COX6B1-Related COX Deficiency

Mendelian MONDO:0033637 Pathograph 50 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

Autosomal recessive COX6B1-related mitochondrial complex IV deficiency spans neonatal encephalomyopathy with hydrocephalus and cardiomyopathy and childhood-onset progressive cavitating leukodystrophy. Biallelic missense variants impair a nuclear-encoded structural subunit of cytochrome c oxidase. Protein abundance and residual enzyme activity vary by allele and tissue: loss of stable incorporation can occur despite preserved total protein. Human cell models identify both an early role in MT-CO2 maturation or incorporation and a later role in holoenzyme stability. ATP depletion is context dependent, and secondary respiratory-chain defects in complete knockout cells should not be assumed in patients.

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1
Inheritance
16
Pathophys.
1
Histopath.
19
Phenotypes
50
Pathograph
1
Genes
4
Variants
7
Medical Actions
3
Datasets
4
Models
10
References
👪

Inheritance

1
Autosomal recessive
Show evidence (1 reference)
PMID:38842388 SUPPORT Human Clinical
"Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease manifestations."
The four previously reported patients precede the new fifth patient in this report; this is not a population frequency.
⚙

Pathophysiology

16
Biallelic COX6B1 dysfunction
Homozygous disease-associated missense variants impair COX6B1 function. The consequences include reduced protein abundance for some alleles and tissues, or impaired holoenzyme incorporation despite stable abundance for Arg20His fibroblasts.
COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Reduced COX6B1 abundance Some patient alleles reduce measured protein abundance.
Impaired stable COX6B1 incorporation Arg20His alters stable incorporation despite retained total protein.
Defective MT-CO2 maturation or incorporation Engineered complete loss blocks MT-CO2-dependent assembly.
Show evidence (2 references)
PMID:38842388 SUPPORT Human Clinical
"Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease manifestations."
The four previously reported patients precede the new fifth patient in this report; this is not a population frequency.
PMID:38842388 SUPPORT Human Clinical
"The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses with biochemical analysis of mitochondrial function showed isolated COX deficiency."
The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
Reduced COX6B1 abundance
COX6B1 protein is severely reduced in Arg20Cys muscle and absent by the reported Trp31Arg muscle assays. This is not universal: Arg20His fibroblasts retain total COX6B1 protein.
COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Reduced mature complex IV abundance Low protein availability accompanies deficient holoenzyme formation; allele-specific intermediates are unresolved.
Show evidence (3 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the mutant protein in highly unstable."
The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete absence.
PMID:38842388 SUPPORT Human Clinical
"Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western blot, enzyme histochemistry, and immuno-histochemistry."
Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
PMID:18499082 REFUTE In Vitro
"Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but failed to be, or to remain, stably incorporated in the COX holocomplex."
Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein numbering for p.Arg20His.
Impaired stable COX6B1 incorporation
Arg20His mutant protein is poorly incorporated or retained in the native holoenzyme despite preserved total fibroblast abundance. Muscle holoenzyme abundance is also reduced.
Experimental models
Patient-derived fibroblasts PRIMARY CELL CULTURE
Downstream
Reduced mature complex IV abundance Poor stable incorporation accompanies reduced holoenzyme stability in patient samples.
Show evidence (2 references)
PMID:18499082 SUPPORT In Vitro
"Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but failed to be, or to remain, stably incorporated in the COX holocomplex."
Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein numbering for p.Arg20His.
PMID:18499082 SUPPORT Human Clinical
"As shown in Figure 4A, fully assembled COX was reduced to approximately 40% in mutant versus control muscle."
Native gels show reduced assembled enzyme in patient muscle, with residual holoenzyme.
Defective MT-CO2 maturation or incorporation
COX6B1-null HEK293 cells accumulate early MT-CO1/COX4/COX5A assemblies while MT-CO2 and mature complex IV are depleted. Redox correction allows partial assembly to resume. These findings identify an early assembly role; direct COX6B1 copper-transfer chemistry is still unresolved.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED 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.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Yeast cox12 deletion and allele complementation OTHER
Downstream
Reduced mature complex IV abundance Failure to mature or incorporate the MT-CO2 module prevents formation of mature enzyme.
Show evidence (1 reference)
PMID:41419202 SUPPORT In Vitro
"Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or incorporation."
Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct copper transfer by COX6B1 remains unproven.
Reduced mature complex IV abundance
Impaired assembly and stability reduce mature cytochrome c oxidase. Arg20His patient muscle retains about 40% of control assembled enzyme, whereas complete knockout cells lose detectable monomer, dimer and III2IV forms.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED 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.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Downstream
Reduced complex IV activity Reduced abundance of mature complex IV limits its enzymatic capacity.
Show evidence (2 references)
PMID:18499082 SUPPORT Human Clinical
"As shown in Figure 4A, fully assembled COX was reduced to approximately 40% in mutant versus control muscle."
Native gels show reduced assembled enzyme in patient muscle, with residual holoenzyme.
PMID:41419202 SUPPORT In Vitro
"These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as well as SC III2IV in 6B1KO."
Complete absence of these native forms is a result of engineered knockout; patient missense alleles can retain holoenzyme.
Reduced complex IV activity
Patient tissues show reduced or undetectable complex IV activity, with other respiratory complexes preserved in the reported clinical assays. Complete knockout abolishes detectable respiratory flux under the tested HEK293 conditions. This node represents terminal respiratory impairment without asserting universal ATP collapse.
COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee.
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED 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.
cytochrome-c oxidase activity GO:0004129 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased cytochrome-c oxidase activity (GO:0004129). GO:0004129 is a molecular function from the Gene Ontology.
Experimental models
Patient-derived fibroblasts PRIMARY CELL CULTURE
HeLa COX6B1 knockdown CELL LINE
Yeast cox12 deletion and allele complementation OTHER
Downstream
Increased OPA1 processing in knockout cells Severe respiratory dysfunction accompanies increased OPA1 processing, partly reversible by AOX; upstream signaling is unresolved.
Reductive imbalance in knockout cells Respiratory blockade shifts the cellular NAD redox balance.
Glycolytic compensation in knockout cells Severe respiratory impairment is accompanied by compensatory glycolytic flux.
ATP depletion under respiratory dependence Patient fibroblasts lose ATP when growth requires oxidative metabolism.
Integrated stress response in knockout cells Severe respiratory dysfunction activates the measured stress response.
Reduced mitochondrial ribosomal abundance Severe-null cells reduce mitoribosome abundance through unresolved signaling.
Mitochondrial cristae remodeling in knockout cells The respiratory defect accompanies cristae remodeling in engineered cells.
Encephalopathy This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Hydrocephalus This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Hypertrophic cardiomyopathy This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Leukodystrophy This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Muscle weakness This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Ataxia This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Visual impairment This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Cognitive deterioration This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Seizures This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Hypotonia This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Feeding difficulties in infancy This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Aspiration This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Cerebral visual impairment This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Short stature This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Pulmonary hypertension This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Elevated circulating lactate This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Lactic acidosis This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Hyperammonemia This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Hyperalaninemia This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening tissue mechanism is not directly resolved.
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit."
The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are preserved.
PMID:39184436 SUPPORT In Vitro
"Evaluation of the “bioenergetic phenotype,” i.e., the cellular oxygen consumption rate (OCR) vs. extracellular acidification rate (ECAR), showed null OCR in cIV-deficient cells (4dKO, 6BKO) and significantly decreased OCR in βKO (cV) cells (Figures 2A and 2C)."
The 6BKO cells have no measurable oxygen-consumption flux in this assay; the other knockout models in the sentence are distinct genes.
Reductive imbalance in knockout cells
The NAD+/NADH ratio falls in COX6B1-null HEK293 cells and normalizes with alternative oxidase expression. Increased mitochondrial ROS and AMPK activation were not observed in this particular knockout model.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (2 references)
PMID:39184436 SUPPORT In Vitro
"We also determined the NAD+/NADH ratio, which was decreased in cIV-deficient cells (4dKO, 6BKO) but was restored to wt levels by AOX expression (Figure 2E)."
The COX6B1 knockout is 6BKO; AOX bypass reverses reductive imbalance in this cell model.
PMID:39184436 SUPPORT In Vitro
"while there was no increase in ROS production in 6BKO (cIV) cells (Figures 4D, 4E, and S4A)."
The COX6B1-null redox phenotype should not be conflated with increased ROS in the other knockout models.
Glycolytic compensation in knockout cells
Increased extracellular acidification in COX6B1-null HEK293 cells accompanies preserved adenylate energy charge. This is a culture-dependent compensatory response rather than evidence that ATP is preserved in every affected tissue.
glycolytic process GO:0006096 ↑ INCREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased glycolytic process (GO:0006096). GO:0006096 is a biological process from the Gene Ontology.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (2 references)
PMID:39184436 SUPPORT In Vitro
"ECAR in the OXPHOS-deficient cells (4dKO, 6BKO, βKO) indicated a higher glycolytic rate (Figures 2B and 2C), providing ATP by substrate-level phosphorylation."
Higher extracellular acidification supports glycolytic compensation in 6BKO, not a measured patient-tissue glycolytic rate.
PMID:39184436 SUPPORT In Vitro
"The differences in P-AMPK could not be explained by a drop in ATP levels relative to ADP or AMP, as energy charge remained the same in all cell lines (Figures 4F and S4B)."
Preserved adenylate energy charge in these cultured knockout cells limits any claim of universal cellular ATP collapse.
ATP depletion under respiratory dependence
Arg20Cys patient fibroblasts exhibit low ATP content and poor growth in galactose medium. This conditional assay supports vulnerability when oxidative metabolism is required; preserved energy charge in glucose-supported knockout cells limits a universal ATP-depletion claim.
Experimental models
Patient-derived fibroblasts PRIMARY CELL CULTURE
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"The mitochondrial dysfunction was evident in the patient's fibroblasts where defective growth and ATP content were clearly observed in GAL medium as compared with glucose-containing (GLU) medium."
ATP depletion is demonstrated under galactose challenge in Arg20Cys fibroblasts; it is not a direct measurement in brain or heart.
PMID:39184436 SUPPORT In Vitro
"The differences in P-AMPK could not be explained by a drop in ATP levels relative to ADP or AMP, as energy charge remained the same in all cell lines (Figures 4F and S4B)."
Preserved adenylate energy charge in these cultured knockout cells limits any claim of universal cellular ATP collapse.
Integrated stress response in knockout cells
COX6B1-null HEK293 cells increase eIF2alpha phosphorylation, ATF4 and eIF4EBP1. Pharmacological or genetic ISR suppression does not restore complex I subunits, so this response is not assigned as their causal mediator.
integrated stress response signaling GO:0140467 ↑ INCREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased integrated stress response signaling (GO:0140467). GO:0140467 is a biological process from the Gene Ontology.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (2 references)
PMID:39184436 SUPPORT In Vitro
"Compared to wt cells, the ATF4 and eIF4EBP1 steady-state levels as well as eIF2α phosphorylation were significantly increased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient models but were normalized by AOX expression only in cIV-deficient cells (4dKO, 6BKO) (Figures 5B and 5C)."
The 6BKO results establish an integrated stress response that is reversible by respiratory bypass.
PMID:39184436 SUPPORT In Vitro
"Despite efficient inhibition of ISR in cIV- (4dKO, 6BKO) and cV- (βKO) lacking cells, documented by (i) a significant decrease of ATF4 and its targets to wt levels (Figures 5E and 5F) and (ii) decreased eIF4EBP1 levels (Figures 5G and 5H), the level of cI subunits was not increased (Figures..."
ISRIB and eIF4EBP1 silencing fail to restore complex I; ISR activation is not established as the mediator of secondary complex I loss.
Reduced mitochondrial ribosomal abundance
Both mitochondrial ribosomal subunits and several assembly factors are reduced in severe COX6B1-null HEK293 cells. The initiating signaling mechanism is unresolved.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Downstream
Attenuated mitochondrial translation Lower mitoribosome abundance correlates with reduced mitochondrial protein synthesis; a selective ribosome rescue was not performed.
Show evidence (1 reference)
PMID:39184436 SUPPORT In Vitro
"LFQ-MS data analysis of mitochondrial proteins revealed that mitochondrial ribosomal proteins (MRPs), the constituents of both large (mtLSU) and small (mtSSU) mitochondrial ribosome subunits, were in general two to four times decreased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient cells compared..."
Proteomics identifies loss of both mitoribosomal subunits in severe COX6B1-null cells.
Attenuated mitochondrial translation
Pulse labeling identifies reduced synthesis of mitochondrial complex I and IV subunits in severe knockout cells. Mitoribosome abundance tracks this defect, while accelerated turnover does not explain the reduction.
mitochondrial translation GO:0032543 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial translation (GO:0032543). GO:0032543 is a biological process from the Gene Ontology.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Downstream
Secondary complex I depletion in knockout cells Reduced synthesis provides a biogenesis explanation for secondary complex I depletion; the upstream sensing mechanism is unresolved.
Show evidence (2 references)
PMID:39184436 SUPPORT In Vitro
"The synthesis of the mtDNA-encoded cIV and cI subunits was the most affected in cIV- (4dKO, 6BKO) and cV- (βKO) deficient cells, which was reduced to 30% of wt (Figures 7B, 7C, and S6A)."
Pulse labeling shows reduced mitochondrial synthesis in 6BKO; this is a cellular secondary defect.
PMID:39184436 SUPPORT In Vitro
"On the other hand, cI and cIII subunits were even more stable in all OXPHOS-deficient models than in wt cells."
Pulse-chase results oppose accelerated degradation as the main explanation for complex I depletion.
Secondary complex I depletion in knockout cells
Severe complete COX6B1 knockout produces secondary complex I loss associated with reduced mitochondrial protein synthesis. This experimental combined defect is distinct from isolated complex IV deficiency in the clinical missense cases.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (2 references)
PMID:39184436 SUPPORT In Vitro
"In summary, severe OXPHOS aberrations in HEK293 cells lead to a specific decrease in cI. AOX expression causes a reversal to the wt phenotype in cIV-, but not in cV-deficient cells."
The severe-null cell phenotype includes secondary complex I loss, unlike the isolated complex IV deficiency documented in patient muscle.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ NO_EVIDENCE Human Clinical
"The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit."
The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are preserved. This clinical contrast does not test the secondary complex I loss in complete-knockout cells.
Mitochondrial cristae remodeling in knockout cells
COX6B1-null HEK293 cells exhibit shorter, wider mitochondrial cristae. AOX improves these abnormalities, but the intermediate pathway coupling respiratory dysfunction to cristae shape remains unresolved.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (1 reference)
PMID:39184436 SUPPORT In Vitro
"All OXPHOS deficiency models (4dKO, 6BKO, and βKO) showed perturbed mitochondrial morphology (Figure 3D), with cristae being shorter and wider than in wt cells (Figure 3E)."
Electron microscopy establishes altered cristae in 6BKO; this is not a clinical muscle histology claim.
Increased OPA1 processing in knockout cells
COX6B1-null HEK293 cells have a reduced long-to-short OPA1 ratio, consistent with increased proteolytic processing. AOX partially restores the ratio. Direct genetic testing of the upstream protease pathway was not reported.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Downstream
Mitochondrial fragmentation in knockout cells Increased OPA1 processing accompanies network fragmentation in the same models; the study did not isolate OPA1 cleavage as the causal mediator.
Show evidence (1 reference)
PMID:39184436 SUPPORT In Vitro
"The three KO cell lines (4dKO, 6BKO, and βKO) showed a significantly decreased long-to-short OPA1 ratio, indicating a higher OPA1 cleavage rate (Figures 5B and 5D)."
The COX6B1-null model shares increased OPA1 processing with the other severe knockout models.
Mitochondrial fragmentation in knockout cells
COX6B1-null HEK293 cells show fragmented mitochondrial networks without a change in measured mitochondrial mass. AOX reverses fragmentation in the complex IV-deficient models.
Experimental models
HEK293 COX6B1 knockout and complementation CELL LINE
Show evidence (1 reference)
PMID:39184436 SUPPORT In Vitro
"Accordingly, mitochondria were significantly more fragmented in OXPHOS-deficient cells, with no changes in mitochondrial mass (Figure S5C), and this fragmentation was reverted by AOX expression only in cIV-deficient cells (4dKO, 6BKO; Figures S5A–S5C)."
The 6BKO model shows altered network morphology, distinct from the cristae ultrastructure measurement.
✶

Histopathology

1
Reduced muscle cytochrome c oxidase staining
Muscle enzyme histochemistry shows low COX activity; immunohistochemistry and immunoblotting can show COX6B1 loss depending on the allele.
Show evidence (2 references)
PMID:18499082 SUPPORT Human Clinical
"The histochemical reaction to COX was diffusely low in a skeletal muscle biopsy from patient AK (Figure 2B)."
The patient muscle biopsy directly demonstrates reduced COX histochemical activity.
PMID:38842388 SUPPORT Human Clinical
"Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western blot, enzyme histochemistry, and immuno-histochemistry."
Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COX6B1-Related COX Deficiency 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

19
Cardiovascular 2
Hypertrophic cardiomyopathy HP:0001639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertrophic cardiomyopathy (HP:0001639). HP:0001639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24781756 SUPPORT Human Clinical
"We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an integral, nuclear-encoded COX subunit."
The Arg20Cys case establishes this combination of clinical manifestations.
Pulmonary hypertension Elevated pulmonary artery pressure HP:0004890 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated pulmonary artery pressure (HP:0004890). HP:0004890 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Chest X-ray revealed cardiomegaly, and cardiac Echo revealed symmetrical left ventricular hypertrophy tricuspid regurge and pulmonary hypertension."
The clinical echo report documents elevated pulmonary pressure without invasive hemodynamic classification.
Digestive 1
Feeding difficulties in infancy HP:0008872 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties in infancy (HP:0008872). HP:0008872 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy (PEG) feeding tube was inserted at age 10 weeks."
The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
Eye 2
Visual impairment HP:0000505 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Visual impairment (HP:0000505). HP:0000505 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity, and moderate cognitive deterioration (IQ = 84)."
The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual disability.
Cerebral visual impairment HP:0100704 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral visual impairment (HP:0100704). HP:0100704 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Eye examination at the age of 15 weeks revealed cortical blindness."
The report localizes this severe visual impairment to the cortex.
Metabolism 4
Elevated circulating lactate Increased circulating lactate concentration HP:0002151 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased circulating lactate concentration (HP:0002151). HP:0002151 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Laboratory investigation showed high serum lactate levels (2.6 mM, normal value ... < 1.8) and cerebrospinal fluid (CSF) (5.1 mM, n.v. < 1.8)."
The younger Arg20His brother had elevated blood and CSF lactate.
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:18499082 SUPPORT Human Clinical
"The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized convulsions and severe metabolic acidosis with very high serum lactic acid levels."
The original report directly documents generalized convulsions during severe metabolic deterioration.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"On the first day of life, the patient developed metabolic acidosis ... and elevated ammonia levels"
The Arg20Cys infant had neonatal metabolic acidosis, lactate elevation and hyperammonemia.
Hyperammonemia HP:0001987 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperammonemia (HP:0001987). HP:0001987 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"On the first day of life, the patient developed metabolic acidosis ... and elevated ammonia levels"
The Arg20Cys infant had neonatal metabolic acidosis, lactate elevation and hyperammonemia.
Hyperalaninemia HP:0003348 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperalaninemia (HP:0003348). HP:0003348 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Metabolic work up showed normal acylcarnitines, elevated alanine level ... and urine organic acids showed increased lactic acidosis and ketones."
The neonatal metabolic work-up documented raised circulating alanine.
Musculoskeletal 2
Muscle weakness HP:0001324 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Muscle weakness (HP:0001324). HP:0001324 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity, and moderate cognitive deterioration (IQ = 84)."
The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual disability.
Hypotonia HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy (PEG) feeding tube was inserted at age 10 weeks."
The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
Nervous System 6
Encephalopathy HP:0001298 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Encephalopathy (HP:0001298). HP:0001298 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:24781756 SUPPORT Human Clinical
"We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an integral, nuclear-encoded COX subunit."
The Arg20Cys case establishes this combination of clinical manifestations.
PMID:38842388 SUPPORT Human Clinical
"We describe the clinical features and follow-up of a patient with a novel homozygous pathogenic variant in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection."
The Trp31Arg case includes acute infection-associated deterioration.
Hydrocephalus HP:0000238 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hydrocephalus (HP:0000238). HP:0000238 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24781756 SUPPORT Human Clinical
"We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an integral, nuclear-encoded COX subunit."
The Arg20Cys case establishes this combination of clinical manifestations.
Leukodystrophy HP:0002415 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Leukodystrophy (HP:0002415). HP:0002415 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:18499082 SUPPORT Human Clinical
"Brain MRI showed symmetrical, diffuse leukodystrophy with cystic lesions in the supratentorial areas of the white matter (Figure 1B)."
The younger Arg20His brother had cystic supratentorial leukodystrophy.
PMID:22277967 SUPPORT Human Clinical
"| P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd | *COX6B1 |"
The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast complex IV measurements are low/normal.
Ataxia HP:0001251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ataxia (HP:0001251). HP:0001251 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity, and moderate cognitive deterioration (IQ = 84)."
The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual disability.
Cognitive deterioration Mental deterioration HP:0001268 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Mental deterioration (HP:0001268). HP:0001268 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity, and moderate cognitive deterioration (IQ = 84)."
The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual disability.
Seizures HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized convulsions and severe metabolic acidosis with very high serum lactic acid levels."
The original report directly documents generalized convulsions during severe metabolic deterioration.
Respiratory 1
Aspiration HP:0002835 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Aspiration (HP:0002835). HP:0002835 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy (PEG) feeding tube was inserted at age 10 weeks."
The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
Growth 1
Short stature HP:0004322 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Birth weight and height are not known but were reported as abnormally low and remained below the 3rd percentile ever since."
The older brother had persistently low height as well as weight. This supports short stature independently of the younger brother's borderline third-centile measurement.
🧬

Genetic Associations

1
COX6B1
Gene: COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive
Show evidence (1 reference)
PMID:38842388 SUPPORT Human Clinical
"Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease manifestations."
The four previously reported patients precede the new fifth patient in this report; this is not a population frequency.
Variants (4)
p.Arg20His Pathogenic
Gene: COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee. missense variant
Homozygous variant in the original two brothers, with childhood-onset neurological disease. Mature-protein R19H numbering refers to this same residue. Fibroblasts retain total mutant protein but show impaired stable holoenzyme incorporation.
Show evidence (2 references)
PMID:18499082 SUPPORT Human Clinical
"We found no change in COX7A1 and COX6B2 genes, but both probands carried a homozygous c.221G→A substitution in exon 2 of COX6B1, predicting a p.R19H amino acid change (numeration according to the mature protein in which the first M is eliminated)."
The original paper establishes homozygosity and explicitly uses mature-protein numbering. Its c.221 notation is legacy sequence numbering, not modern coding HGVS.
PMID:18499082 SUPPORT In Vitro
"Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but failed to be, or to remain, stably incorporated in the COX holocomplex."
Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein numbering for p.Arg20His.
p.Arg20Cys Pathogenic
Gene: COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee. missense variant
Homozygous variant in a neonatal encephalomyopathy, hydrocephalus and cardiomyopathy case. Muscle COX6B1 is severely reduced; the enzyme defect was rescued by wild-type cDNA in fibroblasts.
Show evidence (2 references)
PMID:24781756 SUPPORT Human Clinical
"We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an integral, nuclear-encoded COX subunit."
The Arg20Cys case establishes this combination of clinical manifestations.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the mutant protein in highly unstable."
The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete absence.
p.Thr81Pro Pathogenic
Gene: COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee. missense variant
Homozygous c.241A>C in patient P17 with neonatal mitochondrial encephalopathy and cystic leukodystrophy. The sequencing study reports segregation and protein degradation; fibroblast enzyme activity was normal despite low muscle activity.
Show evidence (2 references)
PMID:22277967 SUPPORT Human Clinical
"| P17 | complex IV deficiency (MIM:220110) | *COX6B1 | hom. | c.241A>C, p.T81P | 3 | protein degradation family segregation |"
The diagnostic table identifies the homozygous Thr81Pro allele and reports segregation and protein degradation as supporting evidence.
PMID:22277967 SUPPORT Human Clinical
"| P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd | *COX6B1 |"
The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast complex IV measurements are low/normal.
p.Trp31Arg Pathogenic
Gene: COX6B1 hgnc:2280 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COX6B1 (hgnc:2280). hgnc:2280 is a gene from the HUGO Gene Nomenclature Committee. missense variant
Homozygous variant associated with acute infection-related encephalomyopathy, isolated complex IV deficiency and lack of detectable muscle COX6B1.
Show evidence (2 references)
PMID:38842388 SUPPORT Human Clinical
"The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses with biochemical analysis of mitochondrial function showed isolated COX deficiency."
The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
PMID:38842388 SUPPORT Human Clinical
"Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western blot, enzyme histochemistry, and immuno-histochemistry."
Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
💊

Medical Actions

7
Ventriculoperitoneal shunting
Action: Ventriculoperitoneal Shunt PlacementNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Ventriculoperitoneal Shunt Placement (NCIT:C168483). NCIT:C168483 is a clinical intervention from the NCI Thesaurus. NCIT:C168483
Platform: Surgery
CSF diversion was used for rapidly progressive hydrocephalus in the Arg20Cys patient; later shunt malfunction required further hospital care.
Mechanism Target:
MODULATES Hydrocephalus — Addresses this clinical manifestation; disease-specific efficacy has not been established.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"At 15 weeks, a ventriculoperitoneal (VP) shunt was inserted."
The Arg20Cys infant underwent CSF diversion for progressive hydrocephalus.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"At 15 weeks, a ventriculoperitoneal (VP) shunt was inserted."
The Arg20Cys infant underwent CSF diversion for progressive hydrocephalus.
Gastrostomy feeding
Action: Percutaneous Endoscopic GastrostomyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Percutaneous Endoscopic Gastrostomy (NCIT:C106040). NCIT:C106040 is a clinical intervention from the NCI Thesaurus. NCIT:C106040
Platform: Surgery
Gastrostomy was placed for hypotonia, feeding difficulty and recurrent aspiration in the Arg20Cys infant.
Mechanism Target:
MODULATES Feeding difficulties in infancy — Addresses this clinical manifestation; disease-specific efficacy has not been established.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy (PEG) feeding tube was inserted at age 10 weeks."
The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy (PEG) feeding tube was inserted at age 10 weeks."
The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
Cardiac pharmacotherapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: Diuretic NCIT:C448 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses Diuretic (NCIT:C448). NCIT:C448 is a therapeutic agent from the NCI Thesaurus. Beta-Adrenergic Antagonist NCIT:C29576 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses Beta-Adrenergic Antagonist (NCIT:C29576). NCIT:C29576 is a therapeutic agent from the NCI Thesaurus. Calcium Channel Blocker NCIT:C333 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses Calcium Channel Blocker (NCIT:C333). NCIT:C333 is a therapeutic agent from the NCI Thesaurus.
Platform: Small molecule
Diuretics, beta blockers and subsequently calcium-channel blockers were used for the Arg20Cys cardiomyopathy. The case documents exposure and later echocardiographic improvement, without isolating treatment efficacy.
Mechanism Target:
MODULATES Hypertrophic cardiomyopathy — Addresses this clinical manifestation; disease-specific efficacy has not been established.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"At the age of 4 months, he started developing hypertrophic obstructive cardiomyopathy, he was started on diuretics and beta blockers and later calcium channel blockers were added; follow-up Echo at the age of 2 years revealed improvement in the LVH and no PHTN."
Several cardiac drugs were used together; later improvement cannot establish the benefit of an individual agent.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"At the age of 4 months, he started developing hypertrophic obstructive cardiomyopathy, he was started on diuretics and beta blockers and later calcium channel blockers were added; follow-up Echo at the age of 2 years revealed improvement in the LVH and no PHTN."
Several cardiac drugs were used together; later improvement cannot establish the benefit of an individual agent.
Coenzyme Q10 supplementation
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: coenzyme Q10 CHEBI:46245 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses coenzyme Q10 (CHEBI:46245). CHEBI:46245 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Coenzyme Q10 was started and later discontinued by the family in the Arg20Cys case. Disease-specific clinical benefit was not demonstrated.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"Coenzyme Q10 supplementation (60 mg twice daily) was initiated at 4 months but discontinued by the parents."
This records treatment exposure and discontinuation, not efficacy.
AICAR in patient fibroblasts (preclinical)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: AICAR Relation: this treatment uses this therapeutic agent This treatment uses AICAR.
Platform: Small molecule
AICAR increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not establish a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
Mechanism Target:
MODULATES ATP depletion under respiratory dependence — Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism remain unproven.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"The favorable response is presumably not due to increased mitochondrial content or improved membrane potential as mitotracker green and TMRE stain did not reveal any significant differences between treated and untreated cells (result not shown)."
These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug mechanism.
Resveratrol in patient fibroblasts (preclinical)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: resveratrol CHEBI:27881 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses resveratrol (CHEBI:27881). CHEBI:27881 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Resveratrol increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not establish a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
Mechanism Target:
MODULATES ATP depletion under respiratory dependence — Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism remain unproven.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"The favorable response is presumably not due to increased mitochondrial content or improved membrane potential as mitotracker green and TMRE stain did not reveal any significant differences between treated and untreated cells (result not shown)."
These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug mechanism.
Ascorbate in patient fibroblasts (preclinical)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: ascorbate CHEBI:22651 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses ascorbate (CHEBI:22651). CHEBI:22651 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Ascorbate increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not establish a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
Mechanism Target:
MODULATES ATP depletion under respiratory dependence — Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism remain unproven.
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"ATP content was markedly improved by AICAR, reveratrol and ascorbate."
The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated clinical efficacy.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"The favorable response is presumably not due to increased mitochondrial content or improved membrane potential as mitotracker green and TMRE stain did not reveal any significant differences between treated and untreated cells (result not shown)."
These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug mechanism.
🔬

Biochemical Markers

2
Reduced tissue complex IV activity (Decreased or undetectable, depending on allele and tissue)
Show evidence (1 reference)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit."
The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are preserved.
Elevated blood and CSF lactate (Increased)
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Laboratory investigation showed high serum lactate levels (2.6 mM, normal value ... < 1.8) and cerebrospinal fluid (CSF) (5.1 mM, n.v. < 1.8)."
The younger Arg20His brother had elevated blood and CSF lactate.
🔬

Diagnosis

3
Molecular confirmation
Identify biallelic COX6B1 variants and interpret segregation alongside biochemical and functional data. Include COX6B1 in isolated complex IV deficiency investigations even when cardiomyopathy is present.
Genetic Testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (2 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"We suggest that genetic analysis of ... COX6B1 ... should be included in the investigation of isolated COX deficiency, including patients with cardiac defects."
The case report recommends inclusion of this structural-subunit gene in molecular investigations.
PMID:38842388 SUPPORT Human Clinical
"The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses with biochemical analysis of mitochondrial function showed isolated COX deficiency."
The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
Respiratory-chain enzymology
Measure complex IV activity relative to mitochondrial controls and other respiratory complexes. Deficiency can vary markedly between muscle, lymphocytes and fibroblasts; normal fibroblast activity in the Thr81Pro case does not exclude the muscle defect.
Show evidence (3 references)
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT Human Clinical
"The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit."
The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are preserved.
PMID:22277967 SUPPORT Human Clinical
"| P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd | *COX6B1 |"
The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast complex IV measurements are low/normal.
PMID:24781756 SUPPORT Human Clinical
"Initial measurement of COX activity in lymphocytes may be useful as it might circumvent the need for invasive muscle biopsy."
This is a case-report diagnostic proposal, not a validated universal sensitivity estimate.
Neuroimaging
Brain MRI can demonstrate progressive cavitating leukodystrophy. Ventricular enlargement from white-matter loss should be distinguished from the rapidly progressive shunt-treated hydrocephalus reported with Arg20Cys.
Magnetic Resonance Imaging NCIT:C16809 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:18499082 SUPPORT Human Clinical
"Brain MRI showed symmetrical, diffuse leukodystrophy with cystic lesions in the supratentorial areas of the white matter (Figure 1B)."
The younger Arg20His brother had cystic supratentorial leukodystrophy.
📊

Related Datasets

3
COX6B1 secures a redox-sensitive step in early cytochrome c oxidase assembly pride:PXD061621
Whole-cell label-free proteomics and complex IV immunocapture proteomics of human HEK293 COX6B1 knockout, allele-expression and AOX models; these are engineered cells, not a patient cohort.
Homo sapiens PROTEOMICS
PMID:41419202
Show evidence (1 reference)
PMID:41419202 SUPPORT Other
"LFQ–MS data are available via ProteomeXchange with identifier PXD061621."
The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently verified.
COX6B1 secures a redox-sensitive step in early cytochrome c oxidase assembly pride:PXD061618
Complexome profiling of wild-type, COX6B1 knockout and AOX-expressing knockout HEK293 mitochondria across 48 blue-native gel slices.
Homo sapiens PROTEOMICS
PMID:41419202
Show evidence (1 reference)
PMID:41419202 SUPPORT Other
"Complexome profiling data are available via ProteomeXchange with identifier PXD061618."
The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently verified.
Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies pride:PXD046331
Label-free proteomics across severe and mild OXPHOS-deficient HEK293 models, including COX6B1 knockout and AOX complementation; other-gene models must be distinguished.
Homo sapiens PROTEOMICS
PMID:39184436
Show evidence (1 reference)
PMID:39184436 SUPPORT Other
"LFQ-MS data are available via ProteomeXchange with identifier PXD046331."
The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently verified.
🧫

Experimental Models

4
Patient-derived fibroblasts PRIMARY_CELL_CULTURE
Arg20His patient fibroblasts, including immortalized derivatives, show impaired stable holoenzyme incorporation despite preserved total COX6B1. Arg20Cys fibroblasts show severe enzymatic deficiency and low ATP under galactose challenge, with rescue by wild-type COX6B1 cDNA. Lentiviral complementation is an experimental pathogenicity test, not demonstrated clinical gene therapy.
Publication
PMID:18499082
Pathograph links
Impaired stable COX6B1 incorporation partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Reduced complex IV activity partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
ATP depletion under respiratory dependence partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Show evidence (3 references)
PMID:18499082 SUPPORT In Vitro
"Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but failed to be, or to remain, stably incorporated in the COX holocomplex."
Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein numbering for p.Arg20His.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/ SUPPORT In Vitro
"The mitochondrial dysfunction was evident in the patient's fibroblasts where defective growth and ATP content were clearly observed in GAL medium as compared with glucose-containing (GLU) medium."
ATP depletion is demonstrated under galactose challenge in Arg20Cys fibroblasts; it is not a direct measurement in brain or heart.
PMID:24781756 SUPPORT In Vitro
"Complementation with the wild-type cDNA by a lentiviral construct restored COX activity, and mitochondrial function was improved by 5-aminoimidazole-4-carboxamide ribonucleotide, resveratrol and ascorbate in the patient's fibroblasts."
Wild-type complementation establishes functional rescue in patient cells; the small-molecule results are also cell based.
HeLa COX6B1 knockdown CELL_LINE
Stable shRNA knockdown lowered COX6B1 transcript and protein and reduced complex IV activity. This partial depletion model complements the complete knockout studies.
Publication
PMID:18499082
Pathograph links
Reduced complex IV activity partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Show evidence (1 reference)
PMID:18499082 SUPPORT In Vitro
"Accordingly, the COX/CS activities were significantly reduced, to around 70%, in either shRNA1- or shRNA14-versus mock-transfected HeLa cells (p < 0.0026 and p < 0.0009 respectively, Figure 3B)."
Two independent knockdown constructs reduce measured complex IV activity.
HEK293 COX6B1 knockout and complementation CELL_LINE
Three CRISPR knockout clones reveal early MT-CO2 assembly failure as well as late holoenzyme instability. Wild-type COX6B1 restores respiration; Arg20His and Arg20Cys partially rescue with a more severe residual defect for Arg20Cys. Tagged COX6B2 does not rescue in this cell context. AOX restores redox balance and permits partial complex IV modules to join respirasomes, but intact-cell respiration flows through AOX and native complex IV activity remains negligible. ISR inhibition does not restore secondary complex I loss.
Publication
PMID:41419202
Pathograph links
Defective MT-CO2 maturation or incorporation partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Reduced mature complex IV abundance partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Reductive imbalance in knockout cells partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Glycolytic compensation in knockout cells partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Integrated stress response in knockout cells partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Reduced mitochondrial ribosomal abundance partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Attenuated mitochondrial translation partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Secondary complex I depletion in knockout cells partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Mitochondrial cristae remodeling in knockout cells partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Increased OPA1 processing in knockout cells partially recapitulates observes: cellular
Limitations: Complete knockout in a cultured human cell line does not establish this mechanism in patient tissues.
Mitochondrial fragmentation in knockout cells partially recapitulates observes: cellular
Limitations: Complete knockout in a cultured human cell line does not establish this mechanism in patient tissues.
Show evidence (7 references)
PMID:41419202 SUPPORT In Vitro
"Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or incorporation."
Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct copper transfer by COX6B1 remains unproven.
PMID:41419202 SUPPORT In Vitro
"These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as well as SC III2IV in 6B1KO."
Complete absence of these native forms is a result of engineered knockout; patient missense alleles can retain holoenzyme.
PMID:41419202 SUPPORT In Vitro
"Even though the AOX-expressing cells displayed robust rates of routine respiration, titration of the AOX inhibitor (salicylhydroxamic acid) completely abolished oxygen consumption, indicating that in intact cells, oxygen consumption was exclusively happening through AOX (Fig. S3, C and D)."
Respiratory bypass restores flux through AOX, not normal native complex IV respiration.
+ 4 more references
Yeast cox12 deletion and allele complementation OTHER
Saccharomyces cerevisiae lacking the COX6B1 ortholog Cox12 has impaired respiratory growth. Human Arg20His retains partial complementation in the 2008 human-protein experiment, whereas the analogous yeast-protein R17H and R17C constructs failed complementation in 2021. Galactose-grown null yeast retain bulk III2IV supercomplexes but have reduced Cox2/Rcf2 association and severe complex IV activity loss. This differs from complete holoenzyme loss in human knockout cells. Coa6/Cox12 double-deletion epistasis additionally supports overlapping roles in Cox2 biogenesis.
Publication
PMID:34937540
Pathograph links
Defective MT-CO2 maturation or incorporation partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Reduced complex IV activity partially recapitulates observes: cellular
Limitations: The system resolves cellular biochemical consequences and does not reproduce the full neurological and cardiac phenotype.
Show evidence (4 references)
PMID:34937540 SUPPORT Model Organism
"Cox12 with arginine 17 residue substituted by histidine (R17H) or cysteine (R17C) (mutations analogous to those observed in human patients) failed to complement the loss of Cox12 function."
These are yeast ortholog substitutions, not the human-protein constructs used in 2008.
PMID:34937540 SUPPORT Model Organism
"However, the association of the respiratory SC factor 2 (Rcf2) and Cox2 subunit within the SCs of cox12Δ cells was reduced, while the specific activity of CIV was downregulated by 90%."
Yeast retain bulk supercomplexes despite a marked activity defect.
PMID:18499082 SUPPORT Model Organism
"Likewise, the activity of COX/CS in COX6B1R19H transformants was 67% to that of the COX6B1wild-type transformants (Figure 5A and Table 3)."
Human Arg20His expressed in yeast retains partial activity relative to wild-type complementation.
+ 1 more reference
{ }

Source YAML

click to show 
name: COX6B1-Related COX Deficiency
category: Mendelian
creation_date: '2026-06-15T00:00:00Z'
synonyms:
- COX6B1 deficiency
- Mitochondrial complex IV deficiency, nuclear type 7
- MC4DN7
- COX6B1-related cytochrome c oxidase deficiency
disease_term:
  preferred_term: COX6B1-related COX deficiency (MC4DN7)
  term:
    id: MONDO:0033637
    label: mitochondrial complex IV deficiency, nuclear type 7
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
description: >-
  Autosomal recessive COX6B1-related mitochondrial complex IV deficiency spans neonatal encephalomyopathy with
  hydrocephalus and cardiomyopathy and childhood-onset progressive cavitating leukodystrophy. Biallelic missense
  variants impair a nuclear-encoded structural subunit of cytochrome c oxidase. Protein abundance and residual
  enzyme activity vary by allele and tissue: loss of stable incorporation can occur despite preserved total
  protein. Human cell models identify both an early role in MT-CO2 maturation or incorporation and a later
  role in holoenzyme stability. ATP depletion is context dependent, and secondary respiratory-chain defects
  in complete knockout cells should not be assumed in patients.
inheritance:
- name: Autosomal recessive
  evidence:
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease
      manifestations.
    explanation: >-
      The four previously reported patients precede the new fifth patient in this report; this is not a population
      frequency.
notes: >-
  The small number of reported families does not establish phenotype frequencies or penetrance. The neonatal
  cardiac presentation and childhood neurological presentations are retained within one COX6B1 disease spectrum.
  Infection-associated deterioration is a precipitating circumstance of this inherited disorder. Mechanisms
  observed only in engineered null cells are distinguished from patient missense phenotypes.
pathophysiology:
- name: Biallelic COX6B1 dysfunction
  description: >-
    Homozygous disease-associated missense variants impair COX6B1 function. The consequences include reduced
    protein abundance for some alleles and tissues, or impaired holoenzyme incorporation despite stable abundance
    for Arg20His fibroblasts.
  evidence:
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease
      manifestations.
    explanation: >-
      The four previously reported patients precede the new fifth patient in this report; this is not a population
      frequency.
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses
      with biochemical analysis of mitochondrial function showed isolated COX deficiency.
    explanation: The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
  genes:
  - preferred_term: COX6B1
    term:
      id: hgnc:2280
      label: COX6B1
  role: trigger
  downstream:
  - target: Reduced COX6B1 abundance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Some patient alleles reduce measured protein abundance.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely
        detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the
        mutant protein in highly unstable.
      explanation: >-
        The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete
        absence.
  - target: Impaired stable COX6B1 incorporation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Arg20His alters stable incorporation despite retained total protein.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts,
        but failed to be, or to remain, stably incorporated in the COX holocomplex.
      explanation: >-
        Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
        numbering for p.Arg20His.
  - target: Defective MT-CO2 maturation or incorporation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Engineered complete loss blocks MT-CO2-dependent assembly.
    evidence:
    - reference: PMID:41419202
      reference_title: >-
        The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
        of complex IV.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or
        incorporation.
      explanation: >-
        Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct
        copper transfer by COX6B1 remains unproven.
- name: Reduced COX6B1 abundance
  description: >-
    COX6B1 protein is severely reduced in Arg20Cys muscle and absent by the reported Trp31Arg muscle assays.
    This is not universal: Arg20His fibroblasts retain total COX6B1 protein.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely
      detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the
      mutant protein in highly unstable.
    explanation: >-
      The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete
      absence.
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western
      blot, enzyme histochemistry, and immuno-histochemistry.
    explanation: Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: >-
      Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but
      failed to be, or to remain, stably incorporated in the COX holocomplex.
    explanation: >-
      Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
      numbering for p.Arg20His.
  genes:
  - preferred_term: COX6B1
    term:
      id: hgnc:2280
      label: COX6B1
  downstream:
  - target: Reduced mature complex IV abundance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Low protein availability accompanies deficient holoenzyme formation; allele-specific intermediates are
      unresolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely
        detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the
        mutant protein in highly unstable.
      explanation: >-
        The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete
        absence.
    - reference: PMID:41419202
      reference_title: >-
        The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
        of complex IV.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as
        well as SC III2IV in 6B1KO.
      explanation: >-
        Complete absence of these native forms is a result of engineered knockout; patient missense alleles
        can retain holoenzyme.
- name: Impaired stable COX6B1 incorporation
  description: >-
    Arg20His mutant protein is poorly incorporated or retained in the native holoenzyme despite preserved total
    fibroblast abundance. Muscle holoenzyme abundance is also reduced.
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but
      failed to be, or to remain, stably incorporated in the COX holocomplex.
    explanation: >-
      Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
      numbering for p.Arg20His.
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As shown in Figure 4A, fully assembled COX was reduced to approximately 40% in mutant versus control
      muscle.
    explanation: Native gels show reduced assembled enzyme in patient muscle, with residual holoenzyme.
  downstream:
  - target: Reduced mature complex IV abundance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Poor stable incorporation accompanies reduced holoenzyme stability in patient samples.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts,
        but failed to be, or to remain, stably incorporated in the COX holocomplex.
      explanation: >-
        Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
        numbering for p.Arg20His.
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        As shown in Figure 4A, fully assembled COX was reduced to approximately 40% in mutant versus control
        muscle.
      explanation: Native gels show reduced assembled enzyme in patient muscle, with residual holoenzyme.
- name: Defective MT-CO2 maturation or incorporation
  description: >-
    COX6B1-null HEK293 cells accumulate early MT-CO1/COX4/COX5A assemblies while MT-CO2 and mature complex
    IV are depleted. Redox correction allows partial assembly to resume. These findings identify an early assembly
    role; direct COX6B1 copper-transfer chemistry is still unresolved.
  evidence:
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or incorporation.
    explanation: >-
      Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct copper
      transfer by COX6B1 remains unproven.
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
  downstream:
  - target: Reduced mature complex IV abundance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Failure to mature or incorporate the MT-CO2 module prevents formation of mature enzyme.
    evidence:
    - reference: PMID:41419202
      reference_title: >-
        The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
        of complex IV.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or
        incorporation.
      explanation: >-
        Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct
        copper transfer by COX6B1 remains unproven.
    - reference: PMID:41419202
      reference_title: >-
        The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
        of complex IV.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as
        well as SC III2IV in 6B1KO.
      explanation: >-
        Complete absence of these native forms is a result of engineered knockout; patient missense alleles
        can retain holoenzyme.
- name: Reduced mature complex IV abundance
  description: >-
    Impaired assembly and stability reduce mature cytochrome c oxidase. Arg20His patient muscle retains about
    40% of control assembled enzyme, whereas complete knockout cells lose detectable monomer, dimer and III2IV
    forms.
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As shown in Figure 4A, fully assembled COX was reduced to approximately 40% in mutant versus control
      muscle.
    explanation: Native gels show reduced assembled enzyme in patient muscle, with residual holoenzyme.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as well
      as SC III2IV in 6B1KO.
    explanation: >-
      Complete absence of these native forms is a result of engineered knockout; patient missense alleles can
      retain holoenzyme.
  conforms_to: complex_iv_assembly_deficiency#Complex IV Biogenesis Failure
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
  downstream:
  - target: Reduced complex IV activity
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Reduced abundance of mature complex IV limits its enzymatic capacity.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed
        undetectable COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit.
      explanation: >-
        The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes
        are preserved.
    - reference: PMID:41419202
      reference_title: >-
        The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
        of complex IV.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as
        well as SC III2IV in 6B1KO.
      explanation: >-
        Complete absence of these native forms is a result of engineered knockout; patient missense alleles
        can retain holoenzyme.
- name: Reduced complex IV activity
  description: >-
    Patient tissues show reduced or undetectable complex IV activity, with other respiratory complexes preserved
    in the reported clinical assays. Complete knockout abolishes detectable respiratory flux under the tested
    HEK293 conditions. This node represents terminal respiratory impairment without asserting universal ATP
    collapse.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable
      COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit.
    explanation: >-
      The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are
      preserved.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Evaluation of the “bioenergetic phenotype,” i.e., the cellular oxygen consumption rate (OCR) vs. extracellular
      acidification rate (ECAR), showed null OCR in cIV-deficient cells (4dKO, 6BKO) and significantly decreased
      OCR in βKO (cV) cells (Figures 2A and 2C).
    explanation: >-
      The 6BKO cells have no measurable oxygen-consumption flux in this assay; the other knockout models in
      the sentence are distinct genes.
  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
  role: central_effector
  genes:
  - preferred_term: COX6B1
    term:
      id: hgnc:2280
      label: COX6B1
  molecular_functions:
  - preferred_term: cytochrome-c oxidase activity
    term:
      id: GO:0004129
      label: cytochrome-c oxidase activity
    modifier: DECREASED
  notes: >-
    The molecular-function binding describes activity of the assembled enzyme to which COX6B1 contributes structurally.
    It does not assign a catalytic copper center or autonomous oxidase activity to this peripheral subunit.
  downstream:
  - target: Increased OPA1 processing in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Severe respiratory dysfunction accompanies increased OPA1 processing, partly reversible by AOX; upstream
      signaling is unresolved.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The three KO cell lines (4dKO, 6BKO, and βKO) showed a significantly decreased long-to-short OPA1 ratio,
        indicating a higher OPA1 cleavage rate (Figures 5B and 5D).
      explanation: The COX6B1-null model shares increased OPA1 processing with the other severe knockout models.
  - target: Reductive imbalance in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Respiratory blockade shifts the cellular NAD redox balance.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We also determined the NAD+/NADH ratio, which was decreased in cIV-deficient cells (4dKO, 6BKO) but
        was restored to wt levels by AOX expression (Figure 2E).
      explanation: The COX6B1 knockout is 6BKO; AOX bypass reverses reductive imbalance in this cell model.
  - target: Glycolytic compensation in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Severe respiratory impairment is accompanied by compensatory glycolytic flux.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        ECAR in the OXPHOS-deficient cells (4dKO, 6BKO, βKO) indicated a higher glycolytic rate (Figures 2B
        and 2C), providing ATP by substrate-level phosphorylation.
      explanation: >-
        Higher extracellular acidification supports glycolytic compensation in 6BKO, not a measured patient-tissue
        glycolytic rate.
  - target: ATP depletion under respiratory dependence
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Patient fibroblasts lose ATP when growth requires oxidative metabolism.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The mitochondrial dysfunction was evident in the patient's fibroblasts where defective growth and ATP
        content were clearly observed in GAL medium as compared with glucose-containing (GLU) medium.
      explanation: >-
        ATP depletion is demonstrated under galactose challenge in Arg20Cys fibroblasts; it is not a direct
        measurement in brain or heart.
  - target: Integrated stress response in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Severe respiratory dysfunction activates the measured stress response.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Compared to wt cells, the ATF4 and eIF4EBP1 steady-state levels as well as eIF2α phosphorylation were
        significantly increased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient models but were normalized by
        AOX expression only in cIV-deficient cells (4dKO, 6BKO) (Figures 5B and 5C).
      explanation: The 6BKO results establish an integrated stress response that is reversible by respiratory bypass.
  - target: Reduced mitochondrial ribosomal abundance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Severe-null cells reduce mitoribosome abundance through unresolved signaling.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        LFQ-MS data analysis of mitochondrial proteins revealed that mitochondrial ribosomal proteins (MRPs),
        the constituents of both large (mtLSU) and small (mtSSU) mitochondrial ribosome subunits, were in general
        two to four times decreased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient cells compared to wt (Figures
        6A–6C).
      explanation: Proteomics identifies loss of both mitoribosomal subunits in severe COX6B1-null cells.
  - target: Mitochondrial cristae remodeling in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: The respiratory defect accompanies cristae remodeling in engineered cells.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        All OXPHOS deficiency models (4dKO, 6BKO, and βKO) showed perturbed mitochondrial morphology (Figure
        3D), with cristae being shorter and wider than in wt cells (Figure 3E).
      explanation: Electron microscopy establishes altered cristae in 6BKO; this is not a clinical muscle histology claim.
  - target: Encephalopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:24781756
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
        and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes
        an integral, nuclear-encoded COX subunit.
      explanation: The Arg20Cys case establishes this combination of clinical manifestations.
    - reference: PMID:38842388
      reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We describe the clinical features and follow-up of a patient with a novel homozygous pathogenic variant
        in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection.
      explanation: The Trp31Arg case includes acute infection-associated deterioration.
  - target: Hydrocephalus
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:24781756
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
        and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes
        an integral, nuclear-encoded COX subunit.
      explanation: The Arg20Cys case establishes this combination of clinical manifestations.
  - target: Hypertrophic cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:24781756
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
        and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes
        an integral, nuclear-encoded COX subunit.
      explanation: The Arg20Cys case establishes this combination of clinical manifestations.
  - target: Leukodystrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Brain MRI showed symmetrical, diffuse leukodystrophy with cystic lesions in the supratentorial areas
        of the white matter (Figure 1B).
      explanation: The younger Arg20His brother had cystic supratentorial leukodystrophy.
  - target: Muscle weakness
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual
        acuity, and moderate cognitive deterioration (IQ = 84).
      explanation: >-
        The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
        disability.
  - target: Ataxia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual
        acuity, and moderate cognitive deterioration (IQ = 84).
      explanation: >-
        The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
        disability.
  - target: Visual impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual
        acuity, and moderate cognitive deterioration (IQ = 84).
      explanation: >-
        The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
        disability.
  - target: Cognitive deterioration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual
        acuity, and moderate cognitive deterioration (IQ = 84).
      explanation: >-
        The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
        disability.
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized
        convulsions and severe metabolic acidosis with very high serum lactic acid levels.
      explanation: The original report directly documents generalized convulsions during severe metabolic deterioration.
  - target: Hypotonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
        (PEG) feeding tube was inserted at age 10 weeks.
      explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
  - target: Feeding difficulties in infancy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
        (PEG) feeding tube was inserted at age 10 weeks.
      explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
  - target: Aspiration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
        (PEG) feeding tube was inserted at age 10 weeks.
      explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
  - target: Cerebral visual impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Eye examination at the age of 15 weeks revealed cortical blindness.
      explanation: The report localizes this severe visual impairment to the cortex.
  - target: Short stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: height is 110 cm (3rd centile).
      explanation: The younger brother had reduced height; the adjacent inconsistent weight percentile is not used.
  - target: Pulmonary hypertension
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Chest X-ray revealed cardiomegaly, and cardiac Echo revealed symmetrical left ventricular hypertrophy
        tricuspid regurge and pulmonary hypertension.
      explanation: >-
        The clinical echo report documents elevated pulmonary pressure without invasive hemodynamic classification.
  - target: Elevated circulating lactate
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Laboratory investigation showed high serum lactate levels (2.6 mM, normal value ... < 1.8) and cerebrospinal
        fluid (CSF) (5.1 mM, n.v. < 1.8).
      explanation: The younger Arg20His brother had elevated blood and CSF lactate.
  - target: Lactic acidosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized
        convulsions and severe metabolic acidosis with very high serum lactic acid levels.
      explanation: The original report directly documents generalized convulsions during severe metabolic deterioration.
  - target: Hyperammonemia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: On the first day of life, the patient developed metabolic acidosis ... and elevated ammonia levels
      explanation: The Arg20Cys infant had neonatal metabolic acidosis, lactate elevation and hyperammonemia.
  - target: Hyperalaninemia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      This manifestation co-occurs with genetically and biochemically established COX6B1 deficiency; the intervening
      tissue mechanism is not directly resolved.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Metabolic work up showed normal acylcarnitines, elevated alanine level ... and urine organic acids
        showed increased lactic acidosis and ketones.
      explanation: The neonatal metabolic work-up documented raised circulating alanine.
- name: Reductive imbalance in knockout cells
  description: >-
    The NAD+/NADH ratio falls in COX6B1-null HEK293 cells and normalizes with alternative oxidase expression.
    Increased mitochondrial ROS and AMPK activation were not observed in this particular knockout model.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We also determined the NAD+/NADH ratio, which was decreased in cIV-deficient cells (4dKO, 6BKO) but was
      restored to wt levels by AOX expression (Figure 2E).
    explanation: The COX6B1 knockout is 6BKO; AOX bypass reverses reductive imbalance in this cell model.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: while there was no increase in ROS production in 6BKO (cIV) cells (Figures 4D, 4E, and S4A).
    explanation: The COX6B1-null redox phenotype should not be conflated with increased ROS in the other knockout models.
- name: Glycolytic compensation in knockout cells
  description: >-
    Increased extracellular acidification in COX6B1-null HEK293 cells accompanies preserved adenylate energy
    charge. This is a culture-dependent compensatory response rather than evidence that ATP is preserved in
    every affected tissue.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      ECAR in the OXPHOS-deficient cells (4dKO, 6BKO, βKO) indicated a higher glycolytic rate (Figures 2B and
      2C), providing ATP by substrate-level phosphorylation.
    explanation: >-
      Higher extracellular acidification supports glycolytic compensation in 6BKO, not a measured patient-tissue
      glycolytic rate.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The differences in P-AMPK could not be explained by a drop in ATP levels relative to ADP or AMP, as energy
      charge remained the same in all cell lines (Figures 4F and S4B).
    explanation: >-
      Preserved adenylate energy charge in these cultured knockout cells limits any claim of universal cellular
      ATP collapse.
  biological_processes:
  - preferred_term: glycolytic process
    term:
      id: GO:0006096
      label: glycolytic process
    modifier: INCREASED
- name: ATP depletion under respiratory dependence
  description: >-
    Arg20Cys patient fibroblasts exhibit low ATP content and poor growth in galactose medium. This conditional
    assay supports vulnerability when oxidative metabolism is required; preserved energy charge in glucose-supported
    knockout cells limits a universal ATP-depletion claim.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The mitochondrial dysfunction was evident in the patient's fibroblasts where defective growth and ATP
      content were clearly observed in GAL medium as compared with glucose-containing (GLU) medium.
    explanation: >-
      ATP depletion is demonstrated under galactose challenge in Arg20Cys fibroblasts; it is not a direct measurement
      in brain or heart.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The differences in P-AMPK could not be explained by a drop in ATP levels relative to ADP or AMP, as energy
      charge remained the same in all cell lines (Figures 4F and S4B).
    explanation: >-
      Preserved adenylate energy charge in these cultured knockout cells limits any claim of universal cellular
      ATP collapse.
- name: Integrated stress response in knockout cells
  description: >-
    COX6B1-null HEK293 cells increase eIF2alpha phosphorylation, ATF4 and eIF4EBP1. Pharmacological or genetic
    ISR suppression does not restore complex I subunits, so this response is not assigned as their causal mediator.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Compared to wt cells, the ATF4 and eIF4EBP1 steady-state levels as well as eIF2α phosphorylation were
      significantly increased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient models but were normalized by AOX
      expression only in cIV-deficient cells (4dKO, 6BKO) (Figures 5B and 5C).
    explanation: The 6BKO results establish an integrated stress response that is reversible by respiratory bypass.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Despite efficient inhibition of ISR in cIV- (4dKO, 6BKO) and cV- (βKO) lacking cells, documented by (i)
      a significant decrease of ATF4 and its targets to wt levels (Figures 5E and 5F) and (ii) decreased eIF4EBP1
      levels (Figures 5G and 5H), the level of cI subunits was not increased (Figures 5E–5H and S5D–S5F).
    explanation: >-
      ISRIB and eIF4EBP1 silencing fail to restore complex I; ISR activation is not established as the mediator
      of secondary complex I loss.
  biological_processes:
  - preferred_term: integrated stress response signaling
    term:
      id: GO:0140467
      label: integrated stress response signaling
    modifier: INCREASED
- name: Reduced mitochondrial ribosomal abundance
  description: >-
    Both mitochondrial ribosomal subunits and several assembly factors are reduced in severe COX6B1-null HEK293
    cells. The initiating signaling mechanism is unresolved.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      LFQ-MS data analysis of mitochondrial proteins revealed that mitochondrial ribosomal proteins (MRPs),
      the constituents of both large (mtLSU) and small (mtSSU) mitochondrial ribosome subunits, were in general
      two to four times decreased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient cells compared to wt (Figures
      6A–6C).
    explanation: Proteomics identifies loss of both mitoribosomal subunits in severe COX6B1-null cells.
  downstream:
  - target: Attenuated mitochondrial translation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Lower mitoribosome abundance correlates with reduced mitochondrial protein synthesis; a selective ribosome
      rescue was not performed.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        LFQ-MS data analysis of mitochondrial proteins revealed that mitochondrial ribosomal proteins (MRPs),
        the constituents of both large (mtLSU) and small (mtSSU) mitochondrial ribosome subunits, were in general
        two to four times decreased in cIV- (4dKO, 6BKO) and cV- (βKO) deficient cells compared to wt (Figures
        6A–6C).
      explanation: Proteomics identifies loss of both mitoribosomal subunits in severe COX6B1-null cells.
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The synthesis of the mtDNA-encoded cIV and cI subunits was the most affected in cIV- (4dKO, 6BKO) and
        cV- (βKO) deficient cells, which was reduced to 30% of wt (Figures 7B, 7C, and S6A).
      explanation: Pulse labeling shows reduced mitochondrial synthesis in 6BKO; this is a cellular secondary defect.
- name: Attenuated mitochondrial translation
  description: >-
    Pulse labeling identifies reduced synthesis of mitochondrial complex I and IV subunits in severe knockout
    cells. Mitoribosome abundance tracks this defect, while accelerated turnover does not explain the reduction.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The synthesis of the mtDNA-encoded cIV and cI subunits was the most affected in cIV- (4dKO, 6BKO) and
      cV- (βKO) deficient cells, which was reduced to 30% of wt (Figures 7B, 7C, and S6A).
    explanation: Pulse labeling shows reduced mitochondrial synthesis in 6BKO; this is a cellular secondary defect.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      On the other hand, cI and cIII subunits were even more stable in all OXPHOS-deficient models than in
      wt cells.
    explanation: Pulse-chase results oppose accelerated degradation as the main explanation for complex I depletion.
  biological_processes:
  - preferred_term: mitochondrial translation
    term:
      id: GO:0032543
      label: mitochondrial translation
    modifier: DECREASED
  downstream:
  - target: Secondary complex I depletion in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced synthesis provides a biogenesis explanation for secondary complex I depletion; the upstream sensing
      mechanism is unresolved.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The synthesis of the mtDNA-encoded cIV and cI subunits was the most affected in cIV- (4dKO, 6BKO) and
        cV- (βKO) deficient cells, which was reduced to 30% of wt (Figures 7B, 7C, and S6A).
      explanation: Pulse labeling shows reduced mitochondrial synthesis in 6BKO; this is a cellular secondary defect.
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In summary, severe OXPHOS aberrations in HEK293 cells lead to a specific decrease in cI. AOX expression
        causes a reversal to the wt phenotype in cIV-, but not in cV-deficient cells.
      explanation: >-
        The severe-null cell phenotype includes secondary complex I loss, unlike the isolated complex IV deficiency
        documented in patient muscle.
- name: Secondary complex I depletion in knockout cells
  description: >-
    Severe complete COX6B1 knockout produces secondary complex I loss associated with reduced mitochondrial
    protein synthesis. This experimental combined defect is distinct from isolated complex IV deficiency in
    the clinical missense cases.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In summary, severe OXPHOS aberrations in HEK293 cells lead to a specific decrease in cI. AOX expression
      causes a reversal to the wt phenotype in cIV-, but not in cV-deficient cells.
    explanation: >-
      The severe-null cell phenotype includes secondary complex I loss, unlike the isolated complex IV deficiency
      documented in patient muscle.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: NO_EVIDENCE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable
      COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit.
    explanation: >-
      The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are
      preserved. This clinical contrast does not test the secondary complex I loss in complete-knockout cells.
- name: Mitochondrial cristae remodeling in knockout cells
  description: >-
    COX6B1-null HEK293 cells exhibit shorter, wider mitochondrial cristae. AOX improves these abnormalities,
    but the intermediate pathway coupling respiratory dysfunction to cristae shape remains unresolved.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      All OXPHOS deficiency models (4dKO, 6BKO, and βKO) showed perturbed mitochondrial morphology (Figure
      3D), with cristae being shorter and wider than in wt cells (Figure 3E).
    explanation: Electron microscopy establishes altered cristae in 6BKO; this is not a clinical muscle histology claim.
- name: Increased OPA1 processing in knockout cells
  description: >-
    COX6B1-null HEK293 cells have a reduced long-to-short OPA1 ratio, consistent with increased proteolytic
    processing. AOX partially restores the ratio. Direct genetic testing of the upstream protease pathway was
    not reported.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The three KO cell lines (4dKO, 6BKO, and βKO) showed a significantly decreased long-to-short OPA1 ratio,
      indicating a higher OPA1 cleavage rate (Figures 5B and 5D).
    explanation: The COX6B1-null model shares increased OPA1 processing with the other severe knockout models.
  downstream:
  - target: Mitochondrial fragmentation in knockout cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Increased OPA1 processing accompanies network fragmentation in the same models; the study did not isolate
      OPA1 cleavage as the causal mediator.
    evidence:
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The three KO cell lines (4dKO, 6BKO, and βKO) showed a significantly decreased long-to-short OPA1 ratio,
        indicating a higher OPA1 cleavage rate (Figures 5B and 5D).
      explanation: The COX6B1-null model shares increased OPA1 processing with the other severe knockout models.
    - reference: PMID:39184436
      reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Accordingly, mitochondria were significantly more fragmented in OXPHOS-deficient cells, with no changes
        in mitochondrial mass (Figure S5C), and this fragmentation was reverted by AOX expression only in cIV-deficient
        cells (4dKO, 6BKO; Figures S5A–S5C).
      explanation: The 6BKO model shows altered network morphology, distinct from the cristae ultrastructure measurement.
- name: Mitochondrial fragmentation in knockout cells
  description: >-
    COX6B1-null HEK293 cells show fragmented mitochondrial networks without a change in measured mitochondrial
    mass. AOX reverses fragmentation in the complex IV-deficient models.
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Accordingly, mitochondria were significantly more fragmented in OXPHOS-deficient cells, with no changes
      in mitochondrial mass (Figure S5C), and this fragmentation was reverted by AOX expression only in cIV-deficient
      cells (4dKO, 6BKO; Figures S5A–S5C).
    explanation: The 6BKO model shows altered network morphology, distinct from the cristae ultrastructure measurement.
phenotypes:
- name: Encephalopathy
  description: >-
    Neonatal severe disease and childhood neurological deterioration are both reported; early milestones were
    normal in the Arg20His brothers.
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
  evidence:
  - reference: PMID:24781756
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
      and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an
      integral, nuclear-encoded COX subunit.
    explanation: The Arg20Cys case establishes this combination of clinical manifestations.
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We describe the clinical features and follow-up of a patient with a novel homozygous pathogenic variant
      in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection.
    explanation: The Trp31Arg case includes acute infection-associated deterioration.
- name: Hydrocephalus
  description: >-
    Rapidly progressive ventricular enlargement required shunting in the neonatal Arg20Cys case. Ex-vacuo ventricular
    enlargement in the Arg20His brothers is a distinct imaging finding.
  phenotype_term:
    preferred_term: Hydrocephalus
    term:
      id: HP:0000238
      label: Hydrocephalus
  evidence:
  - reference: PMID:24781756
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
      and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an
      integral, nuclear-encoded COX subunit.
    explanation: The Arg20Cys case establishes this combination of clinical manifestations.
- name: Hypertrophic cardiomyopathy
  description: >-
    The Arg20Cys patient developed hypertrophic obstructive cardiomyopathy. Cardiac involvement is not obligatory
    across reported genotypes.
  phenotype_term:
    preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  evidence:
  - reference: PMID:24781756
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
      and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes an
      integral, nuclear-encoded COX subunit.
    explanation: The Arg20Cys case establishes this combination of clinical manifestations.
- name: Leukodystrophy
  description: >-
    Progressive, diffuse, cavitating white-matter disease occurred in the Arg20His brothers; the Thr81Pro case
    also had cystic leukodystrophy.
  phenotype_term:
    preferred_term: Leukodystrophy
    term:
      id: HP:0002415
      label: Leukodystrophy
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRI showed symmetrical, diffuse leukodystrophy with cystic lesions in the supratentorial areas
      of the white matter (Figure 1B).
    explanation: The younger Arg20His brother had cystic supratentorial leukodystrophy.
  - reference: PMID:22277967
    reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd | *COX6B1
      |
    explanation: >-
      The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast
      complex IV measurements are low/normal.
- name: Muscle weakness
  description: Weakness and myopathic electrophysiology were reported in the original brothers.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity,
      and moderate cognitive deterioration (IQ = 84).
    explanation: >-
      The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
      disability.
- name: Ataxia
  description: Truncal and limb ataxia occurred in the younger Arg20His brother.
  phenotype_term:
    preferred_term: Ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity,
      and moderate cognitive deterioration (IQ = 84).
    explanation: >-
      The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
      disability.
- name: Visual impairment
  description: Visual loss or reduced acuity occurred in the original brothers.
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity,
      and moderate cognitive deterioration (IQ = 84).
    explanation: >-
      The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
      disability.
- name: Cognitive deterioration
  description: >-
    Progressive cognitive decline was described in the original family; this does not require an intellectual
    disability diagnosis.
  phenotype_term:
    preferred_term: Mental deterioration
    term:
      id: HP:0001268
      label: Mental deterioration
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Presently he is an 8-year-old boy with mild trunk and limb ataxia, muscle weakness, reduced visual acuity,
      and moderate cognitive deterioration (IQ = 84).
    explanation: >-
      The younger brother had these neurological manifestations. The IQ score alone does not establish intellectual
      disability.
- name: Seizures
  description: >-
    Recurrent generalized convulsions accompanied terminal neurological deterioration in the elder Arg20His
    brother.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized
      convulsions and severe metabolic acidosis with very high serum lactic acid levels.
    explanation: The original report directly documents generalized convulsions during severe metabolic deterioration.
- name: Hypotonia
  description: Hypotonia was reported in the neonatal Arg20Cys case.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
      (PEG) feeding tube was inserted at age 10 weeks.
    explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
- name: Feeding difficulties in infancy
  description: Feeding problems necessitated gastrostomy in the Arg20Cys infant.
  phenotype_term:
    preferred_term: Feeding difficulties in infancy
    term:
      id: HP:0008872
      label: Feeding difficulties in infancy
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
      (PEG) feeding tube was inserted at age 10 weeks.
    explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
- name: Aspiration
  description: Recurrent aspiration complicated feeding in the Arg20Cys infant.
  phenotype_term:
    preferred_term: Aspiration
    term:
      id: HP:0002835
      label: Aspiration
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
      (PEG) feeding tube was inserted at age 10 weeks.
    explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
- name: Cerebral visual impairment
  description: Cortical blindness was documented in the neonatal Arg20Cys case.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Eye examination at the age of 15 weeks revealed cortical blindness.
    explanation: The report localizes this severe visual impairment to the cortex.
- name: Short stature
  description: >-
    Growth retardation was reported in the original family. The older brother remained below the third percentile
    for height and weight; the younger brother had height at the third centile.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Birth weight and height are not known but were reported as abnormally low and remained below the 3rd
      percentile ever since.
    explanation: >-
      The older brother had persistently low height as well as weight. This supports short stature independently
      of the younger brother's borderline third-centile measurement.
- name: Pulmonary hypertension
  description: >-
    Pulmonary hypertension was reported on echocardiography in the Arg20Cys infant and later resolved; a specific
    pulmonary vascular subtype was not established.
  phenotype_term:
    preferred_term: Elevated pulmonary artery pressure
    term:
      id: HP:0004890
      label: Elevated pulmonary artery pressure
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest X-ray revealed cardiomegaly, and cardiac Echo revealed symmetrical left ventricular hypertrophy
      tricuspid regurge and pulmonary hypertension.
    explanation: >-
      The clinical echo report documents elevated pulmonary pressure without invasive hemodynamic classification.
- name: Elevated circulating lactate
  description: Serum lactate may be elevated chronically or during severe decompensation.
  phenotype_term:
    preferred_term: Increased circulating lactate concentration
    term:
      id: HP:0002151
      label: Increased circulating lactate concentration
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory investigation showed high serum lactate levels (2.6 mM, normal value ... < 1.8) and cerebrospinal
      fluid (CSF) (5.1 mM, n.v. < 1.8).
    explanation: The younger Arg20His brother had elevated blood and CSF lactate.
- name: Lactic acidosis
  description: >-
    Severe lactic and metabolic acidosis occurred during terminal deterioration in the elder Arg20His brother
    and neonatally in the Arg20Cys case.
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patient died at 10 years by rapidly progressive neurological deterioration after recurrent generalized
      convulsions and severe metabolic acidosis with very high serum lactic acid levels.
    explanation: The original report directly documents generalized convulsions during severe metabolic deterioration.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: On the first day of life, the patient developed metabolic acidosis ... and elevated ammonia levels
    explanation: The Arg20Cys infant had neonatal metabolic acidosis, lactate elevation and hyperammonemia.
- name: Hyperammonemia
  description: Hyperammonemia was documented during neonatal metabolic decompensation in the Arg20Cys infant.
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: On the first day of life, the patient developed metabolic acidosis ... and elevated ammonia levels
    explanation: The Arg20Cys infant had neonatal metabolic acidosis, lactate elevation and hyperammonemia.
- name: Hyperalaninemia
  description: Elevated alanine was documented in the neonatal Arg20Cys case.
  phenotype_term:
    preferred_term: Hyperalaninemia
    term:
      id: HP:0003348
      label: Hyperalaninemia
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Metabolic work up showed normal acylcarnitines, elevated alanine level ... and urine organic acids showed
      increased lactic acidosis and ketones.
    explanation: The neonatal metabolic work-up documented raised circulating alanine.
genetic:
- name: COX6B1
  gene_term:
    preferred_term: COX6B1
    term:
      id: hgnc:2280
      label: COX6B1
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:38842388
      reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease
        manifestations.
      explanation: >-
        The four previously reported patients precede the new fifth patient in this report; this is not a population
        frequency.
  features: >-
    Reported homozygous alleles include p.Arg20His, p.Arg20Cys, p.Thr81Pro and p.Trp31Arg. Arg20His is called
    R19H when the initiator methionine is excluded. Abundance loss is allele- and tissue-dependent; preserved
    total protein does not exclude pathogenic loss of incorporation.
  evidence:
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease
      manifestations.
    explanation: >-
      The four previously reported patients precede the new fifth patient in this report; this is not a population
      frequency.
  variants:
  - name: p.Arg20His
    description: >-
      Homozygous variant in the original two brothers, with childhood-onset neurological disease. Mature-protein
      R19H numbering refers to this same residue. Fibroblasts retain total mutant protein but show impaired
      stable holoenzyme incorporation.
    gene:
      preferred_term: COX6B1
      term:
        id: hgnc:2280
        label: COX6B1
    type: missense_variant
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We found no change in COX7A1 and COX6B2 genes, but both probands carried a homozygous c.221G→A substitution
        in exon 2 of COX6B1, predicting a p.R19H amino acid change (numeration according to the mature protein
        in which the first M is eliminated).
      explanation: >-
        The original paper establishes homozygosity and explicitly uses mature-protein numbering. Its c.221
        notation is legacy sequence numbering, not modern coding HGVS.
    - reference: PMID:18499082
      reference_title: >-
        Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
        c oxidase.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts,
        but failed to be, or to remain, stably incorporated in the COX holocomplex.
      explanation: >-
        Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
        numbering for p.Arg20His.
  - name: p.Arg20Cys
    description: >-
      Homozygous variant in a neonatal encephalomyopathy, hydrocephalus and cardiomyopathy case. Muscle COX6B1
      is severely reduced; the enzyme defect was rescued by wild-type cDNA in fibroblasts.
    gene:
      preferred_term: COX6B1
      term:
        id: hgnc:2280
        label: COX6B1
    type: missense_variant
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:24781756
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We hereby report a case of isolated COX deficiency manifesting with encephalomyopathy, hydrocephalus
        and hypertropic cardiomyopathy due to a missense p.R20C mutation in the COX6B1 gene, which encodes
        an integral, nuclear-encoded COX subunit.
      explanation: The Arg20Cys case establishes this combination of clinical manifestations.
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Urea-PAGE combined with western blotting analysis of patient's muscle mitochondrial revealed a barely
        detectable residual amount of COX6B1 protein (11% of control normalized to SDH), suggesting that the
        mutant protein in highly unstable.
      explanation: >-
        The Arg20Cys muscle sample retains about 11% of control COX6B1; this is severe reduction, not complete
        absence.
  - name: p.Thr81Pro
    description: >-
      Homozygous c.241A>C in patient P17 with neonatal mitochondrial encephalopathy and cystic leukodystrophy.
      The sequencing study reports segregation and protein degradation; fibroblast enzyme activity was normal
      despite low muscle activity.
    gene:
      preferred_term: COX6B1
      term:
        id: hgnc:2280
        label: COX6B1
    type: missense_variant
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:22277967
      reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        | P17 | complex IV deficiency (MIM:220110) | *COX6B1 | hom. | c.241A>C, p.T81P | 3 | protein degradation
        family segregation |
      explanation: >-
        The diagnostic table identifies the homozygous Thr81Pro allele and reports segregation and protein
        degradation as supporting evidence.
    - reference: PMID:22277967
      reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        | P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd |
        *COX6B1 |
      explanation: >-
        The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast
        complex IV measurements are low/normal.
  - name: p.Trp31Arg
    description: >-
      Homozygous variant associated with acute infection-related encephalomyopathy, isolated complex IV deficiency
      and lack of detectable muscle COX6B1.
    gene:
      preferred_term: COX6B1
      term:
        id: hgnc:2280
        label: COX6B1
    type: missense_variant
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:38842388
      reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses
        with biochemical analysis of mitochondrial function showed isolated COX deficiency.
      explanation: The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
    - reference: PMID:38842388
      reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western
        blot, enzyme histochemistry, and immuno-histochemistry.
      explanation: Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
  gene_disease_validity:
  - validity_classification: DEFINITIVE
    classified_by: CLINGEN
    external_id: CGGV:assertion_bc374fc3-050b-4985-9f2f-a2972bb795fe-2022-03-21T040000.000Z
    notes: >-
      The March 2022 expert-panel assertion concerns the broader COX6B1–primary mitochondrial disease relationship
      (MONDO:0044970), which includes this complex IV deficiency. It predates the Trp31Arg report.
    evidence:
    - reference: CGGV:assertion_bc374fc3-050b-4985-9f2f-a2972bb795fe-2022-03-21T040000.000Z
      reference_title: COX6B1 / mitochondrial disease (Definitive)
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        In summary, there is definitive evidence to support this gene-disease relationship, including that
        more than three years have elapsed since the first proposal of the association.
      explanation: ClinGen assigns this classification to the broader gene–mitochondrial disease relationship.
diagnosis:
- name: Molecular confirmation
  description: >-
    Identify biallelic COX6B1 variants and interpret segregation alongside biochemical and functional data.
    Include COX6B1 in isolated complex IV deficiency investigations even when cardiomyopathy is present.
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We suggest that genetic analysis of ... COX6B1 ... should be included in the investigation of isolated
      COX deficiency, including patients with cardiac defects.
    explanation: The case report recommends inclusion of this structural-subunit gene in molecular investigations.
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses
      with biochemical analysis of mitochondrial function showed isolated COX deficiency.
    explanation: The clinical report identifies p.Trp31Arg and a specific biochemical complex IV defect.
- name: Respiratory-chain enzymology
  description: >-
    Measure complex IV activity relative to mitochondrial controls and other respiratory complexes. Deficiency
    can vary markedly between muscle, lymphocytes and fibroblasts; normal fibroblast activity in the Thr81Pro
    case does not exclude the muscle defect.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable
      COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit.
    explanation: >-
      The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are
      preserved.
  - reference: PMID:22277967
    reference_title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | P17 | M | <1wk | neonatal lactic acidosis, cystic leukodystrophy | | skm fib | | | | ↓↓ nl | nd | *COX6B1
      |
    explanation: >-
      The patient table records neonatal lactic acidosis and cystic leukodystrophy; the paired muscle/fibroblast
      complex IV measurements are low/normal.
  - reference: PMID:24781756
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Initial measurement of COX activity in lymphocytes may be useful as it might circumvent the need for
      invasive muscle biopsy.
    explanation: This is a case-report diagnostic proposal, not a validated universal sensitivity estimate.
- name: Neuroimaging
  description: >-
    Brain MRI can demonstrate progressive cavitating leukodystrophy. Ventricular enlargement from white-matter
    loss should be distinguished from the rapidly progressive shunt-treated hydrocephalus reported with Arg20Cys.
  diagnosis_term:
    preferred_term: Magnetic Resonance Imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRI showed symmetrical, diffuse leukodystrophy with cystic lesions in the supratentorial areas
      of the white matter (Figure 1B).
    explanation: The younger Arg20His brother had cystic supratentorial leukodystrophy.
biochemical:
- name: Reduced tissue complex IV activity
  presence: Decreased or undetectable, depending on allele and tissue
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The enzymatic analysis of mitochondrial respiratory chain complexes in muscle mitochondria revealed undetectable
      COX (complex IV) activity, whereas complexes I, II and II+III were within the normal limit.
    explanation: >-
      The Arg20Cys patient has an isolated muscle complex IV defect; other measured respiratory complexes are
      preserved.
  notes: >-
    The Arg20His brothers retained approximately 20% muscle and 50% fibroblast activity; Arg20Cys muscle and
    fibroblast activity was undetectable, with residual lymphocyte activity.
- name: Elevated blood and CSF lactate
  presence: Increased
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Laboratory investigation showed high serum lactate levels (2.6 mM, normal value ... < 1.8) and cerebrospinal
      fluid (CSF) (5.1 mM, n.v. < 1.8).
    explanation: The younger Arg20His brother had elevated blood and CSF lactate.
histopathology:
- name: Reduced muscle cytochrome c oxidase staining
  description: >-
    Muscle enzyme histochemistry shows low COX activity; immunohistochemistry and immunoblotting can show COX6B1
    loss depending on the allele.
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The histochemical reaction to COX was diffusely low in a skeletal muscle biopsy from patient AK (Figure
      2B).
    explanation: The patient muscle biopsy directly demonstrates reduced COX histochemical activity.
  - reference: PMID:38842388
    reference_title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western
      blot, enzyme histochemistry, and immuno-histochemistry.
    explanation: Patient muscle shows loss of detectable COX6B1 and deficient complex IV staining.
treatments:
- name: Ventriculoperitoneal shunting
  description: >-
    CSF diversion was used for rapidly progressive hydrocephalus in the Arg20Cys patient; later shunt malfunction
    required further hospital care.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At 15 weeks, a ventriculoperitoneal (VP) shunt was inserted.
    explanation: The Arg20Cys infant underwent CSF diversion for progressive hydrocephalus.
  treatment_term:
    preferred_term: Ventriculoperitoneal Shunt Placement
    term:
      id: NCIT:C168483
      label: Ventriculoperitoneal Shunt Placement
  therapeutic_modality: SURGERY
  target_mechanisms:
  - target: Hydrocephalus
    treatment_effect: MODULATES
    description: Addresses this clinical manifestation; disease-specific efficacy has not been established.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: At 15 weeks, a ventriculoperitoneal (VP) shunt was inserted.
      explanation: The Arg20Cys infant underwent CSF diversion for progressive hydrocephalus.
- name: Gastrostomy feeding
  description: Gastrostomy was placed for hypotonia, feeding difficulty and recurrent aspiration in the Arg20Cys infant.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
      (PEG) feeding tube was inserted at age 10 weeks.
    explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
  treatment_term:
    preferred_term: Percutaneous Endoscopic Gastrostomy
    term:
      id: NCIT:C106040
      label: Percutaneous Endoscopic Gastrostomy
  therapeutic_modality: SURGERY
  target_mechanisms:
  - target: Feeding difficulties in infancy
    treatment_effect: MODULATES
    description: Addresses this clinical manifestation; disease-specific efficacy has not been established.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Due to hypotonia with feeding difficulties and recurrent aspirations, a percutaneous endoscopic gastrostomy
        (PEG) feeding tube was inserted at age 10 weeks.
      explanation: The neonatal Arg20Cys case had hypotonia, feeding difficulty and aspiration requiring gastrostomy.
- name: Cardiac pharmacotherapy
  description: >-
    Diuretics, beta blockers and subsequently calcium-channel blockers were used for the Arg20Cys cardiomyopathy.
    The case documents exposure and later echocardiographic improvement, without isolating treatment efficacy.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the age of 4 months, he started developing hypertrophic obstructive cardiomyopathy, he was started
      on diuretics and beta blockers and later calcium channel blockers were added; follow-up Echo at the age
      of 2 years revealed improvement in the LVH and no PHTN.
    explanation: >-
      Several cardiac drugs were used together; later improvement cannot establish the benefit of an individual
      agent.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Diuretic
      term:
        id: NCIT:C448
        label: Diuretic
    - preferred_term: Beta-Adrenergic Antagonist
      term:
        id: NCIT:C29576
        label: Beta-Adrenergic Antagonist
    - preferred_term: Calcium Channel Blocker
      term:
        id: NCIT:C333
        label: Calcium Channel Blocker
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Hypertrophic cardiomyopathy
    treatment_effect: MODULATES
    description: Addresses this clinical manifestation; disease-specific efficacy has not been established.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        At the age of 4 months, he started developing hypertrophic obstructive cardiomyopathy, he was started
        on diuretics and beta blockers and later calcium channel blockers were added; follow-up Echo at the
        age of 2 years revealed improvement in the LVH and no PHTN.
      explanation: >-
        Several cardiac drugs were used together; later improvement cannot establish the benefit of an individual
        agent.
- name: Coenzyme Q10 supplementation
  description: >-
    Coenzyme Q10 was started and later discontinued by the family in the Arg20Cys case. Disease-specific clinical
    benefit was not demonstrated.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Coenzyme Q10 supplementation (60 mg twice daily) was initiated at 4 months but discontinued by the parents.
    explanation: This records treatment exposure and discontinuation, not efficacy.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: coenzyme Q10
      term:
        id: CHEBI:46245
        label: coenzyme Q10
  therapeutic_modality: SMALL_MOLECULE
- name: AICAR in patient fibroblasts (preclinical)
  description: >-
    AICAR increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not establish
    a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
    explanation: >-
      The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated
      clinical efficacy.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The favorable response is presumably not due to increased mitochondrial content or improved membrane
      potential as mitotracker green and TMRE stain did not reveal any significant differences between treated
      and untreated cells (result not shown).
    explanation: >-
      These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug
      mechanism.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: AICAR
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: ATP depletion under respiratory dependence
    treatment_effect: MODULATES
    description: >-
      Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism
      remain unproven.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
      explanation: >-
        The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without
        demonstrated clinical efficacy.
  notes: >-
    The primary report names the reagent AICAR and expands it as ribonucleotide; a chemical-identity binding
    is withheld because the ribonucleotide and commonly used riboside reagent should not be conflated.
- name: Resveratrol in patient fibroblasts (preclinical)
  description: >-
    Resveratrol increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not
    establish a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
    explanation: >-
      The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated
      clinical efficacy.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The favorable response is presumably not due to increased mitochondrial content or improved membrane
      potential as mitotracker green and TMRE stain did not reveal any significant differences between treated
      and untreated cells (result not shown).
    explanation: >-
      These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug
      mechanism.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: resveratrol
      term:
        id: CHEBI:27881
        label: resveratrol
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: ATP depletion under respiratory dependence
    treatment_effect: MODULATES
    description: >-
      Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism
      remain unproven.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
      explanation: >-
        The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without
        demonstrated clinical efficacy.
- name: Ascorbate in patient fibroblasts (preclinical)
  description: >-
    Ascorbate increased ATP content in galactose-challenged Arg20Cys fibroblasts. These experiments do not
    establish a clinical treatment, and membrane-potential or mitochondrial-content restoration was not demonstrated.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
    explanation: >-
      The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without demonstrated
      clinical efficacy.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The favorable response is presumably not due to increased mitochondrial content or improved membrane
      potential as mitotracker green and TMRE stain did not reveal any significant differences between treated
      and untreated cells (result not shown).
    explanation: >-
      These assays do not establish mitochondrial biogenesis or membrane-potential restoration as the drug
      mechanism.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ascorbate
      term:
        id: CHEBI:22651
        label: ascorbate
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: ATP depletion under respiratory dependence
    treatment_effect: MODULATES
    description: >-
      Improved ATP content in the patient-cell assay; clinical correction and the biochemical drug mechanism
      remain unproven.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
      reference_title: >-
        Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
        hydrocephalus and cardiomyopathy - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: ATP content was markedly improved by AICAR, reveratrol and ascorbate.
      explanation: >-
        The spelling reveratrol is retained from the source. Increased ATP is a fibroblast result, without
        demonstrated clinical efficacy.
  notes: >-
    The patient died before the experimental results could be applied clinically; the paper proposes, but does
    not report, patient ascorbate treatment.
experimental_models:
- name: Patient-derived fibroblasts
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    Arg20His patient fibroblasts, including immortalized derivatives, show impaired stable holoenzyme incorporation
    despite preserved total COX6B1. Arg20Cys fibroblasts show severe enzymatic deficiency and low ATP under
    galactose challenge, with rescue by wild-type COX6B1 cDNA. Lentiviral complementation is an experimental
    pathogenicity test, not demonstrated clinical gene therapy.
  publication: PMID:18499082
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Taken together, these results suggest that mutant COX6B1R19H was normally expressed in fibroblasts, but
      failed to be, or to remain, stably incorporated in the COX holocomplex.
    explanation: >-
      Patient fibroblasts retain total mutant protein but have impaired stable incorporation; R19H is mature-protein
      numbering for p.Arg20His.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The mitochondrial dysfunction was evident in the patient's fibroblasts where defective growth and ATP
      content were clearly observed in GAL medium as compared with glucose-containing (GLU) medium.
    explanation: >-
      ATP depletion is demonstrated under galactose challenge in Arg20Cys fibroblasts; it is not a direct measurement
      in brain or heart.
  - reference: PMID:24781756
    reference_title: >-
      Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy,
      hydrocephalus and cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Complementation with the wild-type cDNA by a lentiviral construct restored COX activity, and mitochondrial
      function was improved by 5-aminoimidazole-4-carboxamide ribonucleotide, resveratrol and ascorbate in
      the patient's fibroblasts.
    explanation: >-
      Wild-type complementation establishes functional rescue in patient cells; the small-molecule results
      are also cell based.
  modeled_mechanisms:
  - target: Impaired stable COX6B1 incorporation
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Reduced complex IV activity
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: ATP depletion under respiratory dependence
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
- name: HeLa COX6B1 knockdown
  experimental_model_type: CELL_LINE
  description: >-
    Stable shRNA knockdown lowered COX6B1 transcript and protein and reduced complex IV activity. This partial
    depletion model complements the complete knockout studies.
  publication: PMID:18499082
  evidence:
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Accordingly, the COX/CS activities were significantly reduced, to around 70%, in either shRNA1- or shRNA14-versus
      mock-transfected HeLa cells (p < 0.0026 and p < 0.0009 respectively, Figure 3B).
    explanation: Two independent knockdown constructs reduce measured complex IV activity.
  modeled_mechanisms:
  - target: Reduced complex IV activity
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
- name: HEK293 COX6B1 knockout and complementation
  experimental_model_type: CELL_LINE
  description: >-
    Three CRISPR knockout clones reveal early MT-CO2 assembly failure as well as late holoenzyme instability.
    Wild-type COX6B1 restores respiration; Arg20His and Arg20Cys partially rescue with a more severe residual
    defect for Arg20Cys. Tagged COX6B2 does not rescue in this cell context. AOX restores redox balance and
    permits partial complex IV modules to join respirasomes, but intact-cell respiration flows through AOX
    and native complex IV activity remains negligible. ISR inhibition does not restore secondary complex I
    loss.
  publication: PMID:41419202
  evidence:
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Altogether, these results suggest a block in cIV assembly at the stage of MT-CO2 maturation and/or incorporation.
    explanation: >-
      Knockout cells retain MT-CO1/COX4/COX5A intermediates but lose MT-CO2 and mature complex IV; direct copper
      transfer by COX6B1 remains unproven.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      These experiments showed the total loss of fully assembled monomeric cIV (IV), cIV dimer (IV2), as well
      as SC III2IV in 6B1KO.
    explanation: >-
      Complete absence of these native forms is a result of engineered knockout; patient missense alleles can
      retain holoenzyme.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Even though the AOX-expressing cells displayed robust rates of routine respiration, titration of the
      AOX inhibitor (salicylhydroxamic acid) completely abolished oxygen consumption, indicating that in intact
      cells, oxygen consumption was exclusively happening through AOX (Fig. S3, C and D).
    explanation: Respiratory bypass restores flux through AOX, not normal native complex IV respiration.
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Despite efficient inhibition of ISR in cIV- (4dKO, 6BKO) and cV- (βKO) lacking cells, documented by (i)
      a significant decrease of ATF4 and its targets to wt levels (Figures 5E and 5F) and (ii) decreased eIF4EBP1
      levels (Figures 5G and 5H), the level of cI subunits was not increased (Figures 5E–5H and S5D–S5F).
    explanation: >-
      ISRIB and eIF4EBP1 silencing fail to restore complex I; ISR activation is not established as the mediator
      of secondary complex I loss.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      On the other hand, the expression of either a C-terminal or an N-terminal FLAG-tagged COX6B2 isoform
      failed to even marginally rescue either MT-CO2 levels (Figs. 1F, S1D) or mitochondrial respiration (Fig.
      1G).
    explanation: >-
      Non-rescue applies to the tested HEK293 expression context and does not establish behavior in all tissues.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The abundance of both MT-CO1 and all the other tested cIV subunits in SC I III2IVsub was also substantially
      augmented after AOX expression compared with 6B1KO, whereas IV2 and III2IV SCs remained absent (Figs.
      4, C and D, S3B).
    explanation: AOX permits partial assembly and an incomplete respirasome while mature dimer and III2IV remain absent.
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Thus, the introduction of the R20C variant disrupted cIV native forms and respiration to a greater extent
      than R20H, similar to the observations in patient-derived fibroblasts (30, 31).
    explanation: >-
      Direct comparison of human allele-expression models shows a more severe Arg20Cys defect without establishing
      a population genotype–prognosis rule.
  modeled_mechanisms:
  - target: Defective MT-CO2 maturation or incorporation
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Reduced mature complex IV abundance
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Reductive imbalance in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Glycolytic compensation in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Integrated stress response in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Reduced mitochondrial ribosomal abundance
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Attenuated mitochondrial translation
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Secondary complex I depletion in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Mitochondrial cristae remodeling in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Increased OPA1 processing in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: Complete knockout in a cultured human cell line does not establish this mechanism in patient tissues.
  - target: Mitochondrial fragmentation in knockout cells
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: Complete knockout in a cultured human cell line does not establish this mechanism in patient tissues.
- name: Yeast cox12 deletion and allele complementation
  experimental_model_type: OTHER
  description: >-
    Saccharomyces cerevisiae lacking the COX6B1 ortholog Cox12 has impaired respiratory growth. Human Arg20His
    retains partial complementation in the 2008 human-protein experiment, whereas the analogous yeast-protein
    R17H and R17C constructs failed complementation in 2021. Galactose-grown null yeast retain bulk III2IV
    supercomplexes but have reduced Cox2/Rcf2 association and severe complex IV activity loss. This differs
    from complete holoenzyme loss in human knockout cells. Coa6/Cox12 double-deletion epistasis additionally
    supports overlapping roles in Cox2 biogenesis.
  publication: PMID:34937540
  evidence:
  - reference: PMID:34937540
    reference_title: Mutations in the Yeast Cox12 Subunit Severely Compromise the Activity of the Mitochondrial Complex IV.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Cox12 with arginine 17 residue substituted by histidine (R17H) or cysteine (R17C) (mutations analogous
      to those observed in human patients) failed to complement the loss of Cox12 function.
    explanation: These are yeast ortholog substitutions, not the human-protein constructs used in 2008.
  - reference: PMID:34937540
    reference_title: Mutations in the Yeast Cox12 Subunit Severely Compromise the Activity of the Mitochondrial Complex IV.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, the association of the respiratory SC factor 2 (Rcf2) and Cox2 subunit within the SCs of cox12Δ
      cells was reduced, while the specific activity of CIV was downregulated by 90%.
    explanation: Yeast retain bulk supercomplexes despite a marked activity defect.
  - reference: PMID:18499082
    reference_title: >-
      Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
      c oxidase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Likewise, the activity of COX/CS in COX6B1R19H transformants was 67% to that of the COX6B1wild-type transformants
      (Figure 5A and Table 3).
    explanation: Human Arg20His expressed in yeast retains partial activity relative to wild-type complementation.
  - reference: PMID:26669719
    reference_title: Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In order to place Coa6 in the Cox2 copper delivery pathway, we performed a comprehensive genetic epistasis
      analysis in the yeast Saccharomyces cerevisiae and found that simultaneous deletion of Coa6 and Sco2,
      a mitochondrial copper metallochaperone, or Coa6 and Cox12/COX6B, a structural subunit of CcO, completely
      abrogates Cox2 biogenesis.
    explanation: >-
      The double-deletion experiment supports overlapping Cox12/Coa6 functions without establishing direct
      human COX6B1 copper transfer.
  modeled_mechanisms:
  - target: Defective MT-CO2 maturation or incorporation
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
  - target: Reduced complex IV activity
    relationship: PARTIALLY_RECAPITULATES
    model_scale: CELLULAR
    limitations: >-
      The system resolves cellular biochemical consequences and does not reproduce the full neurological and
      cardiac phenotype.
datasets:
- accession: pride:PXD061621
  title: COX6B1 secures a redox-sensitive step in early cytochrome c oxidase assembly
  description: >-
    Whole-cell label-free proteomics and complex IV immunocapture proteomics of human HEK293 COX6B1 knockout,
    allele-expression and AOX models; these are engineered cells, not a patient cohort.
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: PROTEOMICS
  publication: PMID:41419202
  evidence:
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: LFQ–MS data are available via ProteomeXchange with identifier PXD061621.
    explanation: >-
      The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently
      verified.
- accession: pride:PXD061618
  title: COX6B1 secures a redox-sensitive step in early cytochrome c oxidase assembly
  description: >-
    Complexome profiling of wild-type, COX6B1 knockout and AOX-expressing knockout HEK293 mitochondria across
    48 blue-native gel slices.
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: PROTEOMICS
  publication: PMID:41419202
  evidence:
  - reference: PMID:41419202
    reference_title: >-
      The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
      of complex IV.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Complexome profiling data are available via ProteomeXchange with identifier PXD061618.
    explanation: >-
      The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently
      verified.
- accession: pride:PXD046331
  title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies
  description: >-
    Label-free proteomics across severe and mild OXPHOS-deficient HEK293 models, including COX6B1 knockout
    and AOX complementation; other-gene models must be distinguished.
  organism:
    preferred_term: Homo sapiens
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: PROTEOMICS
  publication: PMID:39184436
  evidence:
  - reference: PMID:39184436
    reference_title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: LFQ-MS data are available via ProteomeXchange with identifier PXD046331.
    explanation: >-
      The primary paper deposits this proteomics dataset; the PRIDE accession and title were independently
      verified.
references:
- reference: CGGV:assertion_bc374fc3-050b-4985-9f2f-a2972bb795fe-2022-03-21T040000.000Z
  title: COX6B1 / mitochondrial disease (Definitive)
- reference: PMID:18499082
  title: >-
    Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome
    c oxidase.
- reference: PMID:22277967
  title: Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
- reference: PMID:24781756
  title: >-
    Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy, hydrocephalus
    and cardiomyopathy.
- reference: PMID:26669719
  title: Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.
- reference: PMID:34937540
  title: Mutations in the Yeast Cox12 Subunit Severely Compromise the Activity of the Mitochondrial Complex IV.
- reference: PMID:38842388
  title: 'A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.'
- reference: PMID:39184436
  title: Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
- reference: PMID:41419202
  title: >-
    The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization
    of complex IV.
- reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
  title: >-
    Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy, hydrocephalus
    and cardiomyopathy - PMC
📚

References & Deep Research

References

10
No top-level findings curated for this source.
PMID:18499082
Severe infantile encephalomyopathy caused by a mutation in COX6B1, a nucleus-encoded subunit of cytochrome c oxidase.
No top-level findings curated for this source.
PMID:22277967
Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing.
No top-level findings curated for this source.
PMID:24781756
Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy, hydrocephalus and cardiomyopathy.
No top-level findings curated for this source.
PMID:26669719
Mitochondrial disease genes COA6, COX6B and SCO2 have overlapping roles in COX2 biogenesis.
No top-level findings curated for this source.
PMID:34937540
Mutations in the Yeast Cox12 Subunit Severely Compromise the Activity of the Mitochondrial Complex IV.
No top-level findings curated for this source.
PMID:38842388
A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.
No top-level findings curated for this source.
PMID:39184436
Mitochondrial translation is the primary determinant of secondary mitochondrial complex I deficiencies.
No top-level findings curated for this source.
PMID:41419202
The cytochrome c oxidase subunit COX6B1 is required for redox-sensitive early assembly and late stabilization of complex IV.
No top-level findings curated for this source.
url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4297913/
Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy, hydrocephalus and cardiomyopathy - PMC
No top-level findings curated for this source.