COX6B1-Related COX Deficiency

Mendelian MONDO:0033637 Pathograph 5 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COX6B1-related COX deficiency (mitochondrial complex IV deficiency nuclear type 7, MC4DN7) is a rare nuclear form of isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants in COX6B1. COX6B1 is notable for being one of the very few nuclear-encoded *structural* subunits of Complex IV in which disease-causing mutations have been identified — most nuclear COX defects arise in assembly factors or metallochaperones rather than in the structural subunits themselves. The reported phenotype is severe infantile encephalomyopathy, with additional cases showing hydrocephalus and hypertrophic cardiomyopathy. It conforms to the conserved Complex IV assembly-deficiency mechanism, with the lesion localized to loss of a structural subunit (rather than an assembly factor), destabilizing the holoenzyme and impairing terminal electron transfer and oxidative ATP synthesis.

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2
Pathophys.
3
Phenotypes
5
Pathograph
1
Genes
2
Medical Actions
⚙

Pathophysiology

2
COX6B1 Loss and Defective Complex IV Assembly
Biallelic COX6B1 variants cause loss of a nuclear-encoded structural subunit of cytochrome c oxidase, destabilizing the holoenzyme and impairing assembly of a functional Complex IV. Unlike most nuclear COX defects, which affect assembly factors or metallochaperones, the lesion here is in a structural subunit itself.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED
Downstream
Impaired Terminal Electron Transfer and ATP Synthesis Loss of the structural subunit yields a catalytically deficient enzyme.
Show evidence (2 references)
PMID:18499082 SUPPORT Human Clinical
"We report a disease-associated mutation in one such subunit, COX6B1."
Identifies COX6B1, a structural subunit of Complex IV, as harboring a disease-associated mutation in COX deficiency.
PMID:24781756 SUPPORT Human Clinical
"enzymatic activity was undetectable in muscle and fibroblasts, was severely decreased in lymphocytes and the COX6B1 protein was barely detectable in patient's muscle mitochondria"
Demonstrates that COX6B1 mutation abolishes COX6B1 protein and COX enzymatic activity, i.e., failed Complex IV biogenesis.
Impaired Terminal Electron Transfer and ATP Synthesis
Deficient Complex IV blocks electron transfer from cytochrome c to oxygen and proton pumping, collapsing oxidative ATP synthesis and preferentially injuring high-energy tissues (brain, heart, skeletal muscle).
neuron CL:0000540 cardiac muscle cell CL:0000746
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED ATP synthesis coupled electron transport GO:0042775 ↓ DECREASED
Downstream
Encephalopathy Energy deficit in the CNS produces the infantile encephalomyopathy.
Hydrocephalus CNS vulnerability from Complex IV energy failure can contribute to hydrocephalus through developmental or neurostructural intermediates.
Hypertrophic cardiomyopathy Energy failure in cardiomyocytes drives hypertrophic cardiomyopathy in some patients.
Show evidence (1 reference)
PMID:10545952 SUPPORT Human Clinical
"Mammalian cytochrome c oxidase (COX) catalyses the transfer of reducing equivalents from cytochrome c to molecular oxygen and pumps protons across the inner mitochondrial membrane."
Defines the terminal electron-transfer and proton-pumping function lost in COX6B1-related COX deficiency.
⬡

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.
●

Phenotypes

3
Cardiovascular 1
Hypertrophic cardiomyopathy Hypertrophic cardiomyopathy HP:0001639
Show evidence (1 reference)
PMID:24781756 SUPPORT Human Clinical
"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"
Hypertrophic cardiomyopathy is reported in the COX6B1 phenotype (abstract spelling "hypertropic").
Nervous System 2
Encephalopathy Encephalopathy HP:0001298
Show evidence (2 references)
PMID:24781756 SUPPORT Human Clinical
"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"
Documents encephalomyopathy as a core manifestation of COX6B1-related COX deficiency.
PMID:38842388 SUPPORT Human Clinical
"a patient with a novel homozygous pathogenic variant in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection"
Confirms severe encephalomyopathy, here with acute infection-triggered decompensation.
Hydrocephalus Hydrocephalus HP:0000238
Show evidence (1 reference)
PMID:24781756 SUPPORT Human Clinical
"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"
Hydrocephalus is reported as part of the COX6B1 phenotype.
🧬

Genetic Associations

1
COX6B1 pathogenic variants causing MC4DN7
Gene: COX6B1 hgnc:2280
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."
Establishes COX6B1 as the causal gene with biallelic (recessive) inheritance across reported patients.
💊

Medical Actions

2
Supportive and Metabolic Care
Action: supportive care MAXO:0000950
No curative therapy exists; management is supportive, addressing encephalopathy, cardiomyopathy, hydrocephalus, and metabolic decompensation.
Antioxidant and Metabolic Cofactor Supplementation (investigational)
Action: dietary supplementation Ontology label: dietary intervention MAXO:0000088
In patient fibroblasts, mitochondrial function was improved by AICAR, resveratrol, and ascorbate, and evaluation of ascorbate supplementation in COX6B1 patients has been proposed; clinical benefit is unproven.
Show evidence (1 reference)
PMID:24781756 SUPPORT In Vitro
"mitochondrial function was improved by 5-aminoimidazole-4-carboxamide ribonucleotide, resveratrol and ascorbate in the"
Cell-based (fibroblast) evidence that antioxidant/cofactor supplementation improved mitochondrial function; investigational only.
{ }

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
description: >
  COX6B1-related COX deficiency (mitochondrial complex IV deficiency nuclear
  type 7, MC4DN7) is a rare nuclear form of isolated cytochrome c oxidase (COX,
  Complex IV) deficiency caused by biallelic variants in COX6B1. COX6B1 is
  notable for being one of the very few nuclear-encoded *structural* subunits of
  Complex IV in which disease-causing mutations have been identified — most
  nuclear COX defects arise in assembly factors or metallochaperones rather than
  in the structural subunits themselves. The reported phenotype is severe
  infantile encephalomyopathy, with additional cases showing hydrocephalus and
  hypertrophic cardiomyopathy. It conforms to the conserved Complex IV
  assembly-deficiency mechanism, with the lesion localized to loss of a
  structural subunit (rather than an assembly factor), destabilizing the
  holoenzyme and impairing terminal electron transfer and oxidative ATP
  synthesis.
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
pathophysiology:
- name: COX6B1 Loss and Defective Complex IV Assembly
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  description: >
    Biallelic COX6B1 variants cause loss of a nuclear-encoded structural subunit
    of cytochrome c oxidase, destabilizing the holoenzyme and impairing assembly
    of a functional Complex IV. Unlike most nuclear COX defects, which affect
    assembly factors or metallochaperones, the lesion here is in a structural
    subunit itself.
  biological_processes:
  - preferred_term: mitochondrial respiratory chain complex IV assembly
    term:
      id: GO:0033617
      label: mitochondrial respiratory chain complex IV assembly
    modifier: DECREASED
  evidence:
  - reference: PMID: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 report a disease-associated mutation in one such subunit, COX6B1.
    explanation: Identifies COX6B1, a structural subunit of Complex IV, as harboring a disease-associated mutation in COX deficiency.
  - 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: enzymatic activity was undetectable in muscle and fibroblasts, was severely decreased in lymphocytes and the COX6B1 protein was barely detectable in patient's muscle mitochondria
    explanation: Demonstrates that COX6B1 mutation abolishes COX6B1 protein and COX enzymatic activity, i.e., failed Complex IV biogenesis.
  downstream:
  - target: Impaired Terminal Electron Transfer and ATP Synthesis
    causal_link_type: DIRECT
    description: Loss of the structural subunit yields a catalytically deficient enzyme.
- 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 tissues (brain, heart, skeletal muscle).
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  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:10545952
    reference_title: "Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mammalian cytochrome c oxidase (COX) catalyses the transfer of reducing equivalents from cytochrome c to molecular oxygen and pumps protons across the inner mitochondrial membrane.
    explanation: Defines the terminal electron-transfer and proton-pumping function lost in COX6B1-related COX deficiency.
  downstream:
  - target: Encephalopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Energy deficit in the CNS produces the infantile encephalomyopathy.
  - target: Hydrocephalus
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >
      CNS vulnerability from Complex IV energy failure can contribute to
      hydrocephalus through developmental or neurostructural intermediates.
  - target: Hypertrophic cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Energy failure in cardiomyocytes drives hypertrophic cardiomyopathy in some patients.
phenotypes:
- name: Encephalopathy
  description: Severe infantile encephalomyopathy, the cardinal presentation of COX6B1-related COX deficiency.
  phenotype_term:
    preferred_term: Infantile encephalomyopathy
    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: 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
    explanation: Documents encephalomyopathy as a core manifestation of COX6B1-related COX deficiency.
  - 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: a patient with a novel homozygous pathogenic variant in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection
    explanation: Confirms severe encephalomyopathy, here with acute infection-triggered decompensation.
- name: Hydrocephalus
  description: Hydrocephalus reported in COX6B1-related COX deficiency.
  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: 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
    explanation: Hydrocephalus is reported as part of the COX6B1 phenotype.
- name: Hypertrophic cardiomyopathy
  description: Hypertrophic cardiomyopathy reported in COX6B1-related COX deficiency.
  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: 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
    explanation: Hypertrophic cardiomyopathy is reported in the COX6B1 phenotype (abstract spelling "hypertropic").
genetic:
- name: COX6B1 pathogenic variants causing MC4DN7
  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: a patient with a novel homozygous pathogenic variant in COX6B1
      explanation: A homozygous pathogenic COX6B1 variant indicates autosomal recessive inheritance.
  features: >
    Biallelic COX6B1 variants (e.g., p.R20C, p.Trp31Arg) cause loss of a
    structural Complex IV subunit, producing MC4DN7 with infantile
    encephalomyopathy and variable cardiac and CNS involvement.
  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: Establishes COX6B1 as the causal gene with biallelic (recessive) inheritance across reported patients.
treatments:
- name: Supportive and Metabolic Care
  description: >
    No curative therapy exists; management is supportive, addressing
    encephalopathy, cardiomyopathy, hydrocephalus, and metabolic
    decompensation.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
- name: Antioxidant and Metabolic Cofactor Supplementation (investigational)
  description: >
    In patient fibroblasts, mitochondrial function was improved by AICAR,
    resveratrol, and ascorbate, and evaluation of ascorbate supplementation in
    COX6B1 patients has been proposed; clinical benefit is unproven.
  treatment_term:
    preferred_term: dietary supplementation
    term:
      id: MAXO:0000088
      label: dietary intervention
  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: IN_VITRO
    snippet: mitochondrial function was improved by 5-aminoimidazole-4-carboxamide ribonucleotide, resveratrol and ascorbate in the
    explanation: Cell-based (fibroblast) evidence that antioxidant/cofactor supplementation improved mitochondrial function; investigational only.