COA8-Related COX Deficiency

Mendelian MONDO:0033652 Pathograph 15 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COA8-related COX deficiency (mitochondrial complex IV deficiency nuclear type 17, MC4DN17) is a nuclear form of isolated cytochrome c oxidase (COX, Complex IV) deficiency caused by biallelic loss-of-function variants in COA8 (formerly APOPT1), a Complex IV assembly/stability factor. The classic presentation is a cavitating leukoencephalopathy with a biphasic course (acute regression followed by stabilization), but the spectrum also includes a later-onset, myopathy-predominant phenotype with exercise intolerance, ragged-red fibers, ptosis, peripheral neuropathy, and hearing loss. It conforms to the conserved Complex IV assembly deficiency mechanism, with dominant central white matter and skeletal muscle involvement.

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2
Pathophys.
11
Phenotypes
15
Pathograph
1
Genes
1
Variants
1
Medical Actions
⚙

Pathophysiology

2
COA8 Loss and Defective Complex IV Assembly
Biallelic loss-of-function COA8 variants remove a Complex IV assembly/stability factor, preventing maturation or maintenance of a functional COX holoenzyme.
COA8 hgnc:20492 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves decreased COA8 (hgnc:20492). hgnc:20492 is a gene from the HUGO Gene Nomenclature Committee. ↓ DECREASED
mitochondrial respiratory chain complex IV assembly GO:0033617 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. ↓ DECREASED
Downstream
Impaired Terminal Electron Transfer and ATP Synthesis Failure to assemble or stabilize the holoenzyme abolishes terminal electron transfer.
Decreased Complex IV Activity Reduced COX holoenzyme directly produces decreased Complex IV activity in patient muscle.
Show evidence (2 references)
PMID:38098475 SUPPORT Human Clinical
"Causative mutations are mainly identified in structural COX subunits or in proteins involved in the maturation and assembly of the COX holocomplex."
COA8 is an assembly/maturation factor whose loss produces isolated COX deficiency.
PMID:25175347 SUPPORT In Vitro
"Mutant fibroblasts showed reduced amount of COX holocomplex and higher levels of reactive oxygen species, which both shifted toward control values by expressing a recombinant, wild-type APOPT1 cDNA."
Complementation rescue directly links COA8/APOPT1 loss to reduced Complex IV holoenzyme.
Impaired Terminal Electron Transfer and ATP Synthesis
Loss of functional COX blocks electron transfer from cytochrome c to oxygen and proton pumping, collapsing oxidative ATP synthesis, with prominent central white matter and skeletal muscle involvement.
skeletal muscle cell CL:0000188 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves skeletal muscle cell, annotated with cell of skeletal muscle (CL:0000188). CL:0000188 is a cell type from the Cell Ontology.
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 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. ↓ DECREASED ATP synthesis coupled electron transport GO:0042775 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased ATP synthesis coupled electron transport, annotated with mitochondrial ATP synthesis coupled electron transport (GO:0042775). GO:0042775 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Leukoencephalopathy Energy failure in central white matter produces cavitating leukoencephalopathy.
Ragged-red muscle fibers Bioenergetic deficit in skeletal muscle produces mitochondrial myopathy with ragged-red fibers.
Exercise intolerance Impaired oxidative phosphorylation in skeletal muscle limits exertional energy production.
Hearing impairment High-energy auditory tissues are vulnerable to Complex IV deficiency, producing hearing impairment.
Peripheral neuropathy Bioenergetic failure in peripheral nerves contributes to the neuropathy reported in COA8-related disease.
Ptosis Mitochondrial myopathy from impaired ATP synthesis can involve extraocular and eyelid muscles.
Seizures Central nervous system energy failure contributes to epilepsy in COA8-related COX deficiency.
Retinitis pigmentosa Retinal photoreceptors are energy-dependent cells vulnerable to Complex IV deficiency.
Amenorrhea Systemic mitochondrial dysfunction can disrupt endocrine or reproductive-axis function.
Dysarthria Neuromuscular involvement can impair motor speech.
Show evidence (7 references)
PMID:10545952 SUPPORT Other
"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 COA8-related COX deficiency.
PMID:25175347 SUPPORT Human Clinical
"All three subjects presented a distinctive brain MRI pattern characterized by cavitating leukodystrophy, predominantly in the posterior region of the cerebral hemispheres."
Supports cavitating leukodystrophy as the characteristic CNS outcome.
PMID:38098475 SUPPORT Human Clinical
"showed bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
Supports the neuromuscular and speech-motor manifestations of the later-onset phenotype.
+ 4 more references
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COA8-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

11
Ear 1
Hearing impairment HP:0000365 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hearing impairment (HP:0000365). HP:0000365 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"cramps and myalgia after exercise, and bilateral hearing loss emerged"
Documents bilateral hearing loss in COA8-related disease.
Eye 2
Ptosis HP:0000508 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ptosis (HP:0000508). HP:0000508 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
Documents bilateral ptosis on neurological examination in COA8-related disease.
Retinitis pigmentosa Rod-cone dystrophy HP:0000510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinitis pigmentosa, annotated with Rod-cone dystrophy (HP:0000510). HP:0000510 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"presented generalized epilepsy and retinitis pigmentosa at 10 years of age"
Documents retinitis pigmentosa in a COA8-deficient patient.
Genitourinary 1
Amenorrhea Secondary amenorrhea HP:0000869 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Secondary amenorrhea (HP:0000869). HP:0000869 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"presented secondary amenorrhea"
Documents secondary amenorrhea in COA8-deficient patients.
Nervous System 3
Peripheral neuropathy HP:0009830 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Peripheral neuropathy (HP:0009830). HP:0009830 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
Documents peripheral neuropathy on neurological examination in COA8-related disease.
Dysarthria HP:0001260 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dysarthria (HP:0001260). HP:0001260 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
Neurological examination explicitly documents mild dysarthria.
Seizures HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizures, annotated with Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"presented generalized epilepsy and retinitis pigmentosa at 10 years of age"
Documents generalized epilepsy in a COA8-deficient patient.
Constitutional 1
Exercise intolerance HP:0003546 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Exercise intolerance (HP:0003546). HP:0003546 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"cramps and myalgia after exercise, and bilateral hearing loss emerged"
Documents exercise-related cramps/myalgia in COA8-related myopathy.
Other 3
Leukoencephalopathy Cavitating leukodystrophy HP:0033369 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cavitating leukodystrophy (HP:0033369). HP:0033369 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Loss-of-function COA8 mutations have been associated with cavitating leukoencephalopathy with COX deficiency in 9 reported individuals."
Documents cavitating leukoencephalopathy as the classic COA8-related phenotype.
Decreased Complex IV Activity Decreased activity of mitochondrial complex IV HP:0008347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Decreased activity of mitochondrial complex IV (HP:0008347). HP:0008347 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers."
Muscle biopsy directly demonstrates reduced Complex IV activity.
Ragged-red muscle fibers HP:0003200 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ragged-red muscle fibers (HP:0003200). HP:0003200 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers."
Documents ragged-red fibers and reduced COX staining in COA8-related mitochondrial myopathy.
🧬

Genetic Associations

1
COA8 pathogenic variants causing COX deficiency
Gene: COA8 hgnc:20492 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is COA8 (hgnc:20492). hgnc:20492 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands."
Identifies a homozygous loss-of-function COA8 variant in affected siblings.
Variants (1)
COA8 c.170_173dupGACC (p.Pro59fs)
Gene: COA8 hgnc:20492 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COA8 (hgnc:20492). hgnc:20492 is a gene from the HUGO Gene Nomenclature Committee.
A homozygous COA8 frameshift duplication identified in an Italian familial case of mitochondrial myopathy with COX deficiency.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands."
Identifies the specific homozygous COA8 loss-of-function variant.
💊

Medical Actions

1
Supportive and Metabolic Care
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
No curative therapy; supportive management of myopathy, seizures, hearing loss, and metabolic decompensation.
📊

Prevalence

1
Unspecified population
Isolated COX (Complex IV) deficiency overall is the second most frequent isolated respiratory chain defect; COA8-related disease is a rare cause, reported in a small number of individuals.
Show evidence (1 reference)
PMID:38098475 SUPPORT Human Clinical
"Isolated mitochondrial respiratory chain Complex IV (Cytochrome c Oxidase or COX) deficiency is the second most frequent isolated respiratory chain defect."
Establishes that isolated COX/Complex IV deficiency is the second most frequent isolated respiratory chain defect.
{ }

Source YAML

click to show 
name: COA8-Related COX Deficiency
category: Mendelian
creation_date: "2026-05-30T00:00:00Z"
synonyms:
- COA8 deficiency
- APOPT1-related COX deficiency
- Mitochondrial complex IV deficiency, nuclear type 17
- MC4DN17
- Cavitating leukoencephalopathy with COX deficiency
description: >
  COA8-related COX deficiency (mitochondrial complex IV deficiency nuclear type
  17, MC4DN17) is a nuclear form of isolated cytochrome c oxidase (COX, Complex
  IV) deficiency caused by biallelic loss-of-function variants in COA8 (formerly
  APOPT1), a Complex IV assembly/stability factor. The classic presentation is a
  cavitating leukoencephalopathy with a biphasic course (acute regression
  followed by stabilization), but the spectrum also includes a later-onset,
  myopathy-predominant phenotype with exercise intolerance, ragged-red fibers,
  ptosis, peripheral neuropathy, and hearing loss. It conforms to the conserved
  Complex IV assembly deficiency mechanism, with dominant central white matter
  and skeletal muscle involvement.
disease_term:
  preferred_term: COA8-related COX deficiency (MC4DN17)
  term:
    id: MONDO:0033652
    label: mitochondrial complex IV deficiency, nuclear type 17
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
prevalence:
- notes: >
    Isolated COX (Complex IV) deficiency overall is the second most frequent
    isolated respiratory chain defect; COA8-related disease is a rare cause,
    reported in a small number of individuals.
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Isolated mitochondrial respiratory chain Complex IV (Cytochrome c Oxidase or COX) deficiency is the second most frequent isolated respiratory chain defect.
    explanation: Establishes that isolated COX/Complex IV deficiency is the second most frequent isolated respiratory chain defect.
pathophysiology:
- name: COA8 Loss and Defective Complex IV Assembly
  conforms_to: "complex_iv_assembly_deficiency#Complex IV Biogenesis Failure"
  description: >
    Biallelic loss-of-function COA8 variants remove a Complex IV
    assembly/stability factor, preventing maturation or maintenance of a
    functional COX holoenzyme.
  gene:
    preferred_term: COA8
    modifier: DECREASED
    term:
      id: hgnc:20492
      label: COA8
  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:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Causative mutations are mainly identified in structural COX subunits or in proteins involved in the maturation and assembly of the COX holocomplex.
    explanation: COA8 is an assembly/maturation factor whose loss produces isolated COX deficiency.
  - reference: PMID:25175347
    reference_title: "Mutations in APOPT1, encoding a mitochondrial protein, cause cavitating leukoencephalopathy with cytochrome c oxidase deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Mutant fibroblasts showed reduced amount of COX holocomplex and higher
      levels of reactive oxygen species, which both shifted toward control
      values by expressing a recombinant, wild-type APOPT1 cDNA.
    explanation: Complementation rescue directly links COA8/APOPT1 loss to reduced Complex IV holoenzyme.
  downstream:
  - target: Impaired Terminal Electron Transfer and ATP Synthesis
    causal_link_type: DIRECT
    description: Failure to assemble or stabilize the holoenzyme abolishes terminal electron transfer.
  - target: Decreased Complex IV Activity
    causal_link_type: DIRECT
    description: Reduced COX holoenzyme directly produces decreased Complex IV activity in patient muscle.
- name: Impaired Terminal Electron Transfer and ATP Synthesis
  conforms_to: "complex_iv_assembly_deficiency#Impaired Terminal Electron Transfer and ATP Synthesis"
  description: >
    Loss of functional COX blocks electron transfer from cytochrome c to oxygen
    and proton pumping, collapsing oxidative ATP synthesis, with prominent
    central white matter and skeletal muscle involvement.
  cell_types:
  - preferred_term: skeletal muscle cell
    term:
      id: CL:0000188
      label: cell of skeletal muscle
  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: OTHER
    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 COA8-related COX deficiency.
  - reference: PMID:25175347
    reference_title: "Mutations in APOPT1, encoding a mitochondrial protein, cause cavitating leukoencephalopathy with cytochrome c oxidase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All three subjects presented a distinctive brain MRI pattern characterized
      by cavitating leukodystrophy, predominantly in the posterior region of the
      cerebral hemispheres.
    explanation: Supports cavitating leukodystrophy as the characteristic CNS outcome.
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      showed bilateral ptosis, muscle weakness, peripheral neuropathy, mild
      dysarthria and dysphonia
    explanation: Supports the neuromuscular and speech-motor manifestations of the later-onset phenotype.
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers.
    explanation: Supports decreased Complex IV activity and ragged-red muscle fibers.
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: cramps and myalgia after exercise, and bilateral hearing loss emerged
    explanation: Supports exercise intolerance and bilateral hearing loss.
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented generalized epilepsy and retinitis pigmentosa at 10 years of age
    explanation: Supports epilepsy and retinitis pigmentosa in COA8-related disease.
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented secondary amenorrhea
    explanation: Supports secondary amenorrhea in affected siblings.
  downstream:
  - target: Leukoencephalopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Energy failure in central white matter produces cavitating leukoencephalopathy.
  - target: Ragged-red muscle fibers
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Bioenergetic deficit in skeletal muscle produces mitochondrial myopathy with ragged-red fibers.
  - target: Exercise intolerance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Impaired oxidative phosphorylation in skeletal muscle limits exertional energy production.
  - target: Hearing impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: High-energy auditory tissues are vulnerable to Complex IV deficiency, producing hearing impairment.
  - target: Peripheral neuropathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Bioenergetic failure in peripheral nerves contributes to the neuropathy reported in COA8-related disease.
  - target: Ptosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Mitochondrial myopathy from impaired ATP synthesis can involve extraocular and eyelid muscles.
  - target: Seizures
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Central nervous system energy failure contributes to epilepsy in COA8-related COX deficiency.
  - target: Retinitis pigmentosa
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Retinal photoreceptors are energy-dependent cells vulnerable to Complex IV deficiency.
  - target: Amenorrhea
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Systemic mitochondrial dysfunction can disrupt endocrine or reproductive-axis function.
  - target: Dysarthria
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Neuromuscular involvement can impair motor speech.
phenotypes:
- name: Leukoencephalopathy
  description: Cavitating leukoencephalopathy, the classic CNS phenotype of COA8 deficiency.
  phenotype_term:
    preferred_term: Cavitating leukodystrophy
    term:
      id: HP:0033369
      label: Cavitating leukodystrophy
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Loss-of-function COA8 mutations have been associated with cavitating leukoencephalopathy with COX deficiency in 9 reported individuals.
    explanation: Documents cavitating leukoencephalopathy as the classic COA8-related phenotype.
- name: Decreased Complex IV Activity
  description: Diffusely reduced cytochrome-c oxidase activity in affected muscle.
  phenotype_term:
    preferred_term: Decreased activity of mitochondrial complex IV
    term:
      id: HP:0008347
      label: Decreased activity of mitochondrial complex IV
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers.
    explanation: Muscle biopsy directly demonstrates reduced Complex IV activity.
- name: Ragged-red muscle fibers
  description: Ragged-red fibers and reduced COX staining on muscle biopsy.
  phenotype_term:
    preferred_term: Ragged-red muscle fibers
    term:
      id: HP:0003200
      label: Ragged-red muscle fibers
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers.
    explanation: Documents ragged-red fibers and reduced COX staining in COA8-related mitochondrial myopathy.
- name: Exercise intolerance
  description: Exercise-induced cramps and myalgia in the myopathy-predominant phenotype.
  phenotype_term:
    preferred_term: Exercise intolerance
    term:
      id: HP:0003546
      label: Exercise intolerance
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: cramps and myalgia after exercise, and bilateral hearing loss emerged
    explanation: Documents exercise-related cramps/myalgia in COA8-related myopathy.
- name: Hearing impairment
  description: Bilateral hearing loss.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: cramps and myalgia after exercise, and bilateral hearing loss emerged
    explanation: Documents bilateral hearing loss in COA8-related disease.
- name: Peripheral neuropathy
  description: Peripheral neuropathy in the myopathy-predominant phenotype.
  phenotype_term:
    preferred_term: Peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
    explanation: Documents peripheral neuropathy on neurological examination in COA8-related disease.
- name: Ptosis
  description: Bilateral ptosis.
  phenotype_term:
    preferred_term: Ptosis
    term:
      id: HP:0000508
      label: Ptosis
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
    explanation: Documents bilateral ptosis on neurological examination in COA8-related disease.
- name: Dysarthria
  description: Mild dysarthria in the myopathy-predominant COA8 phenotype.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia"
    explanation: Neurological examination explicitly documents mild dysarthria.
- name: Seizures
  description: Generalized epilepsy reported in COA8-related disease.
  phenotype_term:
    preferred_term: Seizures
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented generalized epilepsy and retinitis pigmentosa at 10 years of age
    explanation: Documents generalized epilepsy in a COA8-deficient patient.
- name: Retinitis pigmentosa
  description: Retinitis pigmentosa reported in a COA8-deficient patient.
  phenotype_term:
    preferred_term: Retinitis pigmentosa
    term:
      id: HP:0000510
      label: Rod-cone dystrophy
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented generalized epilepsy and retinitis pigmentosa at 10 years of age
    explanation: Documents retinitis pigmentosa in a COA8-deficient patient.
- name: Amenorrhea
  description: Secondary amenorrhea reported in COA8-deficient sisters.
  phenotype_term:
    preferred_term: Secondary amenorrhea
    term:
      id: HP:0000869
      label: Secondary amenorrhea
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: presented secondary amenorrhea
    explanation: Documents secondary amenorrhea in COA8-deficient patients.
genetic:
- name: COA8 pathogenic variants causing COX deficiency
  gene_term:
    preferred_term: COA8
    term:
      id: hgnc:20492
      label: COA8
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:38098475
      reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands.
      explanation: Homozygous COA8 variant in affected siblings indicates autosomal recessive inheritance.
  variants:
  - name: COA8 c.170_173dupGACC (p.Pro59fs)
    description: >
      A homozygous COA8 frameshift duplication identified in an Italian familial
      case of mitochondrial myopathy with COX deficiency.
    gene:
      preferred_term: COA8
      term:
        id: hgnc:20492
        label: COA8
    evidence:
    - reference: PMID:38098475
      reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands.
      explanation: Identifies the specific homozygous COA8 loss-of-function variant.
  features: >
    Biallelic loss-of-function COA8 variants cause isolated COX deficiency,
    classically cavitating leukoencephalopathy and, in a familial report, a
    prominent mitochondrial myopathy phenotype.
  evidence:
  - reference: PMID:38098475
    reference_title: "Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands.
    explanation: Identifies a homozygous loss-of-function COA8 variant in affected siblings.
treatments:
- name: Supportive and Metabolic Care
  description: >
    No curative therapy; supportive management of myopathy, seizures, hearing
    loss, and metabolic decompensation.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care