COX16-Related COX Deficiency

Mendelian MONDO:0859160 Pathograph 27 Show in embeddings browser Mitochondrial Disease Inborn Error of Metabolism

COX16-related complex IV deficiency is an autosomal recessive mitochondrial disorder associated with loss of the COX16 assembly factor. COX16 assists SCO1 recruitment to newly synthesized COX2 and subsequent joining of the COX2 and COX1 assembly modules. Deficiency reduces COX2 stability, mature complex IV and respiratory capacity. The founding report described neonatal metabolic disease with different subsequent courses: death in the first days of life or progressive cardiac disease with survival into infancy. Clinical evidence remains limited, while patient-cell complementation and engineered-cell studies support the molecular mechanism. Copper rescue in engineered cells did not reproduce in the tested patient fibroblasts.

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1
Inheritance
6
Pathophys.
28
Phenotypes
2
Gaps
27
Pathograph
1
Genes
1
Variants
10
Medical Actions
3
Models
8
References
👪

Inheritance

1
Autosomal recessive
The founding patients were homozygous for Arg82Ter, with both parents in each family heterozygous. If both parents carry the familial pathogenic variant, each pregnancy has a 25% affected, 50% carrier and 25% unaffected noncarrier probability.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"Segregation analysis revealed that the parents of both patients were heterozygous for the identified COX16 variant."
Parental segregation supports autosomal recessive inheritance.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"If both parents are known to be ... heterozygous ... for a causative ... 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."
General recessive counseling applies when the familial variant and parental carrier states are established.
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Discussions and Knowledge Gaps

2
Why does copper rescue engineered COX16 knockout cells but not the tested patient fibroblasts?
HUMAN MODEL MISMATCH OPEN cox16-copper-response
Model-dependent residual function and assembly context may determine response. COX16 may organize SCO1 recruitment rather than directly supply copper, so increasing copper availability need not bypass its absence. In later engineered-cell experiments, SCO1/SCO2 thiol-trapping patterns remained compatible with oxidized or copper-bound cysteines in COX16 knockout cells. The assay does not distinguish those two states, so it does not directly quantify copper loading or prove a uniform copper shortage.
Show evidence (5 references)
PMID:29355485 SUPPORT In Vitro
"copper supplementation increases COX activity and restores normal steady state levels of COX subunits in COX16 knockout cells"
The earlier engineered HEK293 model showed a biochemical response that was not reproduced in the patient fibroblast experiment.
PMID:33169484 SUPPORT In Vitro
"the complex IV enzyme activity showed no recovery at all after the CuCl2 treatment of the patient cell line"
Copper chloride failed to rescue the tested Arg82Ter patient fibroblasts.
PMID:29381136 SUPPORT In Vitro
"only the association of SCO1 with newly synthesized COX2 was affected in the absence of COX16"
Pulse-labeling and immunoisolation identify a selective SCO1-recruitment defect; this is not proof that COX16 directly transports copper.
+ 2 more references
How broad is the clinical spectrum beyond the founding Arg82Ter families?
OPEN QUESTION OPEN cox16-clinical-spectrum
The same homozygous variant produced markedly different durations of survival. ClinGen classified the gene-disease relationship as Moderate in August 2025 because independent human genetic replication was limited, despite substantial functional evidence. The small clinical dataset does not support population frequencies, penetrance or a universal survival expectation.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"She was palliated with morphine and died almost 7 months old."
The clinical course is not uniformly fatal in the neonatal period.
url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_ea62fb70-3963-4bb4-a7c0-2340cb794f58-2025-08-11T040000.000Z SUPPORT REVIEW SYNTHESIS Other
"there have not yet been two independent scored publications documenting human genetic evidence over at least 3 years. Therefore, the classification comes to Moderate."
The dated ClinGen curation explicitly explains the Moderate classification by limited independent human genetic replication.
⚙

Pathophysiology

6
COX16 Protein Deficiency
The homozygous Arg82Ter variant is associated with loss of detectable COX16 protein in patient fibroblasts. COX16 is an inner-mitochondrial-membrane assembly factor with its C-terminus facing the intermembrane space.
COX16 hgnc:20213 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves COX16 (hgnc:20213). hgnc:20213 is a gene from the HUGO Gene Nomenclature Committee.
COX16-mediated protein recruitment during complex IV assembly GO:0030674 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased COX16-mediated protein recruitment during complex IV assembly, annotated with protein-macromolecule adaptor activity (GO:0030674). GO:0030674 is a molecular function from the Gene Ontology.
Experimental models
Patient fibroblast complementation PRIMARY CELL CULTURE The patient culture lacks detectable COX16.
Downstream
Impaired SCO1 Recruitment to COX2 Loss of COX16 reduces recruitment of SCO1 to newly synthesized COX2.
COX2 Instability Loss of COX16 destabilizes newly synthesized COX2.
Defective COX1-COX2 Module Joining COX16 loss impairs association of COX2 with the COX1 assembly module.
Show evidence (3 references)
PMID:33169484 SUPPORT In Vitro
"undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As"
Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
PMID:29381136 SUPPORT In Vitro
"Cox16 is an inner mitochondrial membrane protein with its C-terminus facing the intermembrane space (IMS)."
Protease protection and carbonate extraction establish localization.
PMID:29381136 SUPPORT In Vitro
"human COX16 functions to stabilize the interaction between SCO1 and newly synthesized COX2."
The human-cell experiments support COX16-dependent protein recruitment as its molecular activity in the assembly pathway.
Impaired SCO1 Recruitment to COX2
COX16-deficient engineered cells show reduced association of SCO1 with newly synthesized COX2, implicating a defect in CuA-site maturation. SCO2 association is preserved. Direct copper transport by COX16 is not demonstrated.
Experimental models
Engineered human COX16 knockout cells CELL LINE COX16 knockout reduces recruitment of SCO1 to newly synthesized COX2.
Downstream
Reduced Complex IV Assembly Defective metallochaperone recruitment limits COX2 maturation and downstream assembly.
Show evidence (2 references)
PMID:29381136 SUPPORT In Vitro
"only the association of SCO1 with newly synthesized COX2 was affected in the absence of COX16"
Pulse-labeling and immunoisolation identify a selective SCO1-recruitment defect; this is not proof that COX16 directly transports copper.
PMID:29381136 SUPPORT In Vitro
"The binding of other COX2 chaperones such as SCO2, COA6, and FAM36A was unaffected by the absence of COX16."
The pulse-labeled COX2 assay discriminates the SCO1 defect from generalized loss of chaperone recruitment.
COX2 Instability
Newly synthesized COX2 turns over more rapidly in COX16-knockout cells, despite preserved mitochondrial translation. Patient fibroblasts also show markedly reduced COX2 protein.
Experimental models
Engineered human COX16 knockout cells CELL LINE Pulse-chase assays show reduced stability of COX2.
Downstream
Reduced Complex IV Assembly Reduced availability of stable COX2 limits incorporation into mature complex IV.
Show evidence (3 references)
PMID:29381136 SUPPORT In Vitro
"COX2 showed a marked reduction in stability in the absence of COX16"
Pulse-chase experiments show instability of newly synthesized COX2.
PMID:33169484 SUPPORT In Vitro
"undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As"
Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
PMID:29381136 SUPPORT In Vitro
"no significant differences were observed in the synthesis of either COX1, COX2, or any other protein"
Pulse labeling argues against a generalized mitochondrial translation defect in the engineered cells.
Defective COX1-COX2 Module Joining
COX16 promotes association of the COX2 module with COX1-containing MITRAC intermediates. Its absence leaves COX1 accumulated in subassemblies. Human COX16 is a transient assembly factor rather than a constitutive component of mature respiratory supercomplexes.
Experimental models
Engineered human COX16 knockout cells CELL LINE Module association is impaired after COX16 loss.
Downstream
Reduced Complex IV Assembly Failure to merge the modules limits formation of mature cytochrome c oxidase.
Show evidence (3 references)
PMID:29381136 SUPPORT In Vitro
"COX2-association with MITRAC12 or C12ORF62 was drastically affected by the absence of COX16"
Immunoisolation supports failure to join COX2 to COX1-containing assembly intermediates.
PMID:33169484 SUPPORT In Vitro
"We observed an accumulation of COX1 in the mitochondrial translation regulation assembly intermediate of cytochrome c oxidase in the patient cell line transduced with GFP"
Patient-fibroblast assembly intermediates support the module-joining defect.
PMID:29381136 SUPPORT In Vitro
"COX16 does not act on respiratory chain supercomplexes"
The human-cell study found COX16 in assembly intermediates rather than mature supercomplexes.
Reduced Complex IV Assembly
Mature complex IV is markedly reduced. It was undetectable by blue-native immunoblot in the tested patient fibroblasts, while engineered knockout cells retained substantial enzyme abundance and activity. Other respiratory complexes were relatively preserved in the patient investigations.
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 PRIMARY CELL CULTURE Wild-type complementation restores complex IV assembly and activity.
Engineered human COX16 knockout cells CELL LINE Engineered cells recapitulate reduced assembly but retain more function and show a different copper response than the patient cells.
Downstream
Reduced Respiratory Capacity Reduced functional complex IV limits terminal respiratory-chain capacity.
Show evidence (3 references)
PMID:33169484 SUPPORT In Vitro
"an absence of the fully assembled complex IV with normal expression levels of the other OXPHOS complexes"
Blue-native immunoblotting of Subject 1 fibroblasts shows a severe, selective assembly defect; undetectable bands do not imply zero enzymatic activity.
PMID:29381136 SUPPORT In Vitro
"the cytochrome c oxidase amount was reduced to ∼50% compared to the wild type control"
Engineered cells retain substantial enzyme; the severity of the assembly defect depends on the experimental system.
PMID:33169484 SUPPORT In Vitro
"Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines."
Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
Reduced Respiratory Capacity
Complex IV deficiency reduces mitochondrial respiration. Residual activity differs between tissues and models; neither absent total oxidative ATP production nor universal collapse of ATP synthesis was demonstrated. Cardiac, neurological, hepatic and metabolic manifestations accompany the respiratory defect.
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
Caenorhabditis elegans COX16 knockdown Caenorhabditis elegans recapitulates Knockdown produces the biochemical COX-deficiency phenotype.
Downstream
Hypertrophic Cardiomyopathy Impaired mitochondrial respiration contributes to cardiac disease through unresolved tissue-level intermediates.
Encephalopathy Respiratory dysfunction contributes to neurological injury through unresolved intermediates.
Lactic Acidosis Impaired oxidative metabolism is associated with lactate accumulation and metabolic acidosis.
Hepatic Failure Mitochondrial dysfunction and systemic decompensation accompany hepatic failure; the intervening mechanisms are unresolved.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"high‐resolution respirometry of the skeletal muscle analyzed with an Oxygraph‐2k (Oroboros Instruments) showed clearly reduced mitochondrial respiration"
Subject 2 muscle respirometry documents impaired respiratory capacity.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"tissues and organs that are highly dependent on aerobic metabolism are preferentially involved in mitochondrial disorders"
General mitochondrial disease physiology provides context for multisystem vulnerability, without specifying COX16 phenotype frequencies.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for COX16-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

28
Blood 1
Coagulopathy Abnormality of coagulation HP:0001928 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormality of coagulation (HP:0001928). HP:0001928 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"He had multisystemic involvement with liver failure and coagulopathy"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Cardiovascular 3
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.
Sequelae: Left Ventricular Outflow Tract Obstruction Congestive Heart Failure
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Repeated echocardiography showed massive left ventricular hypertrophy"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Congestive Heart Failure HP:0001635 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Congestive heart failure (HP:0001635). HP:0001635 is a phenotype from the Human Phenotype Ontology.
Sequelae: Feeding Difficulties in Infancy
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion."
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Left Ventricular Outflow Tract Obstruction HP:0032092 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Left ventricular outflow tract obstruction (HP:0032092). HP:0032092 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"with left ventricular outlet obstruction but with preserved biventricular function"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Digestive 3
Hepatic Failure HP:0001399 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hepatic failure (HP:0001399). HP:0001399 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"He had multisystemic involvement with liver failure and coagulopathy"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Feeding Difficulties in Infancy HP:0008872 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties in infancy (HP:0008872). HP:0008872 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion."
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Diarrhea HP:0002014 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Diarrhea (HP:0002014). HP:0002014 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"From then onwards she had diarrhea and difficulties gaining weight"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Ear 1
Congenital Sensorineural Hearing Impairment HP:0008527 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Congenital sensorineural hearing impairment (HP:0008527), qualified as laterality bilateral. HP:0008527 is a phenotype from the Human Phenotype Ontology.
Laterality: BILATERAL
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"bilateral congenital sensorineural hearing loss"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Genitourinary 1
Ketonuria HP:0002919 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ketonuria (HP:0002919). HP:0002919 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"with a fixed moderate ketonuria"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Metabolism 9
Lactic Acidosis HP:0003128 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lactic acidosis (HP:0003128), qualified as severity severe; neonatal onset. HP:0003128 is a phenotype from the Human Phenotype Ontology.
Severity: SEVERE Onset: NEONATAL
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Severe lactic acidosis was noted at birth"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Neonatal Hypoglycemia HP:0001998 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neonatal hypoglycemia (HP:0001998). HP:0001998 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"After 24 h of life, she was transferred to the neonatal intensive care unit due to tachypnoea, irritability with a high‐pitched cry, regurgitations, and hypoglycemia"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Cerebral Edema HP:0002181 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral edema (HP:0002181). HP:0002181 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"multiple areas of supratentorial and brainstem infarcts with generalized cerebral edema"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Elevated Circulating Creatine Kinase Elevated circulating creatine kinase activity HP:0003236 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating creatine kinase activity (HP:0003236). HP:0003236 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Serum creatine kinase was 3000 U/L (NR < 450)"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Elevated Hepatic Transaminases Elevated circulating hepatic transaminase concentration HP:0002910 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating hepatic transaminase concentration (HP:0002910). HP:0002910 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Liver function tests showed 2–3‐fold increases in the transaminases"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Hyperalaninemia HP:0003348 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperalaninemia (HP:0003348). HP:0003348 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Plasma amino acids showed significant increases in glutamine (1700 μmol/L), alanine (1500 μmol/L), and proline (1400 μmol/L)"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Hyperprolinemia HP:0008358 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperprolinemia (HP:0008358). HP:0008358 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Amino acids in plasma showed an elevated concentration of proline"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Hyperglutaminemia HP:0003217 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperglutaminemia (HP:0003217). HP:0003217 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Plasma amino acids showed significant increases in glutamine (1700 μmol/L), alanine (1500 μmol/L), and proline (1400 μmol/L)"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
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:33169484 SUPPORT Human Clinical
"Spinal‐lactate was 3.3 mmol/L (NR 0.8–2.8)"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Musculoskeletal 1
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:33169484 SUPPORT Human Clinical
"At 40 h of age she was clinically unremarkable except slightly hypotonic"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Nervous System 4
Encephalopathy HP:0001298 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Encephalopathy (HP:0001298). HP:0001298 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"The infant was encephalopathic, extremely floppy, and areflexic with no clinical seizures."
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Human Clinical
"The central nervous system findings are often fluctuating encephalopathy"
Broader mitochondrial clinical context complements the direct COX16 case evidence; it does not establish a frequency or time course for COX16.
Areflexia HP:0001284 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Areflexia (HP:0001284). HP:0001284 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"The infant was encephalopathic, extremely floppy, and areflexic with no clinical seizures."
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Ventriculomegaly HP:0002119 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ventriculomegaly (HP:0002119). HP:0002119 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"Both lateral ventricles and third ventricles were enlarged"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Cerebral Infarct HP:0025722 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral infarct (HP:0025722). HP:0025722 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"multiple areas of supratentorial and brainstem infarcts with generalized cerebral edema"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Respiratory 2
Respiratory Failure Requiring Assisted Ventilation HP:0004887 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Respiratory failure requiring assisted ventilation (HP:0004887). HP:0004887 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"The baby remained obtunded and ventilator dependent"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Tachypnea HP:0002789 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tachypnea (HP:0002789). HP:0002789 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"she was transferred to the neonatal intensive care unit due to tachypnoea"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Voice 1
High-Pitched Cry HP:0025430 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is High-pitched cry (HP:0025430). HP:0025430 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"irritability with a high‐pitched cry, regurgitations, and hypoglycemia"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
Growth 2
Intrauterine Growth Retardation HP:0001511 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intrauterine growth retardation (HP:0001511). HP:0001511 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"He had symmetrical intrauterine growth retardation with a birth weight (BW) of 1700 g"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
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:33169484 SUPPORT Human Clinical
"From then onwards she had diarrhea and difficulties gaining weight"
The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
🧬

Genetic Associations

1
COX16 loss-of-function variants
Gene: COX16 hgnc:20213 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is COX16 (hgnc:20213). hgnc:20213 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"It creates a premature stop codon in exon 4."
The reported variant is protein truncating.
PMID:33169484 SUPPORT Human Clinical
"Segregation analysis revealed that the parents of both patients were heterozygous for the identified COX16 variant."
Independent family segregation supports recessive inheritance.
Variants (1)
COX16 c.244C>T (p.Arg82Ter)
Gene: COX16 hgnc:20213 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in COX16 (hgnc:20213). hgnc:20213 is a gene from the HUGO Gene Nomenclature Committee.
Homozygous nonsense variant in the founding families. Patient fibroblasts lacked detectable COX16 and showed a severe assembly defect; wild-type complementation restored complex IV activity.
Show evidence (3 references)
PMID:33169484 SUPPORT Human Clinical
"To identify the genetic cause of the complex IV deficiency we performed WES and detected a homozygous variant in the gene encoding the complex IV assembly factor COX16 in both patients: Chr14(GRCh37): g.70793127G>A; NM_016468.6: c.244C>T p.(Arg82*)."
The report specifies the transcript and variant.
PMID:33169484 SUPPORT In Vitro
"undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As"
Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
PMID:33169484 SUPPORT In Vitro
"Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines."
Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
💊

Medical Actions

10
Acute metabolic stabilization
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
Treat hypoglycemia, acidosis and cardiorespiratory decompensation in a specialist setting. Glucose corrected neonatal hypoglycemia in the second patient; bicarbonate response differed between the cases. These observations do not establish a disease-modifying therapy.
Target Phenotypes: Neonatal hypoglycemia HP:0001998 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Neonatal hypoglycemia (HP:0001998). HP:0001998 is a phenotype from the Human Phenotype Ontology. Lactic acidosis HP:0003128 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Lactic acidosis (HP:0003128), qualified as severity severe; neonatal onset. HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:33169484 SUPPORT Human Clinical
"The hypoglycemia was quickly resolved by glucose infusion."
A reported acute response supports correction of hypoglycemia.
PMID:33169484 SUPPORT Human Clinical
"persisted despite bicarbonate infusion and THAM"
Acidosis remained refractory in the first patient.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Treatment during acute decompensation should include dextrose-containing IV fluids, stopping exposure to potentially toxic medications, and correction of any metabolic derangements."
General mitochondrial emergency guidance must be individualized, including fluid volume in cardiac disease.
Cardiac treatment and surveillance
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: Beta-Adrenergic Antagonist NCIT:C29576 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses Beta-Adrenergic Antagonist (NCIT:C29576). NCIT:C29576 is a therapeutic agent from the NCI Thesaurus.
Platform: Small molecule
Cardiology-directed care addresses hypertrophic obstruction and heart failure. A beta blocker was used in the longer-surviving infant, with temporary improvement in feeding; later cardiac decline still occurred. Surveillance intensity should reflect the rapid infantile course.
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. Left ventricular outflow tract obstruction HP:0032092 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Left ventricular outflow tract obstruction (HP:0032092). HP:0032092 is a phenotype from the Human Phenotype Ontology. Congestive heart failure HP:0001635 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Congestive heart failure (HP:0001635). HP:0001635 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"She was started on β‐blocker therapy and regained the ability to feed by bottle."
The case reports a symptomatic response without establishing durable cardiac benefit.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Earlier follow-up is suggested for those with new-onset cardiac symptoms or those at higher risk."
General consensus supports individualized frequent monitoring in high-risk infants.
Nutritional 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
Monitor growth and feeding safety and provide enteral support as needed. Nasogastric feeding was required in the longer-surviving infant.
Target Phenotypes: Feeding difficulties in infancy HP:0008872 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Feeding difficulties in infancy (HP:0008872). HP:0008872 is a phenotype from the Human Phenotype Ontology. 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)
PMID:33169484 SUPPORT Human Clinical
"A nasogastric tube was inserted at 4.5 months of age."
Direct case evidence documents enteral feeding support.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Nutritional support must be provided with enteral feeds if tolerated or with peripheral or central parenteral nutrition that is calculated with the help of a trained dietitian."
General mitochondrial critical-care consensus supports individualized nutrition.
Respiratory support
Action: Respiratory TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Respiratory Therapy (NCIT:C15322). NCIT:C15322 is a clinical intervention from the NCI Thesaurus. NCIT:C15322
Platform: Device
Respiratory assessment and assisted ventilation may be necessary during severe neonatal decompensation. Ventilator dependence was documented in the first patient.
Target Phenotypes: Respiratory failure requiring assisted ventilation HP:0004887 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Respiratory failure requiring assisted ventilation (HP:0004887). HP:0004887 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"The baby remained obtunded and ventilator dependent"
The case demonstrates the need for respiratory support in severe disease.
Hearing assessment and support
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: Device
Audiological evaluation and age-appropriate amplification may be considered according to hearing severity, clinical stability and goals of care. The recommendations are extrapolated from broader mitochondrial disease care.
Target Phenotypes: Congenital sensorineural hearing impairment HP:0008527 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Congenital sensorineural hearing impairment (HP:0008527), qualified as laterality bilateral. HP:0008527 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Moderate to severe hearing loss should be treated with digital hearing aids to improve function; when profound, cochlear implantation should be considered."
General mitochondrial consensus describes supportive options, not COX16-specific outcome evidence.
Illness 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
Avoid prolonged fasting and individualize glucose-containing fluids to prevent catabolism, allowing for contraindications or prior adverse glucose responses. Review drug toxicity and anesthesia risks with the treating team; prolonged propofol use warrants particular caution.
Show evidence (3 references)
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Mitochondrial patients should take precautions to prevent entering catabolism"
General mitochondrial guidance supports an individualized emergency plan.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Patients should minimize preoperative fasting and have glucose added to their perioperative IV fluids, unless they are on a ketogenic diet or have been demonstrated to have adverse reaction to higher glucose intake."
Perioperative glucose recommendations include explicit exceptions.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Mitochondrial patients may be at a higher risk for propofol infusion syndrome and propofol use should be avoided or limited to short procedures."
General anesthetic caution is not evidence of a COX16-specific adverse reaction.
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
Coordinate metabolic, cardiac, neurological, hepatic, respiratory and nutritional care. In hepatic dysfunction, assess glucose and coagulation and review medications that can worsen liver injury; mitochondrial hepatocerebral guidance advises avoiding valproate.
Show evidence (3 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"These focus on regular surveillance to detect complications and their management using standard approaches that are not usually specific to mitochondrial disorders."
GeneReviews directs care toward consensus surveillance and standard management.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Hypoglycemia, hypoalbuminemia, or coagulopathy must be excluded if liver dysfunction is suspected."
General mitochondrial critical-care consensus supports focused hepatic assessment.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"hepatocerebral involvement is common in infantile mitochondrial disease; the use of valproate for seizure control must be avoided in these patients as fulminant hepatic failure has been associated with this medication."
The caution applies to mitochondrial hepatocerebral disease; this is not a COX16-specific adverse-event trial.
Palliative symptom management
Action: Palliative TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Palliative Therapy (NCIT:C15292). NCIT:C15292 is a clinical intervention from the NCI Thesaurus. NCIT:C15292
Agent: morphine CHEBI:17303 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses morphine (CHEBI:17303). CHEBI:17303 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Family-centered goals-of-care discussions and symptom relief may be appropriate in severe progressive disease. Morphine was used for palliation during terminal cardiac decline in the longer-surviving infant.
Show evidence (1 reference)
PMID:33169484 SUPPORT Human Clinical
"She was palliated with morphine and died almost 7 months old."
The case documents palliative care without implying that the same approach applies to every patient.
Genetic counseling and reproductive testing
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 carrier status and discuss conditional autosomal recessive recurrence risks. Familial variant identification enables carrier testing and consideration of prenatal or preimplantation testing.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"If both parents are known to be ... heterozygous ... for a causative ... 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."
General recessive counseling applies when the familial variant and parental carrier states are established.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"Once the ... pathogenic variant ... (s) have been identified in an affected family member, ... prenatal testing ... for a pregnancy at increased risk and ... preimplantation genetic testing ... are possible."
The nuclear-gene section of GeneReviews supports reproductive testing after identifying familial variants.
Experimental copper supplementation
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: copper(II) chloride CHEBI:49553 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses copper(II) chloride (CHEBI:49553). CHEBI:49553 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Copper supplementation improved enzyme activity in an engineered HEK293 knockout model, but copper chloride did not improve subunit abundance, assembled complex IV or activity in the tested patient fibroblasts. This conflicting preclinical evidence does not establish patient benefit.
Show evidence (3 references)
PMID:29355485 SUPPORT In Vitro
"copper supplementation increases COX activity and restores normal steady state levels of COX subunits in COX16 knockout cells"
The earlier engineered HEK293 model showed a biochemical response that was not reproduced in the patient fibroblast experiment.
PMID:33169484 REFUTE In Vitro
"the complex IV enzyme activity showed no recovery at all after the CuCl2 treatment of the patient cell line"
Copper chloride failed to rescue the tested Arg82Ter patient fibroblasts. This refutes biochemical rescue by copper in this patient-cell model; it is not a clinical efficacy trial.
PMID:33169484 REFUTE In Vitro
"No positive effect of the copper treatment on the levels of COX subunits or the amount of fully assembled complex IV was observed."
Both protein assembly and enzymatic outcomes were negative in the patient-cell experiment. This refutes biochemical rescue by copper in this patient-cell model; it is not a clinical efficacy trial.
🔬

Biochemical Markers

2
Isolated complex IV deficiency
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"A skeletal muscle biopsy of Subject 2 showed an isolated complex IV deficiency"
Patient muscle enzymology shows the isolated complex IV defect.
PMID:33169484 SUPPORT Human Clinical
"The muscle histology and histochemistry were normal, no COX‐negative fibres were observed with the COX/SDH stain, which could be explained by the residual complex IV activity."
Normal histochemical staining does not imply normal respiratory-chain enzymology.
Metabolic and hepatic biochemical abnormalities
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"the urine polyols showed secondary increases in all fractions"
Secondary metabolic abnormalities can accompany decompensation.
PMID:33169484 SUPPORT Human Clinical
"in C4, C6, C8, C10, C16, and C18) in a nonspecific pattern"
The authors describe the first patient's acylcarnitine profile as nonspecific.
🔬

Diagnosis

3
Molecular diagnosis and segregation
Consider a mitochondrial gene panel or exome/genome testing in neonatal lactic acidosis with multisystem disease. Identify biallelic COX16 variants and assess segregation; uncertain alleles require appropriate interpretation.
Show evidence (2 references)
PMID:33169484 SUPPORT Human Clinical
"we performed WES and detected a homozygous variant in the gene encoding the complex IV assembly factor COX16 in both patients"
Exome sequencing established the genetic diagnosis in the founding cases.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/ SUPPORT REVIEW SYNTHESIS Other
"Approaches to ... molecular genetic testing ... of a ... proband ... to consider are use of a ... multigene panel"
General mitochondrial guidance supports molecular testing rather than obligatory biopsy-first diagnosis.
Respiratory-chain and functional assessment
Respiratory-chain enzymology, respirometry and protein/assembly studies can support diagnosis and uncertain-variant interpretation. Routine muscle histology may be normal; patient fibroblast complementation is experimental functional evidence.
Show evidence (4 references)
PMID:33169484 SUPPORT Human Clinical
"high‐resolution respirometry of the skeletal muscle analyzed with an Oxygraph‐2k (Oroboros Instruments) showed clearly reduced mitochondrial respiration"
Subject 2 muscle respirometry documents impaired respiratory capacity.
PMID:33169484 SUPPORT In Vitro
"Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines."
Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
PMID:33169484 SUPPORT Human Clinical
"The muscle histology and histochemistry were normal, no COX‐negative fibres were observed with the COX/SDH stain, which could be explained by the residual complex IV activity."
Histology alone cannot exclude COX16 deficiency.
+ 1 more reference
Multisystem clinical evaluation
Assess metabolic stability, glucose, liver/coagulation indices, cardiac structure and function, respiration, nutrition, hearing and neurological status. Repeat cardiac assessment when symptoms evolve, because the initial echocardiogram may be normal.
Show evidence (4 references)
PMID:33169484 SUPPORT Human Clinical
"Echocardiography and brain ultrasonography were normal."
The second patient initially had normal screening before later cardiac disease.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Standard 12-lead electrocardiogram (ECG) and echocardiogram (with measurement of left ventricular mass and systolic/diastolic function)"
Mitochondrial consensus recommends baseline cardiac assessment.
PMID:28749475 SUPPORT REVIEW SYNTHESIS Other
"Formal audiology testing should be performed at time of diagnosis"
General consensus supports hearing assessment for the documented COX16 sensory manifestation.
+ 1 more reference
📈

Progression

1
Neonatal presentation and variable infantile course
Both founding cases developed neonatal metabolic disease. One died at 55 hours after withdrawal of care. The other was discharged after initial stabilization, developed progressive hypertrophic cardiac disease and feeding problems, and died almost seven months old. These observations are case histories, not a population survival estimate.
Show evidence (3 references)
PMID:33169484 SUPPORT Human Clinical
"succumbed shortly aftercare was withdrawn at 55 h"
The first patient had rapidly fatal neonatal disease.
PMID:33169484 SUPPORT Human Clinical
"She was discharged from the hospital at 2 weeks of age, slightly hypotonic and bottle‐fed."
The second patient initially stabilized.
PMID:33169484 SUPPORT Human Clinical
"She was palliated with morphine and died almost 7 months old."
The second patient survived into infancy.
🧫

Experimental Models

2
Patient fibroblast complementation PRIMARY_CELL_CULTURE
Fibroblasts from the first Arg82Ter patient exhibit the severe assembly defect. Lentiviral wild-type COX16 complementation restores complex IV assembly and activity; copper chloride fails to rescue the defect.
Cell source
Patient skin fibroblasts
Pathograph links
COX16 Protein Deficiency recapitulates fidelity: moderate observes: molecular The patient culture lacks detectable COX16.
Limitations: Cellular experiments do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:33169484 SUPPORT In Vitro
"undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As"
Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
Reduced Complex IV Assembly rescues fidelity: moderate observes: molecular Wild-type complementation restores complex IV assembly and activity.
Limitations: Cellular experiments do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:33169484 SUPPORT In Vitro
"Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines."
Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
Show evidence (3 references)
PMID:33169484 SUPPORT In Vitro
"undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As"
Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
PMID:33169484 SUPPORT In Vitro
"Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines."
Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
PMID:33169484 SUPPORT In Vitro
"the complex IV enzyme activity showed no recovery at all after the CuCl2 treatment of the patient cell line"
Copper chloride failed to rescue the tested Arg82Ter patient fibroblasts.
Engineered human COX16 knockout cells CELL_LINE
CRISPR-disrupted HEK-derived cells reveal selective SCO1 recruitment, COX2 stability and module-joining defects. Residual enzyme activity and copper responses differ from patient fibroblasts.
Cell source
Engineered HEK293 and HEK Flp-In T-REx 293 cells
Pathograph links
Impaired SCO1 Recruitment to COX2 recapitulates fidelity: moderate observes: molecular COX16 knockout reduces recruitment of SCO1 to newly synthesized COX2.
Limitations: Cellular experiments do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:29381136 SUPPORT In Vitro
"only the association of SCO1 with newly synthesized COX2 was affected in the absence of COX16"
Pulse-labeling and immunoisolation identify a selective SCO1-recruitment defect; this is not proof that COX16 directly transports copper.
COX2 Instability recapitulates fidelity: moderate observes: molecular Pulse-chase assays show reduced stability of COX2.
Limitations: Cellular experiments do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:29381136 SUPPORT In Vitro
"COX2 showed a marked reduction in stability in the absence of COX16"
Pulse-chase experiments show instability of newly synthesized COX2.
Defective COX1-COX2 Module Joining recapitulates fidelity: moderate observes: molecular Module association is impaired after COX16 loss.
Limitations: Cellular experiments do not establish clinical treatment efficacy.
Show evidence (1 reference)
PMID:29381136 SUPPORT In Vitro
"COX2-association with MITRAC12 or C12ORF62 was drastically affected by the absence of COX16"
Immunoisolation supports failure to join COX2 to COX1-containing assembly intermediates.
Reduced Complex IV Assembly recapitulates fidelity: moderate observes: molecular Engineered cells recapitulate reduced assembly but retain more function and show a different copper response than the patient cells.
Limitations: Residual activity and copper response differ from the tested patient fibroblasts; kidney-derived cell lines do not model the clinical organ distribution.
Show evidence (1 reference)
PMID:29381136 SUPPORT In Vitro
"the cytochrome c oxidase amount was reduced to ∼50% compared to the wild type control"
Engineered cells retain substantial enzyme; the severity of the assembly defect depends on the experimental system.
Show evidence (4 references)
PMID:29381136 SUPPORT In Vitro
"only the association of SCO1 with newly synthesized COX2 was affected in the absence of COX16"
Pulse-labeling and immunoisolation identify a selective SCO1-recruitment defect; this is not proof that COX16 directly transports copper.
PMID:29381136 SUPPORT In Vitro
"COX2 showed a marked reduction in stability in the absence of COX16"
Pulse-chase experiments show instability of newly synthesized COX2.
PMID:29381136 SUPPORT In Vitro
"COX2-association with MITRAC12 or C12ORF62 was drastically affected by the absence of COX16"
Immunoisolation supports failure to join COX2 to COX1-containing assembly intermediates.
+ 1 more reference
🐁

Animal Models

1
Caenorhabditis elegans COX16 knockdown
Knockdown produces COX deficiency. The available abstract does not establish reproduction of the human multisystem phenotype.
Species
Caenorhabditis elegans
Genotype
COX16 homolog knockdown
Pathograph links
Reduced Respiratory Capacity recapitulates fidelity: moderate observes: molecular Knockdown produces the biochemical COX-deficiency phenotype.
Limitations: The biochemical phenotype does not establish clinical fidelity to neonatal human cardiomyopathy, liver disease or encephalopathy.
Show evidence (1 reference)
PMID:29355485 SUPPORT Model Organism
"Its knockdown in C. elegans produces COX deficiency"
The whole-organism knockdown supports a conserved role in complex IV biogenesis.
Show evidence (1 reference)
PMID:29355485 SUPPORT Model Organism
"Its knockdown in C. elegans produces COX deficiency"
The whole-organism knockdown supports a conserved role in complex IV biogenesis.
{ }

Source YAML

click to show 
name: COX16-Related COX Deficiency
category: Mendelian
creation_date: '2026-06-23T00:00:00Z'
synonyms:
- COX16 deficiency
- Mitochondrial complex IV deficiency, nuclear type 22
- MC4DN22
- COX16-related cytochrome c oxidase deficiency
disease_term:
  preferred_term: COX16-related COX deficiency (MC4DN22)
  term:
    id: MONDO:0859160
    label: mitochondrial complex IV deficiency, nuclear type 22
parents:
- Mitochondrial Disease
- Inborn Error of Metabolism
description: 'COX16-related complex IV deficiency is an autosomal recessive mitochondrial disorder associated with loss of the COX16 assembly factor. COX16 assists SCO1 recruitment to newly synthesized COX2 and subsequent joining of the COX2 and COX1 assembly modules. Deficiency reduces COX2 stability, mature complex IV and respiratory capacity. The founding report described neonatal metabolic disease with different subsequent courses: death in the first days of life or progressive cardiac disease with survival into infancy. Clinical evidence remains limited, while patient-cell complementation and engineered-cell studies support the molecular mechanism. Copper rescue in engineered cells did not reproduce in the tested patient fibroblasts.'
pathophysiology:
- name: COX16 Protein Deficiency
  description: The homozygous Arg82Ter variant is associated with loss of detectable COX16 protein in patient fibroblasts. COX16 is an inner-mitochondrial-membrane assembly factor with its C-terminus facing the intermembrane space.
  evidence:
  - &id003
    reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: undetectable levels of the COX16 protein and the COX2 subunit of complex IV, and reduced expression levels of the complex IV subunits COX1, COX4, and COX5As
    explanation: Patient-fibroblast immunoblots show loss of detectable COX16 and altered complex IV subunits.
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Cox16 is an inner mitochondrial membrane protein with its C-terminus facing the intermembrane space (IMS).
    explanation: Protease protection and carbonate extraction establish localization.
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: human COX16 functions to stabilize the interaction between SCO1 and newly synthesized COX2.
    explanation: The human-cell experiments support COX16-dependent protein recruitment as its molecular activity in the assembly pathway.
  genes:
  - &id010
    preferred_term: COX16
    term:
      id: hgnc:20213
      label: COX16
  molecular_functions:
  - preferred_term: COX16-mediated protein recruitment during complex IV assembly
    term:
      id: GO:0030674
      label: protein-macromolecule adaptor activity
    modifier: DECREASED
    description: COX16 stabilizes the association of SCO1 with newly synthesized COX2; the adaptor binding represents this protein-recruitment role, not direct copper transport.
  biological_scale: MOLECULAR
  downstream:
  - target: Impaired SCO1 Recruitment to COX2
    description: Loss of COX16 reduces recruitment of SCO1 to newly synthesized COX2.
    causal_link_type: DIRECT
    evidence:
    - &id001
      reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: only the association of SCO1 with newly synthesized COX2 was affected in the absence of COX16
      explanation: Pulse-labeling and immunoisolation identify a selective SCO1-recruitment defect; this is not proof that COX16 directly transports copper.
  - target: COX2 Instability
    description: Loss of COX16 destabilizes newly synthesized COX2.
    causal_link_type: DIRECT
    evidence:
    - &id002
      reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: COX2 showed a marked reduction in stability in the absence of COX16
      explanation: Pulse-chase experiments show instability of newly synthesized COX2.
  - target: Defective COX1-COX2 Module Joining
    description: COX16 loss impairs association of COX2 with the COX1 assembly module.
    causal_link_type: DIRECT
    evidence:
    - &id004
      reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: COX2-association with MITRAC12 or C12ORF62 was drastically affected by the absence of COX16
      explanation: Immunoisolation supports failure to join COX2 to COX1-containing assembly intermediates.
- name: Impaired SCO1 Recruitment to COX2
  description: COX16-deficient engineered cells show reduced association of SCO1 with newly synthesized COX2, implicating a defect in CuA-site maturation. SCO2 association is preserved. Direct copper transport by COX16 is not demonstrated.
  evidence:
  - *id001
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: The binding of other COX2 chaperones such as SCO2, COA6, and FAM36A was unaffected by the absence of COX16.
    explanation: The pulse-labeled COX2 assay discriminates the SCO1 defect from generalized loss of chaperone recruitment.
  biological_scale: MOLECULAR
  downstream:
  - target: Reduced Complex IV Assembly
    description: Defective metallochaperone recruitment limits COX2 maturation and downstream assembly.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: COX16 facilitates the association of SCO1 and thus probably leads to proper COX2 maturation.
      explanation: The authors interpret SCO1 recruitment as a maturation step; intermediary CuA chemistry is not directly measured.
- name: COX2 Instability
  description: Newly synthesized COX2 turns over more rapidly in COX16-knockout cells, despite preserved mitochondrial translation. Patient fibroblasts also show markedly reduced COX2 protein.
  evidence:
  - *id002
  - *id003
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: no significant differences were observed in the synthesis of either COX1, COX2, or any other protein
    explanation: Pulse labeling argues against a generalized mitochondrial translation defect in the engineered cells.
  biological_scale: MOLECULAR
  downstream:
  - target: Reduced Complex IV Assembly
    description: Reduced availability of stable COX2 limits incorporation into mature complex IV.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: These analyses revealed a notable reduction of newly synthesized COX2 in mature cytochrome c oxidase
      explanation: Labeled-subunit assembly analysis shows reduced incorporation of COX2.
- name: Defective COX1-COX2 Module Joining
  description: COX16 promotes association of the COX2 module with COX1-containing MITRAC intermediates. Its absence leaves COX1 accumulated in subassemblies. Human COX16 is a transient assembly factor rather than a constitutive component of mature respiratory supercomplexes.
  evidence:
  - *id004
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: We observed an accumulation of COX1 in the mitochondrial translation regulation assembly intermediate of cytochrome c oxidase in the patient cell line transduced with GFP
    explanation: Patient-fibroblast assembly intermediates support the module-joining defect.
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: COX16 does not act on respiratory chain supercomplexes
    explanation: The human-cell study found COX16 in assembly intermediates rather than mature supercomplexes.
  biological_scale: MOLECULAR
  downstream:
  - target: Reduced Complex IV Assembly
    description: Failure to merge the modules limits formation of mature cytochrome c oxidase.
    causal_link_type: DIRECT
    evidence:
    - *id004
- name: Reduced Complex IV Assembly
  description: Mature complex IV is markedly reduced. It was undetectable by blue-native immunoblot in the tested patient fibroblasts, while engineered knockout cells retained substantial enzyme abundance and activity. Other respiratory complexes were relatively preserved in the patient investigations.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: an absence of the fully assembled complex IV with normal expression levels of the other OXPHOS complexes
    explanation: Blue-native immunoblotting of Subject 1 fibroblasts shows a severe, selective assembly defect; undetectable bands do not imply zero enzymatic activity.
  - reference: PMID:29381136
    reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: the cytochrome c oxidase amount was reduced to ∼50% compared to the wild type control
    explanation: Engineered cells retain substantial enzyme; the severity of the assembly defect depends on the experimental system.
  - &id011
    reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Activity measurements of the RC enzymes showed a complete rescue of complex IV activity in cells transduced with the wt‐COX16 construct compared to the GFP‐transduced patient cell lines.
    explanation: Wild-type COX16 complementation rescues the cellular enzyme defect, supporting variant causality.
  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 Respiratory Capacity
    description: Reduced functional complex IV limits terminal respiratory-chain capacity.
    causal_link_type: DIRECT
    evidence:
    - &id005
      reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: high‐resolution respirometry of the skeletal muscle analyzed with an Oxygraph‐2k (Oroboros Instruments) showed clearly reduced mitochondrial respiration
      explanation: Subject 2 muscle respirometry documents impaired respiratory capacity.
    - reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: reduction of complex IV activity to ∼65%, as compared to the control
      explanation: Activity is reduced rather than abolished in this engineered knockout system.
- name: Reduced Respiratory Capacity
  description: Complex IV deficiency reduces mitochondrial respiration. Residual activity differs between tissues and models; neither absent total oxidative ATP production nor universal collapse of ATP synthesis was demonstrated. Cardiac, neurological, hepatic and metabolic manifestations accompany the respiratory defect.
  evidence:
  - *id005
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: tissues and organs that are highly dependent on aerobic metabolism are preferentially involved in mitochondrial disorders
    explanation: General mitochondrial disease physiology provides context for multisystem vulnerability, without specifying COX16 phenotype frequencies.
    quote_role: REVIEW_SYNTHESIS
  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: Impaired mitochondrial respiration contributes to cardiac disease through unresolved tissue-level intermediates.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id006
      reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Repeated echocardiography showed massive left ventricular hypertrophy
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  - target: Encephalopathy
    description: Respiratory dysfunction contributes to neurological injury through unresolved intermediates.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id007
      reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The infant was encephalopathic, extremely floppy, and areflexic with no clinical seizures.
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  - target: Lactic Acidosis
    description: Impaired oxidative metabolism is associated with lactate accumulation and metabolic acidosis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id008
      reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Severe lactic acidosis was noted at birth
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  - target: Hepatic Failure
    description: Mitochondrial dysfunction and systemic decompensation accompany hepatic failure; the intervening mechanisms are unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - &id009
      reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: He had multisystemic involvement with liver failure and coagulopathy
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
phenotypes:
- name: Hypertrophic Cardiomyopathy
  description: Cardiac hypertrophy affected different ventricles in the two reported patients. The initially normal echocardiogram in the longer-surviving infant was followed by marked left ventricular hypertrophy.
  evidence:
  - *id006
  phenotype_term: &id014
    preferred_term: Hypertrophic cardiomyopathy
    term:
      id: HP:0001639
      label: Hypertrophic cardiomyopathy
  sequelae:
  - target: Left Ventricular Outflow Tract Obstruction
    description: Severe left ventricular hypertrophy was accompanied by outflow obstruction in the longer-surviving infant.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: showed massive left ventricular hypertrophy (end‐diastolic septum thickness Z‐score 6 and left ventricular wall thickness at end‐diastole Z‐score 4) with left ventricular outlet obstruction but with preserved biventricular function.
      explanation: The echocardiographic description links marked hypertrophy to an obstructive cardiac phenotype in this patient.
  - target: Congestive Heart Failure
    description: The hypertrophic cardiac disease progressed to heart failure in the longer-surviving infant; the report does not resolve all intervening cardiac mechanisms.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion.
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
- name: Encephalopathy
  description: Severe neonatal encephalopathy was documented in the first patient; neuroimaging and clinical courses differed between the two cases.
  evidence:
  - *id007
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The central nervous system findings are often fluctuating encephalopathy
    explanation: Broader mitochondrial clinical context complements the direct COX16 case evidence; it does not establish a frequency or time course for COX16.
    quote_role: REVIEW_SYNTHESIS
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
- name: Lactic Acidosis
  description: Severe neonatal lactic acidosis occurred in both reported patients. It remained refractory in one, while the other stabilized initially and later had persistent hyperlactatemia.
  evidence:
  - *id008
  phenotype_term: &id013
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
    severity: SEVERE
    onset:
      onset_category: NEONATAL
- name: Hepatic Failure
  description: Liver failure was described in the severely affected neonate; the other patient had lesser biochemical hepatic involvement.
  evidence:
  - *id009
  phenotype_term:
    preferred_term: Hepatic failure
    term:
      id: HP:0001399
      label: Hepatic failure
- name: Hypotonia
  description: Hypotonia ranged from extreme neonatal floppiness to mild hypotonia after initial metabolic stabilization.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At 40 h of age she was clinically unremarkable except slightly hypotonic
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
- name: Areflexia
  description: Areflexia accompanied severe neonatal encephalopathy in the first patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The infant was encephalopathic, extremely floppy, and areflexic with no clinical seizures.
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Areflexia
    term:
      id: HP:0001284
      label: Areflexia
- name: Neonatal Hypoglycemia
  description: Marked hypoglycemia was reported in both neonates and was corrected with acute treatment; recurrent hypoglycemia is not established.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: After 24 h of life, she was transferred to the neonatal intensive care unit due to tachypnoea, irritability with a high‐pitched cry, regurgitations, and hypoglycemia
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id012
    preferred_term: Neonatal hypoglycemia
    term:
      id: HP:0001998
      label: Neonatal hypoglycemia
- name: Coagulopathy
  description: Coagulopathy accompanied neonatal liver failure; a particular coagulation-factor defect was not defined.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: He had multisystemic involvement with liver failure and coagulopathy
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Abnormality of coagulation
    term:
      id: HP:0001928
      label: Abnormality of coagulation
- name: Congenital Sensorineural Hearing Impairment
  description: Bilateral congenital sensorineural hearing loss was reported in the first patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: bilateral congenital sensorineural hearing loss
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id020
    preferred_term: Congenital sensorineural hearing impairment
    term:
      id: HP:0008527
      label: Congenital sensorineural hearing impairment
    laterality: BILATERAL
- name: Intrauterine Growth Retardation
  description: Symmetric growth restriction was reported in one of the two affected infants.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: He had symmetrical intrauterine growth retardation with a birth weight (BW) of 1700 g
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Intrauterine growth retardation
    term:
      id: HP:0001511
      label: Intrauterine growth retardation
- name: Respiratory Failure Requiring Assisted Ventilation
  description: The severely affected neonate remained ventilator dependent.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The baby remained obtunded and ventilator dependent
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id019
    preferred_term: Respiratory failure requiring assisted ventilation
    term:
      id: HP:0004887
      label: Respiratory failure requiring assisted ventilation
- name: Tachypnea
  description: Tachypnea was part of the second infant's neonatal metabolic presentation.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: she was transferred to the neonatal intensive care unit due to tachypnoea
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Tachypnea
    term:
      id: HP:0002789
      label: Tachypnea
- name: High-Pitched Cry
  description: A high-pitched cry with irritability was reported during neonatal decompensation.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: irritability with a high‐pitched cry, regurgitations, and hypoglycemia
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: High-pitched cry
    term:
      id: HP:0025430
      label: High-pitched cry
- name: Feeding Difficulties in Infancy
  description: Feeding difficulties required nasogastric support in the longer-surviving infant and worsened with cardiac disease.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion.
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id017
    preferred_term: Feeding difficulties in infancy
    term:
      id: HP:0008872
      label: Feeding difficulties in infancy
- name: Failure to Thrive
  description: Poor weight gain developed after an initial period of growth in the longer-surviving infant.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: From then onwards she had diarrhea and difficulties gaining weight
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id018
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
- name: Diarrhea
  description: Diarrhea developed after the first weeks of life in the longer-surviving infant.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: From then onwards she had diarrhea and difficulties gaining weight
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
- name: Ventriculomegaly
  description: Enlargement of the lateral and third ventricles was observed in the longer-surviving infant. The authors considered associated brain atrophy uncertain.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Both lateral ventricles and third ventricles were enlarged
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
- name: Cerebral Edema
  description: Generalized cerebral edema occurred in the severely affected neonate.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: multiple areas of supratentorial and brainstem infarcts with generalized cerebral edema
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Cerebral edema
    term:
      id: HP:0002181
      label: Cerebral edema
- name: Cerebral Infarct
  description: Supratentorial infarcts were reported alongside brainstem injury in the severely affected neonate; these were not classified as MELAS stroke-like episodes.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: multiple areas of supratentorial and brainstem infarcts with generalized cerebral edema
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Cerebral infarct
    term:
      id: HP:0025722
      label: Cerebral infarct
- name: Elevated Circulating Creatine Kinase
  description: Creatine kinase was elevated in the neonatal biochemical investigations.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Serum creatine kinase was 3000 U/L (NR < 450)
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase activity
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase activity
- name: Elevated Hepatic Transaminases
  description: Transaminase elevation ranged from modest elevations to changes accompanying liver failure.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Liver function tests showed 2–3‐fold increases in the transaminases
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Elevated circulating hepatic transaminase concentration
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
- name: Hyperalaninemia
  description: Plasma alanine was markedly increased in the first patient but normal in the second patient's reported plasma sample.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Plasma amino acids showed significant increases in glutamine (1700 μmol/L), alanine (1500 μmol/L), and proline (1400 μmol/L)
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Hyperalaninemia
    term:
      id: HP:0003348
      label: Hyperalaninemia
- name: Hyperprolinemia
  description: Plasma proline elevation occurred in the biochemical workup; this is a secondary metabolic finding rather than primary hyperprolinemia.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Amino acids in plasma showed an elevated concentration of proline
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Hyperprolinemia
    term:
      id: HP:0008358
      label: Hyperprolinemia
- name: Hyperglutaminemia
  description: Plasma glutamine elevation accompanied the severe neonatal metabolic illness in the first patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Plasma amino acids showed significant increases in glutamine (1700 μmol/L), alanine (1500 μmol/L), and proline (1400 μmol/L)
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Hyperglutaminemia
    term:
      id: HP:0003217
      label: Hyperglutaminemia
- name: Ketonuria
  description: Moderate ketonuria was reported in the first patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: with a fixed moderate ketonuria
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Ketonuria
    term:
      id: HP:0002919
      label: Ketonuria
- name: Increased CSF Lactate
  description: CSF lactate was mildly increased in the second patient's neonatal investigation.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Spinal‐lactate was 3.3 mmol/L (NR 0.8–2.8)
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term:
    preferred_term: Increased CSF lactate
    term:
      id: HP:0002490
      label: Increased CSF lactate
- name: Congestive Heart Failure
  description: Heart failure developed during infancy in the longer-surviving patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion.
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id016
    preferred_term: Congestive heart failure
    term:
      id: HP:0001635
      label: Congestive heart failure
  sequelae:
  - target: Feeding Difficulties in Infancy
    description: Progressive heart failure caused secondary feeding problems in the longer-surviving infant.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Her cardiac condition/heart failure gradually deteriorated after 5 months, causing secondary feeding problems and lung congestion.
      explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
- name: Left Ventricular Outflow Tract Obstruction
  description: Marked left ventricular hypertrophy was associated with outflow obstruction in the longer-surviving infant.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: with left ventricular outlet obstruction but with preserved biventricular function
    explanation: The founding COX16 clinical report documents this finding; the small case series does not establish a population frequency.
  phenotype_term: &id015
    preferred_term: Left ventricular outflow tract obstruction
    term:
      id: HP:0032092
      label: Left ventricular outflow tract obstruction
inheritance:
- name: Autosomal recessive
  description: The founding patients were homozygous for Arg82Ter, with both parents in each family heterozygous. If both parents carry the familial pathogenic variant, each pregnancy has a 25% affected, 50% carrier and 25% unaffected noncarrier probability.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Segregation analysis revealed that the parents of both patients were heterozygous for the identified COX16 variant.
    explanation: Parental segregation supports autosomal recessive inheritance.
  - &id021
    reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: If both parents are known to be ... heterozygous ... for a causative ... 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: General recessive counseling applies when the familial variant and parental carrier states are established.
    quote_role: REVIEW_SYNTHESIS
genetic:
- name: COX16 loss-of-function variants
  gene_term: *id010
  features: The founding report identifies homozygous NM_016468.6:c.244C>T (p.Arg82Ter), a premature stop in exon 4, in two unrelated families. Loss of detectable protein and cellular rescue support loss of function. The small clinical literature does not establish a general genotype-prognosis relationship or population prevalence.
  variants:
  - name: COX16 c.244C>T (p.Arg82Ter)
    gene: *id010
    description: Homozygous nonsense variant in the founding families. Patient fibroblasts lacked detectable COX16 and showed a severe assembly defect; wild-type complementation restored complex IV activity.
    evidence:
    - reference: PMID:33169484
      reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 'To identify the genetic cause of the complex IV deficiency we performed WES and detected a homozygous variant in the gene encoding the complex IV assembly factor COX16 in both patients: Chr14(GRCh37): g.70793127G>A; NM_016468.6: c.244C>T p.(Arg82*).'
      explanation: The report specifies the transcript and variant.
    - *id003
    - *id011
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: It creates a premature stop codon in exon 4.
    explanation: The reported variant is protein truncating.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Segregation analysis revealed that the parents of both patients were heterozygous for the identified COX16 variant.
    explanation: Independent family segregation supports recessive inheritance.
  notes: ClinGen assigned Moderate validity in August 2025 under the broader MONDO:0044970 primary mitochondrial disease concept. That source concept differs from the MC4DN22 binding MONDO:0859160 used here. The classification is discussed as supporting context rather than copied into a formal gene_disease_validity assertion for this disease identifier.
progression:
- phase: Neonatal presentation and variable infantile course
  notes: Both founding cases developed neonatal metabolic disease. One died at 55 hours after withdrawal of care. The other was discharged after initial stabilization, developed progressive hypertrophic cardiac disease and feeding problems, and died almost seven months old. These observations are case histories, not a population survival estimate.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: succumbed shortly aftercare was withdrawn at 55 h
    explanation: The first patient had rapidly fatal neonatal disease.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She was discharged from the hospital at 2 weeks of age, slightly hypotonic and bottle‐fed.
    explanation: The second patient initially stabilized.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She was palliated with morphine and died almost 7 months old.
    explanation: The second patient survived into infancy.
biochemical:
- name: Isolated complex IV deficiency
  notes: Muscle and fibroblast investigations showed reduced complex IV activity with residual enzyme function. Normal muscle histology and absence of COX-negative fibers in one patient did not exclude biochemical deficiency.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A skeletal muscle biopsy of Subject 2 showed an isolated complex IV deficiency
    explanation: Patient muscle enzymology shows the isolated complex IV defect.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The muscle histology and histochemistry were normal, no COX‐negative fibres were observed with the COX/SDH stain, which could be explained by the residual complex IV activity.
    explanation: Normal histochemical staining does not imply normal respiratory-chain enzymology.
- name: Metabolic and hepatic biochemical abnormalities
  notes: Blood lactate and pyruvate, amino acids, urinary organic acids, creatine kinase and transaminases can be abnormal. The reported acylcarnitine changes were nonspecific and do not establish a primary fatty-acid oxidation disorder.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the urine polyols showed secondary increases in all fractions
    explanation: Secondary metabolic abnormalities can accompany decompensation.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: in C4, C6, C8, C10, C16, and C18) in a nonspecific pattern
    explanation: The authors describe the first patient's acylcarnitine profile as nonspecific.
diagnosis:
- name: Molecular diagnosis and segregation
  description: Consider a mitochondrial gene panel or exome/genome testing in neonatal lactic acidosis with multisystem disease. Identify biallelic COX16 variants and assess segregation; uncertain alleles require appropriate interpretation.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: we performed WES and detected a homozygous variant in the gene encoding the complex IV assembly factor COX16 in both patients
    explanation: Exome sequencing established the genetic diagnosis in the founding cases.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Approaches to ... molecular genetic testing ... of a ... proband ... to consider are use of a ... multigene panel
    explanation: General mitochondrial guidance supports molecular testing rather than obligatory biopsy-first diagnosis.
    quote_role: REVIEW_SYNTHESIS
- name: Respiratory-chain and functional assessment
  description: Respiratory-chain enzymology, respirometry and protein/assembly studies can support diagnosis and uncertain-variant interpretation. Routine muscle histology may be normal; patient fibroblast complementation is experimental functional evidence.
  evidence:
  - *id005
  - *id011
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The muscle histology and histochemistry were normal, no COX‐negative fibres were observed with the COX/SDH stain, which could be explained by the residual complex IV activity.
    explanation: Histology alone cannot exclude COX16 deficiency.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: In many individuals in whom ... molecular genetic testing ... does not yield or confirm a diagnosis, further investigation of suspected mitochondrial disease can involve a range of different clinical tests, including muscle biopsy for respiratory chain function.
    explanation: Biopsy is considered when molecular testing is inconclusive rather than mandatory in every patient.
    quote_role: REVIEW_SYNTHESIS
- name: Multisystem clinical evaluation
  description: Assess metabolic stability, glucose, liver/coagulation indices, cardiac structure and function, respiration, nutrition, hearing and neurological status. Repeat cardiac assessment when symptoms evolve, because the initial echocardiogram may be normal.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Echocardiography and brain ultrasonography were normal.
    explanation: The second patient initially had normal screening before later cardiac disease.
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Standard 12-lead electrocardiogram (ECG) and echocardiogram (with measurement of left ventricular mass and systolic/diastolic function)
    explanation: Mitochondrial consensus recommends baseline cardiac assessment.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Formal audiology testing should be performed at time of diagnosis
    explanation: General consensus supports hearing assessment for the documented COX16 sensory manifestation.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Electroencephalography (EEG) is indicated in individuals with suspected encephalopathy or seizures.
    explanation: General guidance supports targeted neurological assessment; seizures are not assumed in COX16.
    quote_role: REVIEW_SYNTHESIS
treatments:
- name: Acute metabolic stabilization
  description: Treat hypoglycemia, acidosis and cardiorespiratory decompensation in a specialist setting. Glucose corrected neonatal hypoglycemia in the second patient; bicarbonate response differed between the cases. These observations do not establish a disease-modifying therapy.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The hypoglycemia was quickly resolved by glucose infusion.
    explanation: A reported acute response supports correction of hypoglycemia.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: persisted despite bicarbonate infusion and THAM
    explanation: Acidosis remained refractory in the first patient.
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Treatment during acute decompensation should include dextrose-containing IV fluids, stopping exposure to potentially toxic medications, and correction of any metabolic derangements.
    explanation: General mitochondrial emergency guidance must be individualized, including fluid volume in cardiac disease.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  target_phenotypes:
  - *id012
  - *id013
- name: Cardiac treatment and surveillance
  description: Cardiology-directed care addresses hypertrophic obstruction and heart failure. A beta blocker was used in the longer-surviving infant, with temporary improvement in feeding; later cardiac decline still occurred. Surveillance intensity should reflect the rapid infantile course.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She was started on β‐blocker therapy and regained the ability to feed by bottle.
    explanation: The case reports a symptomatic response without establishing durable cardiac benefit.
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Earlier follow-up is suggested for those with new-onset cardiac symptoms or those at higher risk.
    explanation: General consensus supports individualized frequent monitoring in high-risk infants.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Beta-Adrenergic Antagonist
      term:
        id: NCIT:C29576
        label: Beta-Adrenergic Antagonist
  therapeutic_modality: SMALL_MOLECULE
  target_phenotypes:
  - *id014
  - *id015
  - *id016
- name: Nutritional and feeding support
  description: Monitor growth and feeding safety and provide enteral support as needed. Nasogastric feeding was required in the longer-surviving infant.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A nasogastric tube was inserted at 4.5 months of age.
    explanation: Direct case evidence documents enteral feeding support.
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Nutritional support must be provided with enteral feeds if tolerated or with peripheral or central parenteral nutrition that is calculated with the help of a trained dietitian.
    explanation: General mitochondrial critical-care consensus supports individualized nutrition.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Nutritional Support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  therapeutic_modality: OTHER
  target_phenotypes:
  - *id017
  - *id018
- name: Respiratory support
  description: Respiratory assessment and assisted ventilation may be necessary during severe neonatal decompensation. Ventilator dependence was documented in the first patient.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The baby remained obtunded and ventilator dependent
    explanation: The case demonstrates the need for respiratory support in severe disease.
  treatment_term:
    preferred_term: Respiratory Therapy
    term:
      id: NCIT:C15322
      label: Respiratory Therapy
  therapeutic_modality: DEVICE
  target_phenotypes:
  - *id019
- name: Hearing assessment and support
  description: Audiological evaluation and age-appropriate amplification may be considered according to hearing severity, clinical stability and goals of care. The recommendations are extrapolated from broader mitochondrial disease care.
  evidence:
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Moderate to severe hearing loss should be treated with digital hearing aids to improve function; when profound, cochlear implantation should be considered.
    explanation: General mitochondrial consensus describes supportive options, not COX16-specific outcome evidence.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: DEVICE
  target_phenotypes:
  - *id020
- name: Illness and perioperative precautions
  description: Avoid prolonged fasting and individualize glucose-containing fluids to prevent catabolism, allowing for contraindications or prior adverse glucose responses. Review drug toxicity and anesthesia risks with the treating team; prolonged propofol use warrants particular caution.
  evidence:
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Mitochondrial patients should take precautions to prevent entering catabolism
    explanation: General mitochondrial guidance supports an individualized emergency plan.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Patients should minimize preoperative fasting and have glucose added to their perioperative IV fluids, unless they are on a ketogenic diet or have been demonstrated to have adverse reaction to higher glucose intake.
    explanation: Perioperative glucose recommendations include explicit exceptions.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Mitochondrial patients may be at a higher risk for propofol infusion syndrome and propofol use should be avoided or limited to short procedures.
    explanation: General anesthetic caution is not evidence of a COX16-specific adverse reaction.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
- name: Multidisciplinary supportive care
  description: Coordinate metabolic, cardiac, neurological, hepatic, respiratory and nutritional care. In hepatic dysfunction, assess glucose and coagulation and review medications that can worsen liver injury; mitochondrial hepatocerebral guidance advises avoiding valproate.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: These focus on regular surveillance to detect complications and their management using standard approaches that are not usually specific to mitochondrial disorders.
    explanation: GeneReviews directs care toward consensus surveillance and standard management.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Hypoglycemia, hypoalbuminemia, or coagulopathy must be excluded if liver dysfunction is suspected.
    explanation: General mitochondrial critical-care consensus supports focused hepatic assessment.
  - reference: PMID:28749475
    reference_title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: hepatocerebral involvement is common in infantile mitochondrial disease; the use of valproate for seizure control must be avoided in these patients as fulminant hepatic failure has been associated with this medication.
    explanation: The caution applies to mitochondrial hepatocerebral disease; this is not a COX16-specific adverse-event trial.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
- name: Palliative symptom management
  description: Family-centered goals-of-care discussions and symptom relief may be appropriate in severe progressive disease. Morphine was used for palliation during terminal cardiac decline in the longer-surviving infant.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Palliative Therapy
    term:
      id: NCIT:C15292
      label: Palliative Therapy
    therapeutic_agent:
    - preferred_term: morphine
      term:
        id: CHEBI:17303
        label: morphine
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She was palliated with morphine and died almost 7 months old.
    explanation: The case documents palliative care without implying that the same approach applies to every patient.
- name: Genetic counseling and reproductive testing
  description: Confirm parental carrier status and discuss conditional autosomal recessive recurrence risks. Familial variant identification enables carrier testing and consideration of prenatal or preimplantation testing.
  evidence:
  - *id021
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
    reference_title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Once the ... pathogenic variant ... (s) have been identified in an affected family member, ... prenatal testing ... for a pregnancy at increased risk and ... preimplantation genetic testing ... are possible.
    explanation: The nuclear-gene section of GeneReviews supports reproductive testing after identifying familial variants.
    quote_role: REVIEW_SYNTHESIS
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: OTHER
- name: Experimental copper supplementation
  description: Copper supplementation improved enzyme activity in an engineered HEK293 knockout model, but copper chloride did not improve subunit abundance, assembled complex IV or activity in the tested patient fibroblasts. This conflicting preclinical evidence does not establish patient benefit.
  evidence:
  - &id022
    reference: PMID:29355485
    reference_title: COX16 is required for assembly of cytochrome c oxidase in human cells and is involved in copper delivery to COX2.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: copper supplementation increases COX activity and restores normal steady state levels of COX subunits in COX16 knockout cells
    explanation: The earlier engineered HEK293 model showed a biochemical response that was not reproduced in the patient fibroblast experiment.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: the complex IV enzyme activity showed no recovery at all after the CuCl2 treatment of the patient cell line
    explanation: Copper chloride failed to rescue the tested Arg82Ter patient fibroblasts. This refutes biochemical rescue by copper in this patient-cell model; it is not a clinical efficacy trial.
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: No positive effect of the copper treatment on the levels of COX subunits or the amount of fully assembled complex IV was observed.
    explanation: Both protein assembly and enzymatic outcomes were negative in the patient-cell experiment. This refutes biochemical rescue by copper in this patient-cell model; it is not a clinical efficacy trial.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: copper(II) chloride
      term:
        id: CHEBI:49553
        label: copper(II) chloride
  therapeutic_modality: SMALL_MOLECULE
  context: Preclinical cell-culture intervention; clinical efficacy unestablished
experimental_models:
- name: Patient fibroblast complementation
  description: Fibroblasts from the first Arg82Ter patient exhibit the severe assembly defect. Lentiviral wild-type COX16 complementation restores complex IV assembly and activity; copper chloride fails to rescue the defect.
  evidence:
  - *id003
  - *id011
  - &id024
    reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: the complex IV enzyme activity showed no recovery at all after the CuCl2 treatment of the patient cell line
    explanation: Copper chloride failed to rescue the tested Arg82Ter patient fibroblasts.
  experimental_model_type: PRIMARY_CELL_CULTURE
  cell_source: Patient skin fibroblasts
  modeled_mechanisms:
  - target: COX16 Protein Deficiency
    relationship: RECAPITULATES
    description: The patient culture lacks detectable COX16.
    evidence:
    - *id003
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Cellular experiments do not establish clinical treatment efficacy.
  - target: Reduced Complex IV Assembly
    relationship: RESCUES
    description: Wild-type complementation restores complex IV assembly and activity.
    evidence:
    - *id011
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Cellular experiments do not establish clinical treatment efficacy.
- name: Engineered human COX16 knockout cells
  description: CRISPR-disrupted HEK-derived cells reveal selective SCO1 recruitment, COX2 stability and module-joining defects. Residual enzyme activity and copper responses differ from patient fibroblasts.
  evidence:
  - *id001
  - *id002
  - *id004
  - *id022
  experimental_model_type: CELL_LINE
  cell_source: Engineered HEK293 and HEK Flp-In T-REx 293 cells
  modeled_mechanisms:
  - target: Impaired SCO1 Recruitment to COX2
    relationship: RECAPITULATES
    description: COX16 knockout reduces recruitment of SCO1 to newly synthesized COX2.
    evidence:
    - *id001
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Cellular experiments do not establish clinical treatment efficacy.
  - target: COX2 Instability
    relationship: RECAPITULATES
    description: Pulse-chase assays show reduced stability of COX2.
    evidence:
    - *id002
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Cellular experiments do not establish clinical treatment efficacy.
  - target: Defective COX1-COX2 Module Joining
    relationship: RECAPITULATES
    description: Module association is impaired after COX16 loss.
    evidence:
    - *id004
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Cellular experiments do not establish clinical treatment efficacy.
  - target: Reduced Complex IV Assembly
    relationship: RECAPITULATES
    description: Engineered cells recapitulate reduced assembly but retain more function and show a different copper response than the patient cells.
    evidence:
    - reference: PMID:29381136
      reference_title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: the cytochrome c oxidase amount was reduced to ∼50% compared to the wild type control
      explanation: Engineered cells retain substantial enzyme; the severity of the assembly defect depends on the experimental system.
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: Residual activity and copper response differ from the tested patient fibroblasts; kidney-derived cell lines do not model the clinical organ distribution.
animal_models:
- name: Caenorhabditis elegans COX16 knockdown
  species: Caenorhabditis elegans
  genotype: COX16 homolog knockdown
  description: Knockdown produces COX deficiency. The available abstract does not establish reproduction of the human multisystem phenotype.
  evidence:
  - &id023
    reference: PMID:29355485
    reference_title: COX16 is required for assembly of cytochrome c oxidase in human cells and is involved in copper delivery to COX2.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Its knockdown in C. elegans produces COX deficiency
    explanation: The whole-organism knockdown supports a conserved role in complex IV biogenesis.
  modeled_mechanisms:
  - target: Reduced Respiratory Capacity
    relationship: RECAPITULATES
    description: Knockdown produces the biochemical COX-deficiency phenotype.
    evidence:
    - *id023
    model_scale: MOLECULAR
    fidelity: MODERATE
    limitations: The biochemical phenotype does not establish clinical fidelity to neonatal human cardiomyopathy, liver disease or encephalopathy.
discussions:
- discussion_id: cox16-copper-response
  prompt: Why does copper rescue engineered COX16 knockout cells but not the tested patient fibroblasts?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  rationale: Model-dependent residual function and assembly context may determine response. COX16 may organize SCO1 recruitment rather than directly supply copper, so increasing copper availability need not bypass its absence. In later engineered-cell experiments, SCO1/SCO2 thiol-trapping patterns remained compatible with oxidized or copper-bound cysteines in COX16 knockout cells. The assay does not distinguish those two states, so it does not directly quantify copper loading or prove a uniform copper shortage.
  evidence:
  - *id022
  - *id024
  - *id001
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Each protein can have the two key cysteines forming a disulfide, binding Cu, or reduced and Cu-free. In reverse thiol trapping assays, the first two scenarios would result in the addition of two AMS molecules and none in the latter scenario
    explanation: The assay pools oxidized and copper-bound states and cannot distinguish them.
  - reference: PMID:35750769
    reference_title: Coordination of metal center biogenesis in human cytochrome c oxidase.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In WT HEK293T and COX11-KO cells, 75% of SCO2 bound 2 AMS but increased to 100% in COX16-KO cells
    explanation: The COX16-knockout SCO2 readout differs from a reduced copper-free state; it is not direct copper quantification.
- discussion_id: cox16-clinical-spectrum
  prompt: How broad is the clinical spectrum beyond the founding Arg82Ter families?
  kind: OPEN_QUESTION
  status: OPEN
  rationale: The same homozygous variant produced markedly different durations of survival. ClinGen classified the gene-disease relationship as Moderate in August 2025 because independent human genetic replication was limited, despite substantial functional evidence. The small clinical dataset does not support population frequencies, penetrance or a universal survival expectation.
  evidence:
  - reference: PMID:33169484
    reference_title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She was palliated with morphine and died almost 7 months old.
    explanation: The clinical course is not uniformly fatal in the neonatal period.
  - reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_ea62fb70-3963-4bb4-a7c0-2340cb794f58-2025-08-11T040000.000Z
    reference_title: curation results for Gene-Disease Validity
    supports: SUPPORT
    evidence_source: OTHER
    snippet: there have not yet been two independent scored publications documenting human genetic evidence over at least 3 years. Therefore, the classification comes to Moderate.
    explanation: The dated ClinGen curation explicitly explains the Moderate classification by limited independent human genetic replication.
    quote_role: REVIEW_SYNTHESIS
references:
- reference: PMID:33169484
  title: A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
- reference: PMID:29381136
  title: COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
- reference: PMID:29355485
  title: COX16 is required for assembly of cytochrome c oxidase in human cells and is involved in copper delivery to COX2.
- reference: PMID:28749475
  title: 'Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.'
- reference: PMID:20301403
  title: Primary Mitochondrial Disorders Overview.
  tags:
  - GeneReviews
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
  title: Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
  tags:
  - GeneReviews
- reference: url:https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_ea62fb70-3963-4bb4-a7c0-2340cb794f58-2025-08-11T040000.000Z
  title: curation results for Gene-Disease Validity
- reference: PMID:35750769
  title: Coordination of metal center biogenesis in human cytochrome c oxidase.
📚

References & Deep Research

References

8
PMID:33169484
A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.
No top-level findings curated for this source.
PMID:29381136
COX16 promotes COX2 metallation and assembly during respiratory complex IV biogenesis.
No top-level findings curated for this source.
PMID:29355485
COX16 is required for assembly of cytochrome c oxidase in human cells and is involved in copper delivery to COX2.
No top-level findings curated for this source.
PMID:28749475
Patient care standards for primary mitochondrial disease: a consensus statement from the Mitochondrial Medicine Society.
No top-level findings curated for this source.
PMID:20301403
Primary Mitochondrial Disorders Overview.
No top-level findings curated for this source.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1224/
Primary Mitochondrial Disorders Overview - GeneReviews® - NCBI Bookshelf
No top-level findings curated for this source.
No top-level findings curated for this source.
PMID:35750769
Coordination of metal center biogenesis in human cytochrome c oxidase.
No top-level findings curated for this source.