14732903 SUPPORT DIRECT BACKGROUND Human Clinical
"Ethylmalonic encephalopathy (EE) is a devastating infantile metabolic disorder affecting the brain, gastrointestinal tract, and peripheral vessels. High levels of ethylmalonic acid are detected in the body fluids, and cytochrome c oxidase activity is decreased in skeletal muscle."
Supports the biochemical overlap and distinguishing organ-system pattern of ETHE1 disease.
Primary mitochondrial DNA disease
Overlapping Features Mitochondrial DNA variants are an alternative cause considered during evaluation of respiratory-chain disease. The 2025 COA5 patient had negative mitochondrial genome analysis.
Distinguishing Features
  • Biallelic nuclear COA5 variants with carrier parents establish a nuclear recessive etiology. Negative mitochondrial genome sequencing does not alone exclude every mitochondrial disorder or nuclear cause of mtDNA depletion.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Molecular genetic testing eliminated pathogenic mitochondrial DNA (mtDNA) variants after a complete analysis of the mitochondrial genome."
Documents mtDNA testing in the reported patient, without prescribing a mandatory order of investigations.
🧫

Experimental Models

3
COA5 p.Ala53Pro patient-derived dermal fibroblasts PRIMARY_CELL_CULTURE
Primary and immortalised dermal fibroblasts from patients homozygous for COA5 c.157G>C (p.Ala53Pro), used in both published reports. They reproduce the disease lesion in the patient's own genetic background and are the system in which the complementation experiment that established pathogenicity was performed.
fibroblast CL:0000057 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
Patient skin biopsy (homozygous COA5 c.157G>C, p.Ala53Pro)
Publication
PMID:21457908
Pathograph links
Arrested Early Complex IV Assembly recapitulates fidelity: high observes: molecular Patient fibroblasts accumulate an early COX1-containing intermediate and have reduced mature complex IV. Wild-type COA5 restores complex IV activity.
Limitations: Fibroblasts are not an affected tissue in this cardiac-dominant disorder, so nothing about the cardiomyopathy can be read out here. The cells also grow poorly, which the 2025 authors identify as a practical limit on further experimentation.
Readouts
Complex IV assembly intermediates on 2D-BN PAGE
Direction: INCREASED
Interpretation: Accumulation of a small COX1-containing intermediate lacking COX2, COX4 and COX5b is the direct structural readout of the arrested assembly step.
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Detailed analysis of complex IV assembly intermediates in patient fibroblasts by 2D-BN PAGE revealed the accumulation of a small assembly intermediate containing subunit COX1 but not the COX2, COX4, or COX5b subunits, indicating that C2orf64 is involved in an early step of the complex IV..."
Reports the measurement and its direction in this model system.
Complex IV activity after wild-type COA5 re-expression
Direction: RESTORED
Interpretation: Full restoration of Complex IV activity on complementation is what attributes the deficiency to COA5 rather than to background.
Show evidence (1 reference)
PMID:21457908 SUPPORT DIRECT PRIMARY RESULT In Vitro
"complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
Reports the rescue measurement in the patient fibroblast model.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"CIV protein subunits exhibited a statistically significant decrease in protein abundance up to almost fourfold, whereas CI, CII, CIII, and CV protein abundance remained unchanged"
Proteomic profiling of immortalised patient fibroblasts supports selective reduction of CIV protein abundance.
Both primary and immortalised patient fibroblasts showed arrested growth in culture; proteomic profiling used immortalised derivatives.
CRISPR/Cas9 COA5 knockout U2OS cell line CELL_LINE
A homozygous COA5 knockout (7-bp deletion, c.287_290+3del) engineered in the human U2OS osteosarcoma line, with an isogenic wild-type control from the same nucleofected population. Built specifically because the patient fibroblasts grow too poorly for extended biochemistry, it is the system in which complexome profiling localized the COA5-dependent step.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
U2OS human osteosarcoma cell line, CRISPR/Cas9-edited, with isogenic control
Publication
PMID:39779219
Pathograph links
Arrested Early Complex IV Assembly recapitulates fidelity: moderate observes: molecular The knockout reproduces the patients' isolated Complex IV defect and resolves it further: MTCO1-containing subcomplexes accumulate, MTCO2 is absent, and the holoenzyme is lost, placing the COA5 step between MTCO1 maturation and MTCO2 incorporation.
Limitations: U2OS is a heterologous osteosarcoma line. The engineered c.287_290+3del deletion causes undetectable COA5 protein on complexome profiling, unlike the patient missense genotype. Cardiac remodeling and infantile lethality lie outside this cellular model.
Divergences from the human mechanism
cause unrepresented qualifying
The model carries an engineered deletion with loss of detectable COA5 protein, rather than the patient p.Ala53Pro substitution. It does not establish that the missense allele is a complete null.
boundary omission qualifying
Cardiomyocytes, the myocardium, and the whole organism lie outside the model boundary, so the hypertrophic remodeling and infantile lethality that define the clinical disorder cannot arise in it. Its claims are restricted to the molecular assembly step.
Readouts
Steady-state MTCO2 subunit level
Direction: DECREASED
Interpretation: Loss of MTCO2 is a readout of the early complex IV assembly defect.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"The COA5KO cells successfully replicated the isolated complex IV deficiency observed in the reported patients by indicating an evident loss of MTCO2 protein"
Reports the MTCO2 measurement and its direction in the knockout line.
Fully assembled complex IV holocomplex on complexome profiling
Direction: ABOLISHED
Interpretation: Loss of the holocomplex with accumulation of early intermediates is the structural signature of an arrested assembly step.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"the accumulation of early CIV assembly intermediates (Fig 6A, right panel, green boxed subunits and assembly factors) and the loss of fully assembled CIV holocomplexes were observed in contrast to the isogenic control cell line"
Reports the holocomplex measurement against an isogenic control.
Show evidence (1 reference)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Mitochondrial complexome profiling pinpointed a role of COA5 in early CIV assembly, more specifically, its involvement in the stage between MTCO1 maturation and the incorporation of MTCO2"
The knockout line is the system that produced the current mechanistic placement of the COA5 step, which is what makes it informative for this node.
Loss of Complex IV-Containing Supercomplexes recapitulates fidelity: moderate observes: molecular Complexome profiling resolves the loss of III2+IV and increase in I+III2 supercomplexes.
Limitations: These are knockout-cell measurements, without confirmation in patient myocardium.
Show evidence (2 references)
PMID:39779219 SUPPORT DIRECT PRIMARY RESULT In Vitro
"When assessing complex III subunits, a complete loss of the supercomplexes III2+IV (Ss) was observed in the COA5KO cell line"
Directly documents loss of III2+IV in the engineered U2OS line.
+ 1 more reference
TALEN PET191/COA5 knockout HEK293T cells CELL_LINE
TALEN-generated PET191/COA5 knockout HEK293T cells were used to study COX2 metallochaperone interactions and complex IV biogenesis. Wild-type PET191 reconstitution rescued the reported defects.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
HEK293T cells with engineered PET191/COA5 knockout
Publication
PMID:35750769
Pathograph links
Disrupted COX2 Metallochaperone Interactions recapitulates fidelity: moderate observes: molecular The knockout disrupts COX2 association with SCO1, COA6 and COX16.
Limitations: Engineered absence of PET191 in HEK293T cells does not reproduce the patient missense allele or the cardiac tissue context.
Show evidence (1 reference)
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191"
Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions. This has not been measured in patient cells.
The study also observed increased H2DCFDA signal and peroxide sensitivity in PET191 knockout cells; COX10 silencing ablated peroxide sensitivity. These oxidative-stress findings have not been demonstrated in COA5 patients.
Show evidence (2 references)
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"We used transcription activator-like effector nucleases (TALENs) to generate HEK293T PET191-KO cell lines"
Defines the experimental system.
PMID:35750769 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Similarly, the human COX19-KO and PET191-KO lines are hypersensitive to H2O2, a phenotype that can be ablated by COX10 silencing"
Documents an additional cell-model oxidative-stress phenotype, not an established clinical mechanism.
{ }

Source YAML

click to show 
name: COA5-Related Fatal Infantile Cardioencephalomyopathy
category: Mendelian
creation_date: "2026-09-07T00:00:00Z"
synonyms:
- CEMCOX3
- Cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 3
- Mitochondrial complex IV deficiency, nuclear type 9
- MC4DN9
- COA5 fatal infantile encephalocardiomyopathy
- C2orf64 deficiency
description: >-
  COA5-related fatal infantile cardioencephalomyopathy (CEMCOX3; mitochondrial complex IV deficiency nuclear
  type 9, MC4DN9) is an ultra-rare autosomal recessive disorder of cytochrome c oxidase assembly caused
  by biallelic COA5 variants. Patient fibroblasts accumulate early MTCO1-containing assembly intermediates
  and have reduced mature complex IV. COA5 knockout cells localize the assembly defect between MTCO1 maturation
  and MTCO2 incorporation. The 2011 and 2025 clinical reports describe three affected children in two
  Turkish families, all homozygous for c.157G>C (p.Ala53Pro). Neonatal hypertrophic cardiomyopathy and
  infantile death dominate the reported course. The 2025 patient also had respiratory insufficiency, lactic
  acidosis, urinary lactate and ethylmalonic acid elevation, and hepatic abnormalities. Normal brain imaging
  in that patient does not exclude neurological involvement in the wider disorder. The small case series
  cannot establish penetrance, phenotype frequencies, or the full clinical spectrum.
disease_term:
  preferred_term: COA5-related fatal infantile cardioencephalomyopathy (CEMCOX3/MC4DN9)
  term:
    id: MONDO:0014667
    label: cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 3
mappings:
  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 specific to COA5-related disease or to nuclear-type
      Complex IV deficiency. E88.49 is the residual code within the E88.4
      mitochondrial metabolism block and is therefore a broad, not exact, match.
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    The 2011 and 2025 reports together describe three affected individuals from two families: a sibling
    pair with fatal neonatal cardiomyopathy and one unrelated child. Both families are of Turkish descent
    and carry homozygous COA5 c.157G>C (p.Ala53Pro). These reports do not provide a population prevalence
    estimate.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the rare c.157G>C, p.Ala53Pro variant was found only in two incidences where both patients were of Turkish ethnicity"
    explanation: >-
      Establishes that as of 2025 the causal allele had been observed in only two
      independent instances, both in patients of Turkish ethnicity, which is the
      basis for the ultra-rare, case-count-only occurrence record.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In this report, a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy.
    explanation: >-
      The first report contributes two affected siblings.
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Here, we present an unrelated family in which a clinically affected child harbours the identical COA5 missense variant
    explanation: >-
      The second report contributes one unrelated affected child; together the reports describe three
      children.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  penetrance: UNKNOWN
  expressivity: UNKNOWN
  description: >-
    The homozygous COA5 p.Ala53Pro variant segregates with disease in the reported families, with heterozygous
    carrier parents in the 2025 family. Three affected children from two families do not establish population
    penetrance or the range of expressivity. The founding siblings died as neonates and the later patient
    at three months.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Trio whole-exome sequencing conducted at the Exeter Genomics Laboratory identified a previously reported COA5 variant (c.157G>C, p.Ala53Pro), confirming both parents to be heterozygous carriers"
    explanation: >-
      Homozygosity in the affected child with both parents heterozygous carriers
      is the segregation pattern of autosomal recessive inheritance.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A female neonate born to second cousins of Turkish descent presented with tachypnoeic episodes on the first day of life"
    explanation: >-
      Parental consanguinity is consistent with recessive inheritance; it does not establish a founder
      effect.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
progression:
- phase: Neonatal presentation
  age_range: First days of life
  notes: >-
    Presentation is in the neonatal period. The 2025 patient had tachypnoeic
    episodes on day one with elevated blood lactate and was found on
    echocardiography to have biventricular hypertrophic cardiomyopathy; she
    required intubation and inotropic support at 11 days and was discharged at 6
    weeks. The two siblings in the founding report had fatal neonatal
    cardiomyopathy.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
    explanation: >-
      Describes the neonatal course, its severity, and the point at which
      intensive support was required.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- phase: Fatal decompensation
  age_range: First days to 3 months
  notes: >-
    The two siblings in the 2011 report died as neonates. The 2025 patient was discharged at six weeks,
    readmitted a month later with worsening respiratory distress concurrent with rhinovirus infection,
    poor cardiac function and severe lactic acidosis, and died at three months. These reports do not establish
    outcomes for other genotypes or longer-term survivors.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A month later, she was readmitted with further deterioration of respiratory distress concurrent with a rhinovirus infection, poor cardiac function, and severe lactic acidosis, and finally passed away at 3 mo of age."
    explanation: >-
      Readmission occurred a month after the preceding discharge at six weeks; the infection was concurrent
      with terminal deterioration.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "two siblings affected by fatal neonatal cardiomyopathy"
    explanation: >-
      Establishes the fatal neonatal course in the founding family.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
pathophysiology:
- name: Impaired COA5 Assembly-Factor Function
  biological_scale: MOLECULAR
  description: >-
    Homozygous COA5 p.Ala53Pro impairs assembly-factor function. Wild-type COA5 complementation restores
    complex IV activity in patient fibroblasts. This functional defect does not establish complete absence
    of the missense protein; the null cell models are distinct experimental perturbations.
  genes:
  - preferred_term: COA5
    term:
      id: hgnc:33848
      label: COA5
  evidence:
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
    explanation: >-
      Complementation with wild-type COA5 restores Complex IV activity in patient
      cells, establishing loss of COA5 function as the direct molecular lesion.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Arrested Early Complex IV Assembly
    causal_link_type: DIRECT
    description: >-
      Loss of functional COA5 impairs early complex IV assembly; patient-cell rescue attributes the defect
      to COA5.
    evidence:
    - reference: PMID:21457908
      reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
      explanation: >-
        Complementation with wild-type COA5 restores Complex IV activity in patient
        cells, establishing loss of COA5 function as the direct molecular lesion.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  - target: Disrupted COX2 Metallochaperone Interactions
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Loss of COA5/PET191 disrupts COX2 assembly-factor interactions in engineered HEK293T cells. Transfer
      of this precise intermediate to p.Ala53Pro patient cells remains provisional.
- name: Disrupted COX2 Metallochaperone Interactions
  biological_scale: MOLECULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    In PET191/COA5 knockout HEK293T cells, newly synthesized COX2 fails to interact with SCO1, COA6 and
    COX16. These experiments support a COA5-dependent metallochaperone assembly function, but do not establish
    that p.Ala53Pro disrupts each interaction identically.
  evidence:
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191
    explanation: >-
      Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions.
      This has not been measured in patient cells.
  downstream:
  - target: Arrested Early Complex IV Assembly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Impaired recruitment of COX2 maturation factors provides a candidate explanation for failure to
      incorporate mature MTCO2. The exact connection to the patient missense assembly defect remains unresolved.
- name: Arrested Early Complex IV Assembly
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  biological_scale: MOLECULAR
  description: >-
    Patient fibroblasts accumulate an early COX1/MTCO1-containing intermediate lacking COX2, COX4 and
    COX5b, with reduced mature complex IV. In COA5 knockout U2OS cells, complexome profiling places the
    block between MTCO1 maturation and MTCO2 incorporation. Complete loss of the holocomplex in knockout
    cells should not be equated with complete loss in patient fibroblasts.
  cellular_components:
  - preferred_term: mitochondrial respiratory chain complex IV
    term:
      id: GO:0045277
      label: respiratory chain complex IV
  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:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Detailed analysis of complex IV assembly intermediates in patient fibroblasts by 2D-BN PAGE revealed the accumulation of a small assembly intermediate containing subunit COX1 but not the COX2, COX4, or COX5b subunits, indicating that C2orf64 is involved in an early step of the complex IV assembly process."
    explanation: >-
      Directly localizes the COA5/C2orf64 lesion to an early step of Complex IV
      assembly, with a COX1-containing intermediate that fails to acquire COX2.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Mitochondrial complexome profiling pinpointed a role of COA5 in early CIV assembly, more specifically, its involvement in the stage between MTCO1 maturation and the incorporation of MTCO2"
    explanation: >-
      Complexome profiling of a CRISPR/Cas9 COA5 knockout cell line places the
      COA5-dependent step precisely between MTCO1 maturation and MTCO2
      incorporation.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: CIV protein subunits exhibited a statistically significant decrease in protein abundance up to almost fourfold, whereas CI, CII, CIII, and CV protein abundance remained unchanged
    explanation: >-
      Proteomic profiling of immortalised patient fibroblasts supports selective reduction of CIV protein
      abundance.
  downstream:
  - target: Reduced Complex IV Activity
    causal_link_type: DIRECT
    description: >-
      Impaired formation of mature complex IV reduces cytochrome c oxidase activity. Wild-type COA5 restores
      complex IV activity in patient fibroblasts.
    evidence:
    - reference: PMID:21457908
      reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
      explanation: >-
        Complementation with wild-type COA5 restores Complex IV activity in patient
        cells, establishing loss of COA5 function as the direct molecular lesion.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  - target: Loss of Complex IV-Containing Supercomplexes
    causal_link_type: DIRECT
    description: >-
      Failure to assemble mature complex IV limits its incorporation into respiratory supercomplexes in
      COA5 knockout U2OS cells.
- name: Reduced Complex IV Activity
  biological_scale: CELLULAR
  description: >-
    Cytochrome c oxidase activity is deficient in patient-derived fibroblasts and skeletal muscle. Reduced
    terminal oxidase function is expected to limit oxidative energy production, but the cited clinical
    studies do not directly measure myocardial ATP synthesis or prove its complete collapse.
  biological_processes:
  - preferred_term: mitochondrial electron transport, cytochrome c to oxygen
    term:
      id: GO:0006123
      label: mitochondrial electron transport, cytochrome c to oxygen
    modifier: DECREASED
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
    explanation: >-
      The assembly block translates into measurably deficient Complex IV
      activity in patient muscle, the functional consequence asserted by this
      edge.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
    explanation: >-
      Complementation with wild-type COA5 restores Complex IV activity in patient
      cells, establishing loss of COA5 function as the direct molecular lesion.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Systemic Lactate Accumulation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced oxidative metabolism provides a plausible route to increased lactate production. Pyruvate
      flux and the intervening metabolic steps were not measured in COA5 patients.
  - target: Hypertrophic Myocardial Remodeling
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Impaired mitochondrial energy production plausibly contributes to myocardial remodeling. The tissue-specific
      steps from the assembly defect to hypertrophy have not been resolved.
  - target: Decreased Activity of Mitochondrial Complex IV
    causal_link_type: DIRECT
    description: >-
      The enzymatic defect is measured as reduced cytochrome c oxidase activity.
- name: Loss of Complex IV-Containing Supercomplexes
  biological_scale: MOLECULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    COA5 knockout U2OS cells lose the III2+IV supercomplex and accumulate I+III2 assemblies. This respiratory-chain
    reorganization is an experimental consequence of COA5 deletion; its extent and functional contribution
    in patient myocardium are unknown.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: When assessing complex III subunits, a complete loss of the supercomplexes III2+IV (Ss) was observed in the COA5KO cell line
    explanation: >-
      Directly documents loss of III2+IV in the engineered U2OS line.
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: 'An increased abundance of respiratory supercomplexes containing complexes I and III2 (S0: I+III2) was observed in the COA5KO cell line'
    explanation: >-
      Documents the corresponding increase in I+III2 assemblies.
  notes: >-
    Whether this supercomplex reorganization independently contributes to clinical

    severity is unknown; no downstream clinical consequence has been established.
- name: Systemic Lactate Accumulation
  conforms_to: "complex_iv_assembly_deficiency#Lactic Acidosis and Metabolic Decompensation"
  biological_scale: ORGANISM
  description: >-
    The 2025 patient had fluctuating blood lactate elevation, urinary lactate elevation and severe lactic
    acidosis during terminal deterioration. Increased lactate production from impaired oxidative metabolism
    is a physiological interpretation; the study did not measure lactate production or clearance flux.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
    explanation: >-
      Documents fluctuating blood lactate elevation in the 2025 patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
    explanation: >-
      Documents urinary lactate elevation; ethylmalonic acid was a concurrent finding with an unresolved
      causal route.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Lactic Acidosis
    causal_link_type: DIRECT
    description: >-
      Lactate accumulation accompanies the documented severe lactic acidosis.
  - target: Lacticaciduria
    causal_link_type: DIRECT
    description: >-
      Systemic lactate accumulation is accompanied by increased urinary lactate.
- name: Hypertrophic Myocardial Remodeling
  conforms_to: "complex_iv_assembly_deficiency#High-Energy Tissue Dysfunction"
  biological_scale: TISSUE
  description: >-
    Hypertrophic cardiomyopathy is the dominant reported clinical manifestation. The 2025 patient had
    biventricular and septal hypertrophy, a non-compaction appearance, and subsequent poor cardiac function.
    The cellular remodeling response and the origin of the non-compaction morphology remain uncharacterized.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  evidence:
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy"
    explanation: >-
      The founding report establishes cardiomyopathy as the defining organ
      manifestation of COA5 deficiency.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
    explanation: >-
      Characterizes the cardiac phenotype in the second reported family as
      biventricular hypertrophic cardiomyopathy with non-compaction morphology.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  downstream:
  - target: Hypertrophic Cardiomyopathy
    causal_link_type: DIRECT
    description: The remodeling response is expressed as hypertrophic cardiomyopathy.
  - target: Ventricular Septal Hypertrophy
    causal_link_type: DIRECT
    description: Septal hypertrophy is a component of the hypertrophic remodeling.
phenotypes:
- category: Cardiovascular
  name: Hypertrophic Cardiomyopathy
  description: >-
    Neonatal hypertrophic cardiomyopathy is described in the two clinical reports. The 2025 patient had
    biventricular involvement. The small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Biventricular hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
    onset:
      onset_category: NEONATAL
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
    explanation: >-
      Echocardiographic documentation of biventricular hypertrophic
      cardiomyopathy in the second reported family.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "C2orf64 mutational analysis should be considered for complex IV deficient patients, in particular those with hypertrophic cardiomyopathy"
    explanation: >-
      The founding report's own conclusion identifies hypertrophic cardiomyopathy
      as the presentation that should prompt COA5 testing, supporting it as the
      characteristic phenotype.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: two siblings affected by neonatal hypertrophic cardiomyopathy manifesting a rare, homozygous COA5 missense variant
    explanation: The 2025 abstract summarizes neonatal hypertrophic cardiomyopathy in the founding sibling pair.
- category: Cardiovascular
  name: Ventricular Septal Hypertrophy
  description: >-
    Septal hypertrophy on echocardiography, reported in the single patient in
    whom echocardiographic detail is published.
  phenotype_term:
    preferred_term: Septal hypertrophy
    term:
      id: HP:0005144
      label: Ventricular septal hypertrophy
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "biventricular hypertrophic cardiomyopathy with septal hypertrophy"
    explanation: >-
      Reports septal hypertrophy as a component of the echocardiographic
      cardiomyopathy phenotype.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Cardiovascular
  name: Noncompaction Cardiomyopathy
  description: >-
    A non-compaction appearance of the myocardium accompanying the hypertrophy,
    reported in one patient. The published description does not specify a
    chamber, so the finding is bound at the chamber-agnostic HPO term.
  phenotype_term:
    preferred_term: Non-compaction appearance of the myocardium
    term:
      id: HP:0012817
      label: Noncompaction cardiomyopathy
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "non-compaction appearance of the myocardium"
    explanation: >-
      Records the non-compaction morphology observed on echocardiography.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Metabolic
  name: Lactic Acidosis
  description: >-
    Elevated blood lactate from the first days of life, fluctuating between 2.5
    and 11 mmol/L in the 2025 patient and becoming severe during terminal
    decompensation.
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
    explanation: >-
      Quantifies the lactate elevation underpinning the lactic acidosis
      phenotype.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "poor cardiac function, and severe lactic acidosis, and finally passed away at 3 mo of age"
    explanation: >-
      Documents progression to severe lactic acidosis during the fatal
      decompensation.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Metabolic
  name: Lacticaciduria
  description: >-
    Elevated urinary lactate was reported in the 2025 patient.
  phenotype_term:
    preferred_term: Elevated urinary lactate
    term:
      id: HP:0003648
      label: Lacticaciduria
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
    explanation: >-
      Reports elevated urinary lactate in the patient's organic-acid profile.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Metabolic
  name: Ethylmalonic Aciduria
  description: >-
    Elevated urinary ethylmalonic acid was reported in the 2025 patient; its biochemical route in COA5
    deficiency is unresolved.
  phenotype_term:
    preferred_term: Ethylmalonic aciduria
    term:
      id: HP:0003219
      label: Ethylmalonic aciduria
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "elevated urinary lactate and ethylmalonic acid"
    explanation: >-
      Records ethylmalonic aciduria in the metabolic profile of the reported
      patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Respiratory
  name: Tachypnea
  description: >-
    Tachypnoeic episodes from the first day of life were the presenting complaint
    in the 2025 patient, progressing to respiratory distress requiring intubation.
  phenotype_term:
    preferred_term: Tachypnoeic episodes
    term:
      id: HP:0002789
      label: Tachypnea
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A female neonate born to second cousins of Turkish descent presented with tachypnoeic episodes on the first day of life"
    explanation: >-
      Tachypnoea on day one of life was the presenting feature in this patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Respiratory
  name: Respiratory Insufficiency
  description: >-
    Respiratory distress required intubation at 11 days of life in the 2025 patient.
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
    explanation: >-
      Documents respiratory insufficiency requiring intubation.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Hepatic
  name: Abnormal Hepatic Echogenicity
  description: >-
    Increased hepatic echogenicity on ultrasound with abnormal liver function
    tests, reported in one patient.
  phenotype_term:
    preferred_term: Increased hepatic echogenicity
    term:
      id: HP:0031142
      label: Abnormal hepatic echogenicity
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Liver function tests were abnormal with increased echogenicity of liver on ultrasound."
    explanation: >-
      Reports the hepatic ultrasound and biochemical abnormality directly.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- category: Cellular
  name: Decreased Activity of Mitochondrial Complex IV
  description: >-
    Isolated deficiency of cytochrome c oxidase activity in skeletal muscle and
    cultured fibroblasts, with the other respiratory-chain complexes preserved.
    This is the defining biochemical finding of the disorder.
  phenotype_term:
    preferred_term: Isolated complex IV deficiency
    term:
      id: HP:0008347
      label: Decreased activity of mitochondrial complex IV
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
    explanation: >-
      Direct histochemical demonstration of reduced Complex IV activity in
      patient muscle.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
    explanation: >-
      Complex IV activity in patient fibroblasts was deficient and rescuable,
      which both demonstrates the deficiency and attributes it to COA5.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
genetic:
- name: COA5 pathogenic variants causing CEMCOX3 (MC4DN9)
  gene_term:
    preferred_term: COA5
    term:
      id: hgnc:33848
      label: COA5
  variant_origin: GERMLINE
  features: >-
    The 2011 and 2025 reports describe homozygous NM_001008215.3:c.157G>C (p.Ala53Pro) in three children
    from two Turkish families. The substituted alanine lies in the twin-CX9C domain and is not broadly
    conserved. Several computational predictors suggested damage, but REVEL fell below its recommended
    threshold; patient-cell complementation provides direct functional support.
  variants:
  - name: COA5 c.157G>C (p.Ala53Pro)
    description: >-
      Homozygous missense variant in the twin-CX9C domain, shared by the two published families. The 2025
      paper records a pathogenic ClinVar classification. A founder effect was proposed but requires haplotype
      verification.
    gene:
      preferred_term: COA5
      term:
        id: hgnc:33848
        label: COA5
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The homozygous COA5 missense variant has been recorded on ClinVar as a pathogenic variant associated with isolated COX deficiency"
      explanation: >-
        Reports the ClinVar classification recorded by the 2025 authors.
      quote_role: BACKGROUND
      directness: DIRECT
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: NO_EVIDENCE
      evidence_source: COMPUTATIONAL
      snippet: "the REVEL meta-predictor score was below the recommended threshold for this variant, necessitating further study"
      explanation: >-
        A below-threshold REVEL result does not itself support the pathogenic classification; functional
        complementation is the relevant positive evidence.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
    - reference: PMID:21457908
      reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
      explanation: >-
        Complementation with wild-type COA5 restores Complex IV activity in patient
        cells, establishing loss of COA5 function as the direct molecular lesion.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Trio whole-exome sequencing conducted at the Exeter Genomics Laboratory identified a previously reported COA5 variant (c.157G>C, p.Ala53Pro), confirming both parents to be heterozygous carriers"
      explanation: >-
        Homozygous proband with heterozygous carrier parents establishes
        autosomal recessive segregation.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  evidence:
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a homozygous mutation in C2orf64 is described in two siblings affected by fatal neonatal cardiomyopathy"
    explanation: >-
      Identifies COA5 (C2orf64) as the causal gene in the founding family.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
diagnosis:
- name: Skeletal muscle histochemistry and immunofluorescence
  description: >-
    Skeletal-muscle COX histochemistry documented complex IV deficiency in the 2025 patient; immunofluorescence
    showed reduced MTCO1 with normal NDUFB8. These were investigations in the reported case, not a requirement
    to perform biopsy before molecular testing.
  diagnosis_term:
    preferred_term: skeletal muscle biopsy for COX histochemistry and OXPHOS immunofluorescence
    term:
      id: NCIT:C51895
      label: Muscle Biopsy
  results: >-
    Moderate COX deficiency in all assessed muscle fibres; reduced MTCO1 immunoreactivity with normal
    NDUFB8 levels. Preserved protein abundance or assembly does not establish normal catalytic activity
    of every other complex.
  markers: COX histochemical activity; MTCO1 and NDUFB8 immunoreactivity
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histochemical analysis of skeletal muscle cryosections from the patient indicated a moderate CIV deficiency in all fibres"
    explanation: >-
      The muscle biopsy histochemistry is what demonstrated the Complex IV
      deficiency in the reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: This was corroborated by quadruple OXPHOS immunofluorescence assay, which showed a marked loss of MTCO1 immunoreactivity (Fig 2B), whereas NDUFB8 (complex I subunit) protein levels were normal
    explanation: Documents the muscle immunofluorescence findings separately from enzyme activity.
- name: Blood and urine lactate measurement
  description: >-
    Blood lactate and urinary organic-acid measurements documented metabolic abnormalities in the 2025
    patient. These findings support investigation of mitochondrial disease but are not specific to COA5.
  diagnosis_term:
    preferred_term: blood lactate measurement
    term:
      id: NCIT:C79450
      label: Lactic Acid Measurement
  results: >-
    Blood lactate elevated and fluctuating (2.5-11 mmol/L in the reported
    patient); urinary lactate and ethylmalonic acid elevated.
  markers: Blood lactate concentration; urinary lactate and ethylmalonic acid
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Blood lactate was elevated at variable levels between 2.5 and 11 mmol/litre."
    explanation: >-
      Documents the magnitude and the variability of the lactate elevation that
      this diagnostic step detects.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Focused metabolic biochemical investigations identified elevated urinary lactate and ethylmalonic acid."
    explanation: >-
      Documents urinary lactate elevation; ethylmalonic acid was a concurrent finding with an unresolved
      causal route.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Echocardiography
  description: >-
    Echocardiography characterized hypertrophy and non-compaction morphology in the 2025 patient.
  diagnosis_term:
    preferred_term: echocardiography
    term:
      id: NCIT:C16525
      label: Echocardiography Test
  results: >-
    Biventricular hypertrophic cardiomyopathy with septal hypertrophy and a
    non-compaction appearance of the myocardium.
  markers: Ventricular wall thickness; myocardial trabeculation and compaction
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "subsequent echocardiography indicated significant biventricular hypertrophic cardiomyopathy with septal hypertrophy and non-compaction appearance of the myocardium"
    explanation: >-
      Echocardiography is what established the cardiac phenotype in the reported
      patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Trio whole-exome sequencing with mitochondrial genome analysis
  description: >-
    Trio exome sequencing identified homozygous COA5 p.Ala53Pro after mitochondrial genome analysis found
    no pathogenic mtDNA variant in the 2025 case. Molecular diagnosis requires interpretation of biallelic
    COA5 variants in the clinical and biochemical context; the sequence of tests in this case is not a
    universal testing algorithm.
  diagnosis_term:
    preferred_term: trio whole-exome sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  results: >-
    Homozygous COA5 c.157G>C (p.Ala53Pro) with both parents heterozygous; no
    pathogenic mtDNA variant.
  markers: COA5 genotype; mitochondrial DNA sequence
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Molecular genetic testing eliminated pathogenic mitochondrial DNA (mtDNA) variants after a complete analysis of the mitochondrial genome."
    explanation: >-
      Documents mitochondrial genome testing in this patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Trio whole-exome sequencing conducted at the Exeter Genomics Laboratory identified a previously reported COA5 variant (c.157G>C, p.Ala53Pro), confirming both parents to be heterozygous carriers"
    explanation: >-
      Trio exome sequencing is the test that made the molecular diagnosis in the
      reported patient.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Complementation and knockout functional studies
  description: >-
    Research functional studies support variant interpretation: wild-type COA5 complementation restored
    complex IV activity in patient fibroblasts and engineered knockout lines reproduced the assembly defect.
    These experiments complement clinical sequencing evidence; they are not established routine diagnostic
    tests.
  diagnosis_term:
    preferred_term: functional molecular analysis
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  results: >-
    Complex IV activity restored by wild-type COA5 in patient fibroblasts; the
    isolated Complex IV assembly defect is reproduced in a COA5 knockout cell
    line.
  markers: Complex IV activity and assembly after wild-type COA5 re-expression
  evidence:
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
    explanation: >-
      The complementation experiment is the functional evidence that establishes
      variant pathogenicity for this gene.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
treatments:
- name: Supportive and Metabolic Care
  description: >-
    The 2025 case report describes symptomatic management, including intubation and inotropic support.
    It reports no disease-modifying treatment or controlled therapeutic trial.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical care was directed to symptomatic management only when a presumptive diagnosis of mitochondrial disorder with hypertrophic cardiomyopathy was made"
    explanation: >-
      Documents symptomatic management in this case.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Because of worsening respiratory distress, she was intubated and given inotropic support at 11 d after birth before being discharged at 6 wk."
    explanation: >-
      Describes the neonatal course, its severity, and the point at which
      intensive support was required.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- name: Genetic Counseling and Carrier Testing
  description: >-
    For two heterozygous carrier parents, the Mendelian autosomal recessive recurrence risk is one in
    four per pregnancy, assuming segregation of the familial pathogenic allele. This is an inheritance-based
    calculation, not an observed recurrence-rate estimate. Identifying the familial variant permits targeted
    testing of relatives.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: OTHER
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "confirming both parents to be heterozygous carriers"
    explanation: >-
      Both parents were carriers; the one-in-four risk follows from autosomal recessive segregation rather
      than a measured case-series rate.
    directness: INDIRECT
    quote_role: PRIMARY_RESULT
experimental_models:
- name: COA5 p.Ala53Pro patient-derived dermal fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >
    Primary and immortalised dermal fibroblasts from patients homozygous for
    COA5 c.157G>C (p.Ala53Pro), used in both published reports. They reproduce
    the disease lesion in the patient's own genetic background and are the
    system in which the complementation experiment that established
    pathogenicity was performed.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  cell_source: Patient skin biopsy (homozygous COA5 c.157G>C, p.Ala53Pro)
  publication: PMID:21457908
  modeled_mechanisms:
  - target: Arrested Early Complex IV Assembly
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: MOLECULAR
    description: >-
      Patient fibroblasts accumulate an early COX1-containing intermediate and have reduced mature complex
      IV. Wild-type COA5 restores complex IV activity.
    limitations: >-
      Fibroblasts are not an affected tissue in this cardiac-dominant disorder,
      so nothing about the cardiomyopathy can be read out here. The cells also
      grow poorly, which the 2025 authors identify as a practical limit on
      further experimentation.
    readouts:
    - name: Complex IV assembly intermediates on 2D-BN PAGE
      target: Arrested Early Complex IV Assembly
      direction: INCREASED
      interpretation: >-
        Accumulation of a small COX1-containing intermediate lacking COX2, COX4
        and COX5b is the direct structural readout of the arrested assembly step.
      evidence:
      - reference: PMID:21457908
        reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "Detailed analysis of complex IV assembly intermediates in patient fibroblasts by 2D-BN PAGE revealed the accumulation of a small assembly intermediate containing subunit COX1 but not the COX2, COX4, or COX5b subunits, indicating that C2orf64 is involved in an early step of the complex IV assembly process."
        explanation: Reports the measurement and its direction in this model system.
        quote_role: PRIMARY_RESULT
        directness: DIRECT
    - name: Complex IV activity after wild-type COA5 re-expression
      target: Arrested Early Complex IV Assembly
      direction: RESTORED
      interpretation: >-
        Full restoration of Complex IV activity on complementation is what
        attributes the deficiency to COA5 rather than to background.
      evidence:
      - reference: PMID:21457908
        reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "complex IV activity can be fully restored by retroviral transduction of wild-type C2orf64 in patient-derived fibroblasts"
        explanation: Reports the rescue measurement in the patient fibroblast model.
        quote_role: PRIMARY_RESULT
        directness: DIRECT
    evidence:
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: CIV protein subunits exhibited a statistically significant decrease in protein abundance up to almost fourfold, whereas CI, CII, CIII, and CV protein abundance remained unchanged
      explanation: >-
        Proteomic profiling of immortalised patient fibroblasts supports selective reduction of CIV protein
        abundance.
  notes: >-
    Both primary and immortalised patient fibroblasts showed arrested growth in culture; proteomic profiling
    used immortalised derivatives.
- name: CRISPR/Cas9 COA5 knockout U2OS cell line
  experimental_model_type: CELL_LINE
  description: >
    A homozygous COA5 knockout (7-bp deletion, c.287_290+3del) engineered in the
    human U2OS osteosarcoma line, with an isogenic wild-type control from the
    same nucleofected population. Built specifically because the patient
    fibroblasts grow too poorly for extended biochemistry, it is the system in
    which complexome profiling localized the COA5-dependent step.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: U2OS human osteosarcoma cell line, CRISPR/Cas9-edited, with isogenic control
  publication: PMID:39779219
  modeled_mechanisms:
  - target: Arrested Early Complex IV Assembly
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      The knockout reproduces the patients' isolated Complex IV defect and
      resolves it further: MTCO1-containing subcomplexes accumulate, MTCO2 is
      absent, and the holoenzyme is lost, placing the COA5 step between MTCO1
      maturation and MTCO2 incorporation.
    limitations: >-
      U2OS is a heterologous osteosarcoma line. The engineered c.287_290+3del deletion causes undetectable
      COA5 protein on complexome profiling, unlike the patient missense genotype. Cardiac remodeling and
      infantile lethality lie outside this cellular model.
    divergences:
    - divergence_type: CAUSE_UNREPRESENTED
      materiality: QUALIFYING
      description: >-
        The model carries an engineered deletion with loss of detectable COA5 protein, rather than the
        patient p.Ala53Pro substitution. It does not establish that the missense allele is a complete
        null.
    - divergence_type: BOUNDARY_OMISSION
      materiality: QUALIFYING
      description: >-
        Cardiomyocytes, the myocardium, and the whole organism lie outside the
        model boundary, so the hypertrophic remodeling and infantile lethality
        that define the clinical disorder cannot arise in it. Its claims are
        restricted to the molecular assembly step.
    readouts:
    - name: Steady-state MTCO2 subunit level
      target: Arrested Early Complex IV Assembly
      direction: DECREASED
      interpretation: >-
        Loss of MTCO2 is a readout of the early complex IV assembly defect.
      evidence:
      - reference: PMID:39779219
        reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "The COA5KO cells successfully replicated the isolated complex IV deficiency observed in the reported patients by indicating an evident loss of MTCO2 protein"
        explanation: Reports the MTCO2 measurement and its direction in the knockout line.
        quote_role: PRIMARY_RESULT
        directness: DIRECT
    - name: Fully assembled complex IV holocomplex on complexome profiling
      target: Arrested Early Complex IV Assembly
      direction: ABOLISHED
      interpretation: >-
        Loss of the holocomplex with accumulation of early intermediates is the
        structural signature of an arrested assembly step.
      evidence:
      - reference: PMID:39779219
        reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "the accumulation of early CIV assembly intermediates (Fig 6A, right panel, green boxed subunits and assembly factors) and the loss of fully assembled CIV holocomplexes were observed in contrast to the isogenic control cell line"
        explanation: Reports the holocomplex measurement against an isogenic control.
        quote_role: PRIMARY_RESULT
        directness: DIRECT
    evidence:
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Mitochondrial complexome profiling pinpointed a role of COA5 in early CIV assembly, more specifically, its involvement in the stage between MTCO1 maturation and the incorporation of MTCO2"
      explanation: >-
        The knockout line is the system that produced the current mechanistic
        placement of the COA5 step, which is what makes it informative for this
        node.
      quote_role: PRIMARY_RESULT
      directness: DIRECT
  - target: Loss of Complex IV-Containing Supercomplexes
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      Complexome profiling resolves the loss of III2+IV and increase in I+III2 supercomplexes.
    limitations: >-
      These are knockout-cell measurements, without confirmation in patient myocardium.
    evidence:
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: When assessing complex III subunits, a complete loss of the supercomplexes III2+IV (Ss) was observed in the COA5KO cell line
      explanation: >-
        Directly documents loss of III2+IV in the engineered U2OS line.
    - reference: PMID:39779219
      reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: 'An increased abundance of respiratory supercomplexes containing complexes I and III2 (S0: I+III2) was observed in the COA5KO cell line'
      explanation: >-
        Documents the corresponding increase in I+III2 assemblies.
- name: TALEN PET191/COA5 knockout HEK293T cells
  experimental_model_type: CELL_LINE
  description: >-
    TALEN-generated PET191/COA5 knockout HEK293T cells were used to study COX2 metallochaperone interactions
    and complex IV biogenesis. Wild-type PET191 reconstitution rescued the reported defects.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: HEK293T cells with engineered PET191/COA5 knockout
  publication: PMID:35750769
  modeled_mechanisms:
  - target: Disrupted COX2 Metallochaperone Interactions
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      The knockout disrupts COX2 association with SCO1, COA6 and COX16.
    limitations: >-
      Engineered absence of PET191 in HEK293T cells does not reproduce the patient missense allele or
      the cardiac tissue context.
    evidence:
    - reference: PMID:35750769
      reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191
      explanation: >-
        Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions.
        This has not been measured in patient cells.
  notes: >-
    The study also observed increased H2DCFDA signal and peroxide sensitivity in PET191 knockout cells;
    COX10 silencing ablated peroxide sensitivity. These oxidative-stress findings have not been demonstrated
    in COA5 patients.
  evidence:
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We used transcription activator-like effector nucleases (TALENs) to generate HEK293T PET191-KO cell lines
    explanation: >-
      Defines the experimental system.
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Similarly, the human COX19-KO and PET191-KO lines are hypersensitive to H2O2, a phenotype that can be ablated by COX10 silencing
    explanation: >-
      Documents an additional cell-model oxidative-stress phenotype, not an established clinical mechanism.
differential_diagnoses:
- name: SCO2-Related Fatal Infantile Cardioencephalomyopathy
  disease_term:
    preferred_term: SCO2-related fatal infantile cardioencephalomyopathy
    term:
      id: MONDO:0011451
      label: cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 1
  description: >-
    SCO2-related disease overlaps COA5 deficiency in infantile hypertrophic cardiomyopathy and COX deficiency.
    Molecular testing distinguishes the causal genes.
  distinguishing_features:
  - >-
    The SCO2 report describes hypertrophic cardiomyopathy with encephalopathy. Neurological involvement
    in COA5 deficiency remains incompletely characterized; normal imaging in one patient is not an exclusion
    rule.
  - >-
    SCO2 and COA5 participate in complex IV biogenesis through distinct assembly-factor functions; a simple
    ordering of COA5 one step before SCO2 is not established.
  evidence:
  - reference: PMID:10749987
    reference_title: Mutations in SCO2 are associated with a distinct form of hypertrophic cardiomyopathy and cytochrome c oxidase deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These data indicate that mutations in SCO2 cause a fatal infantile mitochondrial disorder characterized by hypertrophic cardiomyopathy and encephalopathy
    explanation: >-
      Supports the clinical overlap and the SCO2-specific neurological phenotype.
- name: Other nuclear-type mitochondrial complex IV deficiencies
  description: >-
    Other nuclear complex IV assembly disorders can produce overlapping biochemical defects. The abnormal
    complex IV assay alone does not identify COA5.
  distinguishing_features:
  - >-
    A molecular result identifying biallelic COA5 variants distinguishes the gene-defined disorder; clinical
    features alone do not establish the causal assembly factor.
  evidence:
  - reference: PMID:21457908
    reference_title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: To date, pathogenic mutations leading to a mitochondrial disorder have been identified in only seven of the corresponding human genes.
    explanation: >-
      The 2011 introduction describes multiple nuclear assembly-factor causes; its historical gene count
      is not used as a current count.
- name: Ethylmalonic encephalopathy (ETHE1)
  description: >-
    Ethylmalonic encephalopathy overlaps in ethylmalonic acid elevation and reduced muscle cytochrome
    c oxidase activity.
  distinguishing_features:
  - >-
    ETHE1-related disease prominently affects brain, gastrointestinal tract and peripheral vessels. The
    reported COA5 cases are dominated by neonatal cardiomyopathy; gene testing resolves the etiologic
    distinction.
  evidence:
  - reference: PMID:14732903
    reference_title: "Ethylmalonic encephalopathy is caused by mutations in ETHE1, a gene encoding a mitochondrial matrix protein."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Ethylmalonic encephalopathy (EE) is a devastating infantile metabolic disorder affecting the brain, gastrointestinal tract, and peripheral vessels. High levels of ethylmalonic acid are detected in the body fluids, and cytochrome c oxidase activity is decreased in skeletal muscle.
    explanation: >-
      Supports the biochemical overlap and distinguishing organ-system pattern of ETHE1 disease.
- name: Primary mitochondrial DNA disease
  description: >-
    Mitochondrial DNA variants are an alternative cause considered during evaluation of respiratory-chain
    disease. The 2025 COA5 patient had negative mitochondrial genome analysis.
  distinguishing_features:
  - >-
    Biallelic nuclear COA5 variants with carrier parents establish a nuclear recessive etiology. Negative
    mitochondrial genome sequencing does not alone exclude every mitochondrial disorder or nuclear cause
    of mtDNA depletion.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Molecular genetic testing eliminated pathogenic mitochondrial DNA (mtDNA) variants after a complete analysis of the mitochondrial genome."
    explanation: >-
      Documents mtDNA testing in the reported patient, without prescribing a mandatory order of investigations.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
discussions:
- discussion_id: coa5_encephalopathy_not_documented
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - "pathophysiology#Hypertrophic Myocardial Remodeling"
  - "phenotypes#Hypertrophic Cardiomyopathy"
  prompt: >-
    The disease is named a cardioencephalomyopathy, but is there any documented
    central nervous system involvement in COA5 deficiency?
  rationale: >-
    The disease name includes encephalomyopathy, but the available clinical descriptions emphasize neonatal
    cardiomyopathy and the 2025 patient had normal brain imaging. Normal structural imaging does not exclude
    functional or later neurological involvement. The neurological spectrum remains unresolved in this
    small, early-lethal case series.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging of the brain was normal."
    explanation: >-
      Documents normal brain imaging in one patient; it does not establish absence of encephalopathy in
      the disorder.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
- discussion_id: coa5_submitochondrial_localisation_and_metallochaperone_role
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - "pathophysiology#Arrested Early Complex IV Assembly"
  prompt: >-
    Where does human COA5 sit within the mitochondrion, and does it act purely as
    an assembly factor at the MTCO1-to-MTCO2 transition or also as a regulator of
    the copper and haem metallochaperone modules?
  rationale: >-
    COA5 knockout experiments implicate both early MTCO1-to-MTCO2 assembly and COX2 metallochaperone interactions.
    The 2022 study supports a dynamic apo-metallochaperone complex-stabilizing role in engineered human
    cells, while the 2025 study leaves the precise structural role and localization for further investigation.
    How p.Ala53Pro affects these interactions is unresolved; yeast import findings do not establish human
    import dependence.
  evidence:
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "identified the twin CX9C protein PET191/COA5 as a key contributor in human cells"
    explanation: >-
      Places COA5 in the copper-centre biogenesis machinery in human knockout
      cells, which is the alternative role this question is about.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:18503002
    reference_title: Pet191 is a cytochrome c oxidase assembly factor in Saccharomyces cerevisiae.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The import of Pet191 differs from that of other twin-Cx(9)C motif class of proteins in being independent of the Mia40 pathway."
    explanation: >-
      Evidence about the yeast orthologue Pet191, not about human COA5. It is
      cited only to substantiate why yeast import and localisation data cannot be
      read across to the human protein.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Furthermore, SCO1, COA6, and COX16 failed to interact with the newly synthesized COX2 in the absence of PET191
    explanation: >-
      Immunoprecipitation in PET191/COA5 knockout human cells identifies loss of these COX2 interactions.
      This has not been measured in patient cells.
- discussion_id: coa5_founder_allele_unverified
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - "genetic#COA5 pathogenic variants causing CEMCOX3 (MC4DN9)"
  - "prevalence#Worldwide"
  prompt: >-
    Is COA5 c.157G>C (p.Ala53Pro) a Turkish founder allele, or has the same
    variant arisen independently?
  rationale: >-
    The two reported Turkish families share homozygous p.Ala53Pro. The authors propose a founder effect
    but explicitly require haplotype analysis to establish it. Recurrence alone is insufficient.
  evidence:
  - reference: PMID:39779219
    reference_title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "this could point towards the likelihood of the variant being a founder pathogenic variant within the Turkish population"
    explanation: >-
      States the founder hypothesis as a possibility, in the authors' own hedged
      terms, which is exactly the epistemic status recorded here.
    quote_role: PRIMARY_RESULT
    directness: DIRECT
notes: >-
  The clinical evidence base consists of the 2011 sibling report and the 2025 unrelated child. Phenotype
  frequencies, penetrance, broader allelic diversity and long-term outcomes cannot be estimated from these
  reports. The human null-cell experiments resolve assembly-factor biology but do not establish identical
  molecular effects or clinical severity for the patient missense allele. COA5 is a gene-defined member
  of the Mitochondrial Complex IV Deficiency grouping; it is not interchangeable with the broader fatal
  infantile COX-deficiency syndrome.
references:
- reference: PMID:10749987
  title: Mutations in SCO2 are associated with a distinct form of hypertrophic cardiomyopathy and cytochrome c oxidase deficiency.
- reference: PMID:14732903
  title: "Ethylmalonic encephalopathy is caused by mutations in ETHE1, a gene encoding a mitochondrial matrix protein."
- reference: PMID:18503002
  title: Pet191 is a cytochrome c oxidase assembly factor in Saccharomyces cerevisiae.
- reference: PMID:21457908
  title: A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
- reference: PMID:35750769
  title: Coordination of metal center biogenesis in human cytochrome c oxidase.
- reference: PMID:39779219
  title: COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
📚

References & Deep Research

References

6
PMID:10749987
Mutations in SCO2 are associated with a distinct form of hypertrophic cardiomyopathy and cytochrome c oxidase deficiency.
No top-level findings curated for this source.
PMID:14732903
Ethylmalonic encephalopathy is caused by mutations in ETHE1, a gene encoding a mitochondrial matrix protein.
No top-level findings curated for this source.
PMID:18503002
Pet191 is a cytochrome c oxidase assembly factor in Saccharomyces cerevisiae.
No top-level findings curated for this source.
PMID:21457908
A mutation in C2orf64 causes impaired cytochrome c oxidase assembly and mitochondrial cardiomyopathy.
No top-level findings curated for this source.
PMID:35750769
Coordination of metal center biogenesis in human cytochrome c oxidase.
No top-level findings curated for this source.
PMID:39779219
COA5 has an essential role in the early stage of mitochondrial complex IV assembly.
No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: COA5-Related Fatal Infantile Cardioencephalomyopathy (CEMCOX3/MC4DN9) · 2026-09-08T06:50:15Z · View source

De novo curation of MONDO:0014667 (CEMCOX3 / MC4DN9), the COA5 (hgnc:33848) nuclear-type isolated complex IV deficiency, against the entire human literature for the gene: Huigsloot et al. 2011 (PMID:21457908, abstract only) and Tang et al. 2025 (PMID:39779219, PMC full text), plus Nyvltova et al. 2022 (PMID:35750769) for the metallochaperone-module role and Khalimonchuk et al. 2008 (PMID:18503002) for the yeast orthologue Pet191, cited only where the yeast/human difference is itself the point. Lump/split: curated as a standalone Disease. MONDO:0014667 is a gene-defined disease_series_by_gene leaf with one causal gene and no descendants; its parent MONDO:0015487 is the gene-agnostic umbrella that issue #5060 / PR #5064 decided not to curate as a Disease, redirecting content into the Mitochondrial_Complex_IV_Deficiency grouping. Grouping: added as a member of kb/groupings/Mitochondrial_Complex_IV_Deficiency.yaml; the evaluator reports the NECESSARY_AND_SUFFICIENT module-conformance criterion SATISFIED. Recorded in a separate history record for the grouping. Pathograph: four nodes conforming to complex_iv_assembly_deficiency (Complex IV Biogenesis Failure, Impaired Terminal Electron Transfer and ATP Synthesis, Lactic Acidosis and Metabolic Decompensation, High-Energy Tissue Dysfunction), with bare-name downstream targets. Key curation decisions. (1) No encephalopathy phenotype is curated despite the disease name: the founding abstract describes fatal neonatal cardiomyopathy, the OMIM summary describes neonatal hypertrophic cardiomyopathy, and neuroimaging was normal in the only patient with imaging reported. A KNOWLEDGE_GAP discussion records the discrepancy and cites the normal-neuroimaging sentence as REFUTE evidence. (2) penetrance and expressivity are UNKNOWN: three patients, two families, one allele, no unaffected homozygote and no genotype contrast. (3) HP:0031320 (cardiomyocyte mitochondrial proliferation), listed for this concept in MedGen, is deliberately not curated - searching every occurrence of proliferat/ultrastruct/electron microscop across all four cached references returns nothing about cardiomyocyte mitochondria. (4) The founder-allele question is an OPEN_QUESTION, not an assertion; the authors hedge and no haplotype study exists. (5) HP:0001522 (Death in infancy) is a clinical modifier and not reachable from HP:0000118, so the fatal course is carried in a progression block rather than as a phenotype. Deep research: claude_code provider, 3/3 references verified, 20/23 terms verified. Two report errors were caught and not curated - it proposed hgnc:24704 for COA5 (that CURIE is LARP1B; the correct one is hgnc:33848) and HP:0005633, which does not resolve (the correct septal-hypertrophy term is HP:0005144). GO:0005751 was also rejected as obsolete in favour of GO:0045277. Validation run to completion: just validate (schema, terms, references) passed with 53/53 snippets verified; validate-terms, count-verified-snippets, check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms, check-enum-values, check-snippet-length, check-title-snippets, check-snippet-grading, check-folded-hyphens and check-source-defect-claims all clean for this file; validate-disorders run last as the authoritative gate. Every snippet was extracted programmatically from references_cache and re-verified as an exact substring.

Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-sonnet-5 8 citations 2026-09-07T22:57:30.354438

1. Disease Information

Overview. An autosomal recessive, neonatal/early-infantile mitochondrial disorder caused by biallelic loss-of-function variants in COA5 (Cytochrome c Oxidase Assembly Factor 5, formerly C2orf64), which encodes a small CHCH-domain protein required for an early step of respiratory chain Complex IV (cytochrome c oxidase, COX) assembly. Disease is defined by isolated Complex IV deficiency producing rapidly fatal hypertrophic cardiomyopathy with lactic acidosis in the neonatal period; the "cardioencephalomyopathy" nosology reflects the broader OMIM disease-class naming convention for this group of nuclear COX-assembly disorders rather than a documented, prominent primary CNS lesion in the reported cases (see §3, §7).

Key identifiers: - OMIM gene: 613920 — COA5 (Huigsloot et al. 2011) - OMIM phenotype: #616500 — Mitochondrial Complex IV Deficiency, Nuclear Type 9 (MC4DN9); also referenced in the literature as CEMCOX3 (Cardioencephalomyopathy, Fatal Infantile, due to Cytochrome c Oxidase Deficiency 3) (omim.org/entry/616500) - MONDO: MONDO:0014667 (corresponds to MC4DN9) - Gene location: 2q11.2; NCBI Gene ID 493753; RefSeq NM_001008215.3; also historically NCOA5-adjacent nomenclature confusion should be avoided — COA5 ≠ NCOA5 (nuclear receptor coactivator 5), a distinct, unrelated gene that surfaces in naive searches - Orphanet: ORPHA:1561 — Fatal infantile cytochrome C oxidase deficiency (the broader COX-deficiency umbrella term Orphanet uses; COA5 is one of several causal genes grouped here) (orpha.net/en/disease/detail/1561) - Yeast ortholog: PET191

Synonyms: Cytochrome c oxidase assembly factor 5 deficiency; C2ORF64-related mitochondrial disease; MC4DN9; CEMCOX3.

Evidence base. This is an extremely narrowly-documented Mendelian entity: the primary clinical source is a single index report of one consanguineous Turkish family (2 affected sibs) (Huigsloot et al. 2011, PMID:21457908), corroborated by one additional, unrelated family carrying the identical variant, reported in a 2024–2025 mechanistic follow-up (Stroud lab / Life Science Alliance, PMID:39779219). All published human genotype-phenotype data currently trace to these two families and the single recurrent variant p.Ala53Pro — this is aggregated disease-level literature (case reports), not an EHR/registry-derived dataset.

Sources: OMIM #616500 · OMIM *613920 · Orphanet ORPHA:1561 · NCBI Gene 493753

2. Etiology

Disease causal factor: Purely monogenic/genetic — biallelic (homozygous, in both reported families) pathogenic variants in COA5 (hgnc gene; lowercase-hgnc: CURIE per local convention would be hgnc:24704, ENSG00000183513). No environmental, infectious, or multifactorial contribution has been reported or is biologically plausible for this class of nuclear mitochondrial assembly-factor disorder.

Genetic risk factor / founder variant: The only variant reported in humans to date is c.157G>C (p.Ala53Pro, NM_001008215.3), identified in homozygosity in both unrelated reported families, both of Turkish ethnicity — strongly suggestive of a Turkish founder allele, though a formal haplotype/founder-effect study has not been published (this is an inference from the recurrence pattern, not an established finding). PMID:21457908 originally identified the variant in a consanguineous Turkish pedigree; the second, independently ascertained Turkish family carrying the same allele was reported in the 2024/2025 functional-mechanism paper (PMID:39779219), which itself functions as a form of independent case confirmation.

  • Population allele frequency: gnomAD frequency data specific to c.157G>C were not retrieved in this search pass; given its apparent restriction to Turkish founder chromosomes and the ultra-rare disease phenotype, expect it to be present at very low frequency or absent from gnomAD's predominantly non-Turkish-enriched reference panels — this should be confirmed directly in gnomAD before KB entry, as it was not independently verified here.
  • No modifier genes, susceptibility loci, or protective variants have been reported for this disorder — there is no literature to draw on for §2's "Protective Factors" or "Gene-Environment Interactions" subsections; state this as a genuine gap rather than inferring an absence.

Consanguinity: Explicitly documented in the index family ("consanguineous Turkish parents," PMID:21457908), consistent with autosomal recessive transmission of a rare founder allele.

Sources: OMIM *613920 · Huigsloot et al. 2011, PMID:21457908 · PMC11711468/PMID:39779219

3. Phenotypes

Phenotype data derive entirely from the two reported Turkish families (Huigsloot 2011 index sibs, died at 8 and 10 days of age per the OMIM/NORD abstraction, though one search summary reported "3 months" — this discrepancy should be resolved against the primary PMID:21457908 full text before curation, since GARD/OMIM abstractions and AI-search summaries of the same paper conflicted on exact age at death).

Phenotype Type Onset Notes / suggested HP term
Hypertrophic cardiomyopathy (biventricular, septal hypertrophy, non-compaction appearance) Clinical sign Neonatal HP:0001639 (Hypertrophic cardiomyopathy); consider HP:0005633 (Ventricular septal hypertrophy) and HP:0000006 context terms as applicable
Elevated blood lactate (2.5–11 mmol/L reported range) Laboratory abnormality Neonatal HP:0002151 (Increased serum lactate)
Elevated urinary lactate Laboratory abnormality Neonatal Consider HP:0003128 (Lactic acidosis) at the systemic level
Elevated urinary ethylmalonic acid Laboratory abnormality Neonatal Organic aciduria pattern consistent with respiratory chain dysfunction; no dedicated HP term confirmed in this pass
Respiratory distress / respiratory insufficiency requiring intubation Clinical sign Neonatal HP:0002093 (Respiratory insufficiency)
Hypotonia Clinical sign Neonatal (per NORD/GTR abstraction) HP:0001252 (Hypotonia)
Abnormal liver function tests Laboratory abnormality Neonatal HP:0001410 (Decreased liver function) or specific transaminase terms
Isolated Complex IV (COX) enzymatic deficiency in fibroblasts and heart muscle Laboratory/biochemical — HP:0011927 (Reduced cytochrome C oxidase activity) — verify exact HP CURIE before binding
Death in infancy Outcome 8–10 days to ~3 months (source-discrepant, see above) Fatal course; HP:0031307 or comparable "sudden death"/"fatal in infancy" outcome framing

Severity/progression: Uniformly severe and rapidly fatal in both reported families; no surviving patients, no reported milder allelic series, and therefore no data exist on variable severity, later-onset presentations, or long-term natural history — unlike many other MC4DN subtypes (e.g., SURF1-Leigh syndrome), which have a phenotypic spectrum, COA5-disease as currently documented is a single, severe, lethal-in-infancy phenotype defined by n=2 families.

CNS/encephalopathy phenotype specifically: The disease-class name ("cardioencephalomyopathy") implies CNS involvement, but the retrieved abstracts and summaries emphasize the cardiac and biochemical phenotype far more than a distinct, well-characterized encephalopathic phenotype (e.g., no MRI/neuroimaging findings, no seizure phenotype, and no dedicated neurological exam findings were surfaced in this search). This is a gap that should be resolved by reading the PMID:21457908 full text directly — the CNS component of the phenotype may be present in the primary paper but was not captured by the search summaries used here, or the "cardioencephalomyopathy" label may be inherited from the broader disease-class nomenclature (OMIM's naming convention for this class of COX-deficiency disorders) rather than from a specific encephalopathy documented in these two families. Flag this explicitly rather than asserting a CNS phenotype without primary-source confirmation.

Quality of life impact: Not applicable/not reported — given uniform neonatal/early-infantile lethality, no QOL instrument data (EQ-5D, SF-36) exist or would be expected.

Sources: PMID:21457908 (Huigsloot et al. 2011, Am J Hum Genet 88:488–493) · NORD/MONDO abstraction · GTR test record · PMID:39779219

4. Genetic/Molecular Information

Causal gene: COA5 (OMIM 613920; NCBI Gene 493753; chr2q11.2; NM_001008215.3). Historical alias: C2orf64*.

Reported pathogenic variant: - c.157G>C, p.(Ala53Pro) — the sole variant reported in humans across both families. - Variant type: Missense, homozygous (biallelic) in both reported pedigrees. - ACMG classification: Not independently retrieved from ClinVar in this pass — should be pulled directly from ClinVar before KB curation, but functional data (below) strongly support a damaging/loss-of-function-type mechanism. - Location: Falls within a conserved motif of the COA5/PET191 protein predicted to be important for protein folding/structure (per PMID:21457908's original functional characterization). - Population frequency: Not independently confirmed here (see §2) — recommend a direct gnomAD/ClinVar pull. - Origin: Germline (both reported cases), consistent with autosomal recessive constitutional disease; not a somatic/cancer-associated gene.

Protein and functional consequence: - COA5 is a small mitochondrial intermembrane-space protein containing a CHCH domain with twin CX9C motifs — a structural class that depends on the MIA40/CHCHD4 disulfide-relay import pathway for mitochondrial localization (general class-level inference; not explicitly confirmed for COA5 in the sources retrieved here, so should be flagged as inferred-from-domain-architecture rather than COA5-specific experimental confirmation). - Ortholog of yeast Pet191, a subunit of an oligomeric inner-membrane-associated complex required for COX assembly; early yeast Pet191 studies suggested a role in COX assembly without direct impact on mitochondrial translation or copper metalation of COX subunits. - Functional impact category: Best characterized as loss-of-function / partial loss-of-function — p.Ala53Pro patient fibroblasts show: - Isolated Complex IV enzymatic deficiency (both fibroblasts and patient heart muscle) - Accumulation of Complex IV assembly intermediates/subcomplexes rather than mature holocomplex - Subcomplexes lacking COX1 (MT-CO1), COX2 (MT-CO2), COX4 (COX4I1), and COX5A subunits (PMID:21457908) - The 2024/2025 mechanistic paper (PMID:39779219) refined this: complexome profiling in a CRISPR/Cas9 COA5-knockout U2OS cell line (7-bp frameshift deletion) showed COA5 acts specifically between MT-CO1 maturation and the incorporation of MT-CO2 into the earliest CIV assembly intermediate — i.e., COA5 loss blocks a discrete, early step, with accumulation of MT-CO1-containing subcomplexes (100–300 kDa) that cannot progress to a functional holocomplex. - No modifier genes have been reported. - No epigenetic data (methylation, histone modification) have been reported for this gene/disease — genuine gap, not to be inferred. - No chromosomal-abnormality (CNV, translocation, aneuploidy) mechanism has been reported; disease is driven by a point missense variant only.

Suggested ontology bindings: hgnc gene term for COA5 (verify exact HGNC ID before binding — do not guess the numeric CURIE without an OAK/HGNC lookup); GO:0033617 (mitochondrial respiratory chain complex IV assembly) as the key biological-process term; molecular function terms around CHCH-domain/protein-folding chaperone activity should be verified against UniProt/GO rather than asserted from this search pass.

Sources: PMID:21457908 · PMID:39779219 (PMC11711468) · OMIM *613920 · NCBI Gene 493753

5. Environmental Information

No environmental, lifestyle, or infectious causal/risk factors have been reported for this disorder, consistent with its status as a fully penetrant, biallelic monogenic mitochondrial assembly-factor disease presenting at birth/neonatally. This is a genuine "not applicable" rather than an unresearched gap — nuclear-encoded COX-assembly-factor disorders of this class are not known to have environmental modifiers of onset or severity in the pediatric mitochondrial disease literature generally, though a disease-specific search for gene-environment interaction data specific to COA5 returned nothing to cite.

6. Mechanism / Pathophysiology

Causal chain (numbered, from molecular lesion to clinical phenotype):

  1. Biallelic COA5 c.157G>C (p.Ala53Pro) variant → destabilizes a conserved motif of the COA5/PET191-family CHCH-domain protein, impairing its folding/structural integrity (PMID:21457908; mechanism of destabilization is inferred from conservation and structural prediction in the original paper, not from a solved crystal structure).
  2. Loss of functional COA5 protein → arrest of Complex IV (cytochrome c oxidase) assembly at an early, discrete step — specifically between maturation of the mitochondrially-encoded COX1 (MT-CO1) subunit and its combination with COX2 (MT-CO2) to form the earliest CIV assembly intermediate (PMID:39779219, complexome profiling in the COA5-knockout cellular model). This step is directly demonstrated in the CRISPR-knockout cell system; its equivalence to the patient p.A53P mechanism is supported by concordant biochemical findings in patient fibroblasts (accumulating the same class of subcomplexes) but the knockout and missense mechanisms are not proven identical at the structural level — this is a reasonable inference, not a demonstrated one-to-one mechanistic match.
  3. Failure to progress past this intermediate → accumulation of stalled MT-CO1-containing subcomplexes (~100–300 kDa) that cannot mature into the CIV holocomplex; these appear to be routed toward a prohibitin-complex-associated pathway, consistent with a degradative/quality-control fate for unassembled respiratory-chain subunits (PMID:39779219 — described as "colocalisation with prohibitin complexes," suggestive of degradation but not directly proven to be degradation via a specific proteolytic mechanism in the retrieved summary).
  4. Net loss of mature Complex IV holocomplex → markedly reduced Complex IV enzymatic activity and abundance, while Complexes I, II, III, and V remain relatively unaffected (isolated CIV deficiency) — directly demonstrated in both patient fibroblasts/heart muscle (PMID:21457908) and the knockout cell model (PMID:39779219).
  5. Loss of CIV activity → secondary loss of respiratory supercomplex assembly, specifically loss of the III₂+IV supercomplex and a compensatory increase in the CI+III₂ "S0" supercomplex (PMID:39779219) — this represents a downstream structural reorganization of the respiratory chain rather than a separate causal branch.
  6. Combined loss of CIV activity and supercomplex disruption → impaired oxidative phosphorylation capacity, particularly in high-energy-demand tissues (cardiac and skeletal muscle, and — per the disease-class "cardioencephalomyopathy" designation — potentially CNS, though the CNS mechanistic link is not directly documented in the sources retrieved here; flag as an assumed-by-nosology rather than demonstrated link) → compensatory anaerobic glycolysis, producing the observed lactic acidosis (elevated blood and urinary lactate) and elevated urinary ethylmalonic acid (a marker of disrupted mitochondrial fatty-acid/energy metabolism).
  7. Chronic energy failure in cardiomyocytes → hypertrophic cardiomyopathy with septal hypertrophy and non-compaction features, the dominant clinical phenotype in both reported families.
  8. Combined cardiac pump failure, respiratory insufficiency (from concurrent skeletal/respiratory muscle energy failure and possible CNS respiratory drive involvement — again, the CNS component is asserted by disease-class nomenclature more than by a directly cited mechanistic finding in this search pass), and multisystem metabolic decompensation → death in early infancy.

Molecular pathway: Mitochondrial respiratory chain Complex IV (cytochrome c oxidase) biogenesis pathway; GO:0033617 (mitochondrial respiratory chain complex IV assembly) is the key suggested GO term. No involvement of canonical signaling cascades (Wnt/MAPK/mTOR/PI3K-AKT) — this is a structural/metabolic assembly-factor disorder, not a signaling disorder.

Cellular process: Impaired oxidative phosphorylation; compensatory glycolytic shift; likely proteostatic/degradative handling of stalled assembly intermediates via prohibitin-associated pathways (PMID:39779219).

Protein dysfunction: Loss-of-function/misfolding of a small CHCH-domain chaperone-like assembly factor (COA5), leading to failure of a specific protein-protein assembly step (MT-CO1 + MT-CO2 incorporation) rather than a defect in COX catalytic chemistry itself.

Tissue damage mechanism: Energy-failure-driven cardiomyocyte dysfunction/hypertrophy; no evidence retrieved here for oxidative-stress, fibrotic, or necrotic mechanisms specifically documented in COA5 disease (though these are plausible extrapolations from mitochondrial cardiomyopathy biology generally — do not assert them as COA5-specific findings).

Cell types/anatomical involvement (see also §7): Cardiomyocytes (primary, best-documented); skeletal muscle/fibroblasts (biochemically characterized, PMID:21457908); U2OS (human osteosarcoma) cell line used as the mechanistic knockout model (PMID:39779219) — note this is an experimental/heterologous cell model, not a disease-relevant tissue, and should be labeled accordingly in any experimental_models entry.

Omics/advanced technologies: Complexome profiling (a specialized proteomic/native-PAGE-based technique resolving native protein complex composition across a molecular-weight gradient) was the key advanced technology used in PMID:39779219 to map the precise assembly stage at which COA5 acts. No transcriptomic (RNA-seq/GEO), standard proteomic (PRIDE), metabolomic, lipidomic, single-cell, or spatial transcriptomic datasets specific to COA5 disease were identified in this search — a genuine gap, not to be inferred as absent from all databases without a direct GEO/PRIDE query.

Suggested GO terms: GO:0033617 (mitochondrial respiratory chain complex IV assembly). Suggested CL terms: CL:0000746 (cardiac muscle cell) for the primary affected cell type; CL:0000057 (fibroblast) for the biochemically characterized cell type.

Sources: PMID:21457908 · PMID:39779219 (Life Science Alliance / PMC11711468)

7. Anatomical Structures Affected

Organ level: - Primary: Heart (hypertrophic cardiomyopathy — the dominant, best-documented organ manifestation in both families) - Secondary/systemic: Liver (abnormal LFTs reported); respiratory system (respiratory insufficiency, though this may be secondary to cardiac failure and/or generalized hypotonia/muscle weakness rather than a distinct primary respiratory-organ lesion) - Body systems: Cardiovascular (primary); metabolic/endocrine (lactic acidosis, organic aciduria); neuromuscular (hypotonia); the "encephalo-" component of the disease-class name implies CNS involvement, but a specific CNS lesion (imaging finding, defined encephalopathy phenotype) was not identified in the sources retrieved in this pass and should be confirmed from the PMID:21457908 full text before being curated as a distinct phenotype/organ node.

Tissue and cell level: Cardiac muscle tissue (myocardium — septal hypertrophy, non-compaction pattern) is the most specifically documented; skeletal muscle biopsy tissue was studied in at least the second reported family (per the 2024/2025 paper's mention of "skeletal muscle biopsies"); dermal fibroblasts were the primary cultured cell type used for biochemical/functional characterization in both the original and follow-up studies.

Subcellular level: Mitochondrial inner membrane / intermembrane space — COA5 is an intermembrane-space CHCH-domain protein associated with the assembly machinery on the matrix side of the inner membrane where nascent Complex IV subcomplexes form. Suggested GO Cellular Component term: GO:0005758 (mitochondrial intermembrane space) — verify against UniProt subcellular-location annotation before binding, as the exact sub-compartment (inner membrane vs. IMS-soluble vs. IMS-membrane-associated) was not confirmed to UniProt-level precision in this search pass.

Localization/laterality: Not applicable — this is a systemic/biventricular process (biventricular hypertrophic cardiomyopathy reported), not a lateralized or focal anatomical process.

Suggested UBERON terms: UBERON:0000948 (heart); UBERON:0002349 (myocardium); UBERON:0001133 (cardiac ventricle) for biventricular involvement — verify specificity against the primary source before binding.

8. Temporal Development

  • Onset: Congenital/neonatal — both reported families presented at birth or within the first days of life (hypotonia and respiratory insufficiency at birth per one abstraction; cardiomyopathy identified in the neonatal period in both families).
  • Onset pattern: Acute-to-subacute, rapidly progressive.
  • Disease course: Uniformly progressive to death — no stable, relapsing-remitting, or spontaneously-improving course has been documented. This is a monophasic, rapidly fatal natural history as currently reported.
  • Duration/outcome: Death reported at 8 and 10 days of age in the index sibs per the OMIM/NORD-derived abstraction; one search-tool summary of the same paper stated "fatal outcome at 3 months of age" — this is a direct conflict in secondary sources that must be resolved against the PMID:21457908 primary text before any age-at-death value is entered into the KB. Do not average or guess between these two conflicting figures.
  • Stages: No formal staging system exists for this ultra-rare, uniformly fatal infantile disorder.
  • Critical periods: The entire disease course occurs within a critical early-infantile window; no data exist on any therapeutic window or intervention timing given the absence of reported surviving/treated patients.

9. Inheritance and Population

  • Inheritance pattern: Autosomal recessive (biallelic), confirmed in both reported families, including documented parental consanguinity in the index pedigree.
  • Penetrance: Appears fully penetrant in the (very small, n=2-family) reported cohort — both affected sibs in the index family were symptomatic and died; no asymptomatic or mildly-affected biallelic carriers have been reported. Given the extremely small sample size, a formal penetrance estimate cannot be responsibly asserted beyond "apparently complete in the cases reported."
  • Expressivity: Cannot be meaningfully assessed — only a single recurrent variant (p.Ala53Pro) has been reported in humans, in two families with a grossly concordant, severe, lethal phenotype; there is no allelic series to demonstrate variable expressivity.
  • Genetic anticipation, germline mosaicism: Not applicable/not reported — no repeat-expansion mechanism, and no mosaicism data reported.
  • Founder effect: Strongly suspected (see §2) — both reported unrelated families are Turkish, and the identical c.157G>C variant was found in both, but a formal founder-haplotype study has not been published in the sources retrieved here.
  • Carrier frequency: Not established/not reported.
  • Epidemiology (prevalence/incidence): No formal prevalence or incidence estimate exists. This is one of the rarest entries in the MC4DN (mitochondrial Complex IV deficiency, nuclear type) disease group, with only two published families worldwide. Orphanet's ORPHA:1561 entry covers the broader "fatal infantile cytochrome C oxidase deficiency" umbrella (multiple causal genes), not a COA5-specific prevalence figure — do not conflate the umbrella-term prevalence with a COA5-specific number, as none exists.
  • Population demographics: Both reported families of Turkish ethnicity; no data on prevalence or geographic distribution beyond this. Sex ratio: not distinctively reported (mitochondrial nuclear-gene AR disorders generally show no sex bias, consistent with autosomal — not X-linked or mitochondrial-DNA — transmission here).

10. Diagnostics

Laboratory tests: - Blood lactate (elevated, 2.5–11 mmol/L reported range) - Urinary lactate and ethylmalonic acid (elevated) - Liver function tests (abnormal) - Muscle/fibroblast Complex IV (cytochrome c oxidase) enzymatic activity assay — the key confirmatory biochemical test, showing isolated, severe CIV deficiency with normal activity of Complexes I, II, III, V

Imaging: Echocardiography — demonstrated biventricular hypertrophic cardiomyopathy with septal hypertrophy and a non-compaction myocardial appearance in the reported cases; no further imaging modality detail (cardiac MRI, brain MRI) was retrieved in this search pass.

Genetic testing: Clinically available as a targeted sequence-analysis test for all coding COA5 exons (postnatal), listed in NCBI's Genetic Testing Registry under the CEMCOX3/MC4DN9 indication (GTR test 586086); would also be captured on any mitochondrial Complex IV deficiency gene panel and on exome/genome sequencing given the nonspecific, phenotypically-overlapping presentation shared across the MC4DN gene group (COA5, COA6, COA7, SURF1, SCO1/2, COX10/15, PET100, NDUFA4, etc.).

Confirmatory functional/research-level testing: Complexome profiling and immunoblotting for COX assembly intermediates (as performed in PMID:39779219) — this is a research-level rather than routine clinical diagnostic tool at present.

Differential diagnosis: Other nuclear-encoded Complex IV assembly-factor disorders presenting with neonatal hypertrophic cardiomyopathy and lactic acidosis — notably SCO2-related fatal infantile cardioencephalomyopathy (a classic, better-characterized member of this disease class and likely the original prototype for the "cardioencephalomyopathy" naming convention), COX15, COA6, and other MC4DN subtypes; also mitochondrial DNA-encoded COX-subunit defects and other primary mitochondrial cardiomyopathies (e.g., MTO1, TAZ/Barth syndrome, and other respiratory-chain-complex disorders) should be considered and excluded biochemically/genetically.

Screening: No population or newborn-screening program specifically targets COA5-related disease; given its rarity this would not be expected to appear on standard newborn metabolic screening panels (which target treatable inborn errors of metabolism, and this disorder currently has no disease-modifying treatment — see §12).

11. Outcome/Prognosis

  • Survival/mortality: Uniformly fatal in early infancy in all reported cases (8–10 days per one source; "3 months" per a conflicting secondary summary — resolve against primary text, see §8). No long-term survivors have been reported in the literature retrieved here.
  • Life expectancy: Days to at most a few months, based on the two reported families; this is among the most rapidly fatal entries in the mitochondrial Complex IV deficiency disease group as currently documented.
  • Morbidity/complications: Respiratory insufficiency requiring intubation, hepatic dysfunction, and progressive cardiac failure were the reported proximate complications leading to death.
  • Recovery potential: None reported/expected given the uniformly fatal course and absence of any reported disease-modifying intervention.
  • Prognostic factors/biomarkers: No prognostic stratification exists — the extremely small reported cohort (n=2 families) with concordant severe outcomes precludes any meaningful biomarker-based prognostic modeling at this time.

12. Treatment

No disease-specific, disease-modifying, or FDA-approved treatment exists for COA5-related disease. No pharmacotherapy, gene therapy, cell therapy, or targeted molecular therapy trial was identified for this specific gene/disease in this search pass, and none would be expected given its ultra-rarity (two published families) and the absence of any registered clinical trial.

What can be stated, by extrapolation from general mitochondrial disease management (and should be clearly labeled in any KB entry as general supportive-care extrapolation, not COA5-specific evidence): - Supportive care for hypertrophic cardiomyopathy and respiratory insufficiency (e.g., NCIT:C15747 Supportive Care; NCIT:C15986 Pharmacotherapy for symptomatic cardiac management such as diuretics/beta-blockers, though no COA5-specific citation supports their use) - Standard "mitochondrial cocktail" supplementation (CoQ10, riboflavin, carnitine, thiamine) is commonly used empirically across the broader mitochondrial respiratory chain disease group, but no COA5-specific evidence of efficacy was found in this search — do not curate this as evidence-supported for this specific gene without a direct citation. - No gene therapy, RNA-based therapy, or targeted precision-medicine approach has been reported or is in development specifically for COA5 disease.

Clinical trials: No registered ClinicalTrials.gov entry specific to COA5-related disease was identified in this search pass.

This is a genuine and clinically important gap to flag explicitly in the KB entry: treatment content for this disorder should be limited to general supportive-care framing, clearly distinguished from disease-specific evidence, consistent with the two-family, no-survivor natural history described above.

13. Prevention

  • Primary prevention: Genetic counseling for consanguineous families/carrier couples, particularly relevant given the documented consanguinity in the index family and the apparent Turkish founder-variant pattern (see §2, §9). Suggested NCIT term: NCIT:C15240 (Genetic Counseling).
  • Secondary prevention/screening: Carrier screening and prenatal/preimplantation genetic testing are reasonable extrapolated recommendations for families with a known COA5 pathogenic variant (standard practice for any severe, early-lethal autosomal recessive disorder with an identified causal variant), but no COA5-specific carrier-screening program, prenatal-testing case report, or PGD case has been published in the sources retrieved here — this should be flagged as inferred-by-analogy rather than directly evidenced.
  • Tertiary prevention: Not applicable given the absence of any reported surviving/treated patients in whom complication-prevention strategies could be documented.
  • No population-level, public-health, immunization, or environmental-intervention prevention strategy is applicable to this purely monogenic disorder.

14. Other Species / Natural Disease

No naturally-occurring COA5-related disease has been reported in any non-human species (companion animal, livestock, or wildlife) in the sources retrieved here — a search of veterinary/OMIA-type sources specific to COA5 did not surface any hits, and this should be treated as a genuine absence rather than an unresearched gap, consistent with COA5 disease being an ultra-rare human founder-variant condition rather than a naturally recurring animal phenotype.

Orthology: COA5 is conserved from yeast (Pet191) through mouse (Coa5, MGI:1923428) to human, consistent with its fundamental, evolutionarily conserved role in Complex IV biogenesis (see §15 for mouse-specific data).

15. Model Organisms

  • Yeast (Saccharomyces cerevisiae): PET191 — the original ortholog studied; early yeast work established a role in COX assembly without a demonstrated direct effect on mitochondrial translation or copper metalation of COX subunits (per the mechanistic background cited in PMID:39779219's discussion). This represents indirect/orthology-based model support rather than a disease-recapitulating model.
  • Mouse: Coa5 (MGI:1923428) has multiple targeted, gene-trapped, and chemically-induced alleles catalogued (9 total alleles; 7 strains available via IMSR), with phenotype annotations spanning behavioral/neurological, embryonic development, endocrine, growth, integument, mortality/aging, and reproductive categories per the MGI summary retrieved. However, the specific phenotypic details, zygosity (heterozygous vs. homozygous), and whether homozygous null is embryonic lethal were not resolved in this search pass — this is an important gap: if Coa5-null mice are embryonic lethal, that would be a directly relevant "does the null model recapitulate/exceed the human phenotype" finding (bearing on human-model-fidelity assessment) and should be pulled from MGI's detailed phenotype allele pages before KB curation, rather than asserted here without direct confirmation.
  • Human cellular model (heterologous): CRISPR/Cas9-engineered COA5-knockout U2OS (human osteosarcoma) cell line (7-bp frameshift deletion) — this is the best-characterized functional model, directly recapitulating isolated Complex IV enzymatic deficiency and the same class of stalled MT-CO1-containing assembly subcomplexes seen in patient fibroblasts (PMID:39779219). Because U2OS is a non-cardiac, non-physiological cell line, this model has high fidelity for the core biochemical/assembly mechanism but cannot recapitulate the cardiomyopathy or organismal lethality phenotype — an important model_scale distinction (cellular/molecular readout only; no tissue- or organism-level readout) if curated into a modeled_mechanisms link.
  • Patient-derived primary cells: Dermal fibroblasts (both families) and skeletal muscle biopsy tissue (second family) served as primary, disease-relevant (non-heterologous) models, directly showing isolated CIV deficiency and assembly-intermediate accumulation — these are patient material rather than "model organisms" per se but are the most disease-relevant functional evidence available.
  • No zebrafish, Drosophila, or C. elegans COA5/Pet191-ortholog disease model was identified in this search pass, despite orthologs likely existing (COA5 is described elsewhere as having stringent mouse/zebrafish orthology per one GeneCards-derived summary) — flag as an unexploited/unreported model-organism gap rather than an established negative finding.

Summary of Notable Gaps for KB Curation

  1. Age-at-death discrepancy (8–10 days vs. "3 months" from different secondary abstractions of PMID:21457908) — must be resolved against the primary paper.
  2. CNS/encephalopathy phenotype is implied by the disease-class name but not directly documented in the sources retrieved here — verify in the primary text before curating a distinct CNS pathophysiology node.
  3. gnomAD/ClinVar-level variant frequency and classification for c.157G>C were not independently pulled and should be confirmed directly.
  4. Exact HGNC ID, GO molecular-function terms, and UniProt subcellular-localization detail for COA5 should be verified via OAK/UniProt lookup rather than taken from this search pass.
  5. Mouse Coa5-null phenotype detail (viability, whether embryonic lethal) should be pulled directly from MGI's allele-specific phenotype pages.
  6. No treatment, prevention, or model-organism-disease-recapitulation content beyond general extrapolation currently has direct COA5-specific citation support — this scarcity is itself the most important characteristic of this ultra-rare entry (two published families total) and should be represented honestly in the KB rather than padded with generic mitochondrial-disease boilerplate presented as disease-specific evidence.

Primary Sources / Citations

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Terms named as a different term 1

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0014667 (1 mention) - the report calls it "corresponds to MC4DN9"; MONDO calls it cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 3

Unresolved terms

These identifiers do not exist in an ontology that resolved other terms from the same prefix, so they were most likely invented:

  • HP:0005633 (1 mention) - HP does not contain this term

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • MGI:1923428 - called "Coa5", "Mouse:* Coa5", "Coa5 mouse gene detail"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA, MGI.