COX11-related COX deficiency (mitochondrial complex IV deficiency nuclear type 23, MC4DN23) is a rare autosomal recessive nuclear form of isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants in COX11. COX11 is a copper metallochaperone that delivers copper to the CuB centre of the mitochondrially encoded core catalytic subunit COX1 (MT-CO1) during Complex IV biogenesis. It is mechanistically complementary to the SCO1/SCO2 metallochaperones, which instead metallate the CuA centre of COX2, so COX11 completes the copper-delivery picture for the holoenzyme. Loss of COX11 impairs CuB metallation and stalls assembly of a functional Complex IV, producing an isolated Complex IV deficiency. The disorder was first defined in 2022 as an infantile-onset mitochondrial encephalopathy in two unrelated families, with a subsequently reported patient showing Leigh-like features. A distinctive feature is that the cellular bioenergetic defect (reduced respiration-derived ATP) can be partially rescued in patient fibroblasts by coenzyme Q10 supplementation, suggesting a candidate metabolic therapeutic strategy despite COX11 having no known role in CoQ10 biosynthesis. It conforms to the conserved Complex IV assembly-deficiency mechanism, with the lesion localized to defective copper delivery to the CuB centre of COX1.
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name: COX11-Related COX Deficiency
category: Mendelian
creation_date: "2026-06-15T00:00:00Z"
synonyms:
- COX11 deficiency
- Mitochondrial complex IV deficiency, nuclear type 23
- MC4DN23
- COX11-related cytochrome c oxidase deficiency
- COX11-related infantile-onset mitochondrial encephalopathy
description: >
COX11-related COX deficiency (mitochondrial complex IV deficiency nuclear
type 23, MC4DN23) is a rare autosomal recessive nuclear form of isolated
cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants
in COX11. COX11 is a copper metallochaperone that delivers copper to the CuB
centre of the mitochondrially encoded core catalytic subunit COX1 (MT-CO1)
during Complex IV biogenesis. It is mechanistically complementary to the
SCO1/SCO2 metallochaperones, which instead metallate the CuA centre of COX2,
so COX11 completes the copper-delivery picture for the holoenzyme. Loss of
COX11 impairs CuB metallation and stalls assembly of a functional Complex IV,
producing an isolated Complex IV deficiency. The disorder was first defined in
2022 as an infantile-onset mitochondrial encephalopathy in two unrelated
families, with a subsequently reported patient showing Leigh-like features.
A distinctive feature is that the cellular bioenergetic defect (reduced
respiration-derived ATP) can be partially rescued in patient fibroblasts by
coenzyme Q10 supplementation, suggesting a candidate metabolic therapeutic
strategy despite COX11 having no known role in CoQ10 biosynthesis. It conforms
to the conserved Complex IV assembly-deficiency mechanism, with the lesion
localized to defective copper delivery to the CuB centre of COX1.
disease_term:
preferred_term: COX11-related COX deficiency (MC4DN23)
term:
id: MONDO:0859520
label: mitochondrial complex IV deficiency, nuclear type 23
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
pathophysiology:
- name: COX11 Loss and Defective Copper Delivery to the CuB Centre
conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
description: >
Biallelic COX11 variants impair the copper metallochaperone that delivers
copper to the CuB centre of the core catalytic subunit COX1, preventing
assembly of a functional Complex IV holoenzyme. This lesion is complementary
to the SCO1/SCO2 defects, which disrupt CuA metallation of COX2; together
they account for the two copper centres of the enzyme.
biological_processes:
- preferred_term: copper ion transport
term:
id: GO:0006825
label: copper ion transport
modifier: DECREASED
- preferred_term: mitochondrial respiratory chain complex IV assembly
term:
id: GO:0033617
label: mitochondrial respiratory chain complex IV assembly
modifier: DECREASED
evidence:
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: COX11 encodes a copper chaperone that participates in the assembly of complex IV and has not been previously linked to human disease.
explanation: Establishes COX11 as a copper chaperone required for Complex IV assembly, the function lost in MC4DN23.
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: we report a novel gene-disease association by identifying biallelic pathogenic variants in COX11 associated with infantile-onset mitochondrial encephalopathies in two unrelated families using trio genome and exome sequencing
explanation: Defines the COX11 gene-disease association through biallelic variants in two unrelated families.
downstream:
- target: Impaired Terminal Electron Transfer and ATP Synthesis
causal_link_type: DIRECT
description: Failure to metallate the CuB centre of COX1 yields a catalytically deficient Complex IV.
- name: Impaired Terminal Electron Transfer and ATP Synthesis
conforms_to: "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"
description: >
Deficient Complex IV blocks electron transfer from cytochrome c to oxygen
and proton pumping, collapsing oxidative ATP synthesis and preferentially
injuring high-energy neural tissue. In patient fibroblasts the respiration-
derived ATP deficit is demonstrable and is partially rescuable by coenzyme
Q10 supplementation.
cell_types:
- preferred_term: neuron
term:
id: CL:0000540
label: neuron
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
- preferred_term: ATP synthesis coupled electron transport
term:
id: GO:0042775
label: mitochondrial ATP synthesis coupled electron transport
modifier: DECREASED
evidence:
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: COX11 knockdown decreased cellular adenosine triphosphate (ATP) derived from respiration
explanation: Loss of COX11 reduces respiration-derived ATP, the bioenergetic consequence of impaired terminal electron transfer.
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: mutant COX11 fibroblasts had decreased ATP levels which could be rescued by CoQ10
explanation: Patient fibroblasts show an ATP deficit rescuable by CoQ10, confirming the impaired ATP-synthesis phenotype.
downstream:
- target: Encephalopathy
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: Bioenergetic failure in the developing brain produces an infantile-onset mitochondrial encephalopathy.
phenotypes:
- name: Encephalopathy
description: >
Infantile-onset mitochondrial encephalopathy is the defining clinical
presentation of COX11-related disease; a later-reported patient showed
Leigh-like features.
phenotype_term:
preferred_term: Encephalopathy
term:
id: HP:0001298
label: Encephalopathy
evidence:
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: we report a novel gene-disease association by identifying biallelic pathogenic variants in COX11 associated with infantile-onset mitochondrial encephalopathies in two unrelated families using trio genome and exome sequencing
explanation: Infantile-onset mitochondrial encephalopathy is reported in the two index families.
- reference: PMID:38068960
reference_title: "Novel COX11 Mutations Associated with Mitochondrial Disorder: Functional Characterization in Patient Fibroblasts and Saccharomyces cerevisiae."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: here we report on a new patient harboring novel heterozygous variants in COX11, presenting with Leigh-like features
explanation: A third patient with Leigh-like features expands the encephalopathic phenotype of COX11-related disease.
genetic:
- name: COX11 pathogenic variants causing MC4DN23
gene_term:
preferred_term: COX11
term:
id: hgnc:2261
label: COX11
inheritance:
- name: Autosomal recessive
evidence:
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: we report a novel gene-disease association by identifying biallelic pathogenic variants in COX11 associated with infantile-onset mitochondrial encephalopathies in two unrelated families using trio genome and exome sequencing
explanation: Biallelic (recessive) COX11 variants in two unrelated families establish autosomal recessive inheritance.
features: >
Biallelic COX11 variants cause MC4DN23. The disorder was defined by trio
genome/exome sequencing in two unrelated families with infantile-onset
mitochondrial encephalopathy, with a further patient subsequently reported
carrying additional novel variants and Leigh-like features.
evidence:
- reference: PMID:38068960
reference_title: "Novel COX11 Mutations Associated with Mitochondrial Disorder: Functional Characterization in Patient Fibroblasts and Saccharomyces cerevisiae."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: Biallelic pathogenic variants in the COX11 protein were previously identified in two unrelated children with infantile-onset mitochondrial encephalopathies
explanation: Independent report confirming biallelic COX11 variants as the cause of the disorder.
- reference: PMID:38068960
reference_title: "Novel COX11 Mutations Associated with Mitochondrial Disorder: Functional Characterization in Patient Fibroblasts and Saccharomyces cerevisiae."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: the functional deficits observed in patient fibroblasts are recapitulated in yeast models
explanation: Yeast modelling of the patient variants supports their pathogenicity at the COX11 locus.
treatments:
- name: Supportive and Metabolic Care
description: >
No curative therapy exists; management is supportive, addressing the
encephalopathy and associated neurological features, with physiotherapy and
rehabilitation and treatment of any metabolic decompensation.
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
- name: Coenzyme Q10 Supplementation
description: >
Coenzyme Q10 (CoQ10) supplementation is a candidate metabolic strategy:
in COX11-mutant patient fibroblasts the respiration-derived ATP deficit was
rescued by CoQ10, despite COX11 having no known role in CoQ10 biosynthesis.
This remains an experimental/investigational rationale rather than an
established therapy.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: coenzyme Q10
term:
id: CHEBI:46245
label: coenzyme Q10
evidence:
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: mutant COX11 fibroblasts had decreased ATP levels which could be rescued by CoQ10
explanation: Provides the in vitro rationale for CoQ10 as a candidate metabolic therapy in COX11-related disease.
- reference: PMID:36030551
reference_title: "Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: These results not only suggest that COX11 variants cause defects in energy production but reveal a potential metabolic therapeutic strategy for patients with COX11 variants
explanation: The authors frame CoQ10 rescue as a potential metabolic therapeutic strategy.