COX5A-Related COX Deficiency

Mendelian MONDO:0033655 Pathograph 7 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COX5A-related COX deficiency (mitochondrial complex IV deficiency nuclear type 20, MC4DN20) is a rare autosomal recessive nuclear form of isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants in COX5A. Unlike most members of the nuclear complex IV deficiency group, which arise from assembly-factor or metallochaperone defects, COX5A encodes a nuclear-encoded *structural* subunit of the holoenzyme. The reported pathogenic variant lies within the evolutionarily conserved COX5A/COX4 interface domain and is thought to disrupt the interaction between these two subunits during Complex IV biogenesis, so that the monomeric COX1 assembly intermediate accumulates and the mature holoenzyme is not formed, producing an isolated Complex IV deficiency. It was first identified in two affected siblings of a consanguineous family who presented with early-onset pulmonary arterial hypertension, lactic acidemia, and failure to thrive. It conforms to the conserved Complex IV assembly-deficiency mechanism, with the lesion localized to a destabilized structural subunit at the COX5A/COX4 interface.

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4
Pathophys.
3
Phenotypes
7
Pathograph
1
Genes
2
Medical Actions
1
References
⚙

Pathophysiology

4
COX5A Structural Subunit Loss and Failed Complex IV Assembly
Biallelic COX5A variants disrupt a nuclear-encoded structural subunit of Complex IV. The reported variant lies within the conserved COX5A/COX4 interface domain, altering the interaction between these subunits during holoenzyme biogenesis. As a result the monomeric COX1 assembly intermediate accumulates and the mature enzyme fails to assemble, yielding isolated Complex IV biogenesis failure.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED
Downstream
Impaired Terminal Electron Transfer and ATP Synthesis Failure to assemble Complex IV yields a catalytically deficient holoenzyme.
Show evidence (3 references)
PMID:28247525 SUPPORT Human Clinical
"COX5A is a nuclear-encoded subunit of mitochondrial respiratory chain complex IV"
Establishes COX5A as a nuclear-encoded structural subunit of Complex IV, the protein lost in this disorder.
PMID:28247525 SUPPORT Computational
"the variant lies within the evolutionarily conserved COX5A/COX4 interface domain, suggesting that it alters the interaction between these two subunits during complex IV biogenesis"
Localizes the lesion to the COX5A/COX4 interface, the structural basis for impaired Complex IV biogenesis.
PMID:28247525 SUPPORT In Vitro
"The monomeric COX1 assembly intermediate accumulates demonstrating a function of COX5A in complex IV biogenesis"
Accumulation of the monomeric COX1 assembly intermediate in patient cells demonstrates a stalled, failed assembly.
Impaired Terminal Electron Transfer and ATP Synthesis
Reduced amounts and activity of assembled Complex IV block electron transfer from cytochrome c to oxygen and proton pumping, collapsing oxidative ATP synthesis. In COX5A-deficient patient fibroblasts the enzymatic activity and protein levels of Complex IV and several of its subunits are reduced.
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED ATP synthesis coupled electron transport GO:0042775 ↓ DECREASED
Downstream
Lactic Acidosis and Metabolic Decompensation Loss of oxidative ATP synthesis forces anaerobic glycolysis and lactate accumulation.
High-Energy Tissue Dysfunction The bioenergetic deficit injures high-demand tissues, including the pulmonary vasculature.
Show evidence (1 reference)
PMID:28247525 SUPPORT In Vitro
"the enzymatic activity and protein levels of complex IV and several of its subunits are reduced"
Reduced Complex IV enzymatic activity and protein levels establish the functional terminal-electron-transfer deficit.
Lactic Acidosis and Metabolic Decompensation
With oxidative phosphorylation impaired, pyruvate is shunted to lactate, elevating blood lactate; in COX5A-related disease this presented as lactic acidemia in both affected siblings.
lactate biosynthetic process GO:0019249 ↑ INCREASED
Downstream
Lactic acidemia Lactate overproduction manifests clinically as lactic acidemia.
Show evidence (1 reference)
PMID:28247525 SUPPORT Human Clinical
"early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
Lactic acidemia in the affected siblings is the metabolic consequence of failed oxidative ATP synthesis.
High-Energy Tissue Dysfunction
The bioenergetic deficit manifests in high-demand tissues. In COX5A-related disease the dominant organ phenotype is early-onset pulmonary arterial hypertension, accompanied by failure to thrive, distinguishing it from the encephalopathy/cardiomyopathy presentations of other nuclear COX deficiencies.
aerobic respiration GO:0009060 ↓ DECREASED
Downstream
Pulmonary arterial hypertension Pulmonary vascular involvement manifests as early-onset pulmonary arterial hypertension.
Failure to thrive Systemic energy failure manifests as failure to thrive.
Show evidence (1 reference)
PMID:28247525 SUPPORT Human Clinical
"early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
Early-onset pulmonary arterial hypertension and failure to thrive are the high-energy-tissue manifestations of the bioenergetic deficit.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COX5A-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
Pulmonary arterial hypertension Pulmonary arterial hypertension HP:0002092
Onset: INFANTILE
Show evidence (1 reference)
PMID:28247525 SUPPORT Human Clinical
"early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
The affected siblings presented with early-onset pulmonary arterial hypertension.
Metabolism 1
Lactic acidemia Lactic acidosis HP:0003128
Show evidence (1 reference)
PMID:28247525 SUPPORT Human Clinical
"early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
Lactic acidemia was present in the affected siblings.
Growth 1
Failure to thrive Failure to thrive HP:0001508
Show evidence (1 reference)
PMID:28247525 SUPPORT Human Clinical
"early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
Failure to thrive was a presenting feature in the affected siblings.
🧬

Genetic Associations

1
COX5A pathogenic variants causing MC4DN20
Gene: COX5A hgnc:2267
Autosomal recessive
Show evidence (2 references)
PMID:28247525 SUPPORT Human Clinical
"We present patients with a homozygous pathogenic variant in the COX5A gene"
Identifies the homozygous COX5A variant as the causal lesion.
PMID:28247525 SUPPORT In Vitro
"Lentiviral complementation rescues complex IV deficiency"
Re-expression of wild-type COX5A rescued the biochemical defect in patient fibroblasts, confirming causality.
💊

Medical Actions

2
Supportive and Metabolic Care
Action: supportive care MAXO:0000950
No curative therapy exists; management is supportive, addressing the pulmonary arterial hypertension, lactic acidemia, and failure to thrive with multidisciplinary supportive care.
Copper Supplementation (investigational)
Action: Pharmacotherapy NCIT:C15986
Agent: copper CHEBI:28694
A preclinical therapeutic lead: copper supplementation partially rescued Complex IV deficiency in patient fibroblasts in vitro. This is an experimental finding in cells, not an established clinical therapy.
Show evidence (1 reference)
PMID:28247525 SUPPORT In Vitro
"copper supplementation leads to partial rescue of complex IV deficiency in patient fibroblasts"
Copper supplementation partially rescued Complex IV deficiency in patient fibroblasts, identifying a potential therapeutic lead.
{ }

Source YAML

click to show 
name: COX5A-Related COX Deficiency
category: Mendelian
creation_date: "2026-06-19T00:00:00Z"
synonyms:
- COX5A deficiency
- Mitochondrial complex IV deficiency, nuclear type 20
- MC4DN20
- COX5A-related cytochrome c oxidase deficiency
description: >
  COX5A-related COX deficiency (mitochondrial complex IV deficiency nuclear
  type 20, MC4DN20) is a rare autosomal recessive nuclear form of isolated
  cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants
  in COX5A. Unlike most members of the nuclear complex IV deficiency group, which
  arise from assembly-factor or metallochaperone defects, COX5A encodes a
  nuclear-encoded *structural* subunit of the holoenzyme. The reported pathogenic
  variant lies within the evolutionarily conserved COX5A/COX4 interface domain
  and is thought to disrupt the interaction between these two subunits during
  Complex IV biogenesis, so that the monomeric COX1 assembly intermediate
  accumulates and the mature holoenzyme is not formed, producing an isolated
  Complex IV deficiency. It was first identified in two affected siblings of a
  consanguineous family who presented with early-onset pulmonary arterial
  hypertension, lactic acidemia, and failure to thrive. It conforms to the
  conserved Complex IV assembly-deficiency mechanism, with the lesion localized
  to a destabilized structural subunit at the COX5A/COX4 interface.
disease_term:
  preferred_term: COX5A-related COX deficiency (MC4DN20)
  term:
    id: MONDO:0033655
    label: mitochondrial complex IV deficiency, nuclear type 20
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
references:
- reference: PMID:28247525
  title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
pathophysiology:
- name: COX5A Structural Subunit Loss and Failed Complex IV Assembly
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  description: >
    Biallelic COX5A variants disrupt a nuclear-encoded structural subunit of
    Complex IV. The reported variant lies within the conserved COX5A/COX4
    interface domain, altering the interaction between these subunits during
    holoenzyme biogenesis. As a result the monomeric COX1 assembly intermediate
    accumulates and the mature enzyme fails to assemble, yielding isolated
    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
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "COX5A is a nuclear-encoded subunit of mitochondrial respiratory chain complex IV"
    explanation: Establishes COX5A as a nuclear-encoded structural subunit of Complex IV, the protein lost in this disorder.
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "the variant lies within the evolutionarily conserved COX5A/COX4 interface domain, suggesting that it alters the interaction between these two subunits during complex IV biogenesis"
    explanation: Localizes the lesion to the COX5A/COX4 interface, the structural basis for impaired Complex IV biogenesis.
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The monomeric COX1 assembly intermediate accumulates demonstrating a function of COX5A in complex IV biogenesis"
    explanation: Accumulation of the monomeric COX1 assembly intermediate in patient cells demonstrates a stalled, failed assembly.
  downstream:
  - target: Impaired Terminal Electron Transfer and ATP Synthesis
    causal_link_type: DIRECT
    description: Failure to assemble Complex IV yields a catalytically deficient holoenzyme.
- name: Impaired Terminal Electron Transfer and ATP Synthesis
  conforms_to: "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"
  description: >
    Reduced amounts and activity of assembled Complex IV block electron transfer
    from cytochrome c to oxygen and proton pumping, collapsing oxidative ATP
    synthesis. In COX5A-deficient patient fibroblasts the enzymatic activity and
    protein levels of Complex IV and several of its subunits are reduced.
  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:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the enzymatic activity and protein levels of complex IV and several of its subunits are reduced"
    explanation: Reduced Complex IV enzymatic activity and protein levels establish the functional terminal-electron-transfer deficit.
  downstream:
  - target: Lactic Acidosis and Metabolic Decompensation
    causal_link_type: DIRECT
    description: Loss of oxidative ATP synthesis forces anaerobic glycolysis and lactate accumulation.
  - target: High-Energy Tissue Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: The bioenergetic deficit injures high-demand tissues, including the pulmonary vasculature.
- name: Lactic Acidosis and Metabolic Decompensation
  conforms_to: "complex_iv_assembly_deficiency#Lactic Acidosis and Metabolic Decompensation"
  description: >
    With oxidative phosphorylation impaired, pyruvate is shunted to lactate,
    elevating blood lactate; in COX5A-related disease this presented as
    lactic acidemia in both affected siblings.
  biological_processes:
  - preferred_term: lactate biosynthetic process
    term:
      id: GO:0019249
      label: lactate biosynthetic process
    modifier: INCREASED
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
    explanation: Lactic acidemia in the affected siblings is the metabolic consequence of failed oxidative ATP synthesis.
  downstream:
  - target: Lactic acidemia
    causal_link_type: DIRECT
    description: Lactate overproduction manifests clinically as lactic acidemia.
- name: High-Energy Tissue Dysfunction
  conforms_to: "complex_iv_assembly_deficiency#High-Energy Tissue Dysfunction"
  description: >
    The bioenergetic deficit manifests in high-demand tissues. In COX5A-related
    disease the dominant organ phenotype is early-onset pulmonary arterial
    hypertension, accompanied by failure to thrive, distinguishing it from the
    encephalopathy/cardiomyopathy presentations of other nuclear COX deficiencies.
  biological_processes:
  - preferred_term: aerobic respiration
    term:
      id: GO:0009060
      label: aerobic respiration
    modifier: DECREASED
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
    explanation: Early-onset pulmonary arterial hypertension and failure to thrive are the high-energy-tissue manifestations of the bioenergetic deficit.
  downstream:
  - target: Pulmonary arterial hypertension
    causal_link_type: DIRECT
    description: Pulmonary vascular involvement manifests as early-onset pulmonary arterial hypertension.
  - target: Failure to thrive
    causal_link_type: DIRECT
    description: Systemic energy failure manifests as failure to thrive.
phenotypes:
- name: Pulmonary arterial hypertension
  description: >
    Early-onset pulmonary arterial hypertension, the dominant presenting feature
    of COX5A-related Complex IV deficiency in the two reported siblings.
  phenotype_term:
    preferred_term: Pulmonary arterial hypertension
    term:
      id: HP:0002092
      label: Pulmonary arterial hypertension
    onset:
      onset_category: INFANTILE
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
    explanation: The affected siblings presented with early-onset pulmonary arterial hypertension.
- name: Lactic acidemia
  description: >
    Lactic acidemia (elevated blood lactate), a presenting metabolic feature of
    COX5A-related Complex IV deficiency.
  phenotype_term:
    preferred_term: Lactic acidemia
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
    explanation: Lactic acidemia was present in the affected siblings.
- name: Failure to thrive
  description: >
    Failure to thrive accompanied the pulmonary arterial hypertension and
    lactic acidemia in the affected siblings.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset pulmonary arterial hypertension, lactic acidemia, failure to thrive, and isolated complex IV deficiency"
    explanation: Failure to thrive was a presenting feature in the affected siblings.
genetic:
- name: COX5A pathogenic variants causing MC4DN20
  gene_term:
    preferred_term: COX5A
    term:
      id: hgnc:2267
      label: COX5A
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:28247525
      reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We present patients with a homozygous pathogenic variant in the COX5A gene"
      explanation: A homozygous COX5A variant in affected siblings of a consanguineous family establishes autosomal recessive inheritance.
  features: >
    Biallelic COX5A variants cause MC4DN20. The reported siblings carried a
    homozygous pathogenic COX5A variant within the conserved COX5A/COX4 interface
    domain; lentiviral complementation of patient fibroblasts rescued the Complex
    IV deficiency, confirming pathogenicity.
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present patients with a homozygous pathogenic variant in the COX5A gene"
    explanation: Identifies the homozygous COX5A variant as the causal lesion.
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Lentiviral complementation rescues complex IV deficiency"
    explanation: Re-expression of wild-type COX5A rescued the biochemical defect in patient fibroblasts, confirming causality.
treatments:
- name: Supportive and Metabolic Care
  description: >
    No curative therapy exists; management is supportive, addressing the
    pulmonary arterial hypertension, lactic acidemia, and failure to thrive with
    multidisciplinary supportive care.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
- name: Copper Supplementation (investigational)
  description: >
    A preclinical therapeutic lead: copper supplementation partially rescued
    Complex IV deficiency in patient fibroblasts in vitro. This is an
    experimental finding in cells, not an established clinical therapy.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: copper
      term:
        id: CHEBI:28694
        label: copper atom
  evidence:
  - reference: PMID:28247525
    reference_title: "Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "copper supplementation leads to partial rescue of complex IV deficiency in patient fibroblasts"
    explanation: Copper supplementation partially rescued Complex IV deficiency in patient fibroblasts, identifying a potential therapeutic lead.
📚

References & Deep Research

References

1
PMID:28247525
Mutation in mitochondrial complex IV subunit COX5A causes pulmonary arterial hypertension, lactic acidemia, and failure to thrive.
No top-level findings curated for this source.