COX8A-Related COX Deficiency

Mendelian MONDO:0033650 Pathograph 4 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COX8A-related COX deficiency (mitochondrial complex IV deficiency nuclear type 15, MC4DN15) is an ultra-rare autosomal recessive nuclear form of isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic variants in COX8A. COX8A encodes the ubiquitously expressed isoform of subunit VIII, the smallest nuclear-encoded structural subunit of Complex IV. Unlike the much more common nuclear COX defects in assembly factors (e.g., SURF1, SCO1/2, COX10/15), pathogenic variants in nuclear-encoded structural subunits are very rare. Loss of the wild-type COX8A protein severely destabilizes the entire cytochrome c oxidase holoenzyme, producing an isolated Complex IV deficiency in skeletal muscle and fibroblasts that biochemically resembles SURF1 disease. The reported presentation is a severe infantile/childhood Leigh-like syndrome with leukodystrophy and severe, drug-resistant epilepsy. It conforms to the conserved Complex IV assembly/biogenesis-deficiency mechanism, with the lesion localized to loss of a core structural subunit rather than an assembly factor.

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2
Pathophys.
2
Phenotypes
4
Pathograph
1
Genes
1
Medical Actions
⚙

Pathophysiology

2
COX8A Loss and Complex IV Destabilization
A homozygous COX8A splice-site variant abolishes the wild-type smallest structural subunit of Complex IV. Because COX8A is an integral structural subunit rather than a transient assembly factor, its loss severely impairs the stability of the entire cytochrome c oxidase holoenzyme, stalling biogenesis and yielding an isolated Complex IV deficiency in skeletal muscle and fibroblasts comparable to that caused by SURF1 mutations.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED
Downstream
Impaired Terminal Electron Transfer and ATP Synthesis A destabilized, COX8A-deficient holoenzyme is catalytically deficient, impairing terminal electron transfer and oxidative ATP synthesis.
Show evidence (3 references)
PMID:26685157 SUPPORT Human Clinical
"we identified a homozygous splice site mutation in COX8A, which codes for the ubiquitously expressed isoform of subunit VIII, the smallest nuclear-encoded subunit of complex IV"
Establishes biallelic COX8A as the cause and identifies it as the smallest nuclear-encoded structural subunit of Complex IV.
PMID:26685157 SUPPORT Human Clinical
"The loss of the wild-type COX8A protein severely impairs the stability of the entire cytochrome c oxidase enzyme complex and manifests in isolated complex IV deficiency in skeletal muscle and fibroblasts"
Demonstrates that loss of the COX8A structural subunit destabilizes the holoenzyme, i.e. failed Complex IV biogenesis with isolated Complex IV deficiency.
PMID:26685157 SUPPORT In Vitro
"Stability and activity of complex IV could be rescued in the patient's fibroblasts by lentiviral expression of wild-type COX8A"
Rescue of Complex IV stability/activity by re-expressing wild-type COX8A in patient fibroblasts confirms COX8A loss as the direct molecular lesion.
Impaired Terminal Electron Transfer and ATP Synthesis
Deficient Complex IV blocks electron transfer from cytochrome c to oxygen and the coupled proton pumping, collapsing oxidative ATP synthesis. High-energy neural tissue is preferentially injured, producing the Leigh-like encephalopathy with leukodystrophy and epilepsy.
neuron CL:0000540
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED ATP synthesis coupled electron transport GO:0042775 ↓ DECREASED
Downstream
Seizures Bioenergetic failure in the central nervous system produces severe, drug-resistant epilepsy.
Leukodystrophy Energy deficit and oxidative stress drive white-matter degeneration (leukodystrophy) as part of the Leigh-like syndrome.
Show evidence (1 reference)
PMID:26685157 SUPPORT Human Clinical
"manifests in isolated complex IV deficiency in skeletal muscle and fibroblasts"
Reduced Complex IV in patient muscle and fibroblasts is the biochemical basis for impaired terminal electron transfer and ATP synthesis.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COX8A-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

2
Seizures HP:0001250
Severity: SEVERE
Show evidence (1 reference)
PMID:26685157 SUPPORT Human Clinical
"In a patient with Leigh-like syndrome presenting with leukodystrophy and severe epilepsy"
Severe epilepsy is a presenting feature of the index COX8A patient.
Leukodystrophy HP:0002415
Show evidence (1 reference)
PMID:26685157 SUPPORT Human Clinical
"In a patient with Leigh-like syndrome presenting with leukodystrophy and severe epilepsy"
Leukodystrophy is a presenting feature of the index COX8A patient.
🧬

Genetic Associations

1
COX8A pathogenic variants causing MC4DN15
Gene: COX8A hgnc:2294
Autosomal recessive
Show evidence (1 reference)
PMID:26685157 SUPPORT Human Clinical
"The mutation, affecting the last nucleotide of intron 1, leads to aberrant splicing, a frame-shift in the highly conserved exon 2, and decreased amount of the COX8A transcript"
Defines the molecular consequence of the causal COX8A splice-site variant.
💊

Medical Actions

1
Supportive and Metabolic Care
Action: supportive care MAXO:0000950
No curative therapy exists; management is supportive, focused on anticonvulsant control of the severe epilepsy, treatment of metabolic decompensation, and multidisciplinary care of the Leigh-like encephalopathy.
{ }

Source YAML

click to show 
name: COX8A-Related COX Deficiency
category: Mendelian
creation_date: "2026-06-20T00:00:00Z"
synonyms:
- COX8A deficiency
- Mitochondrial complex IV deficiency, nuclear type 15
- MC4DN15
- COX8A-related cytochrome c oxidase deficiency
- COX8A-related Leigh-like syndrome
description: >
  COX8A-related COX deficiency (mitochondrial complex IV deficiency nuclear
  type 15, MC4DN15) is an ultra-rare autosomal recessive nuclear form of
  isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic
  variants in COX8A. COX8A encodes the ubiquitously expressed isoform of subunit
  VIII, the smallest nuclear-encoded structural subunit of Complex IV. Unlike the
  much more common nuclear COX defects in assembly factors (e.g., SURF1, SCO1/2,
  COX10/15), pathogenic variants in nuclear-encoded structural subunits are very
  rare. Loss of the wild-type COX8A protein severely destabilizes the entire
  cytochrome c oxidase holoenzyme, producing an isolated Complex IV deficiency in
  skeletal muscle and fibroblasts that biochemically resembles SURF1 disease.
  The reported presentation is a severe infantile/childhood Leigh-like syndrome
  with leukodystrophy and severe, drug-resistant epilepsy. It conforms to the
  conserved Complex IV assembly/biogenesis-deficiency mechanism, with the lesion
  localized to loss of a core structural subunit rather than an assembly factor.
disease_term:
  preferred_term: COX8A-related COX deficiency (MC4DN15)
  term:
    id: MONDO:0033650
    label: mitochondrial complex IV deficiency, nuclear type 15
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
pathophysiology:
- name: COX8A Loss and Complex IV Destabilization
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  description: >
    A homozygous COX8A splice-site variant abolishes the wild-type smallest
    structural subunit of Complex IV. Because COX8A is an integral structural
    subunit rather than a transient assembly factor, its loss severely impairs
    the stability of the entire cytochrome c oxidase holoenzyme, stalling
    biogenesis and yielding an isolated Complex IV deficiency in skeletal muscle
    and fibroblasts comparable to that caused by SURF1 mutations.
  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:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: we identified a homozygous splice site mutation in COX8A, which codes for the ubiquitously expressed isoform of subunit VIII, the smallest nuclear-encoded subunit of complex IV
    explanation: Establishes biallelic COX8A as the cause and identifies it as the smallest nuclear-encoded structural subunit of Complex IV.
  - reference: PMID:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The loss of the wild-type COX8A protein severely impairs the stability of the entire cytochrome c oxidase enzyme complex and manifests in isolated complex IV deficiency in skeletal muscle and fibroblasts
    explanation: Demonstrates that loss of the COX8A structural subunit destabilizes the holoenzyme, i.e. failed Complex IV biogenesis with isolated Complex IV deficiency.
  - reference: PMID:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Stability and activity of complex IV could be rescued in the patient's fibroblasts by lentiviral expression of wild-type COX8A
    explanation: Rescue of Complex IV stability/activity by re-expressing wild-type COX8A in patient fibroblasts confirms COX8A loss as the direct molecular lesion.
  downstream:
  - target: Impaired Terminal Electron Transfer and ATP Synthesis
    causal_link_type: DIRECT
    description: A destabilized, COX8A-deficient holoenzyme is catalytically deficient, impairing terminal electron transfer and oxidative ATP synthesis.
    evidence:
    - reference: PMID:26685157
      reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Our findings demonstrate that COX8A is indispensable for function of human complex IV and its mutation causes human disease
      explanation: COX8A is indispensable for Complex IV function, linking subunit loss to loss of enzyme activity.
- 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
    the coupled proton pumping, collapsing oxidative ATP synthesis. High-energy
    neural tissue is preferentially injured, producing the Leigh-like
    encephalopathy with leukodystrophy and epilepsy.
  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:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: manifests in isolated complex IV deficiency in skeletal muscle and fibroblasts
    explanation: Reduced Complex IV in patient muscle and fibroblasts is the biochemical basis for impaired terminal electron transfer and ATP synthesis.
  downstream:
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Bioenergetic failure in the central nervous system produces severe, drug-resistant epilepsy.
  - target: Leukodystrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Energy deficit and oxidative stress drive white-matter degeneration (leukodystrophy) as part of the Leigh-like syndrome.
phenotypes:
- name: Seizures
  description: Severe, drug-resistant epilepsy reported as a presenting feature of COX8A-related Leigh-like syndrome.
  phenotype_term:
    preferred_term: Severe epilepsy
    term:
      id: HP:0001250
      label: Seizure
    severity: SEVERE
  evidence:
  - reference: PMID:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In a patient with Leigh-like syndrome presenting with leukodystrophy and severe epilepsy
    explanation: Severe epilepsy is a presenting feature of the index COX8A patient.
- name: Leukodystrophy
  description: White-matter abnormality (leukodystrophy) accompanying the Leigh-like syndrome.
  phenotype_term:
    preferred_term: Leukodystrophy
    term:
      id: HP:0002415
      label: Leukodystrophy
  evidence:
  - reference: PMID:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In a patient with Leigh-like syndrome presenting with leukodystrophy and severe epilepsy
    explanation: Leukodystrophy is a presenting feature of the index COX8A patient.
genetic:
- name: COX8A pathogenic variants causing MC4DN15
  gene_term:
    preferred_term: COX8A
    term:
      id: hgnc:2294
      label: COX8A
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:26685157
      reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: we identified a homozygous splice site mutation in COX8A
      explanation: A homozygous COX8A splice-site mutation in the affected patient is consistent with autosomal recessive inheritance.
  features: >
    A homozygous COX8A splice-site variant affecting the last nucleotide of
    intron 1 causes aberrant splicing, a frame-shift in the highly conserved
    exon 2, and a decreased amount of the COX8A transcript, abolishing the
    wild-type structural subunit.
  evidence:
  - reference: PMID:26685157
    reference_title: "Loss of the smallest subunit of cytochrome c oxidase, COX8A, causes Leigh-like syndrome and epilepsy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The mutation, affecting the last nucleotide of intron 1, leads to aberrant splicing, a frame-shift in the highly conserved exon 2, and decreased amount of the COX8A transcript
    explanation: Defines the molecular consequence of the causal COX8A splice-site variant.
treatments:
- name: Supportive and Metabolic Care
  description: >
    No curative therapy exists; management is supportive, focused on
    anticonvulsant control of the severe epilepsy, treatment of metabolic
    decompensation, and multidisciplinary care of the Leigh-like
    encephalopathy.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
notes: >
  COX8A-related disease is reported in a single patient to date (Hallmann et al.,
  2016) and is among the very rare nuclear-encoded structural-subunit causes of
  isolated Complex IV deficiency, in contrast to the more common assembly-factor
  defects. The biochemical phenotype (isolated Complex IV deficiency in muscle
  and fibroblasts) and the Leigh-like clinical picture parallel SURF1 disease.