COX15-Related COX Deficiency

Mendelian MONDO:0014051 Pathograph 29 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COX15-related COX deficiency is an autosomal recessive mitochondrial disease caused by biallelic variants affecting heme A synthase. Reduced heme A availability impairs complex IV biogenesis and respiratory function. The clinical spectrum includes rapidly fatal neonatal cardioencephalomyopathy and more slowly progressive Leigh syndrome spectrum with developmental impairment, movement disorders and variable cardiac involvement. Residual enzyme activity and assembled complex IV vary between tissues and alleles. Muscle-specific mouse models reveal additional mitochondrial quality-control defects and experimental intervention responses that have not established efficacy in patients.

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1
Inheritance
7
Pathophys.
33
Phenotypes
2
Gaps
29
Pathograph
1
Genes
12
Medical Actions
4
Models
13
References
👪

Inheritance

1
Autosomal recessive
Biallelic COX15 variants cause disease; the recurrence risks below assume both parents carry the familial pathogenic variants.
Show evidence (2 references)
PMID:32232962 SUPPORT Human Clinical
"Through linkage analysis and whole-exome sequencing, we identified a homozygous p.R217W mutation"
The homozygous variant segregated in the consanguineous kindred.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"If both parents are known to be ... heterozygous ... for an LSS-related ... pathogenic variant ... each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic ... carrier ... and a 25% chance of being unaffected and not a carrier."
Standard recessive recurrence risks apply when both parents carry the relevant COX15 pathogenic variants.
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Discussions and Knowledge Gaps

2
What determines cardiac versus neurological severity and the relationship to residual complex IV activity?
INTERPRETATION OPEN cox15-clinical-biochemical-variability
Marked tissue differences, a patient with normal fibroblast holoenzyme abundance, and clinical differences within families argue against a simple universal activity threshold or a reliable genotype-severity rule. The small case literature cannot establish penetrance or manifestation frequencies.
Show evidence (2 references)
PMID:15863660 SUPPORT Human Clinical
"The clinical and biochemical phenotypes in COX15 defects are more heterogeneous than in other conditions associated with COX deficiency"
The early long-surviving case establishes biochemical and clinical heterogeneity.
PMID:40439182 SUPPORT Human Clinical
"However, additional cases are needed to confirm a genotype–phenotype correlation."
The recent report explicitly limits genotype-based prognosis.
Do the muscle-model quality-control defects and intervention responses apply to human COX15 disease?
HUMAN MODEL MISMATCH OPEN cox15-quality-control-translation
Conditional muscle deletion reveals impaired flux and damaged mitochondrial accumulation. Rapamycin, AICAR, bezafibrate, rilmenidine and OPA1 overexpression have different biochemical and motor effects; none of these experiments demonstrates benefit in human COX15 disease or reproduces its complete neurological and cardiac spectrum.
Show evidence (4 references)
PMID:21723506 SUPPORT Model Organism
"Contrariwise, and in spite of partial biochemical recovery, we found no change by treadmill test in ACTA-Cox15−/− mice"
Biochemical improvement did not yield detectable motor benefit in the Cox15 model.
PMID:21723506 SUPPORT Model Organism
"No such effect was obtained by treating both Surf1(-/-) and Cox15(-/-) mice with the pan-PPAR agonist bezafibrate, which instead showed adverse effects in either model."
The tested intervention failed and caused adverse effects in mice.
PMID:30309855 SUPPORT Model Organism
"Although rilmenidine increased the autophagic flux ... it had no effect on the motor performance of Cox15 sm/sm mice ... and failed to improve muscle morphology"
Increasing flux alone did not improve the model phenotype.
+ 1 more reference
⚙

Pathophysiology

7
COX15 Heme A Synthase Deficiency
Biallelic variants reduce COX15 enzymatic function through allele-dependent defects in protein stability or catalytic properties. COX15 is a heme biosynthetic enzyme rather than a structural subunit of the mature respiratory complex.
COX15 hgnc:2263 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COX15 (hgnc:2263). hgnc:2263 is a gene from the HUGO Gene Nomenclature Committee.
heme A synthase activity GO:0120547 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased heme A synthase activity (GO:0120547). GO:0120547 is a molecular function from the Gene Ontology.
Experimental models
Yeast COX15 pathogenic-variant model OTHER Homologous pathogenic substitution compromises catalytic function.
Downstream
Reduced Heme A Availability Reduced heme A synthase function restricts synthesis of the complex IV heme cofactor.
Show evidence (2 references)
PMID:12474143 SUPPORT In Vitro
"This splicing error introduces a frameshift and a premature stop codon, resulting in an unstable mRNA and, likely, a null allele."
The founding splice allele reduces functional COX15 through abnormal splicing and transcript instability.
PMID:26940873 SUPPORT In Vitro
"COX15 protein in the S344P/S151X cells was intrinsically unstable. However, steady-state levels of COX15 protein in cells with R217W/C447–3G were comparable with the control"
Patient fibroblast experiments show that deficient function need not entail reduced protein abundance.
Reduced Heme A Availability
Heme A production is impaired. In the founding patient, heart mitochondria accumulated heme O, whereas patient fibroblasts did not show a detectable heme O peak; accumulation should not be assumed in every tissue.
heme A biosynthetic process GO:0006784 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased heme A biosynthetic process (GO:0006784). GO:0006784 is a biological process from the Gene Ontology.
Experimental models
Patient fibroblast complementation CELL LINE Wild-type COX15 expression raises cellular heme A.
Downstream
Deficient Complex IV Biogenesis Limited heme A compromises maturation and assembly of functional complex IV.
Show evidence (2 references)
PMID:12474143 SUPPORT Human Clinical
"Patient N heart mitochondria contained markedly reduced levels of heme A and increased levels of heme O"
The founding patient heart shows impaired heme A production and accumulated precursor.
PMID:12474143 SUPPORT In Vitro
"Low heme A was also detected in patient fibroblasts; however, no heme O peak could be detected"
The heme profile differs between heart and cultured fibroblasts.
Deficient Complex IV Biogenesis
Insufficient cofactor supply can reduce the amount of assembled complex IV. This is allele- and tissue-dependent: normal amounts of assembled enzyme were reported in fibroblasts of a slowly progressive Leigh patient despite reduced activity.
mitochondrial respiratory chain complex IV assembly GO:0033617 ↓ DECREASED 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.
Experimental models
Patient fibroblast complementation CELL LINE Patient cells reproduce deficient assembly and partial complementation rescue.
Animal models
Cox15 knockout with OPA1 overexpression Mouse rescues OPA1 overexpression stabilizes residual complex IV and supercomplexes.
Downstream
Reduced Complex IV Respiratory Capacity Deficient maturation or activity lowers the functional capacity of terminal respiratory electron transfer.
Show evidence (2 references)
PMID:12474143 SUPPORT In Vitro
"These results suggest that reduced availability of heme A stalls the assembly of COX."
Heme measurements and complementation support a cofactor-dependent assembly defect.
PMID:15863660 SUPPORT In Vitro
"COX deficiency was mild in muscle and a normal amount of fully assembled COX was present in cultured fibroblasts."
A patient-cell exception limits a universal claim that all COX15 variants abolish assembly.
Reduced Complex IV Respiratory Capacity
Complex IV activity is reduced with variable residual function and marked tissue differences. This compromises oxidative metabolism and is associated with cardiac, neurological and metabolic disease.
mitochondrial electron transport, cytochrome c to oxygen GO:0006123 ↓ DECREASED 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.
Animal models
Muscle-specific Cox15 knockout mouse Mouse partially recapitulates The conditional knockout reproduces severe muscle COX deficiency.
Downstream
Hypertrophic cardiomyopathy The cardiac respiratory defect contributes to cardiomyopathy through incompletely resolved intermediates.
Lactic acidosis Deficient oxidative metabolism is associated with lactate accumulation and acidosis.
Increased CSF lactate Impaired oxidative metabolism can be accompanied by cerebrospinal fluid lactate accumulation; the tissue-level intermediates are not resolved by the clinical report.
Developmental regression Impaired mitochondrial energy metabolism contributes to neurological deterioration; intermediate injury mechanisms remain incompletely resolved.
Bilateral basal ganglia lesions The neurological phenotype can include bilateral Leigh-pattern lesions.
Disorganized Mitochondrial Cristae Severe respiratory dysfunction is associated with disrupted mitochondrial ultrastructure in the muscle model.
Impaired Autophagic Flux Muscle-specific COX15 loss is associated with impaired autophagic clearance; the intervening signaling mechanism is unresolved.
Show evidence (2 references)
PMID:12474143 SUPPORT In Vitro
"COX activity and the total amount of fully assembled enzyme were reduced by 50%–70% in patient fibroblasts."
The founding patient cells retain substantial complex IV activity; deficiency is not equivalent to complete ATP collapse.
PMID:21412973 SUPPORT Human Clinical
"Postmortem cardiac muscle study showed marked complex IV deficiency. In contrast, complex IV activity was only slightly decreased in the skeletal muscle."
Cardiac and skeletal-muscle activities can be substantially discordant.
Disorganized Mitochondrial Cristae
Abnormal mitochondrial cristae occur in affected cardiac tissue and are reproduced in Cox15-deficient mouse muscle. OPA1 overexpression improves cristae organization in the model, supporting a potentially modifiable structural component of respiratory dysfunction.
inner mitochondrial membrane organization GO:0007007 ⚠ ABNORMAL Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal inner mitochondrial membrane organization (GO:0007007). GO:0007007 is a biological process from the Gene Ontology.
Animal models
Cox15 knockout with OPA1 overexpression Mouse rescues OPA1 overexpression improves cristae organization.
Show evidence (2 references)
PMID:26039449 SUPPORT Model Organism
"While Cox15sm/sm muscle mitochondria showed profound cristae disorganization and prominent vacuolar degeneration of the inner mitochondrial compartment"
Electron microscopy shows disrupted cristae in the muscle-specific mouse model.
PMID:12474143 SUPPORT Human Clinical
"greatly increased numbers of mitochondria with abnormal shapes, abnormally arranged cristae, and numerous matrix densities"
Electron microscopy of the founding patient heart documents mitochondrial ultrastructural abnormalities.
Impaired Autophagic Flux
Mechanism confidence: Provisional
Autophagic flux is blocked in skeletal muscle of the conditional mouse model. This has not been demonstrated in COX15 patient tissues. Basal mTOR signaling was not significantly increased in the model, so constitutive mTOR activation is not established as the lesion.
autophagy GO:0006914 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased autophagy (GO:0006914). GO:0006914 is a biological process from the Gene Ontology.
Animal models
Muscle-specific Cox15 knockout mouse Mouse recapitulates Colchicine experiments reveal deficient clearance in the mutant muscle.
Downstream
Accumulation of Damaged Mitochondria Reduced clearance may permit damaged organelles to accumulate in mouse skeletal muscle.
Show evidence (2 references)
PMID:30309855 SUPPORT Model Organism
"Colchicine increased LC3‐II in WT but not in Cox15 sm/sm muscles, suggesting a block of the autophagic flux in the latter."
The flux experiment distinguishes impaired clearance from increased steady-state autophagosome abundance.
PMID:30309855 SUPPORT Model Organism
"While mTOR signaling was not significantly changed in naïve Cox15 sm/sm versus WT mice, autophagy flux was reduced"
Impaired flux does not imply basal mTOR overactivation.
Accumulation of Damaged Mitochondria
Mechanism confidence: Provisional
The muscle-specific Cox15 model accumulates damaged mitochondria. Coordinated restoration of autophagic flux and lysosomal biogenesis improves clearance in rapamycin-treated mice; applicability to patient disease is unresolved.
Show evidence (2 references)
PMID:30309855 SUPPORT Model Organism
"A block of the autophagic flux may result in reduced clearance of dysfunctional mitochondria in Cox15 sm/sm muscle."
The study proposes defective clearance as a contributor to mitochondrial accumulation in mouse muscle.
PMID:30309855 SUPPORT Model Organism
"Our results suggest that rapamycin induced the removal of damaged mitochondria, as demonstrated by correction of muscle morphology, reduction of mtDNA amount, normalization of CS activity, and increased mitochondrial respiration."
Multiple model readouts support the organelle-clearance interpretation.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COX15-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.
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Phenotypes

33
Cardiovascular 1
Hypertrophic cardiomyopathy HP:0001639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertrophic cardiomyopathy (HP:0001639). HP:0001639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:21412973 SUPPORT Human Clinical
"a female infant with a neonatal rapidly progressive fatal course characterized by microcephaly, encephalopathy, persistent lactic acidosis, and hypertrophic cardiomyopathy."
The COX15 clinical report directly documents this finding.
Digestive 2
Pseudobulbar paralysis HP:0007024 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pseudobulbar paralysis (HP:0007024). HP:0007024 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32232962 SUPPORT Human Clinical
"Toward the end of their second year, both patients developed progressive quadriparesis, convulsions, and pseudobulbar palsy."
The COX15 clinical report directly documents this finding.
Hepatic steatosis HP:0001397 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hepatic steatosis (HP:0001397). HP:0001397 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"COX15 ... Seizures, retinopathy ... HCM, hepatic steatosis ... Complex IV deficiency"
The COX15 row of the Leigh-spectrum table specifically lists this manifestation; pooled Leigh-spectrum frequencies are not applied.
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:32232962 SUPPORT Human Clinical
"one of the two affected siblings had severe hypertrophic obstructive cardiomyopathy, hearing loss, and no visual response."
The COX15 clinical report directly documents this finding.
Eye 5
Nystagmus HP:0000639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nystagmus (HP:0000639). HP:0000639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32232962 SUPPORT Human Clinical
"two siblings of consanguineous kindred presented in infancy with a syndrome of hypotonia, nystagmus, psychomotor retardation, and pyramidal signs."
The COX15 clinical report directly documents this finding.
Visual impairment HP:0000505 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Visual impairment (HP:0000505). HP:0000505 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32232962 SUPPORT Human Clinical
"one of the two affected siblings had severe hypertrophic obstructive cardiomyopathy, hearing loss, and no visual response."
The COX15 clinical report directly documents this finding.
Esotropia HP:0000565 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Esotropia (HP:0000565). HP:0000565 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia"
The COX15 clinical report directly documents this finding.
Retinopathy HP:0000488 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Retinopathy (HP:0000488). HP:0000488 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"COX15 ... Seizures, retinopathy ... HCM, hepatic steatosis ... Complex IV deficiency"
The COX15 row of the Leigh-spectrum table specifically lists this manifestation; pooled Leigh-spectrum frequencies are not applied.
Optic atrophy HP:0000648 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Optic atrophy (HP:0000648). HP:0000648 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT REVIEW SYNTHESIS Human Clinical
"Additional features include hypertrophic cardiomyopathy, optic atrophy, hearing impairment, and FTT"
This passage summarizes earlier COX15 cases rather than an examination finding in the two newly reported siblings.
Head and Neck 3
Microcephaly HP:0000252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcephaly (HP:0000252). HP:0000252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:21412973 SUPPORT Human Clinical
"a neonatal rapidly progressive fatal course characterized by microcephaly, encephalopathy, persistent lactic acidosis, and hypertrophic cardiomyopathy"
The COX15 clinical report directly documents this finding.
Midface retrusion HP:0011800 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Midface retrusion (HP:0011800). HP:0011800 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:12474143 SUPPORT Human Clinical
"Shortly after birth, patient N presented with midfacial hypoplasia, lactic acidosis, seizures, and hypotonia."
The COX15 clinical report directly documents this finding.
Coarse facial features HP:0000280 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Coarse facial features (HP:0000280). HP:0000280 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis."
The COX15 clinical report directly documents this finding.
Integument 1
Hirsutism HP:0001007 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hirsutism (HP:0001007). HP:0001007 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis."
The COX15 clinical report directly documents this finding.
Limbs 1
Brachydactyly HP:0001156 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Brachydactyly (HP:0001156). HP:0001156 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis."
The COX15 clinical report directly documents this finding.
Metabolism 3
Lactic acidosis HP:0003128 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:21412973 SUPPORT Human Clinical
"persistent lactic acidosis, and hypertrophic cardiomyopathy. Postmortem cardiac muscle study showed marked complex IV deficiency."
The COX15 clinical report directly documents this finding.
Increased CSF lactate HP:0002490 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased CSF lactate (HP:0002490). HP:0002490 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33746038 SUPPORT Human Clinical
"a male newborn with hypertrophic cardiomyopathy and serum and cerebrospinal fluid hyperlacticaemia"
The COX15 clinical report directly documents this finding.
Hypertriglyceridemia HP:0002155 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertriglyceridemia (HP:0002155). HP:0002155 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Both siblings had elevated blood lactate (6.0 mmol/L in patient 1 and 4.5 mmol/L in patient 2; range, 0.6–2.1 mmol/L), liver enzymes, and triglycerides, with normal creatine kinase and carnitine levels."
The COX15 clinical report directly documents this finding.
Musculoskeletal 4
Hypotonia HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:26959537 SUPPORT Human Clinical
"Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression."
The COX15 clinical report directly documents this finding.
Thoracic kyphosis HP:0002942 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thoracic kyphosis (HP:0002942). HP:0002942 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis."
The COX15 clinical report directly documents this finding.
Spasticity HP:0001257 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spasticity (HP:0001257). HP:0001257 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia"
The COX15 clinical report directly documents this finding.
Osteopenia HP:0000938 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Osteopenia (HP:0000938). HP:0000938 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Hand X‐ray demonstrated diffuse osteopenia with broadening of the metacarpals and phalanges"
The COX15 clinical report directly documents this finding.
Nervous System 10
Global developmental delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"was evaluated for global developmental delay (GDD) and failure to thrive (FTT)."
The 2025 COX15 sibling report explicitly identifies global developmental delay.
Developmental regression HP:0002376 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Developmental regression (HP:0002376). HP:0002376 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:26959537 SUPPORT Human Clinical
"Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression."
The COX15 clinical report directly documents this finding.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Onset of nuclear ... gene ... -encoded LSS is typically in infancy or early childhood with sudden neurodevelopmental regression."
General Leigh-spectrum context supports the clinical interpretation, without assigning pooled LSS frequencies to COX15.
Tremor HP:0001337 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tremor (HP:0001337). HP:0001337 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:26959537 SUPPORT Human Clinical
"Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression."
The COX15 clinical report directly documents this finding.
Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:12474143 SUPPORT Human Clinical
"Shortly after birth, patient N presented with midfacial hypoplasia, lactic acidosis, seizures, and hypotonia."
The COX15 clinical report directly documents this finding.
Tetraparesis HP:0002273 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tetraparesis (HP:0002273). HP:0002273 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32232962 SUPPORT Human Clinical
"Toward the end of their second year, both patients developed progressive quadriparesis, convulsions, and pseudobulbar palsy."
The COX15 clinical report directly documents this finding.
Generalized dystonia HP:0007325 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Generalized dystonia (HP:0007325). HP:0007325 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Both patients developed progressive generalized dystonia at ages 12 and 14, leading to wheelchair dependence in the younger sister and limited fine motor skills in the older sibling."
The COX15 clinical report directly documents this finding.
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:40439182 SUPPORT Human Clinical
"Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia"
The COX15 clinical report directly documents this finding.
Hyperreflexia HP:0001347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperreflexia (HP:0001347). HP:0001347 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia"
The COX15 clinical report directly documents this finding.
Bilateral basal ganglia lesions HP:0007146 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bilateral basal ganglia lesions (HP:0007146). HP:0007146 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"symmetrical hyperintensity in the bilateral cerebellar white matter, middle cerebellar peduncles, and putamen, along with volume loss and globus pallidi blooming."
The COX15 clinical report directly documents this finding.
Cerebellar atrophy HP:0001272 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebellar atrophy (HP:0001272). HP:0001272 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"Coronal T2 image revealing symmetric hyperintensity in the cerebellar white matter (solid arrows) along with volume loss (dotted arrows)"
The COX15 clinical report directly documents this finding.
Growth 2
Short stature HP:0004322 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis."
The COX15 clinical report directly documents this finding.
Failure to thrive HP:0001508 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Failure to thrive (HP:0001508). HP:0001508 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"She had bulbar dysfunction and FTT requiring gastrostomy tube insertion at 2 years of age."
The COX15 clinical report directly documents this finding.
🧬

Genetic Associations

1
COX15 pathogenic variants
Gene: COX15 hgnc:2263 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is COX15 (hgnc:2263). hgnc:2263 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive
Show evidence (4 references)
PMID:12474143 SUPPORT Human Clinical
"Mutation analysis of COX15 in the patient identified a missense mutation (C700T) on one allele, changing a conserved arginine to tryptophan (R217W), and a splice-site mutation in intron 3 on the other allele (C447-3G), resulting in a deletion of exon 4."
The original report establishes two different variant classes and records the historical numbering.
PMID:33746038 SUPPORT Human Clinical
"c.232G > A; p.(Gly78Arg), classified as likely pathogenic, and c.452C > G; p.(Ser151Ter), as pathogenic"
Retains the reported distinction between likely pathogenic and pathogenic variants.
PMID:40439182 SUPPORT Human Clinical
"A homozygous likely pathogenic variant in c.T1019C (p.L340P) in the exon 8 of COX15 gene was identified."
The 2025 siblings extend the missense spectrum; the report classifies the variant as likely pathogenic.
+ 1 more reference
💊

Medical Actions

12
Multidisciplinary supportive 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. NCIT:C15747
Platform: Other
Care aims to improve function, quality of life and complication management, with neurological, cardiological, respiratory, nutritional, sensory and developmental support. The reviewed sources do not establish a COX15-specific disease-modifying treatment.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Supportive care to improve quality of life, maximize function, and reduce complications is recommended."
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
Cardiac care and surveillance
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. NCIT:C15747
Platform: Other
Cardiologist-directed treatment of cardiomyopathy or arrhythmia and longitudinal cardiac assessment are appropriate. A normal early echocardiogram does not guarantee that cardiomyopathy will not develop.
Target Phenotypes: Hypertrophic cardiomyopathy HP:0001639 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Hypertrophic cardiomyopathy (HP:0001639). HP:0001639 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Anticongestive therapy or antiarrhythmic therapy may be required ... treatment should be managed by a cardiologist."
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
Nutrition and feeding support
Action: Nutritional SupportNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Nutritional Support (NCIT:C15433). NCIT:C15433 is a clinical intervention from the NCI Thesaurus. NCIT:C15433
Platform: Other
Assess growth, swallow safety and nutritional intake. Feeding therapy, supplementation and gastrostomy may be needed; gastrostomy was used in the younger 2025 sibling.
Target Phenotypes: Failure to thrive HP:0001508 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Failure to thrive (HP:0001508). HP:0001508 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"gastrostomy tube placement may improve nutritional intake for those w/persistent feeding issues, choking, or aspiration risk due to dysphagia"
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
PMID:40439182 SUPPORT Human Clinical
"She had bulbar dysfunction and FTT requiring gastrostomy tube insertion at 2 years of age."
Direct COX15 case evidence supports the need for enteral feeding in some patients.
Seizure management
Action: Anticonvulsant TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Anticonvulsant Therapy (NCIT:C64172). NCIT:C64172 is a clinical intervention from the NCI Thesaurus. NCIT:C64172
Platform: Small molecule
Use neurologist-directed antiseizure therapy with mitochondrial drug-safety considerations. Sodium valproate should be avoided when possible; the absolute contraindication described for POLG disease is not a COX15-specific finding.
Target Phenotypes: Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Treatment w/ASM by experienced neurologist"
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Sodium valproate should be avoided if possible, because of its inhibitory effect on respiratory chain enzymes."
General Leigh-spectrum guidance qualifies valproate use; absolute contraindication is specifically described for POLG-related disease.
Dystonia management
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: Trihexyphenidyl CHEBI:9720 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses Trihexyphenidyl (CHEBI:9720). CHEBI:9720 is a therapeutic agent from Chemical Entities of Biological Interest. baclofen CHEBI:2972 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses baclofen (CHEBI:2972). CHEBI:2972 is a therapeutic agent from Chemical Entities of Biological Interest. tetrabenazine CHEBI:9467 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses tetrabenazine (CHEBI:9467). CHEBI:9467 is a therapeutic agent from Chemical Entities of Biological Interest. gabapentin CHEBI:42797 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses gabapentin (CHEBI:42797). CHEBI:42797 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Movement-disorder treatment can include individually selected oral agents and rehabilitation. GeneReviews lists benzhexol, baclofen, tetrabenazine and gabapentin; these recommendations do not establish a response in COX15 patients.
Target Phenotypes: Generalized dystonia HP:0007325 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Generalized dystonia (HP:0007325). HP:0007325 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Benzhexol, baclofen, tetrabenazine ... gabapentin may be useful, alone or in various combinations."
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
Rehabilitation and communication support
Action: Physical TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Physical Therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. NCIT:C15302
Platform: Behavioral / lifestyle
Physical and occupational therapy, mobility equipment and communication aids support function. The younger 2025 sibling used augmentative communication.
Target Phenotypes: Tetraparesis HP:0002273 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Tetraparesis (HP:0002273). HP:0002273 is a phenotype from the Human Phenotype Ontology. Generalized dystonia HP:0007325 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Generalized dystonia (HP:0007325). HP:0007325 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Equipment to prevent falling, maintain independent mobility as appropriate"
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
Metabolic and perioperative precautions
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. NCIT:C15747
Platform: Other
Minimize fasting and prevent catabolism during illness or procedures; consider perioperative glucose as appropriate, with individualized diet-related exceptions. Monitor respiratory status during anesthesia, avoid prolonged propofol exposure where possible, and avoid lactate-containing fluids in those at risk of lactic acidosis.
Target Phenotypes: Lactic acidosis HP:0003128 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Catabolism should be prevented by minimizing preoperative fasting and considering intravenous glucose perioperatively during prolonged anesthesia (unless the individual is on a ketogenic diet)."
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Prolonged propofol use during maintenance anesthesia may increase the risk of lactic acidosis."
General mitochondrial anesthesia caution.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Avoid lactate-containing agents (e.g., Ringer's lactate) in those at risk of lactic acidosis"
General mitochondrial fluid-selection precaution.
Genetic counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Platform: Other
Confirm parental segregation, explain autosomal recessive recurrence risks when both parents are carriers, and discuss reproductive testing after identification of the familial pathogenic variants.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Once the LSS-related ... pathogenic variant ... (s) have been identified in an affected family member, prenatal and ... preimplantation genetic testing ... are possible."
General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"If both parents are known to be ... heterozygous ... for an LSS-related ... pathogenic variant ... each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic ... carrier ... and a 25% chance of being unaffected and not a carrier."
Standard recessive recurrence risks apply when both parents carry the relevant COX15 pathogenic variants.
Experimental AICAR
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: acadesine CHEBI:28498 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses acadesine (CHEBI:28498). CHEBI:28498 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
AICAR partially improved complex IV biochemistry in muscle-specific Cox15-knockout mice, without detectable treadmill improvement. This does not establish patient efficacy.
Show evidence (1 reference)
PMID:21723506 SUPPORT Model Organism
"Contrariwise, and in spite of partial biochemical recovery, we found no change by treadmill test in ACTA-Cox15−/− mice"
Biochemical improvement did not yield detectable motor benefit in the Cox15 model.
Experimental bezafibrate
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: bezafibrate CHEBI:47612 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses bezafibrate (CHEBI:47612). CHEBI:47612 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Bezafibrate failed to correct the respiratory defect and caused toxicity in the tested mouse model. It is recorded as a negative preclinical result, not a recommended COX15 therapy.
Show evidence (1 reference)
PMID:21723506 SUPPORT Model Organism
"No such effect was obtained by treating both Surf1(-/-) and Cox15(-/-) mice with the pan-PPAR agonist bezafibrate, which instead showed adverse effects in either model."
The tested intervention failed and caused adverse effects in mice.
Experimental rapamycin
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: sirolimus CHEBI:9168 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses sirolimus (CHEBI:9168). CHEBI:9168 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Rapamycin improved autophagic flux, lysosomal biogenesis, mitochondrial clearance and motor performance in muscle-specific Cox15-knockout mice. Absolute complex IV specific activity remained unchanged, while the COX/citrate-synthase ratio increased as citrate synthase normalized. Treated mice remained impaired relative to wild type; human efficacy is unestablished.
Mechanism Target:
INHIBITS Impaired Autophagic Flux — Reduces the modeled block in autophagic flux; this is a mouse-system effect.
Show evidence (1 reference)
PMID:30309855 SUPPORT Model Organism
"rapamycin treatment was associated with an increase in the autophagic flux revealed by the addition of colchicine."
Direct flux measurements support the intervention effect in mouse skeletal muscle.
INHIBITS Accumulation of Damaged Mitochondria — Promotes removal of damaged mitochondria in the muscle-specific mouse model; patient efficacy remains unestablished.
Show evidence (1 reference)
PMID:30309855 SUPPORT Model Organism
"Our results suggest that rapamycin induced the removal of damaged mitochondria, as demonstrated by correction of muscle morphology, reduction of mtDNA amount, normalization of CS activity, and increased mitochondrial respiration."
The study interprets the convergent morphology, mitochondrial content and respiration measurements as improved mitochondrial clearance.
Show evidence (2 references)
PMID:30309855 SUPPORT Model Organism
"rapamycin treatment was associated with an increase in the autophagic flux revealed by the addition of colchicine."
Direct flux measurements support the intervention effect in mouse skeletal muscle.
PMID:30309855 SUPPORT Model Organism
"The specific activity of COX (cIV) was significantly lower in Cox15 sm/sm samples and remained unchanged under rapamycin treatment."
Distinguishes absolute activity from a ratio altered by normalization.
Experimental rilmenidine
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: Rilmenidine CHEBI:8862 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses Rilmenidine (CHEBI:8862). CHEBI:8862 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Rilmenidine increased autophagic flux in Cox15-deficient mice but did not improve motor performance, muscle morphology or lysosomal biogenesis. This negative comparison argues against assuming that autophagy induction alone is sufficient.
Mechanism Target:
INHIBITS Impaired Autophagic Flux — Reduces the modeled block in autophagic flux; this is a mouse-system effect.
Show evidence (1 reference)
PMID:30309855 SUPPORT Model Organism
"Although rilmenidine increased the autophagic flux ... it had no effect on the motor performance of Cox15 sm/sm mice ... and failed to improve muscle morphology"
Increasing flux alone did not improve the model phenotype.
Show evidence (1 reference)
PMID:30309855 SUPPORT Model Organism
"Although rilmenidine increased the autophagic flux ... it had no effect on the motor performance of Cox15 sm/sm mice ... and failed to improve muscle morphology"
Increasing flux alone did not improve the model phenotype.
🔬

Biochemical Markers

2
Tissue-dependent complex IV deficiency
Show evidence (1 reference)
PMID:21412973 SUPPORT Human Clinical
"Postmortem cardiac muscle study showed marked complex IV deficiency. In contrast, complex IV activity was only slightly decreased in the skeletal muscle."
Direct human tissue comparison supports this diagnostic caveat.
Elevated liver enzymes
Show evidence (1 reference)
PMID:40439182 SUPPORT Human Clinical
"liver enzymes, and triglycerides, with normal creatine kinase and carnitine levels."
Reports the laboratory observation without inferring liver failure or a specific enzyme.
🔬

Diagnosis

3
Molecular genetic diagnosis
Confirm biallelic pathogenic or likely pathogenic COX15 variants and assess segregation. Broader mitochondrial panels or genomic testing are appropriate for overlapping cardioencephalomyopathy and Leigh presentations; variants of uncertain significance require additional interpretation.
Show evidence (3 references)
PMID:33746038 SUPPORT Human Clinical
"whose exome sequencing revealed two variants in a compound heterozygous state"
The case demonstrates genomic identification of the biallelic cause.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Molecular genetic testing approaches can include a combination of ... gene ... -targeted testing ... and ... comprehensive ... genomic ... testing"
General Leigh-spectrum guidance supports panel or genomic investigation.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Genome sequencing is preferred (if available), as it allows analysis of the mitochondrial and nuclear genome, and typically has the highest diagnostic rate."
This recommendation is for the heterogeneous Leigh differential, not a COX15-specific diagnostic yield.
Biochemical and functional assessment
Assess lactate and respiratory-chain function when clinically indicated. Mild muscle deficiency, normal serum lactate or normal fibroblast holoenzyme abundance does not exclude COX15 disease. Functional complementation can support variant interpretation.
Show evidence (3 references)
PMID:26959537 SUPPORT Human Clinical
"However, serum lactate level as well as brain magnetic resonance imaging were normal."
A reported COX15-associated presentation lacks these common screening abnormalities.
PMID:21412973 SUPPORT Human Clinical
"complex IV activity was only slightly decreased in the skeletal muscle. Subsequent molecular investigations showed compound heterozygosity for two known pathogenic mutations in the COX15 gene."
Mild skeletal-muscle findings did not exclude severe genetically confirmed disease.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"the widespread use of ... genomic ... testing has obviated the need for muscle biopsy in many instances"
Current broader guidance does not require invasive biopsy before genetic testing.
Cardiac and neurological evaluation
Assess cardiac structure and function, neurodevelopment, movement disorders, vision and hearing. MRI can show bilateral putaminal and cerebellar abnormalities, but normal imaging does not exclude the reported spectrum.
Show evidence (2 references)
PMID:40439182 SUPPORT Human Clinical
"Electrocardiogram and echocardiogram were normal in both. Muscle biopsy showed COX‐negative fibers and pleomorphic mitochondria."
Normal cardiac evaluation can coexist with molecularly and functionally supported COX15 disease.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/ SUPPORT REVIEW SYNTHESIS Other
"Neurologic, ophthalmologic, audiologic, and cardiologic evaluations are recommended"
Broader Leigh-spectrum surveillance is relevant to the documented COX15 organ involvement.
📈

Progression

1
Variable infantile and childhood course
Severe neonatal cases may die rapidly, while other patients survive into adolescence with slowly progressive neurological disease and no cardiomyopathy. Published ages describe individual cases rather than a survival estimate.
Show evidence (3 references)
PMID:12474143 SUPPORT Human Clinical
"Echocardiogram on day 6 showed no ventricular enlargement, but she died at age 24 d from a massive biventricular hypertrophic cardiomyopathy."
The founding patient had rapid cardiac progression.
PMID:15863660 SUPPORT Human Clinical
"our patient had a slowly progressive course with no heart involvement."
A contrasting course prevents treating neonatal fatality or cardiomyopathy as obligatory.
PMID:40439182 SUPPORT Human Clinical
"Both patients developed progressive generalized dystonia at ages 12 and 14"
Neurological progression can extend into adolescence.
🧫

Experimental Models

2
Patient fibroblast complementation CELL_LINE
Immortalized fibroblasts from the founding patient show reduced heme A and mature complex IV. COX15.1 expression partially rescues enzyme activity. The mild cellular defect does not reproduce the severity of the neonatal cardiac presentation.
Cell source
Patient skin fibroblasts immortalized with HPV E6/E7 and human telomerase
Publication
PMID:12474143
Pathograph links
Deficient Complex IV Biogenesis recapitulates fidelity: high observes: molecular Patient cells reproduce deficient assembly and partial complementation rescue.
Limitations: Cellular and animal results do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:12474143 SUPPORT In Vitro
"These results suggest that reduced availability of heme A stalls the assembly of COX."
Heme measurements and complementation support a cofactor-dependent assembly defect.
Reduced Heme A Availability rescues fidelity: high observes: molecular Wild-type COX15 expression raises cellular heme A.
Limitations: Cellular and animal results do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:12474143 SUPPORT In Vitro
"Overexpression of COX15 in patient fibroblasts increased the heme A levels threefold"
The rescue links the gene to the cofactor deficit.
Show evidence (1 reference)
PMID:12474143 SUPPORT In Vitro
"Overexpression of COX15 restored COX activity to ∼60% of the control levels when normalized to citrate synthase"
Partial functional rescue supports the causal gene.
Yeast COX15 pathogenic-variant model OTHER
Yeast Cox15 Thr236Trp models human Arg217Trp, with Thr236Arg as a functional humanized control. The pathogenic analogue is stably expressed but impairs heme A synthesis, respiration and COX-subunit maintenance and alters oligomer migration.
Cell source
Saccharomyces cerevisiae cox15 deletion strain expressing Cox15 variants
Publication
PMID:26940873
Pathograph links
COX15 Heme A Synthase Deficiency partially recapitulates fidelity: moderate observes: molecular Homologous pathogenic substitution compromises catalytic function.
Limitations: The human Arg217 site corresponds to a naturally occurring threonine in baker yeast; this system cannot model neurological or cardiac presentation.
Show evidence (1 reference)
PMID:26940873 SUPPORT Model Organism
"impairs enzymatic activity and affects oligomerization of the Cox15 complex."
Functional and native-gel studies support a catalytic and oligomeric consequence.
Show evidence (1 reference)
PMID:26940873 SUPPORT Model Organism
"The T236R variant rescued respiratory growth similarly to the yeast WT; however, the T236W variant was unable to support respiratory growth of the heme a synthase-deficient strain"
The homologous variant perturbs a conserved biochemical function.
🐁

Animal Models

2
Muscle-specific Cox15 knockout mouse
Conditional deletion under the skeletal-muscle ACTA1 promoter produces severe COX-deficient myopathy with residual Cox15 expression. The model tests muscle respiratory and quality-control defects, not the complete human Leigh/cardioencephalomyopathy spectrum.
Species
Mouse
Genotype
Muscle-specific Cox15 deletion driven by ACTA1-Cre; also reported as Cox15 sm/sm
Publication
PMID:21723506
Pathograph links
Reduced Complex IV Respiratory Capacity partially recapitulates fidelity: moderate observes: organism The conditional knockout reproduces severe muscle COX deficiency.
Limitations: Muscle-restricted deletion does not reproduce the full clinical organ distribution.
Show evidence (1 reference)
PMID:21723506 SUPPORT Model Organism
"the amount of Cox15 mRNA in ACTA-Cox15−/− mouse skeletal muscle was ≤16% than that of WT muscle"
The model retains residual expression.
Impaired Autophagic Flux recapitulates fidelity: moderate observes: cellular Colchicine experiments reveal deficient clearance in the mutant muscle.
Limitations: The autophagy defect has not been demonstrated in patient tissues.
Show evidence (1 reference)
PMID:30309855 SUPPORT Model Organism
"Colchicine increased LC3‐II in WT but not in Cox15 sm/sm muscles, suggesting a block of the autophagic flux in the latter."
The flux experiment distinguishes impaired clearance from increased steady-state autophagosome abundance.
Show evidence (2 references)
PMID:21723506 SUPPORT Model Organism
"Recombination of the Cox15 locus by the cre recombinase was detected only in skeletal muscle and, in trace amount, in the heart, whereas no recombination occurs in other tissues"
Defines the tissue limitation of the model.
PMID:30309855 SUPPORT Model Organism
"Colchicine increased LC3‐II in WT but not in Cox15 sm/sm muscles, suggesting a block of the autophagic flux in the latter."
The flux experiment distinguishes impaired clearance from increased steady-state autophagosome abundance.
Cox15 knockout with OPA1 overexpression
Crossing muscle-specific Cox15 mutants with Opa1 transgenic mice improves cristae organization, stabilizes residual complex IV and respiratory supercomplexes, and improves respiration, endurance and survival. It is a genetic proof of principle, not a tested patient gene therapy.
Species
Mouse
Genotype
Cox15 sm/sm crossed with Opa1 transgenic mice
Publication
PMID:26039449
Pathograph links
Disorganized Mitochondrial Cristae rescues fidelity: moderate observes: cellular OPA1 overexpression improves cristae organization.
Limitations: Transgenic rescue in muscle-specific mice does not establish human efficacy or safety.
Show evidence (1 reference)
PMID:26039449 SUPPORT Model Organism
"the Cox15sm/sm::Opa1tg cristae were organized in an ordered and parallel array and were tightly folded"
Ultrastructure documents rescue of the structural phenotype.
Deficient Complex IV Biogenesis rescues fidelity: moderate observes: molecular OPA1 overexpression stabilizes residual complex IV and supercomplexes.
Limitations: Cellular and animal results do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:26039449 SUPPORT Model Organism
"Mechanistically, respiratory chain supercomplexes were increased in Cox15(sm/sm)::Opa1(tg) mice, and residual monomeric complex IV was stabilized."
The biochemical rescue preserves residual enzyme rather than replacing COX15.
Show evidence (1 reference)
PMID:26039449 SUPPORT Model Organism
"correction of cristae ultrastructure and mitochondrial respiration, improvement of motor performance and prolongation of lifespan were remarkable in Cox15(sm/sm)::Opa1(tg) mice."
Reports multiple preclinical rescue outcomes.
{ }

Source YAML

click to show 
name: COX15-Related COX Deficiency
category: Mendelian
creation_date: '2026-05-30T00:00:00Z'
synonyms:
- COX15 deficiency
- Cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 2
- COX15-related cytochrome c oxidase deficiency
- Mitochondrial complex IV deficiency, nuclear type 6
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
disease_term:
  preferred_term: COX15-related mitochondrial complex IV deficiency
  term:
    id: MONDO:0014051
    label: cardioencephalomyopathy, fatal infantile, due to cytochrome c oxidase deficiency 2
description: COX15-related COX deficiency is an autosomal recessive mitochondrial disease caused by biallelic variants affecting heme A synthase. Reduced heme A availability impairs complex IV biogenesis and respiratory function. The clinical spectrum includes rapidly fatal neonatal cardioencephalomyopathy and more slowly progressive Leigh syndrome spectrum with developmental impairment, movement disorders and variable cardiac involvement. Residual enzyme activity and assembled complex IV vary between tissues and alleles. Muscle-specific mouse models reveal additional mitochondrial quality-control defects and experimental intervention responses that have not established efficacy in patients.
references:
- reference: PMID:12474143
  title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
- reference: PMID:15863660
  title: Novel mutations in COX15 in a long surviving Leigh syndrome patient with cytochrome c oxidase deficiency.
- reference: PMID:21412973
  title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
- reference: PMID:26959537
  title: Leigh syndrome associated with a novel mutation in the COX15 gene.
- reference: PMID:32232962
  title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
- reference: PMID:33746038
  title: 'A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.'
- reference: PMID:40439182
  title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
- reference: PMID:26940873
  title: Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.
- reference: PMID:21723506
  title: In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
- reference: PMID:26039449
  title: Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
- reference: PMID:30309855
  title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
  title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
  tags:
  - GeneReviews
- reference: PMID:26425749
  title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview.
  tags:
  - GeneReviews
pathophysiology:
- name: COX15 Heme A Synthase Deficiency
  description: Biallelic variants reduce COX15 enzymatic function through allele-dependent defects in protein stability or catalytic properties. COX15 is a heme biosynthetic enzyme rather than a structural subunit of the mature respiratory complex.
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: This splicing error introduces a frameshift and a premature stop codon, resulting in an unstable mRNA and, likely, a null allele.
    explanation: The founding splice allele reduces functional COX15 through abnormal splicing and transcript instability.
  - reference: PMID:26940873
    reference_title: Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: COX15 protein in the S344P/S151X cells was intrinsically unstable. However, steady-state levels of COX15 protein in cells with R217W/C447–3G were comparable with the control
    explanation: Patient fibroblast experiments show that deficient function need not entail reduced protein abundance.
  genes:
  - &id007
    preferred_term: COX15
    term:
      id: hgnc:2263
      label: COX15
  biological_scale: MOLECULAR
  molecular_functions:
  - preferred_term: heme A synthase activity
    term:
      id: GO:0120547
      label: heme A synthase activity
    modifier: DECREASED
  downstream:
  - target: Reduced Heme A Availability
    description: Reduced heme A synthase function restricts synthesis of the complex IV heme cofactor.
    causal_link_type: DIRECT
    evidence:
    - &id001
      reference: PMID:12474143
      reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patient N heart mitochondria contained markedly reduced levels of heme A and increased levels of heme O
      explanation: The founding patient heart shows impaired heme A production and accumulated precursor.
- name: Reduced Heme A Availability
  description: Heme A production is impaired. In the founding patient, heart mitochondria accumulated heme O, whereas patient fibroblasts did not show a detectable heme O peak; accumulation should not be assumed in every tissue.
  evidence:
  - *id001
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Low heme A was also detected in patient fibroblasts; however, no heme O peak could be detected
    explanation: The heme profile differs between heart and cultured fibroblasts.
  biological_scale: MOLECULAR
  biological_processes:
  - preferred_term: heme A biosynthetic process
    term:
      id: GO:0006784
      label: heme A biosynthetic process
    modifier: DECREASED
  downstream:
  - target: Deficient Complex IV Biogenesis
    description: Limited heme A compromises maturation and assembly of functional complex IV.
    causal_link_type: DIRECT
    evidence:
    - &id002
      reference: PMID:12474143
      reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: These results suggest that reduced availability of heme A stalls the assembly of COX.
      explanation: Heme measurements and complementation support a cofactor-dependent assembly defect.
- name: Deficient Complex IV Biogenesis
  description: 'Insufficient cofactor supply can reduce the amount of assembled complex IV. This is allele- and tissue-dependent: normal amounts of assembled enzyme were reported in fibroblasts of a slowly progressive Leigh patient despite reduced activity.'
  evidence:
  - *id002
  - reference: PMID:15863660
    reference_title: Novel mutations in COX15 in a long surviving Leigh syndrome patient with cytochrome c oxidase deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: COX deficiency was mild in muscle and a normal amount of fully assembled COX was present in cultured fibroblasts.
    explanation: A patient-cell exception limits a universal claim that all COX15 variants abolish assembly.
  biological_scale: MOLECULAR
  conforms_to: complex_iv_assembly_deficiency#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
  downstream:
  - target: Reduced Complex IV Respiratory Capacity
    description: Deficient maturation or activity lowers the functional capacity of terminal respiratory electron transfer.
    causal_link_type: DIRECT
    evidence:
    - &id003
      reference: PMID:12474143
      reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: COX activity and the total amount of fully assembled enzyme were reduced by 50%–70% in patient fibroblasts.
      explanation: The founding patient cells retain substantial complex IV activity; deficiency is not equivalent to complete ATP collapse.
- name: Reduced Complex IV Respiratory Capacity
  description: Complex IV activity is reduced with variable residual function and marked tissue differences. This compromises oxidative metabolism and is associated with cardiac, neurological and metabolic disease.
  evidence:
  - *id003
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Postmortem cardiac muscle study showed marked complex IV deficiency. In contrast, complex IV activity was only slightly decreased in the skeletal muscle.
    explanation: Cardiac and skeletal-muscle activities can be substantially discordant.
  biological_scale: CELLULAR
  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
  downstream:
  - target: Hypertrophic cardiomyopathy
    description: The cardiac respiratory defect contributes to cardiomyopathy through incompletely resolved intermediates.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:21412973
      reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: a neonatal rapidly progressive fatal course characterized by microcephaly, encephalopathy, persistent lactic acidosis, and hypertrophic cardiomyopathy
      explanation: The case links severe cardiac COX deficiency with hypertrophy and metabolic disease.
  - target: Lactic acidosis
    description: Deficient oxidative metabolism is associated with lactate accumulation and acidosis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:21412973
      reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: persistent lactic acidosis, and hypertrophic cardiomyopathy. Postmortem cardiac muscle study showed marked complex IV deficiency.
      explanation: A genetically confirmed COX15 patient had persistent lactic acidosis and tissue COX deficiency.
  - target: Increased CSF lactate
    description: Impaired oxidative metabolism can be accompanied by cerebrospinal fluid lactate accumulation; the tissue-level intermediates are not resolved by the clinical report.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33746038
      reference_title: 'A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: a male newborn with hypertrophic cardiomyopathy and serum and cerebrospinal fluid hyperlacticaemia
      explanation: The genetically confirmed COX15 case documents CSF lactate accumulation; the intermediate causal steps were not experimentally tested.
  - target: Developmental regression
    description: Impaired mitochondrial energy metabolism contributes to neurological deterioration; intermediate injury mechanisms remain incompletely resolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:26959537
      reference_title: Leigh syndrome associated with a novel mutation in the COX15 gene.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression.
      explanation: The case directly establishes the neurological phenotype in COX15-associated disease.
  - target: Bilateral basal ganglia lesions
    description: The neurological phenotype can include bilateral Leigh-pattern lesions.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:40439182
      reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: symmetrical hyperintensity in the bilateral cerebellar white matter, middle cerebellar peduncles, and putamen, along with volume loss and globus pallidi blooming.
      explanation: The two COX15 siblings have symmetric basal-ganglia and cerebellar lesions.
  - target: Disorganized Mitochondrial Cristae
    description: Severe respiratory dysfunction is associated with disrupted mitochondrial ultrastructure in the muscle model.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id004
      reference: PMID:26039449
      reference_title: Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: While Cox15sm/sm muscle mitochondria showed profound cristae disorganization and prominent vacuolar degeneration of the inner mitochondrial compartment
      explanation: Electron microscopy shows disrupted cristae in the muscle-specific mouse model.
  - target: Impaired Autophagic Flux
    description: Muscle-specific COX15 loss is associated with impaired autophagic clearance; the intervening signaling mechanism is unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id005
      reference: PMID:30309855
      reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Colchicine increased LC3‐II in WT but not in Cox15 sm/sm muscles, suggesting a block of the autophagic flux in the latter.
      explanation: The flux experiment distinguishes impaired clearance from increased steady-state autophagosome abundance.
- name: Disorganized Mitochondrial Cristae
  description: Abnormal mitochondrial cristae occur in affected cardiac tissue and are reproduced in Cox15-deficient mouse muscle. OPA1 overexpression improves cristae organization in the model, supporting a potentially modifiable structural component of respiratory dysfunction.
  evidence:
  - *id004
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: greatly increased numbers of mitochondria with abnormal shapes, abnormally arranged cristae, and numerous matrix densities
    explanation: Electron microscopy of the founding patient heart documents mitochondrial ultrastructural abnormalities.
  biological_scale: CELLULAR
  biological_processes:
  - preferred_term: inner mitochondrial membrane organization
    term:
      id: GO:0007007
      label: inner mitochondrial membrane organization
    modifier: ABNORMAL
- name: Impaired Autophagic Flux
  description: Autophagic flux is blocked in skeletal muscle of the conditional mouse model. This has not been demonstrated in COX15 patient tissues. Basal mTOR signaling was not significantly increased in the model, so constitutive mTOR activation is not established as the lesion.
  evidence:
  - *id005
  - reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: While mTOR signaling was not significantly changed in naïve Cox15 sm/sm versus WT mice, autophagy flux was reduced
    explanation: Impaired flux does not imply basal mTOR overactivation.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  biological_processes:
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
    modifier: DECREASED
  downstream:
  - target: Accumulation of Damaged Mitochondria
    description: Reduced clearance may permit damaged organelles to accumulate in mouse skeletal muscle.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id006
      reference: PMID:30309855
      reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: A block of the autophagic flux may result in reduced clearance of dysfunctional mitochondria in Cox15 sm/sm muscle.
      explanation: The study proposes defective clearance as a contributor to mitochondrial accumulation in mouse muscle.
- name: Accumulation of Damaged Mitochondria
  description: The muscle-specific Cox15 model accumulates damaged mitochondria. Coordinated restoration of autophagic flux and lysosomal biogenesis improves clearance in rapamycin-treated mice; applicability to patient disease is unresolved.
  evidence:
  - *id006
  - reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Our results suggest that rapamycin induced the removal of damaged mitochondria, as demonstrated by correction of muscle morphology, reduction of mtDNA amount, normalization of CS activity, and increased mitochondrial respiration.
    explanation: Multiple model readouts support the organelle-clearance interpretation.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
phenotypes:
- name: Hypertrophic cardiomyopathy
  description: Severe neonatal or childhood hypertrophic cardiomyopathy occurs in some patients, including obstructive disease. Other genetically affected individuals have normal cardiac evaluations.
  evidence:
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: a female infant with a neonatal rapidly progressive fatal course characterized by microcephaly, encephalopathy, persistent lactic acidosis, and hypertrophic cardiomyopathy.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id009
    preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
- name: Lactic acidosis
  description: Persistent lactic acidosis is reported in severe infantile disease; normal serum lactate in another reported patient shows that it is not obligatory.
  evidence:
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: persistent lactic acidosis, and hypertrophic cardiomyopathy. Postmortem cardiac muscle study showed marked complex IV deficiency.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id014
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
- name: Increased CSF lactate
  description: Cerebrospinal fluid hyperlactatemia has been documented in infantile cardioencephalomyopathy.
  evidence:
  - reference: PMID:33746038
    reference_title: 'A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: a male newborn with hypertrophic cardiomyopathy and serum and cerebrospinal fluid hyperlacticaemia
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Increased CSF lactate
    term:
      id: HP:0002490
      label: Increased CSF lactate
- name: Hypotonia
  description: Reported in individuals with COX15-associated neurological disease; severity and onset vary.
  evidence:
  - reference: PMID:26959537
    reference_title: Leigh syndrome associated with a novel mutation in the COX15 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
- name: Global developmental delay
  description: Reported in individuals with COX15-associated neurological disease; severity and onset vary.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: was evaluated for global developmental delay (GDD) and failure to thrive (FTT).
    explanation: The 2025 COX15 sibling report explicitly identifies global developmental delay.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
- name: Developmental regression
  description: Reported in individuals with COX15-associated neurological disease; severity and onset vary.
  evidence:
  - reference: PMID:26959537
    reference_title: Leigh syndrome associated with a novel mutation in the COX15 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression.
    explanation: The COX15 clinical report directly documents this finding.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Onset of nuclear ... gene ... -encoded LSS is typically in infancy or early childhood with sudden neurodevelopmental regression.
    explanation: General Leigh-spectrum context supports the clinical interpretation, without assigning pooled LSS frequencies to COX15.
    quote_role: REVIEW_SYNTHESIS
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
- name: Tremor
  description: Reported in individuals with COX15-associated neurological disease; severity and onset vary.
  evidence:
  - reference: PMID:26959537
    reference_title: Leigh syndrome associated with a novel mutation in the COX15 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Here we report a 7-year-old girl with hypotonia, tremor, developmental delay and psychomotor regression.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
- name: Seizure
  description: Seizures occur in neonatal and later neurological presentations.
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Shortly after birth, patient N presented with midfacial hypoplasia, lactic acidosis, seizures, and hypotonia.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id011
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
- name: Microcephaly
  description: Microcephaly occurs in severe infantile cardioencephalopathy.
  evidence:
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: a neonatal rapidly progressive fatal course characterized by microcephaly, encephalopathy, persistent lactic acidosis, and hypertrophic cardiomyopathy
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
- name: Midface retrusion
  description: Midfacial hypoplasia was described in the founding infant.
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Shortly after birth, patient N presented with midfacial hypoplasia, lactic acidosis, seizures, and hypotonia.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Midface retrusion
    term:
      id: HP:0011800
      label: Midface retrusion
- name: Nystagmus
  description: Nystagmus was reported in the consanguineous family with homozygous Arg217Trp.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: two siblings of consanguineous kindred presented in infancy with a syndrome of hypotonia, nystagmus, psychomotor retardation, and pyramidal signs.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
- name: Tetraparesis
  description: Progressive motor and bulbar dysfunction developed toward the end of the second year in the reported siblings.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Toward the end of their second year, both patients developed progressive quadriparesis, convulsions, and pseudobulbar palsy.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id013
    preferred_term: Tetraparesis
    term:
      id: HP:0002273
      label: Tetraparesis
- name: Pseudobulbar paralysis
  description: Progressive motor and bulbar dysfunction developed toward the end of the second year in the reported siblings.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Toward the end of their second year, both patients developed progressive quadriparesis, convulsions, and pseudobulbar palsy.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Pseudobulbar paralysis
    term:
      id: HP:0007024
      label: Pseudobulbar paralysis
- name: Hearing impairment
  description: Hearing loss was documented in one of the homozygous Arg217Trp siblings; the abstract does not establish its physiological subtype.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: one of the two affected siblings had severe hypertrophic obstructive cardiomyopathy, hearing loss, and no visual response.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
- name: Visual impairment
  description: Absent visual response was reported in one Arg217Trp patient; this observation alone does not identify a retinal or optic-nerve mechanism.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: one of the two affected siblings had severe hypertrophic obstructive cardiomyopathy, hearing loss, and no visual response.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
- name: Generalized dystonia
  description: Progressive generalized dystonia emerged in adolescence in the 2025 siblings and substantially impaired mobility and hand use.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Both patients developed progressive generalized dystonia at ages 12 and 14, leading to wheelchair dependence in the younger sister and limited fine motor skills in the older sibling.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id012
    preferred_term: Generalized dystonia
    term:
      id: HP:0007325
      label: Generalized dystonia
- name: Coarse facial features
  description: Documented in the 2025 sibling report; available cases do not establish population frequency.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Coarse facial features
    term:
      id: HP:0000280
      label: Coarse facial features
- name: Hirsutism
  description: Documented in the 2025 sibling report; available cases do not establish population frequency.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Hirsutism
    term:
      id: HP:0001007
      label: Hirsutism
- name: Brachydactyly
  description: Documented in the 2025 sibling report; available cases do not establish population frequency.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
- name: Thoracic kyphosis
  description: Documented in the 2025 sibling report; available cases do not establish population frequency.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Thoracic kyphosis
    term:
      id: HP:0002942
      label: Thoracic kyphosis
- name: Short stature
  description: Documented in the 2025 sibling report; available cases do not establish population frequency.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: General examination revealed weight and height less than the third centile, coarse facies, hirsutism, short and stubby fingers, and thoracic kyphosis.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
- name: Dysarthria
  description: Documented during neurological assessment in the 2025 report.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
- name: Esotropia
  description: Documented during neurological assessment in the 2025 report.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Esotropia
    term:
      id: HP:0000565
      label: Esotropia
- name: Spasticity
  description: Documented during neurological assessment in the 2025 report.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
- name: Hyperreflexia
  description: Documented during neurological assessment in the 2025 report.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurological assessment showed dysarthria, esotropia, spasticity of lower limbs, brisk deep tendon reflexes (DTR), and generalized dystonia
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
- name: Failure to thrive
  description: Growth and feeding impairment may require enteral nutritional support.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She had bulbar dysfunction and FTT requiring gastrostomy tube insertion at 2 years of age.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term: &id010
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
- name: Osteopenia
  description: Hand radiography in the sibling report showed reduced bone density.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Hand X‐ray demonstrated diffuse osteopenia with broadening of the metacarpals and phalanges
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Osteopenia
    term:
      id: HP:0000938
      label: Osteopenia
- name: Bilateral basal ganglia lesions
  description: MRI may show symmetric putaminal signal abnormalities and volume loss, with additional cerebellar white-matter and peduncular involvement. One other reported patient had normal MRI.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: symmetrical hyperintensity in the bilateral cerebellar white matter, middle cerebellar peduncles, and putamen, along with volume loss and globus pallidi blooming.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Bilateral basal ganglia lesions
    term:
      id: HP:0007146
      label: Bilateral basal ganglia lesions
- name: Cerebellar atrophy
  description: Cerebellar white-matter signal change with volume loss was shown in the 2025 report.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Coronal T2 image revealing symmetric hyperintensity in the cerebellar white matter (solid arrows) along with volume loss (dotted arrows)
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
- name: Hypertriglyceridemia
  description: Elevated triglycerides were reported in both 2025 siblings.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Both siblings had elevated blood lactate (6.0 mmol/L in patient 1 and 4.5 mmol/L in patient 2; range, 0.6–2.1 mmol/L), liver enzymes, and triglycerides, with normal creatine kinase and carnitine levels.
    explanation: The COX15 clinical report directly documents this finding.
  phenotype_term:
    preferred_term: Hypertriglyceridemia
    term:
      id: HP:0002155
      label: Hypertriglyceridemia
- name: Retinopathy
  description: Listed among COX15-associated findings in the GeneReviews gene-specific table; the available data do not establish its frequency.
  phenotype_term:
    preferred_term: Retinopathy
    term:
      id: HP:0000488
      label: Retinopathy
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: COX15 ... Seizures, retinopathy ... HCM, hepatic steatosis ... Complex IV deficiency
    explanation: The COX15 row of the Leigh-spectrum table specifically lists this manifestation; pooled Leigh-spectrum frequencies are not applied.
- name: Hepatic steatosis
  description: Listed among COX15-associated findings in the GeneReviews gene-specific table; the available data do not establish its frequency.
  phenotype_term:
    preferred_term: Hepatic steatosis
    term:
      id: HP:0001397
      label: Hepatic steatosis
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: COX15 ... Seizures, retinopathy ... HCM, hepatic steatosis ... Complex IV deficiency
    explanation: The COX15 row of the Leigh-spectrum table specifically lists this manifestation; pooled Leigh-spectrum frequencies are not applied.
- name: Optic atrophy
  description: Reported in the COX15 case literature summarized by the 2025 clinical review; its frequency is uncertain.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: Additional features include hypertrophic cardiomyopathy, optic atrophy, hearing impairment, and FTT
    explanation: This passage summarizes earlier COX15 cases rather than an examination finding in the two newly reported siblings.
inheritance:
- name: Autosomal recessive
  description: Biallelic COX15 variants cause disease; the recurrence risks below assume both parents carry the familial pathogenic variants.
  evidence:
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Through linkage analysis and whole-exome sequencing, we identified a homozygous p.R217W mutation
    explanation: The homozygous variant segregated in the consanguineous kindred.
  - &id008
    reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: If both parents are known to be ... heterozygous ... for an LSS-related ... pathogenic variant ... each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic ... carrier ... and a 25% chance of being unaffected and not a carrier.
    explanation: Standard recessive recurrence risks apply when both parents carry the relevant COX15 pathogenic variants.
    quote_role: REVIEW_SYNTHESIS
genetic:
- name: COX15 pathogenic variants
  gene_term: *id007
  inheritance:
  - name: Autosomal recessive
    evidence:
    - *id008
  features: Missense, splice-altering and truncating alleles are reported. Arg217Trp recurs across families with different clinical severity. The founding paper used historical nucleotide coordinates C700T and C447-3G; these should not be confused with modern transcript-specific HGVS coordinates. Ser151Ter has occurred in compound heterozygosity with other alleles. Gly78Arg and Leu340Pro were described as likely pathogenic in their respective reports. A reliable genotype-severity prediction is not established.
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mutation analysis of COX15 in the patient identified a missense mutation (C700T) on one allele, changing a conserved arginine to tryptophan (R217W), and a splice-site mutation in intron 3 on the other allele (C447-3G), resulting in a deletion of exon 4.
    explanation: The original report establishes two different variant classes and records the historical numbering.
  - reference: PMID:33746038
    reference_title: 'A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: c.232G > A; p.(Gly78Arg), classified as likely pathogenic, and c.452C > G; p.(Ser151Ter), as pathogenic
    explanation: Retains the reported distinction between likely pathogenic and pathogenic variants.
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A homozygous likely pathogenic variant in c.T1019C (p.L340P) in the exon 8 of COX15 gene was identified.
    explanation: The 2025 siblings extend the missense spectrum; the report classifies the variant as likely pathogenic.
  - reference: PMID:32232962
    reference_title: Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: several phenotypic features were markedly distinguished between the affected siblings and in relation to previous reports of COX15 mutations.
    explanation: Even identical familial genotypes do not imply identical organ involvement.
progression:
- phase: Variable infantile and childhood course
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Echocardiogram on day 6 showed no ventricular enlargement, but she died at age 24 d from a massive biventricular hypertrophic cardiomyopathy.
    explanation: The founding patient had rapid cardiac progression.
  - reference: PMID:15863660
    reference_title: Novel mutations in COX15 in a long surviving Leigh syndrome patient with cytochrome c oxidase deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: our patient had a slowly progressive course with no heart involvement.
    explanation: A contrasting course prevents treating neonatal fatality or cardiomyopathy as obligatory.
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Both patients developed progressive generalized dystonia at ages 12 and 14
    explanation: Neurological progression can extend into adolescence.
  notes: Severe neonatal cases may die rapidly, while other patients survive into adolescence with slowly progressive neurological disease and no cardiomyopathy. Published ages describe individual cases rather than a survival estimate.
biochemical:
- name: Tissue-dependent complex IV deficiency
  evidence:
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Postmortem cardiac muscle study showed marked complex IV deficiency. In contrast, complex IV activity was only slightly decreased in the skeletal muscle.
    explanation: Direct human tissue comparison supports this diagnostic caveat.
  notes: Enzyme deficiency can be severe in heart while mild or low-normal in skeletal muscle. Biopsy results must be interpreted in their tissue and clinical context.
- name: Elevated liver enzymes
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: liver enzymes, and triglycerides, with normal creatine kinase and carnitine levels.
    explanation: Reports the laboratory observation without inferring liver failure or a specific enzyme.
  notes: The 2025 siblings had elevated liver enzymes; the available primary narrative does not specify the enzyme identities.
diagnosis:
- name: Molecular genetic diagnosis
  description: Confirm biallelic pathogenic or likely pathogenic COX15 variants and assess segregation. Broader mitochondrial panels or genomic testing are appropriate for overlapping cardioencephalomyopathy and Leigh presentations; variants of uncertain significance require additional interpretation.
  evidence:
  - reference: PMID:33746038
    reference_title: 'A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: whose exome sequencing revealed two variants in a compound heterozygous state
    explanation: The case demonstrates genomic identification of the biallelic cause.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Molecular genetic testing approaches can include a combination of ... gene ... -targeted testing ... and ... comprehensive ... genomic ... testing
    explanation: General Leigh-spectrum guidance supports panel or genomic investigation.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Genome sequencing is preferred (if available), as it allows analysis of the mitochondrial and nuclear genome, and typically has the highest diagnostic rate.
    explanation: This recommendation is for the heterogeneous Leigh differential, not a COX15-specific diagnostic yield.
    quote_role: REVIEW_SYNTHESIS
- name: Biochemical and functional assessment
  description: Assess lactate and respiratory-chain function when clinically indicated. Mild muscle deficiency, normal serum lactate or normal fibroblast holoenzyme abundance does not exclude COX15 disease. Functional complementation can support variant interpretation.
  evidence:
  - reference: PMID:26959537
    reference_title: Leigh syndrome associated with a novel mutation in the COX15 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: However, serum lactate level as well as brain magnetic resonance imaging were normal.
    explanation: A reported COX15-associated presentation lacks these common screening abnormalities.
  - reference: PMID:21412973
    reference_title: 'Infantile cardioencephalopathy due to a COX15 gene defect: report and review.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: complex IV activity was only slightly decreased in the skeletal muscle. Subsequent molecular investigations showed compound heterozygosity for two known pathogenic mutations in the COX15 gene.
    explanation: Mild skeletal-muscle findings did not exclude severe genetically confirmed disease.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: the widespread use of ... genomic ... testing has obviated the need for muscle biopsy in many instances
    explanation: Current broader guidance does not require invasive biopsy before genetic testing.
    quote_role: REVIEW_SYNTHESIS
- name: Cardiac and neurological evaluation
  description: Assess cardiac structure and function, neurodevelopment, movement disorders, vision and hearing. MRI can show bilateral putaminal and cerebellar abnormalities, but normal imaging does not exclude the reported spectrum.
  evidence:
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Electrocardiogram and echocardiogram were normal in both. Muscle biopsy showed COX‐negative fibers and pleomorphic mitochondria.
    explanation: Normal cardiac evaluation can coexist with molecularly and functionally supported COX15 disease.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Neurologic, ophthalmologic, audiologic, and cardiologic evaluations are recommended
    explanation: Broader Leigh-spectrum surveillance is relevant to the documented COX15 organ involvement.
    quote_role: REVIEW_SYNTHESIS
treatments:
- name: Multidisciplinary supportive care
  description: Care aims to improve function, quality of life and complication management, with neurological, cardiological, respiratory, nutritional, sensory and developmental support. The reviewed sources do not establish a COX15-specific disease-modifying treatment.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Supportive care to improve quality of life, maximize function, and reduce complications is recommended.
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
- name: Cardiac care and surveillance
  description: Cardiologist-directed treatment of cardiomyopathy or arrhythmia and longitudinal cardiac assessment are appropriate. A normal early echocardiogram does not guarantee that cardiomyopathy will not develop.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Anticongestive therapy or antiarrhythmic therapy may be required ... treatment should be managed by a cardiologist.
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_phenotypes:
  - *id009
- name: Nutrition and feeding support
  description: Assess growth, swallow safety and nutritional intake. Feeding therapy, supplementation and gastrostomy may be needed; gastrostomy was used in the younger 2025 sibling.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: gastrostomy tube placement may improve nutritional intake for those w/persistent feeding issues, choking, or aspiration risk due to dysphagia
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She had bulbar dysfunction and FTT requiring gastrostomy tube insertion at 2 years of age.
    explanation: Direct COX15 case evidence supports the need for enteral feeding in some patients.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Nutritional Support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  target_phenotypes:
  - *id010
- name: Seizure management
  description: Use neurologist-directed antiseizure therapy with mitochondrial drug-safety considerations. Sodium valproate should be avoided when possible; the absolute contraindication described for POLG disease is not a COX15-specific finding.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Treatment w/ASM by experienced neurologist
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Sodium valproate should be avoided if possible, because of its inhibitory effect on respiratory chain enzymes.
    explanation: General Leigh-spectrum guidance qualifies valproate use; absolute contraindication is specifically described for POLG-related disease.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Anticonvulsant Therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
  target_phenotypes:
  - *id011
- name: Dystonia management
  description: Movement-disorder treatment can include individually selected oral agents and rehabilitation. GeneReviews lists benzhexol, baclofen, tetrabenazine and gabapentin; these recommendations do not establish a response in COX15 patients.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Benzhexol, baclofen, tetrabenazine ... gabapentin may be useful, alone or in various combinations.
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Trihexyphenidyl
      term:
        id: CHEBI:9720
        label: Trihexyphenidyl
    - preferred_term: baclofen
      term:
        id: CHEBI:2972
        label: baclofen
    - preferred_term: tetrabenazine
      term:
        id: CHEBI:9467
        label: tetrabenazine
    - preferred_term: gabapentin
      term:
        id: CHEBI:42797
        label: gabapentin
  target_phenotypes:
  - *id012
  notes: These are alternative symptomatic agents listed in general Leigh-spectrum guidance, not a fixed combination regimen.
- name: Rehabilitation and communication support
  description: Physical and occupational therapy, mobility equipment and communication aids support function. The younger 2025 sibling used augmentative communication.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Equipment to prevent falling, maintain independent mobility as appropriate
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - *id013
  - *id012
- name: Metabolic and perioperative precautions
  description: Minimize fasting and prevent catabolism during illness or procedures; consider perioperative glucose as appropriate, with individualized diet-related exceptions. Monitor respiratory status during anesthesia, avoid prolonged propofol exposure where possible, and avoid lactate-containing fluids in those at risk of lactic acidosis.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Catabolism should be prevented by minimizing preoperative fasting and considering intravenous glucose perioperatively during prolonged anesthesia (unless the individual is on a ketogenic diet).
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Prolonged propofol use during maintenance anesthesia may increase the risk of lactic acidosis.
    explanation: General mitochondrial anesthesia caution.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Avoid lactate-containing agents (e.g., Ringer's lactate) in those at risk of lactic acidosis
    explanation: General mitochondrial fluid-selection precaution.
    quote_role: REVIEW_SYNTHESIS
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_phenotypes:
  - *id014
- name: Genetic counseling
  description: Confirm parental segregation, explain autosomal recessive recurrence risks when both parents are carriers, and discuss reproductive testing after identification of the familial pathogenic variants.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
    reference_title: Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Once the LSS-related ... pathogenic variant ... (s) have been identified in an affected family member, prenatal and ... preimplantation genetic testing ... are possible.
    explanation: General Leigh-spectrum guidance is applied to the relevant COX15 manifestation; this is not a COX15-specific efficacy trial.
    quote_role: REVIEW_SYNTHESIS
  - *id008
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
- name: Experimental AICAR
  description: AICAR partially improved complex IV biochemistry in muscle-specific Cox15-knockout mice, without detectable treadmill improvement. This does not establish patient efficacy.
  evidence:
  - &id017
    reference: PMID:21723506
    reference_title: In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Contrariwise, and in spite of partial biochemical recovery, we found no change by treadmill test in ACTA-Cox15−/− mice
    explanation: Biochemical improvement did not yield detectable motor benefit in the Cox15 model.
  context: Preclinical mouse intervention
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: acadesine
      term:
        id: CHEBI:28498
        label: acadesine
- name: Experimental bezafibrate
  description: Bezafibrate failed to correct the respiratory defect and caused toxicity in the tested mouse model. It is recorded as a negative preclinical result, not a recommended COX15 therapy.
  evidence:
  - &id018
    reference: PMID:21723506
    reference_title: In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: No such effect was obtained by treating both Surf1(-/-) and Cox15(-/-) mice with the pan-PPAR agonist bezafibrate, which instead showed adverse effects in either model.
    explanation: The tested intervention failed and caused adverse effects in mice.
  context: Preclinical mouse intervention
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: bezafibrate
      term:
        id: CHEBI:47612
        label: bezafibrate
- name: Experimental rapamycin
  description: Rapamycin improved autophagic flux, lysosomal biogenesis, mitochondrial clearance and motor performance in muscle-specific Cox15-knockout mice. Absolute complex IV specific activity remained unchanged, while the COX/citrate-synthase ratio increased as citrate synthase normalized. Treated mice remained impaired relative to wild type; human efficacy is unestablished.
  evidence:
  - &id015
    reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: rapamycin treatment was associated with an increase in the autophagic flux revealed by the addition of colchicine.
    explanation: Direct flux measurements support the intervention effect in mouse skeletal muscle.
  - reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The specific activity of COX (cIV) was significantly lower in Cox15 sm/sm samples and remained unchanged under rapamycin treatment.
    explanation: Distinguishes absolute activity from a ratio altered by normalization.
  context: Preclinical mouse intervention
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sirolimus
      term:
        id: CHEBI:9168
        label: sirolimus
  target_mechanisms:
  - target: Impaired Autophagic Flux
    treatment_effect: INHIBITS
    description: Reduces the modeled block in autophagic flux; this is a mouse-system effect.
    evidence:
    - *id015
  - target: Accumulation of Damaged Mitochondria
    treatment_effect: INHIBITS
    description: Promotes removal of damaged mitochondria in the muscle-specific mouse model; patient efficacy remains unestablished.
    evidence:
    - reference: PMID:30309855
      reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Our results suggest that rapamycin induced the removal of damaged mitochondria, as demonstrated by correction of muscle morphology, reduction of mtDNA amount, normalization of CS activity, and increased mitochondrial respiration.
      explanation: The study interprets the convergent morphology, mitochondrial content and respiration measurements as improved mitochondrial clearance.
- name: Experimental rilmenidine
  description: Rilmenidine increased autophagic flux in Cox15-deficient mice but did not improve motor performance, muscle morphology or lysosomal biogenesis. This negative comparison argues against assuming that autophagy induction alone is sufficient.
  evidence:
  - &id016
    reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Although rilmenidine increased the autophagic flux ... it had no effect on the motor performance of Cox15 sm/sm mice ... and failed to improve muscle morphology
    explanation: Increasing flux alone did not improve the model phenotype.
  context: Preclinical mouse intervention
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Rilmenidine
      term:
        id: CHEBI:8862
        label: Rilmenidine
  target_mechanisms:
  - target: Impaired Autophagic Flux
    treatment_effect: INHIBITS
    description: Reduces the modeled block in autophagic flux; this is a mouse-system effect.
    evidence:
    - *id016
experimental_models:
- name: Patient fibroblast complementation
  description: Immortalized fibroblasts from the founding patient show reduced heme A and mature complex IV. COX15.1 expression partially rescues enzyme activity. The mild cellular defect does not reproduce the severity of the neonatal cardiac presentation.
  evidence:
  - reference: PMID:12474143
    reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Overexpression of COX15 restored COX activity to ∼60% of the control levels when normalized to citrate synthase
    explanation: Partial functional rescue supports the causal gene.
  experimental_model_type: CELL_LINE
  publication: PMID:12474143
  cell_source: Patient skin fibroblasts immortalized with HPV E6/E7 and human telomerase
  modeled_mechanisms:
  - target: Deficient Complex IV Biogenesis
    relationship: RECAPITULATES
    description: Patient cells reproduce deficient assembly and partial complementation rescue.
    evidence:
    - *id002
    limitations: Cellular and animal results do not establish clinical treatment efficacy.
    fidelity: HIGH
    model_scale: MOLECULAR
  - target: Reduced Heme A Availability
    relationship: RESCUES
    description: Wild-type COX15 expression raises cellular heme A.
    evidence:
    - reference: PMID:12474143
      reference_title: Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Overexpression of COX15 in patient fibroblasts increased the heme A levels threefold
      explanation: The rescue links the gene to the cofactor deficit.
    limitations: Cellular and animal results do not establish clinical treatment efficacy.
    fidelity: HIGH
    model_scale: MOLECULAR
- name: Yeast COX15 pathogenic-variant model
  description: Yeast Cox15 Thr236Trp models human Arg217Trp, with Thr236Arg as a functional humanized control. The pathogenic analogue is stably expressed but impairs heme A synthesis, respiration and COX-subunit maintenance and alters oligomer migration.
  evidence:
  - reference: PMID:26940873
    reference_title: Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The T236R variant rescued respiratory growth similarly to the yeast WT; however, the T236W variant was unable to support respiratory growth of the heme a synthase-deficient strain
    explanation: The homologous variant perturbs a conserved biochemical function.
  experimental_model_type: OTHER
  publication: PMID:26940873
  cell_source: Saccharomyces cerevisiae cox15 deletion strain expressing Cox15 variants
  modeled_mechanisms:
  - target: COX15 Heme A Synthase Deficiency
    relationship: PARTIALLY_RECAPITULATES
    description: Homologous pathogenic substitution compromises catalytic function.
    evidence:
    - reference: PMID:26940873
      reference_title: Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: impairs enzymatic activity and affects oligomerization of the Cox15 complex.
      explanation: Functional and native-gel studies support a catalytic and oligomeric consequence.
    limitations: The human Arg217 site corresponds to a naturally occurring threonine in baker yeast; this system cannot model neurological or cardiac presentation.
    fidelity: MODERATE
    model_scale: MOLECULAR
animal_models:
- name: Muscle-specific Cox15 knockout mouse
  description: Conditional deletion under the skeletal-muscle ACTA1 promoter produces severe COX-deficient myopathy with residual Cox15 expression. The model tests muscle respiratory and quality-control defects, not the complete human Leigh/cardioencephalomyopathy spectrum.
  evidence:
  - reference: PMID:21723506
    reference_title: In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Recombination of the Cox15 locus by the cre recombinase was detected only in skeletal muscle and, in trace amount, in the heart, whereas no recombination occurs in other tissues
    explanation: Defines the tissue limitation of the model.
  - *id005
  species: Mouse
  genotype: Muscle-specific Cox15 deletion driven by ACTA1-Cre; also reported as Cox15 sm/sm
  publication: PMID:21723506
  modeled_mechanisms:
  - target: Reduced Complex IV Respiratory Capacity
    relationship: PARTIALLY_RECAPITULATES
    description: The conditional knockout reproduces severe muscle COX deficiency.
    evidence:
    - reference: PMID:21723506
      reference_title: In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: the amount of Cox15 mRNA in ACTA-Cox15−/− mouse skeletal muscle was ≤16% than that of WT muscle
      explanation: The model retains residual expression.
    limitations: Muscle-restricted deletion does not reproduce the full clinical organ distribution.
    fidelity: MODERATE
    model_scale: ORGANISM
  - target: Impaired Autophagic Flux
    relationship: RECAPITULATES
    description: Colchicine experiments reveal deficient clearance in the mutant muscle.
    evidence:
    - *id005
    limitations: The autophagy defect has not been demonstrated in patient tissues.
    fidelity: MODERATE
    model_scale: CELLULAR
- name: Cox15 knockout with OPA1 overexpression
  description: Crossing muscle-specific Cox15 mutants with Opa1 transgenic mice improves cristae organization, stabilizes residual complex IV and respiratory supercomplexes, and improves respiration, endurance and survival. It is a genetic proof of principle, not a tested patient gene therapy.
  evidence:
  - reference: PMID:26039449
    reference_title: Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: correction of cristae ultrastructure and mitochondrial respiration, improvement of motor performance and prolongation of lifespan were remarkable in Cox15(sm/sm)::Opa1(tg) mice.
    explanation: Reports multiple preclinical rescue outcomes.
  species: Mouse
  genotype: Cox15 sm/sm crossed with Opa1 transgenic mice
  publication: PMID:26039449
  modeled_mechanisms:
  - target: Disorganized Mitochondrial Cristae
    relationship: RESCUES
    description: OPA1 overexpression improves cristae organization.
    evidence:
    - reference: PMID:26039449
      reference_title: Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: the Cox15sm/sm::Opa1tg cristae were organized in an ordered and parallel array and were tightly folded
      explanation: Ultrastructure documents rescue of the structural phenotype.
    limitations: Transgenic rescue in muscle-specific mice does not establish human efficacy or safety.
    fidelity: MODERATE
    model_scale: CELLULAR
  - target: Deficient Complex IV Biogenesis
    relationship: RESCUES
    description: OPA1 overexpression stabilizes residual complex IV and supercomplexes.
    evidence:
    - reference: PMID:26039449
      reference_title: Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Mechanistically, respiratory chain supercomplexes were increased in Cox15(sm/sm)::Opa1(tg) mice, and residual monomeric complex IV was stabilized.
      explanation: The biochemical rescue preserves residual enzyme rather than replacing COX15.
    limitations: Cellular and animal results do not establish clinical treatment efficacy.
    fidelity: MODERATE
    model_scale: MOLECULAR
discussions:
- discussion_id: cox15-clinical-biochemical-variability
  kind: INTERPRETATION
  status: OPEN
  prompt: What determines cardiac versus neurological severity and the relationship to residual complex IV activity?
  rationale: Marked tissue differences, a patient with normal fibroblast holoenzyme abundance, and clinical differences within families argue against a simple universal activity threshold or a reliable genotype-severity rule. The small case literature cannot establish penetrance or manifestation frequencies.
  evidence:
  - reference: PMID:15863660
    reference_title: Novel mutations in COX15 in a long surviving Leigh syndrome patient with cytochrome c oxidase deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The clinical and biochemical phenotypes in COX15 defects are more heterogeneous than in other conditions associated with COX deficiency
    explanation: The early long-surviving case establishes biochemical and clinical heterogeneity.
  - reference: PMID:40439182
    reference_title: 'Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: However, additional cases are needed to confirm a genotype–phenotype correlation.
    explanation: The recent report explicitly limits genotype-based prognosis.
- discussion_id: cox15-quality-control-translation
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: Do the muscle-model quality-control defects and intervention responses apply to human COX15 disease?
  rationale: Conditional muscle deletion reveals impaired flux and damaged mitochondrial accumulation. Rapamycin, AICAR, bezafibrate, rilmenidine and OPA1 overexpression have different biochemical and motor effects; none of these experiments demonstrates benefit in human COX15 disease or reproduces its complete neurological and cardiac spectrum.
  evidence:
  - *id017
  - *id018
  - *id016
  - reference: PMID:30309855
    reference_title: Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: treated mice still perform much less than the WT littermates.
    explanation: Even the beneficial rapamycin effect leaves substantial motor impairment.
📚

References & Deep Research

References

13
PMID:12474143
Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.
No top-level findings curated for this source.
PMID:15863660
Novel mutations in COX15 in a long surviving Leigh syndrome patient with cytochrome c oxidase deficiency.
No top-level findings curated for this source.
PMID:21412973
Infantile cardioencephalopathy due to a COX15 gene defect: report and review.
No top-level findings curated for this source.
PMID:26959537
Leigh syndrome associated with a novel mutation in the COX15 gene.
No top-level findings curated for this source.
PMID:32232962
Phenotypic variability and mutation hotspot in COX15-related Leigh syndrome.
No top-level findings curated for this source.
PMID:33746038
A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: A case report with clinical and molecular review.
No top-level findings curated for this source.
PMID:40439182
Clinical Phenotype and Neuroimaging Findings in Siblings with COX15 Deficiency: Case Report and Review of Previously Reported Cases.
No top-level findings curated for this source.
PMID:26940873
Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.
No top-level findings curated for this source.
PMID:21723506
In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis.
No top-level findings curated for this source.
PMID:26039449
Opa1 overexpression ameliorates the phenotype of two mitochondrial disease mouse models.
No top-level findings curated for this source.
PMID:30309855
Rapamycin rescues mitochondrial myopathy via coordinated activation of autophagy and lysosomal biogenesis.
No top-level findings curated for this source.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK320989/
Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview - GeneReviews® - NCBI Bookshelf
No top-level findings curated for this source.
PMID:26425749
Nuclear Gene-Encoded Leigh Syndrome Spectrum Overview.
No top-level findings curated for this source.