Combined Oxidative Phosphorylation Deficiency 51

Mendelian MONDO:0033631 Pathograph 24 Show in embeddings browser Mitochondrial Disease

Combined oxidative phosphorylation deficiency 51 (COXPD51) is an autosomal recessive mitochondrial disease caused by biallelic variants in PTCD3 (also called MRPS39, and mS39 in the standardised mitoribosome nomenclature). PTCD3 is a pentatricopeptide-repeat RNA-binding protein of the small subunit of the mitochondrial ribosome, where it forms the mRNA entry channel. The lesion therefore sits in the mitochondrial translation apparatus itself rather than in any single respiratory-chain subunit. The consequence follows from where mitochondria get their proteins. Thirteen respiratory-chain subunits are encoded by mitochondrial DNA and made on the mitoribosome; every other subunit is nuclear-encoded and imported. Losing PTCD3 destabilises the small mitoribosomal subunit and impairs translation of all thirteen at once, so several complexes fail together - the "combined" of the name. What the published patients actually show is a consistent complex I and complex IV defect, a variable complex III defect, and unchanged complex V and complex II subunit levels. Complex II is built entirely from nuclear-encoded subunits, so its being spared is a mechanistically informative negative and a pointer toward translation rather than toward an individual complex. Two clinical poles have been described from a total of seven patients. The severe pole is Leigh or Leigh-like syndrome: onset in the first weeks to months of life with psychomotor delay, respiratory insufficiency, feeding difficulties, dystonia, seizures, optic atrophy and nystagmus, with bilateral basal-ganglia and thalamic MRI change, and death in the first or second decade. The mild pole, described in 2024, is an adult sibling pair in their thirties with optic atrophy, nystagmus, tremor, truncal ataxia, spasticity and a motor polyneuropathy but only mild cognitive decline - a chronic ataxia/optic-neuropathy phenotype that would not usually prompt a Leigh-syndrome workup. Optic atrophy and nystagmus are the features that run through both poles, present in six of the seven reported patients. Management is entirely supportive; every cofactor and mitochondrial-cocktail regimen reported in these patients was ineffective.

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1
Mappings
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Inheritance
10
Pathophys.
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Histopath.
16
Phenotypes
5
Gaps
24
Pathograph
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Genes
5
Variants
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Medical Actions
3
Differentials
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Models
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Deep Research
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Classifications

Harrison's Part
GENETICS ENVIRONMENT DISEASE NEUROLOGIC
Mechanistic Nosology
mitochondrial disease
ICIMD (Inherited Metabolic Disorders)
mitoribosome
🔗

Mappings

MONDO
MONDO:0033631 combined oxidative phosphorylation deficiency 51
skos:exactMatch MONDO
👪

Inheritance

1
Autosomal recessive HP:0000007
All seven reported patients carry biallelic PTCD3 variants - compound heterozygous in the first six, homozygous for an intronic splice variant in the seventh, whose parents are double first cousins. Segregation in trans has been confirmed by parental testing in every family in which it was assessed.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"WES and RNA-seq identified compound heterozygous variants in PTCD3 in both families"
Compound heterozygous, trans-configured variants in two independent families.
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Discussions and Knowledge Gaps

5
Is PTCD3 deficiency a cause of Leigh syndrome, or of a Leigh-like syndrome that does not meet the diagnostic criteria?
CONTROVERSY OPEN coxpd51_leigh_versus_leigh_like
Attached to
pathophysiology#Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus disease#Combined Oxidative Phosphorylation Deficiency 51
The founding 2019 report diagnosed its patient with Leigh syndrome. A letter in the same journal argued the imaging and clinical picture met criteria only for a Leigh-like syndrome. The 2023 series then titled itself "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency" and set out to settle the question in favour of Leigh syndrome; the 2024 report nonetheless describes its own severe patient as Leigh-like, and its two adult patients as neither. This entry does not adjudicate. It records the position of each report and keeps the pathophysiology node named for the lesion (necrotizing degeneration of basal ganglia and thalamus) rather than for either syndrome label, so that the mechanism does not inherit the dispute. This entry quotes the 2023 series' summary of the challenge rather than the challenging Letter itself. The reason is recorded in the entry notes.
Show evidence (3 references)
PMID:30607703 SUPPORT Human Clinical
"Brain MRI showed abnormal bilateral signals at the basal ganglia and brainstem, and the patient was diagnosed as Leigh syndrome."
The original Leigh-syndrome diagnosis.
PMID:36450274 SUPPORT Human Clinical
"The diagnosis was compatible with Leigh Syndrome, but it was questioned by some authors, that classified the patient as Leigh‐like rather than Leigh syndrome"
The 2023 authors' account of the challenge. This entry quotes their summary rather than the challenging Letter itself, for the reason given in the entry notes.
PMID:39544688 REFUTE Human Clinical
"These clinical manifestations align with a Leigh‐like syndrome."
The most recent report describes its own severe patient as Leigh-like, so the 2023 paper's title did not close the question.
Does the amount of residual PTCD3 protein explain why one genotype kills at 16 months and another allows independent survival into the fourth decade?
KNOWLEDGE GAP OPEN coxpd51_residual_protein_hypothesis_untested
Attached to
pathophysiology#Depletion of PTCD3 Protein genetic#PTCD3
The only proposed explanation for the disorder's enormous severity range is quantitative: the index patient's two truncating alleles leave PTCD3 nearly absent, while the leaky splice alleles of the later patients leave 15-30% of normal protein, and the 2024 authors extend the same reasoning to a missense allele. It is a plausible dose-response account and it is entirely uncontrolled - each level was measured in a different laboratory, in a different patient, with a different second allele, and nobody has plotted protein level against any severity measure. What is missing is a graded series. Titrating PTCD3 in one cell background and measuring mitoribosome assembly, translation and respiration at each level would test whether the relationship is even monotonic. Until that exists the entry treats the residual-protein account as a hypothesis and does not use it for prognosis.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"As a result, the absence of PTCD3 protein is nearly complete, whereas in our patients, although reduced, was not absent."
The observation on which the hypothesis rests.
PMID:39544688 SUPPORT Human Clinical
"We hypothesise that PTCD3 missense pathogenic variants lead to a milder form of combined oxidative phosphorylation deficiency, probably due the higher level of residual PTCD3."
The 2024 authors state it as a hypothesis in their own words, which is how this entry records it.
If an unaffected heterozygous carrier has the same reduced fibroblast basal respiration as her affected son, what does a reduced basal respiration rate actually establish in this disorder?
KNOWLEDGE GAP OPEN coxpd51_carrier_respirometry_confound
Attached to
pathophysiology#Reduced Mitochondrial Respiratory Capacity and ATP Deficit diagnosis#Functional complementation in patient fibroblasts
In the 2024 report the mother of the adult proband - clinically unaffected, carrying one PTCD3 allele - had a basal respiration rate as low as her son's, with no significant difference between them. The authors draw the conclusion themselves: a lower oxygen consumption rate is seen in both affected and unaffected carriers, and that reduction is not by itself sufficient to cause disease. The gap this leaves is a measurement gap. Basal respiration is being used as supporting functional evidence for variant classification in this gene, and in this family it did not discriminate patient from carrier. What has discriminated, in the two other functionally characterised families, is the complementation assay: subunit levels and maximal uncoupled capacity restored by wild-type PTCD3. Nobody has reported a maximal-capacity or complementation result on a heterozygous carrier, so it is not known whether those assays are any more discriminating.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"The similar results were observed in his unaffected mother, who is a carrier of the His269Tyr variant, concluding that both heterozygous unaffected and affected carriers exhibit a lower OCR."
The carrier result and the authors' own reading of it.
Why do the optic nerve and the basal ganglia and thalamus degenerate when the translation defect is present in every cell?
KNOWLEDGE GAP OPEN coxpd51_regional_selectivity_unexplained
Attached to
pathophysiology#Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus pathophysiology#Optic Nerve Degeneration
PTCD3 is expressed in all tissues and the mitoribosome is required in all of them, yet the disease is focal: the optic nerve in essentially every patient, the basal ganglia and thalamus in the severe pole, the peripheral nerve in several, and almost nothing else. Cardiac, hepatic and renal involvement, which is common across the mitoribosomal protein disorders as a class, has been minimal in these patients. The only explanation offered is a general one - that retinal ganglion cells are especially vulnerable to defects in mitochondrial gene expression - and it is asserted rather than tested in PTCD3. It also does not address the basal-ganglia selectivity, which is shared with more than 75 unrelated Leigh-syndrome genes and is unexplained for all of them. The two selectivities may not have the same cause, and nothing in the PTCD3 literature distinguishes them. This is recorded as a gap rather than a controversy because no source argues the other side; the question has not been addressed.
Show evidence (1 reference)
PMID:39544688 SUPPORT Other
"Defects in mitochondrial replication, RNA transcription and translation initiate early‐onset optic atrophy, as these cells are highly vulnerable to mitochondrial dysfunction."
The whole of the published explanation for the optic-nerve selectivity - a general vulnerability claim about the cell type, not a PTCD3-specific result.
The only published whole-organism PTCD3 model is a lethal Drosophila null. Does any available model reproduce the human disease, in which every reported genotype retains residual protein?
HUMAN MODEL MISMATCH OPEN coxpd51_no_mammalian_model
Attached to
animal_models#Drosophila melanogaster PTCD3 loss-of-function mutant pathophysiology#Depletion of PTCD3 Protein
Evidence exists in a model system, and its translational validity is the open question - which is what separates this from the gaps above. The Drosophila null dies in the second instar and mouse loss of function is reported as causing neurodevelopmental defects and early lethality. Both are null phenotypes. No reported human patient is null: the severity range that defines this disorder lies entirely in the hypomorphic range, and neither organism has been studied at a hypomorphic dose. Neither organism has the tissues the disease targets, either - a fly has no optic nerve or basal ganglia, and no mouse study reporting optic atrophy or basal-ganglia lesions on partial PTCD3 loss has been published. So the models establish that the gene is essential and say nothing about why partial loss produces this particular focal degeneration. What would resolve it is a hypomorphic mammalian allele - a knock-in of one of the human leaky splice alleles, or a graded conditional knockdown - assessed for optic nerve and basal-ganglia pathology rather than for lethality.
Show evidence (2 references)
PMID:38074476 SUPPORT Model Organism
"A loss-of-function mutant of PTCD3 is lethal during the second instar."
The invertebrate null phenotype - lethality, not the human disease.
PMID:39544688 SUPPORT Human Clinical
"Similarly, PTCD3 loss‐of‐function mice exhibit neurodevelopmental defects and early lethality."
The mouse null phenotype as summarised by the 2024 authors. Cited from their review sentence because the entry does not cite the underlying mouse study; a curator with that primary reference should cite it directly here.
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Pathophysiology

10
Biallelic PTCD3 Variants Disrupting mRNA Processing
Mechanism confidence: Established
Germline biallelic PTCD3 variants, most of which act on splicing. Canonical acceptor-site variants, an intronic +4 variant and two exonic variants that read as missense changes all produce exon-skipped transcripts; a frameshift and a nonsense allele complete the reported spectrum. The splice-acting alleles were proven to act that way by minigene assay in HAP1 cells, not inferred from prediction algorithms.
Genetic context PTCD3 hgnc:24717 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns PTCD3 (hgnc:24717). hgnc:24717 is a gene from the HUGO Gene Nomenclature Committee. variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION
Compound heterozygous in six of the seven reported patients, homozygous for the intronic c.538+4A>G allele in the seventh.
mitochondrion GO:0005739 Gene Ontology (GO) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in mitochondrion (GO:0005739). GO:0005739 is an anatomical location from the Gene Ontology.
Downstream
Depletion of PTCD3 Protein Exon-skipped transcripts are either degraded by nonsense-mediated decay or translated into truncated protein that cannot be incorporated into the mitoribosome; either route lowers the amount of functional PTCD3.
Show evidence (2 references)
PMID:36450274 SUPPORT In Vitro
"Overall, these results demonstrated that the c.1918C>G, c.1453‐1G>C, and c.902C>T variants were responsible for the PTCD3 mRNA processing defects observed in patients' fibroblasts."
Direct experimental attribution of the mRNA-processing defect to the variants.
PMID:39544688 SUPPORT Human Clinical
"However, PTCD3 seems to be particularly vulnerable to pathological splice site errors"
States the generalisation across the allelic spectrum that makes splicing the dominant mechanism of loss of function in this gene.
Depletion of PTCD3 Protein
Mechanism confidence: Established
PTCD3 protein is reduced but, in the patients with a leaky splice allele, not absent - 70% and 85% below control in the two 2023 patients tested. The index patient's two truncating alleles leave it nearly absent. This quantitative difference is the residual-function hypothesis the field currently uses to explain why some patients die in infancy and others reach their thirties.
mRNA binding GO:0003729 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased mRNA binding (GO:0003729). GO:0003729 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Destabilization of the Mitochondrial Small Ribosomal Subunit
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"The PTCD3 gene product (protein PTCD3 or MRPS39) forms the entry channel of the mitochondrial small ribosomal subunit and binds to single-stranded mRNA."
The molecular function that is lost when the protein is depleted.
Destabilization of the Mitochondrial Small Ribosomal Subunit
Mechanism confidence: Established
Quantitative proteomics in the index patient's fibroblasts showed the small mitoribosomal subunit as a whole is depleted, not just PTCD3. PTCD3 sits at the mRNA entry channel, so its loss removes both a structural component and the site at which mitochondrial mRNA is engaged.
mitochondrial small ribosomal subunit GO:0005763 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves decreased mitochondrial small ribosomal subunit (GO:0005763). GO:0005763 is a cellular component from the Gene Ontology.
Downstream
Impaired Mitochondrial mRNA Translation
Show evidence (1 reference)
PMID:30607703 SUPPORT Human Clinical
"PTCD3, a member of the pentatricopeptide repeat domain protein family, is a component of the small mitoribosomal subunit."
Places PTCD3 structurally within the subunit whose steady-state level falls.
Impaired Mitochondrial mRNA Translation
Mechanism confidence: Established
Mitochondrial protein synthesis falls across the board. In patient fibroblasts this was measured directly as a generalized translation defect; the same effect was produced in control cells a decade earlier by knocking PTCD3 down, which establishes the direction of the relationship independently of any patient genotype.
fibroblast CL:0000057 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology.
mitochondrial translation GO:0032543 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial translation (GO:0032543). GO:0032543 is a biological process from the Gene Ontology. ↓ DECREASED
Animal models
Drosophila melanogaster PTCD3 loss-of-function mutant Drosophila melanogaster partially recapitulates Transcriptional evidence of a coordinated loss of mitochondrial and ribosome-biogenesis gene expression on loss of the PTCD3 ortholog.
Downstream
Reduced Synthesis of mtDNA-Encoded OXPHOS Subunits Only thirteen OXPHOS subunits are made on the mitoribosome; a generalized translation defect under-supplies all of them at once.
Show evidence (1 reference)
PMID:19427859 SUPPORT In Vitro
"PTCD3 knockdown and over expression did not affect mitochondrial mRNA levels, suggesting that PTCD3 is not involved in RNA processing and stability."
A negative result that constrains the mechanism: the lesion is in translation, not in mitochondrial mRNA processing or stability. Cell-line knockdown, not a patient study.
Reduced Synthesis of mtDNA-Encoded OXPHOS Subunits
Mechanism confidence: Established
Steady-state levels of mtDNA-encoded and mtDNA-dependent respiratory-chain subunits fall. In the 2023 patients this was measured as reduced NDUFB8 (complex I) and MT-CO2 (complex IV) in both, with UQCRC2 (complex III) reduced in one of the two.
mitochondrial ATP synthesis coupled electron transport GO:0042775 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial ATP synthesis coupled electron transport (GO:0042775). GO:0042775 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Combined Respiratory Chain Deficiency with Complex II Spared
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"A significant reduction of NDUFB8 (complex I) and MT‐CO2 (complex IV) in both patients"
The measured subunit-level deficit in patient fibroblasts.
PMID:36450274 SUPPORT Human Clinical
"Furthermore, steady‐state levels of UQCRC2 (complex III) were significantly reduced in P1, but not in P2.1"
The complex III deficit is real but inconsistent between patients, which is why this entry does not present complex III as an obligate part of the signature.
Combined Respiratory Chain Deficiency with Complex II Spared
Mechanism confidence: Established
The biochemical signature of the disorder, and the reason it is named a "combined" deficiency. Complex I and complex IV activities are reduced in fibroblasts across the reported patients; complex III is reduced in some. Complex V subunit levels were unchanged in the two patients in whom they were measured, and complex II - alone among the five complexes, built entirely from nuclear-encoded subunits - was not reduced and in fact ran slightly above the control range once normalised to citrate synthase. The spared complex II is not an incidental negative. It is the finding that points the differential at the translation apparatus rather than at an assembly factor or a structural subunit of one complex, and it is what a curator or clinician should look for in the enzymology report.
oxidative phosphorylation GO:0006119 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased oxidative phosphorylation (GO:0006119). GO:0006119 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Patient-derived fibroblasts with wild-type PTCD3 lentiviral rescue PRIMARY CELL CULTURE Re-expression of wild-type PTCD3 restores the OXPHOS subunit levels and the maximal respiratory capacity that are reduced in the patients' own cells, with an empty-vector arm as the specificity control. This is what converts the biochemical phenotype from a correlate of the genotype into a consequence of it.
Downstream
Reduced Mitochondrial Respiratory Capacity and ATP Deficit
Show evidence (3 references)
PMID:36450274 SUPPORT Human Clinical
"Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex I, complexes I + III and complex IV"
The enzymatic deficit measured in one of the 2023 patients.
PMID:36450274 SUPPORT Human Clinical
"Indeed, complex II is known to be largely unaltered in mitochondrial protein translation deficiencies."
States why complex II is spared and generalises it to the class of mitochondrial translation defects, of which this disorder is one.
PMID:36450274 SUPPORT Human Clinical
"ATP5A1 (complex V) and SDHB (complex II) protein levels remained unaltered."
The measured negative for complexes II and V. Recorded because the generic "complexes I, III, IV and V" description of a combined OXPHOS deficiency is not what these patients showed.
Reduced Mitochondrial Respiratory Capacity and ATP Deficit
Mechanism confidence: Established
High-resolution respirometry in patient fibroblasts shows a modest fall in basal respiration and a marked fall in maximal (uncoupled) respiratory capacity; the index patient also had reduced ATP biosynthesis. Functional complementation with wild-type PTCD3 restored both the subunit levels and the respiratory capacity, which is what makes this a consequence of the PTCD3 lesion rather than a correlate of it.
cellular respiration GO:0045333 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cellular respiration (GO:0045333). GO:0045333 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Lactate and Pyruvate Accumulation
Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus The step from a cell-level bioenergetic deficit to selective necrosis of the basal ganglia and thalamus is the least explained link in the chain. It is the shared final pathway of more than 75 Leigh-syndrome genes, and no PTCD3-specific account of the regional selectivity has been published.
Optic Nerve Degeneration
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Treatment with the mitochondrial uncoupler CCCP resulted in a significant reduction in maximal respiratory capacity in both patients"
The respirometry result behind this node.
Lactate and Pyruvate Accumulation
Mechanism confidence: Established
Blocked oxidative disposal of pyruvate shifts it to lactate and to alanine by transamination. Two of the reported patients had high blood lactate, pyruvate, alanine, glycine and glutamine; a third had only mild elevation, and in two others blood lactate was normal - so the finding is characteristic but not obligate, and a normal lactate does not exclude the diagnosis.
Downstream
Lactic Acidosis
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
The metabolic profile in the patient with the fullest workup.
PMID:39544688 REFUTE Human Clinical
"Laboratory investigation revealed normal results of blood lactate, ammonia, creatine phosphokinase, cholesterol and electrolytes in variable ages"
Refutes lactate elevation as an obligate feature - the third 2024 patient, who has a Leigh-like phenotype with an MRI lactate peak, had repeatedly normal blood lactate.
Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus
Mechanism confidence: Established
The neuropathological substrate of the Leigh and Leigh-like pole. Imaging shows bilateral symmetrical signal change and volume loss in the thalamus and globus pallidus, and in the index patient punctate brainstem lesions with thalamic, caudate and putaminal T2 hyperintensity. One 2024 patient's repeat MRI showed cystic change, gliosis and volume loss in the posterior putamina, which is the necrotizing character the syndrome is named for.
basal ganglia UBERON:0002420 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in basal ganglia, annotated with basal ganglion (UBERON:0002420). UBERON:0002420 is an anatomical location from the Uberon multi-species anatomy ontology. thalamus UBERON:0001897 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in thalamus, annotated with dorsal plus ventral thalamus (UBERON:0001897). UBERON:0001897 is an anatomical location from the Uberon multi-species anatomy ontology. brainstem UBERON:0002298 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in brainstem (UBERON:0002298). UBERON:0002298 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Developmental Regression
Global Developmental Delay
Dystonia
Show evidence (2 references)
PMID:30607703 SUPPORT Human Clinical
"Brain MRI showed abnormal bilateral signals at the basal ganglia and brainstem, and the patient was diagnosed as Leigh syndrome."
The imaging finding that anchored the Leigh-syndrome diagnosis in the index patient.
PMID:39544688 SUPPORT Human Clinical
"Brain magnetic resonance imaging (MRI) at 6 years of age showed a bilateral symmetrical globus pallidus signal intensity with an elevated lactate peak."
The same regional pattern in an independently reported patient, with the MRS lactate peak that accompanies it.
Optic Nerve Degeneration
Mechanism confidence: Established
Optic-nerve atrophy is visible on MRI and on fundoscopy and is the single most consistent finding in the disorder, present with nystagmus in six of the seven reported patients and at both clinical poles. The adult siblings are legally blind with only light perception, and both had absent or poorly structured visual evoked potentials.
retinal ganglion cell CL:0000740 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves retinal ganglion cell (CL:0000740). CL:0000740 is a cell type from the Cell Ontology.
optic nerve UBERON:0000941 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in optic nerve, annotated with cranial nerve II (UBERON:0000941). UBERON:0000941 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Optic Atrophy
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"showed optic atrophy and nystagmus in six of seven patients"
The cross-cohort frequency, from the authors' own heat map of previously and newly published patients.
✶

Histopathology

1
COX-negative fibres in a mosaic distribution in skeletal muscle
Muscle biopsy in the oldest patient of the 2023 series showed a mosaic population of cytochrome c oxidase-negative fibres with increased lipid, alongside angulated hyperchromatic fibres consistent with denervation. There were no ragged-red fibres and no subsarcolemmal mitochondrial accumulation, so the classic mitochondrial myopathy picture is absent - the informative stain here is COX, not Gomori trichrome.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"COX staining showed a population of COX‐negative fibres in mosaic, with increased amounts of lipid material"
The histochemical finding that supported the diagnosis of mitochondrial disease.
PMID:36450274 SUPPORT Human Clinical
"Gomori's modified trichrome staining showed no increased endomysial or perimysial connective tissue and no subsarcolemmal reinforcements of mitochondria or ragged‐red fibers."
The accompanying negative - no ragged-red fibres - which is why a normal trichrome does not argue against the diagnosis.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Combined Oxidative Phosphorylation Deficiency 51 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

16
Digestive 1
Feeding Difficulties and Dysphagia FREQUENT HP:0011968 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties (HP:0011968), qualified as course progressive. HP:0011968 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"He was admitted a few more times due to respiratory symptoms (bronchospasm), developing chronic respiratory failure and progressive dysphagia requiring gastrostomy."
The course of the feeding problem and the intervention it required.
Ear 1
Sensorineural Hearing Impairment OCCASIONAL HP:0000407 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorineural hearing impairment (HP:0000407). HP:0000407 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"Nystagmus was also observed in two of our patients, but only P1 had optic atrophy and hearing loss."
Hearing loss in one of three patients of the 2023 series.
PMID:39544688 REFUTE Human Clinical
"EEG, echocardiography and hearing tests did not reveal any pathology, but EMG/NCV showed motor polyneuropathy"
Refutes hearing loss as a general feature - it was explicitly normal in the two adult patients.
Eye 2
Optic Atrophy VERY_FREQUENT HP:0000648 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Optic atrophy (HP:0000648), qualified as course progressive. HP:0000648 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:39544688 SUPPORT Human Clinical
"showed optic atrophy and nystagmus in six of seven patients"
Quantifies the frequency across the whole published cohort.
PMID:30607703 SUPPORT Human Clinical
"We describe a patient who presented with low birth weight, mental retardation, and optic atrophy."
Optic atrophy as a presenting feature in the index patient.
Nystagmus VERY_FREQUENT HP:0000639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nystagmus (HP:0000639). HP:0000639 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39544688 SUPPORT Human Clinical
"A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
The adult presentation, in which nystagmus is one of the cardinal signs.
PMID:36450274 SUPPORT Human Clinical
"The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures."
Nystagmus in the severe infantile-onset pole as well.
Metabolism 1
Lactic Acidosis FREQUENT HP:0003128 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
The lactate elevation with its accompanying amino-acid profile.
Musculoskeletal 2
Spasticity FREQUENT HP:0001257 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spasticity (HP:0001257). HP:0001257 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"Severely affected PTCD3 patients have spasticity, abnormal EEG, seizures, myoclonus, dystonia, dysphagia, polyneuropathy"
Spasticity listed among the features of the severely affected patients.
Scoliosis OCCASIONAL HP:0002650 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Scoliosis (HP:0002650). HP:0002650 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"P2.1 and P2.2 suffered from scoliosis, which had not been reported in the previous PTCD3 individual"
Scoliosis in the two longest-surviving patients of the 2023 series.
Nervous System 8
Developmental Regression FREQUENT HP:0002376 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Developmental regression (HP:0002376), qualified as course progressive. HP:0002376 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"Until now, functional evidence of disease‐causing variants in PTCD3 has only been reported in a single individual presenting psychomotor regression, optic atrophy, and Leigh syndrome"
Names psychomotor regression as one of the three defining features of the index patient. The quote preserves the source's non-ASCII hyphen in "disease-causing".
PMID:36450274 SUPPORT Human Clinical
"Neurodevelopment was considered normal until the 10th month of life, when delayed adquisicion of milestones and hypertonia were noted."
The normal interval preceding decline in the 2023 Spanish patient, which is what distinguishes regression from static delay. The quote reproduces the source's own "adquisicion" typo, as an exact quote must.
Global Developmental Delay FREQUENT HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties."
The presenting triad of the severe pole.
PMID:39544688 REFUTE Human Clinical
"Global developmental delay was described in all Leigh‐like patients, except our presented cases 1 and 2, who have only mild cognitive decline."
Refutes global developmental delay as universal - the two adult patients do not have it, which is why the frequency here is FREQUENT rather than VERY_FREQUENT.
Dystonia FREQUENT HP:0001332 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dystonia (HP:0001332), qualified as course progressive. HP:0001332 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Sequelae: Scoliosis
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Remarkably, dystonia was observed in all three individuals reported here."
Dystonia in all three patients of the 2023 series.
Bilateral Tonic-Clonic Seizures FREQUENT HP:0002069 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bilateral tonic-clonic seizure (HP:0002069). HP:0002069 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures."
Seizures as part of the neurologic phenotype of the 2023 series.
Hyperreflexia FREQUENT HP:0001347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperreflexia (HP:0001347). HP:0001347 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
Hyperreflexia in the two adult patients.
Truncal Ataxia OCCASIONAL HP:0002078 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Truncal ataxia (HP:0002078), qualified as course progressive. HP:0002078 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
The ataxic phenotype of the adult sibling pair.
Tremor OCCASIONAL HP:0001337 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tremor (HP:0001337). HP:0001337 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
The tremor in the adult siblings.
Motor Polyneuropathy OCCASIONAL Peripheral axonal neuropathy HP:0003477 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Peripheral axonal neuropathy (HP:0003477). HP:0003477 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39544688 SUPPORT Human Clinical
"EEG, echocardiography and hearing tests did not reveal any pathology, but EMG/NCV showed motor polyneuropathy"
The electrophysiological finding in the adult siblings, quoted with the negative studies that accompanied it.
PMID:36450274 SUPPORT Human Clinical
"At 4 years old, he had a diffuse sensory and motor axonal neuropathy"
An axonal neuropathy in the severe pole as well, so this is not exclusive to the adult phenotype.
Respiratory 1
Respiratory Insufficiency FREQUENT HP:0002093 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Respiratory insufficiency (HP:0002093), qualified as course progressive. HP:0002093 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties."
Respiratory insufficiency as a presenting feature.
PMID:39544688 SUPPORT Human Clinical
"Three additional patients from two families had developmental delay, seizures, respiratory insufficiency, optic nerve hypoplasia, abnormal brain magnetic resonance imaging and died in the first or second decade."
Recurrence of respiratory insufficiency across the reported severe cases.
🧬

Genetic Associations

1
PTCD3 (PTCD3 (MRPS39, mS39) encodes a pentatricopeptide-repeat RNA-binding protein that forms the mRNA entry channel of the small mitoribosomal subunit. Its function was established a decade before any patient was reported: knockdown in human cells reduced mitochondrial protein synthesis, respiration, and complex III and IV activity without changing mitochondrial mRNA levels, which located it in translation rather than in RNA processing or stability. The striking feature of the reported allelic spectrum is how many of the pathogenic alleles act through splicing. Of the nine variants published across the three case reports, six alter mRNA processing - two canonical acceptor-site variants, one intronic +4 variant, and two exonic variants initially called variants of uncertain significance that turned out on minigene assay to cause exon skipping. That last pair matters practically: an exonic missense-looking change in PTCD3 cannot be assumed to act as a missense change.)
Gene: PTCD3 hgnc:24717 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PTCD3 (hgnc:24717). hgnc:24717 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:30607703 SUPPORT Human Clinical
"This is the first report of an association of PTCD3 mutations with Leigh syndrome along with combined oxidative phosphorylation deficiencies caused by defects in the mitochondrial translation machinery."
The founding report establishing PTCD3 as a human disease gene.
PMID:19427859 SUPPORT In Vitro
"lowering PTCD3 in 143B osteosarcoma cells decreased mitochondrial protein synthesis, mitochondrial respiration and the activity of Complexes III and IV, suggesting that PTCD3 has a role in mitochondrial translation."
Establishes the gene's normal function in mitochondrial translation, a decade before any patient was reported. This is a cell-line knockdown, not a PTCD3 patient study.
Variants (5)
PTCD3 c.415-2A>G Pathogenic
Canonical splice acceptor variant, in trans with a frameshift allele in the index patient. Together the two alleles leave the protein nearly absent, which is the genotype the 2023 series proposes as the explanation for that patient's exceptionally severe course.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"As a result, the absence of PTCD3 protein is nearly complete, whereas in our patients, although reduced, was not absent."
Contrasts the index patient's near-null genotype with the residual protein in the later, longer-surviving patients.
PTCD3 c.1453-1G>C Pathogenic
Canonical acceptor-site variant abolishing the intron 18 splice site, causing exon 19 skipping and a transcript degraded by nonsense-mediated decay. On minigene assay it had the strongest effect of the four variants tested.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"cDNA analysis of P1 revealed a skipping of exon 19 caused by the c.1453‐1G>C substitution, which altered a canonical splice acceptor site"
Establishes the splicing consequence of this allele in patient fibroblasts.
PTCD3 c.902C>T Pathogenic
Initially classified as a variant of uncertain significance because it sits inside exon 12 and reads as a missense change. Minigene assay showed it causes skipping of the exon it sits in, producing a truncating transcript alongside a leaky pool of correctly spliced mRNA.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing."
The functional result that reclassified this and two neighbouring variants from uncertain significance to pathogenic-by-splicing.
PTCD3 c.538+4A>G Pathogenic
Homozygous intronic variant in a consanguineous family, absent from gnomAD, shown by RT-PCR to cause skipping of the 124 bp exon 7. The only homozygous genotype reported to date.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"This genetic change abolishes the consensus splice site and causes exon 7 skipping"
The splicing consequence demonstrated for the homozygous intronic allele.
PTCD3 c.1182T>A (p.Tyr394Ter) Pathogenic
Nonsense allele carried by the adult sibling pair, in trans with the p.His269Tyr missense allele. It removes the C-terminal half of the protein including much of the central fold, so the product cannot be incorporated into the mitoribosome; western blot showed it is not cleared by nonsense-mediated decay.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"The whole genome sequencing analysis revealed two heterozygous variants in the PTCD3: c.1182T>A, p.(Tyr394Ter) and c.805C>T, p.(His269Tyr)."
Names the two alleles of the mild adult phenotype.
💊

Medical Actions

4
Supportive and Organ-Directed 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: Behavioral / lifestyle
There is no disease-modifying therapy. Management follows the organs involved: respiratory support and eventually ventilation, gastrostomy or nasogastric feeding for dysphagia, antiseizure medication, antispasticity and antidystonic agents, and palliative care. Two of the reported patients were managed to death in the second decade on this basis, one at home under a palliative care team.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Considering her overall condition, it was decided that she should be monitored by the palliative care unit."
The endpoint of supportive management in one reported patient, recorded because it is the honest description of what treatment achieves here.
Mitochondrial Cofactor Cocktail
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: coenzyme Q10 CHEBI:46245 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses coenzyme Q10 (CHEBI:46245). CHEBI:46245 is a therapeutic agent from Chemical Entities of Biological Interest. carnitine CHEBI:16347 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses carnitine, annotated with (R)-carnitine (CHEBI:16347). CHEBI:16347 is a therapeutic agent from Chemical Entities of Biological Interest. thiamine CHEBI:26948 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses thiamine, annotated with vitamin B1 (CHEBI:26948). CHEBI:26948 is a therapeutic agent from Chemical Entities of Biological Interest. biotin CHEBI:15956 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses biotin (CHEBI:15956). CHEBI:15956 is a therapeutic agent from Chemical Entities of Biological Interest. vitamin C CHEBI:29073 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses vitamin C, annotated with L-ascorbic acid (CHEBI:29073). CHEBI:29073 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Coenzyme Q10, carnitine, thiamine, biotin and vitamin C have all been given to these patients, individually or as a "mitochondrial cocktail". In every reported case the effect was recorded as none. One patient did have a low plasma coenzyme Q10, which is the only result that gives a specific rationale for any of these agents, and even in that patient the cocktail produced no perceptible improvement. This is curated as a treatment with refuting evidence rather than omitted, because "the mitochondrial cocktail was tried and did not work" is a clinically useful thing for the entry to say.
Show evidence (2 references)
PMID:36450274 REFUTE Human Clinical
"Treatment with carnitine, thiamine, biotin, gabapentin, baclofen, and risperidone was also ineffective and had no effect on the disease progression."
Refutes benefit from cofactor supplementation in the first patient of the 2023 series, in the authors' own words.
PMID:36450274 REFUTE Human Clinical
"However, this treatment did not result in a perceptible improvement of the clinical condition."
Refutes benefit from the coenzyme Q10 and carnitine cocktail in a second, unrelated patient - including one with a documented low plasma coenzyme Q10.
Levodopa Trial for the Movement Disorder
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: levodopa CHEBI:15765 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses levodopa, annotated with L-dopa (CHEBI:15765). CHEBI:15765 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
Levodopa was tried in the akinetic-rigid patient of the 2023 series and did not help. Recorded because the akinetic-rigid presentation of a basal-ganglia mitochondrial disorder invites a levodopa trial, and the one reported trial was negative.
Show evidence (1 reference)
PMID:36450274 REFUTE Human Clinical
"The patient was initially treated with L‐Dopa, but no improvement was observed."
The negative levodopa trial, stated directly.
Genetic Counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Platform: Behavioral / lifestyle
Autosomal recessive, 25% recurrence risk. Counselling here has to convey an unusual uncertainty: the same gene has produced death at 16 months and independent living into the fourth decade, and the residual-protein hypothesis that is meant to explain the difference is a hypothesis, not a validated genotype-phenotype rule. A carrier parent in one family had a measurably reduced fibroblast basal respiration rate while being entirely unaffected, so a functional assay result on a heterozygote must not be over-read.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"The similar results were observed in his unaffected mother, who is a carrier of the His269Tyr variant, concluding that both heterozygous unaffected and affected carriers exhibit a lower OCR."
The carrier finding that makes over-interpretation of a heterozygote's respirometry a real counselling hazard.
🔬

Biochemical Markers

6
Blood lactate
Context: Plasma, measured on metabolic workup in six of the seven reported patients.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
The elevated result in the patient with the fullest metabolic workup.
PMID:39544688 REFUTE Human Clinical
"Laboratory investigation revealed normal results of blood lactate, ammonia, creatine phosphokinase, cholesterol and electrolytes in variable ages"
A true negative in a genetically confirmed, MRI-positive patient. This is the reason the marker is recorded as FREQUENT rather than VERY_FREQUENT.
Brain lactate peak on MR spectroscopy
Context: MR spectroscopy of the basal ganglia.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"Brain magnetic resonance imaging (MRI) at 6 years of age showed a bilateral symmetrical globus pallidus signal intensity with an elevated lactate peak."
The MRS lactate peak in the patient whose blood lactate was normal.
Fibroblast respiratory chain complex I activity
Context: Cultured skin fibroblasts, respiratory-chain enzymology normalised to citrate synthase.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex I, complexes I + III and complex IV"
The measured complex I deficit in fibroblasts.
Fibroblast respiratory chain complex IV activity
Context: Cultured skin fibroblasts; also COX-negative fibres on muscle histochemistry.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex IV."
The complex IV deficit in the first patient of the 2023 series.
Fibroblast respiratory chain complex II activity (Absent)
Context: Cultured skin fibroblasts, normalised to citrate synthase.
Show evidence (1 reference)
PMID:36450274 REFUTE Human Clinical
"the activity of CII (after normalization to citrate synthetase activity) was slightly above the control range in both individuals"
Refutes a complex II deficit in this disorder - the measurement that makes the sparing of complex II a curated finding rather than an assumption.
Plasma GDF-15 and FGF-21 (Normal)
Context: Plasma, 2023 series.
Show evidence (1 reference)
PMID:36450274 REFUTE Human Clinical
"Other mitochondrial biomarkers such as plasma GDF‐15/GFG21 or urine organic acids disclosed normal results."
Refutes the usefulness of these biomarkers as a screen in this disorder. Note the source's own typo, GFG21 for FGF21, quoted as printed.
🔬

Diagnosis

3
Exome or genome sequencing, with RNA-seq or minigene assay for splicing alleles
The molecular diagnosis has been made by whole-exome and by whole-genome sequencing, but sequencing alone has repeatedly been insufficient in this gene. Two of the reported alleles were initially called variants of uncertain significance because they sit in exons and read as missense changes; both turned out to cause exon skipping. RNA-seq of patient fibroblasts prioritised PTCD3 in one family through an aberrant splicing signal, and minigene assays established causality for three alleles. The practical rule: an exonic PTCD3 variant of uncertain significance in a compatible phenotype warrants an RNA-level test before it is dismissed.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"In addition, RNA‐seq was also performed on P1 fibroblasts, which prioritized PTCD3 as a candidate disease gene, as an aberrant splicing was detected."
RNA-seq, not exome interpretation, is what identified the gene in that family.
PMID:36450274 SUPPORT In Vitro
"Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing."
The functional assay that reclassified the uncertain alleles.
Respiratory chain enzymology in fibroblasts, read for the pattern rather than the magnitude
Fibroblast enzymology shows reduced complex I and complex IV with normal or above-range complex II. Two cautions from the reported patients: the deficit can be modest, and in one patient a decreased complex IV activity fell back inside the control range once normalised to citrate synthase - so a normalised-only report may read as normal. Muscle histochemistry showed COX-negative fibres in the same patient whose normalised fibroblast values were unremarkable.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex IV. However, when normalized to citrate synthetase, the values fall within the control range"
The normalisation caveat, quoted from the patient in whom it occurred. This is the practical reason not to treat a normal normalised panel as a rule-out.
Functional complementation in patient fibroblasts
Lentiviral re-expression of wild-type PTCD3 in immortalised patient fibroblasts restores OXPHOS subunit levels and respiratory capacity. It is not a routine clinical test, but it is the assay that has been used in both functionally characterised families to convert candidate variants into a diagnosis, and it is what a reference laboratory would be asked for when the genotype is ambiguous.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"The expression of wild‐type PTCD3 cDNA using a lentiviral vector resulted in a complete recovery of the steady‐state levels of the altered OXPHOS subunits in both patients (Figure 7A,B). Furthermore, the mitochondrial respiratory capacity, which was significantly reduced in naïve patient's..."
The rescue result that establishes causality.
📈

Progression

3
Onset
Age: first weeks of life to early childhood, with one sibling pair whose first sign appeared at age 2
Onset spans the severe and mild poles. In the severe pole symptoms begin in the first weeks to three months of life, or from birth in the index patient, who also had intrauterine growth retardation. In the mild pole the first sign was nystagmus at age two with normal early development, and gait disturbance did not appear until age six.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"In contrast, none of the individuals reported here had intrauterine growth retardation, and the onset age ranged from the first weeks to 3 months of life."
The onset range in the 2023 series, contrasted with the index patient.
Established disease
Two distinct courses. The severe course is a progressive neurodegeneration with accumulating dystonia, epilepsy, dysphagia and respiratory failure, punctuated by intensive-care admissions. The mild course is a slowly progressive ataxia and optic neuropathy in which patients remain cognitively near-normal into their thirties but become blind and non-ambulatory. The disorder has no described plateau in either course.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"Both are legally blind, retaining only light perception, experiencing mild cognitive decline and being non‐ambulatory."
The established state of the mild course in the fourth decade.
Outcome
The index patient died at 16 months. Two patients of the 2023 series died at 11 and 17 years, one of pneumonia with respiratory failure and one at home under palliative care; the third was alive at 19. The 2024 sibling pair were alive in their thirties. Survival therefore ranges over more than three decades within one gene.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"They survived longer than the previously reported patient, being exitus at the ages of 11 and 17 years old, or still alive at 19 years of age."
The survival range in the 2023 series against the index patient.
PMID:31967322 SUPPORT INDIRECT Human Clinical
"Nearly 90% of deaths occurred by age 6. Mortality rate of patients with onset before 6 months of age was significantly higher than that of onset after 6 months."
Class-level prognostic data. This is a 166-patient Japanese Leigh syndrome cohort, not a PTCD3 series - no natural-history study of COXPD51 exists, and seven patients cannot support one. It is cited to give the infantile-onset pole a base rate, and the inference from Leigh syndrome generally to PTCD3 specifically is the reason this item is graded INDIRECT.
📊

Prevalence

1
Worldwide (published cases)
Cases In Literature Ultra Rare
Seven patients in three reports: one index patient in 2019, three from two unrelated families in 2023, and three more (an adult sibling pair and an unrelated child) in 2024. Reported families are Spanish, Brazilian, Latvian and Saudi; the ancestry of the index patient is not stated in that report and is not asserted here. No population prevalence has been estimated and none is asserted here; the 2024 report's own cross-cohort tally of seven patients is the best available denominator.
Show evidence (2 references)
PMID:39544688 SUPPORT Human Clinical
"showed optic atrophy and nystagmus in six of seven patients"
The seven-patient denominator, from the authors' tabulation of previously and newly published cases.
PMID:36450274 SUPPORT Human Clinical
"To date, mutations in PTCD3, encoding a component of the mitochondrial ribosome, have only been reported in a single individual with clinical evidence of Leigh syndrome."
The count as it stood before the 2023 series, showing how small the literature is.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Combined Oxidative Phosphorylation Deficiency 51:

Leigh syndrome of other genetic cause
Overlapping Features More than 75 genes, mitochondrial and nuclear, produce Leigh syndrome, and nothing in the clinical picture or the neuroimaging distinguishes PTCD3 from them. Optic atrophy, which is the most consistent PTCD3 feature, occurs in Leigh syndrome of other aetiologies too, and the reporting authors say explicitly that it is not useful for guiding the clinical diagnosis.
Distinguishing Features
  • Not separable clinically or radiologically; the distinction is molecular.
  • A combined complex I and IV deficiency with spared complex II narrows the differential to the mitochondrial gene-expression disorders but does not identify the gene.
Show evidence (1 reference)
PMID:36450274 SUPPORT Human Clinical
"On the other hand, optic atrophy is a clinical sign that has been observed in patients with Leigh syndrome of other etiologies, and thus it is not useful in guiding the clinical diagnosis"
The authors' own statement that the disorder's most consistent feature does not discriminate it from other Leigh syndromes.
Other mitochondrial ribosomal protein (MRP) disorders
Overlapping Features Thirteen genes encoding mitoribosomal proteins had been implicated in human disease by 2023. As a class they present neonatally or in infancy with lactic acidosis and combined OXPHOS deficiency, and with myopathy, cardiac, hepatic, renal or hearing involvement. PTCD3 sits inside that class and shares its biochemistry; what distinguishes it clinically, on the evidence available, is the near-constant optic atrophy and nystagmus rather than the multiorgan pattern.
Distinguishing Features
  • Shared biochemistry - lactic acidosis with combined OXPHOS deficiency - across the whole class, so enzymology does not separate them.
  • Cardiac, hepatic and renal involvement is common in the MRP class but has not been a feature of the reported PTCD3 patients, one of whom had only slight left ventricular hypertrophy.
Show evidence (2 references)
PMID:36450274 SUPPORT Human Clinical
"Myopathy, cardiac abnormalities, hepatopathy, renal dysfunction, deafness and dysmorphic features are the most common clinical phenotypes associated with MRP deficiencies."
The class phenotype against which PTCD3 has to be distinguished.
PMID:34008913 SUPPORT INDIRECT Human Clinical
"Similar to previously reported individuals, this reported female proband presented with psychomotor retardation, sensorineural hearing loss, hypertrophic cardiomyopathy, failure to thrive, and lactic acidosis."
A worked example of the sibling class, and INDIRECT for that reason: this is COXPD9 caused by MRPL3, a large-subunit mitoribosomal protein, not PTCD3. It is cited to show what the differential looks like in practice - the cardiomyopathy, deafness and failure to thrive that dominate COXPD9 have not been features of the PTCD3 patients.
Hereditary optic neuropathy and hereditary ataxia
Overlapping Features The adult pole of COXPD51 was worked up for years as hereditary ataxia and hereditary optic neuropathy. Mitochondrial DNA sequencing, Friedreich ataxia repeat testing, an NGS ataxia panel, spinocerebellar ataxia repeat analysis and whole-exome sequencing were all negative in that family before whole-genome sequencing found PTCD3. This is the practical reason to keep PTCD3 in an adult ataxia-with-optic-atrophy differential.
Distinguishing Features
  • A standard ataxia gene panel and exome will miss it; the reported adult family was diagnosed only on whole-genome sequencing.
  • The combination of optic atrophy, nystagmus, ataxia and a motor polyneuropathy with preserved cognition is the phenotype that should prompt mitochondrial testing.
Show evidence (1 reference)
PMID:39544688 SUPPORT Human Clinical
"The results of mtDNA sequencing, Friedreich ataxia repeat expansion analysis, NGS ataxia gene panel (case 1), nucleotide repeat expansion analysis for all known types of spinocerebellar ataxia (case 1) and whole exome sequencing (case 2) did not reveal the cause of the disease."
The diagnostic odyssey that the adult phenotype produced.
🧫

Experimental Models

1
Patient-derived fibroblasts with wild-type PTCD3 lentiviral rescue PRIMARY_CELL_CULTURE
Immortalised fibroblasts from two patients of the 2023 series, with lentiviral re-expression of GFP-tagged wild-type PTCD3 as the rescue arm and an empty vector as the control. Untransduced cells show reduced complex I, III and IV subunits and reduced respiratory capacity; the rescue arm restores both. The same design was used in the founding report on the index patient's cells.
fibroblast CL:0000057 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:36450274
Pathograph links
Combined Respiratory Chain Deficiency with Complex II Spared rescues fidelity: high observes: cellular Re-expression of wild-type PTCD3 restores the OXPHOS subunit levels and the maximal respiratory capacity that are reduced in the patients' own cells, with an empty-vector arm as the specificity control. This is what converts the biochemical phenotype from a correlate of the genotype into a consequence of it.
Limitations: Fibroblasts are not the tissue in which this disease manifests. In one patient the complex IV deficit disappeared on normalisation to citrate synthase, so the cellular model understates the defect that the brain and optic nerve evidently sustain.
Readouts
Steady-state levels of NDUFB8, MT-CO2 and UQCRC2 after wild-type PTCD3 transduction
Direction: RESTORED
Interpretation: Restoration of the reduced OXPHOS subunits, establishing PTCD3-dependence.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"The expression of wild‐type PTCD3 cDNA using a lentiviral vector resulted in a complete recovery of the steady‐state levels of the altered OXPHOS subunits in both patients"
Reports the rescue measurement behind this readout.
Maximal uncoupled respiratory capacity after wild-type PTCD3 transduction
Direction: RESTORED
Interpretation: The functional counterpart of the subunit rescue, with an empty-vector arm showing the effect is not an artefact of transduction.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"Transduction with wild‐type PTCD3, but not with the empty vector, restored the mitochondrial respiratory capacity in immortalized patients' fibroblasts."
Reports the respirometry rescue with its vector control.
Show evidence (1 reference)
PMID:30607703 SUPPORT In Vitro
"Complementation experiments rescued oxidative phosphorylation complex I and IV levels and activities, ATP biosynthesis, and MT-RNR1 rRNA transcript level, providing functional validation of the pathogenicity of identified variants."
The same rescue design applied independently to the index patient's cells, which is what makes this model informative rather than a single-laboratory result.
Show evidence (1 reference)
PMID:36450274 SUPPORT In Vitro
"Functional complementation studies demonstrated the pathogenic effect of the identified variants since the expression of wild-type PTCD3 in immortalized fibroblasts restored the steady-state levels of complexes I and IV subunits as well as the mitochondrial respiratory capacity."
Establishes the model system and what it demonstrated, which is why this entry treats patient fibroblasts with wild-type rescue as informative for the biochemical node.
🐁

Animal Models

1
Drosophila melanogaster PTCD3 loss-of-function mutant
The only published whole-organism model of PTCD3 loss. The mutant dies during the second larval instar with reduced expression of mitochondrial-function and ribosome-biogenesis genes and, unexpectedly, up-regulated neuronal-development genes. It establishes that the gene is essential for development in an intact animal, which no patient genotype can show, but it cannot model the human disease: every reported human genotype retains some function, and the fly has no basal-ganglia or optic-nerve counterpart to the human lesions.
Species
Drosophila melanogaster
Genotype
Loss-of-function mutant of CG4679, the Drosophila PTCD3 ortholog
Publication
PMID:38074476
Pathograph links
Impaired Mitochondrial mRNA Translation partially recapitulates fidelity: low observes: organism Transcriptional evidence of a coordinated loss of mitochondrial and ribosome-biogenesis gene expression on loss of the PTCD3 ortholog.
Limitations: A null allele in an invertebrate, lethal at the second instar, against a human disease in which every reported genotype retains residual protein. The readout is transcriptomic rather than a direct measurement of mitochondrial protein synthesis, and no respiratory-chain enzymology was reported, so the link to the human translation defect is inferential.
Divergences from the human mechanism
species mismatch qualifying
Drosophila has no optic nerve, basal ganglia or thalamus, so the two tissue-level nodes that define the human disease have no counterpart in this organism. The model can speak to the molecular and cellular nodes only.
proxy quantity qualifying
The model's measured quantity is the expression level of mitochondrial-function and ribosome-biogenesis genes. The node's quantity is the rate of mitochondrial protein synthesis. Reduced transcript abundance for ribosome components is a proxy for, not a measurement of, translation output.
Readouts
Expression of mitochondrial-function and ribosome-biogenesis genes
Direction: DECREASED
Interpretation: Coordinated down-regulation of the mitochondrial translation apparatus on loss of the PTCD3 ortholog.
Show evidence (1 reference)
PMID:38074476 SUPPORT Model Organism
"In addition, mutants exhibit reduced expression of a group of genes related to mitochondrial function and ribosome biogenesis, and conversely, they show up-regulated expression of neuronal development-related genes."
Reports the transcriptomic measurement behind this readout.
Show evidence (1 reference)
PMID:38074476 SUPPORT Model Organism
"A loss-of-function mutant of PTCD3 is lethal during the second instar."
Establishes that the gene is developmentally essential in an intact animal, which is why this model is treated as informative for the translation node despite its low fidelity to the human phenotype.
Show evidence (1 reference)
PMID:38074476 SUPPORT Model Organism
"we focus on the Drosophila melanogaster homolog of PPR domain 3"
Establishes that the studied gene is the Drosophila ortholog of human PTCD3, which is the only thing that makes this model relevant to this disease at all.
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Source YAML

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name: Combined Oxidative Phosphorylation Deficiency 51
category: Mendelian
creation_date: "2026-09-07T00:00:00Z"
synonyms:
- COXPD51
- PTCD3 deficiency
- MRPS39-related combined oxidative phosphorylation deficiency
description: >-
  Combined oxidative phosphorylation deficiency 51 (COXPD51) is an autosomal
  recessive mitochondrial disease caused by biallelic variants in PTCD3 (also
  called MRPS39, and mS39 in the standardised mitoribosome nomenclature). PTCD3
  is a pentatricopeptide-repeat RNA-binding protein of the small subunit of the
  mitochondrial ribosome, where it forms the mRNA entry channel. The lesion
  therefore sits in the mitochondrial translation apparatus itself rather than in
  any single respiratory-chain subunit.

  The consequence follows from where mitochondria get their proteins. Thirteen
  respiratory-chain subunits are encoded by mitochondrial DNA and made on the
  mitoribosome; every other subunit is nuclear-encoded and imported. Losing
  PTCD3 destabilises the small mitoribosomal subunit and impairs translation of
  all thirteen at once, so several complexes fail together - the "combined" of
  the name. What the published patients actually show is a consistent complex I
  and complex IV defect, a variable complex III defect, and unchanged complex V
  and complex II subunit levels. Complex II is built entirely from
  nuclear-encoded subunits, so its being spared is a mechanistically informative
  negative and a pointer toward translation rather than toward an individual
  complex.

  Two clinical poles have been described from a total of seven patients. The
  severe pole is Leigh or Leigh-like syndrome: onset in the first weeks to months
  of life with psychomotor delay, respiratory insufficiency, feeding difficulties,
  dystonia, seizures, optic atrophy and nystagmus, with bilateral basal-ganglia
  and thalamic MRI change, and death in the first or second decade. The mild pole,
  described in 2024, is an adult sibling pair in their thirties with optic atrophy,
  nystagmus, tremor, truncal ataxia, spasticity and a motor polyneuropathy but
  only mild cognitive decline - a chronic ataxia/optic-neuropathy phenotype that
  would not usually prompt a Leigh-syndrome workup. Optic atrophy and nystagmus
  are the features that run through both poles, present in six of the seven
  reported patients. Management is entirely supportive; every cofactor and
  mitochondrial-cocktail regimen reported in these patients was ineffective.
parents:
- Mitochondrial Disease
disease_term:
  preferred_term: combined oxidative phosphorylation deficiency 51
  term:
    id: MONDO:0033631
    label: combined oxidative phosphorylation deficiency 51
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0033631
      label: combined oxidative phosphorylation deficiency 51
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    notes: >-
      MONDO:0033631 is equivalent to OMIM:619057 and carries COXPD51 as its only
      synonym. It has no MONDO descendants and one causal gene (PTCD3), which is the
      leaf signature that settles the lump/split call in favour of a single DISEASE
      entry.
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      A Mendelian nuclear-gene mitochondrial disease; Harrison's covers the
      mitochondrial disorders under the genetics Part rather than under a single
      organ system, which matches a disorder whose presentations span the eye, the
      basal ganglia, the peripheral nerve and the respiratory drive.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Biochemically, MRP defects are characterized by lactic acidosis and combined OXPHOS deficiencies"
      explanation: >-
        Places the disorder among the inherited metabolic and respiratory-chain diseases
        that this Part covers.
  - classification_value: NEUROLOGIC
    notes: >-
      Every reported patient presented neurologically - Leigh/Leigh-like
      encephalopathy at the severe pole, a chronic ataxia with optic neuropathy and
      polyneuropathy at the mild pole.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Mitochondrial translation defects are a continuously growing group of disorders showing a large variety of clinical symptoms including a wide range of neurological abnormalities."
      explanation: >-
        The neurological dominance of this disease class, which is why a second, neurologic
        Part is assigned alongside the genetics one.
  mechanistic_category:
  - classification_value: mitochondrial disease
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Leigh syndrome is the most prevalent manifestation of mitochondrial disease in children."
      explanation: >-
        Situates the disorder's dominant presentation within mitochondrial disease as a
        mechanistic class.
  icimd_category:
  - classification_value: mitoribosome
    notes: >-
      PTCD3 is a structural component of the mitoribosomal small subunit, which
      places the disorder in the ICIMD mitoribosome group within disorders of
      mitochondrial gene expression - not with the respiratory-chain subunit or
      assembly-factor groups, even though the measured biochemical phenotype is a
      respiratory-chain one.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "PTCD3 (MIM* 614918), also known as MRPS39, encodes a member of the pentatricopeptide repeat domain protein family, which is associated with the small subunit of the mitochondrial ribosome"
      explanation: >-
        Establishes the gene product as a mitoribosomal small-subunit protein, which is the
        assignment criterion for this ICIMD group.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    All seven reported patients carry biallelic PTCD3 variants - compound
    heterozygous in the first six, homozygous for an intronic splice variant in the
    seventh, whose parents are double first cousins. Segregation in trans has been
    confirmed by parental testing in every family in which it was assessed.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "WES and RNA-seq identified compound heterozygous variants in PTCD3 in both families"
    explanation: Compound heterozygous, trans-configured variants in two independent families.
genetic:
- name: PTCD3
  gene_term:
    preferred_term: PTCD3
    term:
      id: hgnc:24717
      label: PTCD3
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  association: >-
    PTCD3 (MRPS39, mS39) encodes a pentatricopeptide-repeat RNA-binding protein
    that forms the mRNA entry channel of the small mitoribosomal subunit. Its
    function was established a decade before any patient was reported: knockdown in
    human cells reduced mitochondrial protein synthesis, respiration, and complex
    III and IV activity without changing mitochondrial mRNA levels, which located it
    in translation rather than in RNA processing or stability.

    The striking feature of the reported allelic spectrum is how many of the
    pathogenic alleles act through splicing. Of the nine variants published across
    the three case reports, six alter mRNA processing - two canonical acceptor-site
    variants, one intronic +4 variant, and two exonic variants initially called
    variants of uncertain significance that turned out on minigene assay to cause
    exon skipping. That last pair matters practically: an exonic missense-looking
    change in PTCD3 cannot be assumed to act as a missense change.
  variants:
  - name: "PTCD3 c.415-2A>G"
    description: >-
      Canonical splice acceptor variant, in trans with a frameshift allele in the
      index patient. Together the two alleles leave the protein nearly absent, which
      is the genotype the 2023 series proposes as the explanation for that patient's
      exceptionally severe course.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "As a result, the absence of PTCD3 protein is nearly complete, whereas in our patients, although reduced, was not absent."
      explanation: >-
        Contrasts the index patient's near-null genotype with the residual protein in
        the later, longer-surviving patients.
  - name: "PTCD3 c.1453-1G>C"
    description: >-
      Canonical acceptor-site variant abolishing the intron 18 splice site, causing
      exon 19 skipping and a transcript degraded by nonsense-mediated decay. On
      minigene assay it had the strongest effect of the four variants tested.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "cDNA analysis of P1 revealed a skipping of exon 19 caused by the c.1453‐1G>C substitution, which altered a canonical splice acceptor site"
      explanation: Establishes the splicing consequence of this allele in patient fibroblasts.
  - name: "PTCD3 c.902C>T"
    description: >-
      Initially classified as a variant of uncertain significance because it sits
      inside exon 12 and reads as a missense change. Minigene assay showed it causes
      skipping of the exon it sits in, producing a truncating transcript alongside a
      leaky pool of correctly spliced mRNA.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing."
      explanation: >-
        The functional result that reclassified this and two neighbouring variants from
        uncertain significance to pathogenic-by-splicing.
  - name: "PTCD3 c.538+4A>G"
    description: >-
      Homozygous intronic variant in a consanguineous family, absent from gnomAD,
      shown by RT-PCR to cause skipping of the 124 bp exon 7. The only homozygous
      genotype reported to date.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:39544688
      reference_title: "The phenotypic spectrum of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This genetic change abolishes the consensus splice site and causes exon 7 skipping"
      explanation: The splicing consequence demonstrated for the homozygous intronic allele.
  - name: "PTCD3 c.1182T>A (p.Tyr394Ter)"
    description: >-
      Nonsense allele carried by the adult sibling pair, in trans with the
      p.His269Tyr missense allele. It removes the C-terminal half of the protein
      including much of the central fold, so the product cannot be incorporated into
      the mitoribosome; western blot showed it is not cleared by nonsense-mediated
      decay.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:39544688
      reference_title: "The phenotypic spectrum of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The whole genome sequencing analysis revealed two heterozygous variants in the PTCD3: c.1182T>A, p.(Tyr394Ter) and c.805C>T, p.(His269Tyr)."
      explanation: Names the two alleles of the mild adult phenotype.
  evidence:
  - reference: PMID:30607703
    reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first report of an association of PTCD3 mutations with Leigh syndrome along with combined oxidative phosphorylation deficiencies caused by defects in the mitochondrial translation machinery."
    explanation: The founding report establishing PTCD3 as a human disease gene.
  - reference: PMID:19427859
    reference_title: "Pentatricopeptide repeat domain protein 3 associates with the mitochondrial small ribosomal subunit and regulates translation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "lowering PTCD3 in 143B osteosarcoma cells decreased mitochondrial protein synthesis, mitochondrial respiration and the activity of Complexes III and IV, suggesting that PTCD3 has a role in mitochondrial translation."
    explanation: >-
      Establishes the gene's normal function in mitochondrial translation, a decade
      before any patient was reported. This is a cell-line knockdown, not a PTCD3
      patient study.
pathophysiology:
- name: Biallelic PTCD3 Variants Disrupting mRNA Processing
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  description: >-
    Germline biallelic PTCD3 variants, most of which act on splicing. Canonical
    acceptor-site variants, an intronic +4 variant and two exonic variants that read
    as missense changes all produce exon-skipped transcripts; a frameshift and a
    nonsense allele complete the reported spectrum. The splice-acting alleles were
    proven to act that way by minigene assay in HAP1 cells, not inferred from
    prediction algorithms.
  genetic_context:
    genes:
    - preferred_term: PTCD3
      term:
        id: hgnc:24717
        label: PTCD3
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Compound heterozygous in six of the seven reported patients, homozygous for the
      intronic c.538+4A>G allele in the seventh.
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Overall, these results demonstrated that the c.1918C>G, c.1453‐1G>C, and c.902C>T variants were responsible for the PTCD3 mRNA processing defects observed in patients' fibroblasts."
    explanation: Direct experimental attribution of the mRNA-processing defect to the variants.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, PTCD3 seems to be particularly vulnerable to pathological splice site errors"
    explanation: >-
      States the generalisation across the allelic spectrum that makes splicing the
      dominant mechanism of loss of function in this gene.
  downstream:
  - target: Depletion of PTCD3 Protein
    causal_link_type: DIRECT
    description: >-
      Exon-skipped transcripts are either degraded by nonsense-mediated decay or
      translated into truncated protein that cannot be incorporated into the
      mitoribosome; either route lowers the amount of functional PTCD3.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Results demonstrated that PTCD3 protein was significantly reduced in patients' cells, with 70% (P1) and 85% (P2.1) reduction when compared to controls"
      explanation: >-
        Quantifies the protein consequence of the splicing lesion in the same patients'
        fibroblasts in which the splicing defect was demonstrated.
- name: Depletion of PTCD3 Protein
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    PTCD3 protein is reduced but, in the patients with a leaky splice allele, not
    absent - 70% and 85% below control in the two 2023 patients tested. The index
    patient's two truncating alleles leave it nearly absent. This quantitative
    difference is the residual-function hypothesis the field currently uses to
    explain why some patients die in infancy and others reach their thirties.
  molecular_functions:
  - preferred_term: mRNA binding
    term:
      id: GO:0003729
      label: mRNA binding
    modifier: DECREASED
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The PTCD3 gene product (protein PTCD3 or MRPS39) forms the entry channel of the mitochondrial small ribosomal subunit and binds to single-stranded mRNA."
    explanation: The molecular function that is lost when the protein is depleted.
  downstream:
  - target: Destabilization of the Mitochondrial Small Ribosomal Subunit
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30607703
      reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Quantitative proteomic analysis revealed decreased levels of the small mitoribosomal subunits."
      explanation: >-
        Loss of PTCD3 is accompanied by loss of the rest of the small subunit, which is
        what makes this a subunit-destabilisation mechanism rather than the loss of one
        protein's activity.
- name: Destabilization of the Mitochondrial Small Ribosomal Subunit
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Quantitative proteomics in the index patient's fibroblasts showed the small
    mitoribosomal subunit as a whole is depleted, not just PTCD3. PTCD3 sits at the
    mRNA entry channel, so its loss removes both a structural component and the site
    at which mitochondrial mRNA is engaged.
  cellular_components:
  - preferred_term: mitochondrial small ribosomal subunit
    term:
      id: GO:0005763
      label: mitochondrial small ribosomal subunit
    modifier: DECREASED
  evidence:
  - reference: PMID:30607703
    reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PTCD3, a member of the pentatricopeptide repeat domain protein family, is a component of the small mitoribosomal subunit."
    explanation: Places PTCD3 structurally within the subunit whose steady-state level falls.
  downstream:
  - target: Impaired Mitochondrial mRNA Translation
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30607703
      reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The patient had marked decreases in mitochondrial complex I and IV levels and activities, oxygen consumption and ATP biosynthesis, and generalized mitochondrial translation defects in fibroblasts."
      explanation: >-
        The translation defect is described as generalized, which is the expected
        signature of losing ribosome capacity rather than of losing a single transcript.
- name: Impaired Mitochondrial mRNA Translation
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Mitochondrial protein synthesis falls across the board. In patient fibroblasts
    this was measured directly as a generalized translation defect; the same effect
    was produced in control cells a decade earlier by knocking PTCD3 down, which
    establishes the direction of the relationship independently of any patient
    genotype.
  biological_processes:
  - preferred_term: mitochondrial translation
    term:
      id: GO:0032543
      label: mitochondrial translation
    modifier: DECREASED
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  evidence:
  - reference: PMID:19427859
    reference_title: "Pentatricopeptide repeat domain protein 3 associates with the mitochondrial small ribosomal subunit and regulates translation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "PTCD3 knockdown and over expression did not affect mitochondrial mRNA levels, suggesting that PTCD3 is not involved in RNA processing and stability."
    explanation: >-
      A negative result that constrains the mechanism: the lesion is in translation, not
      in mitochondrial mRNA processing or stability. Cell-line knockdown, not a patient
      study.
  downstream:
  - target: Reduced Synthesis of mtDNA-Encoded OXPHOS Subunits
    causal_link_type: DIRECT
    description: >-
      Only thirteen OXPHOS subunits are made on the mitoribosome; a generalized
      translation defect under-supplies all of them at once.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "the mtDNA encodes only 13 OXPHOS structural subunits which are transcribed in the mitochondrial matrix as polycistronic mRNAs and translated by the mitoribosomes before their incorporation into the OXPHOS complexes"
      explanation: >-
        States the dependency that turns a translation defect into an OXPHOS defect. This
        is the review paragraph of a primary report, not its own experimental result.
- name: Reduced Synthesis of mtDNA-Encoded OXPHOS Subunits
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Steady-state levels of mtDNA-encoded and mtDNA-dependent respiratory-chain
    subunits fall. In the 2023 patients this was measured as reduced NDUFB8 (complex
    I) and MT-CO2 (complex IV) in both, with UQCRC2 (complex III) reduced in one of
    the two.
  biological_processes:
  - preferred_term: mitochondrial ATP synthesis coupled electron transport
    term:
      id: GO:0042775
      label: mitochondrial ATP synthesis coupled electron transport
    modifier: DECREASED
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A significant reduction of NDUFB8 (complex I) and MT‐CO2 (complex IV) in both patients"
    explanation: The measured subunit-level deficit in patient fibroblasts.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, steady‐state levels of UQCRC2 (complex III) were significantly reduced in P1, but not in P2.1"
    explanation: >-
      The complex III deficit is real but inconsistent between patients, which is why
      this entry does not present complex III as an obligate part of the signature.
  downstream:
  - target: Combined Respiratory Chain Deficiency with Complex II Spared
    causal_link_type: DIRECT
- name: Combined Respiratory Chain Deficiency with Complex II Spared
  biological_scale: CELLULAR
  role: effector
  mechanism_confidence: ESTABLISHED
  conforms_to: "mitochondrial_dysfunction#Bioenergetic Decline and Oxidative Stress"
  description: >-
    The biochemical signature of the disorder, and the reason it is named a
    "combined" deficiency. Complex I and complex IV activities are reduced in
    fibroblasts across the reported patients; complex III is reduced in some. Complex
    V subunit levels were unchanged in the two patients in whom they were measured,
    and complex II - alone among the five complexes, built entirely from
    nuclear-encoded subunits - was not reduced and in fact ran slightly above the
    control range once normalised to citrate synthase.

    The spared complex II is not an incidental negative. It is the finding that
    points the differential at the translation apparatus rather than at an assembly
    factor or a structural subunit of one complex, and it is what a curator or
    clinician should look for in the enzymology report.
  biological_processes:
  - preferred_term: oxidative phosphorylation
    term:
      id: GO:0006119
      label: oxidative phosphorylation
    modifier: DECREASED
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex I, complexes I + III and complex IV"
    explanation: The enzymatic deficit measured in one of the 2023 patients.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Indeed, complex II is known to be largely unaltered in mitochondrial protein translation deficiencies."
    explanation: >-
      States why complex II is spared and generalises it to the class of mitochondrial
      translation defects, of which this disorder is one.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ATP5A1 (complex V) and SDHB (complex II) protein levels remained unaltered."
    explanation: >-
      The measured negative for complexes II and V. Recorded because the generic
      "complexes I, III, IV and V" description of a combined OXPHOS deficiency is not
      what these patients showed.
  downstream:
  - target: Reduced Mitochondrial Respiratory Capacity and ATP Deficit
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30607703
      reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The patient had marked decreases in mitochondrial complex I and IV levels and activities, oxygen consumption and ATP biosynthesis, and generalized mitochondrial translation defects in fibroblasts."
      explanation: >-
        Reduced complex activity and reduced oxygen consumption and ATP synthesis were
        measured in the same cells, which is the edge from the enzymology to the
        bioenergetic consequence.
- name: Reduced Mitochondrial Respiratory Capacity and ATP Deficit
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    High-resolution respirometry in patient fibroblasts shows a modest fall in basal
    respiration and a marked fall in maximal (uncoupled) respiratory capacity; the
    index patient also had reduced ATP biosynthesis. Functional complementation with
    wild-type PTCD3 restored both the subunit levels and the respiratory capacity,
    which is what makes this a consequence of the PTCD3 lesion rather than a
    correlate of it.
  biological_processes:
  - preferred_term: cellular respiration
    term:
      id: GO:0045333
      label: cellular respiration
    modifier: DECREASED
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with the mitochondrial uncoupler CCCP resulted in a significant reduction in maximal respiratory capacity in both patients"
    explanation: The respirometry result behind this node.
  downstream:
  - target: Lactate and Pyruvate Accumulation
    causal_link_type: DIRECT
  - target: Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The step from a cell-level bioenergetic deficit to selective necrosis of the
      basal ganglia and thalamus is the least explained link in the chain. It is the
      shared final pathway of more than 75 Leigh-syndrome genes, and no PTCD3-specific
      account of the regional selectivity has been published.
  - target: Optic Nerve Degeneration
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39544688
      reference_title: "The phenotypic spectrum of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Defects in mitochondrial replication, RNA transcription and translation initiate early‐onset optic atrophy, as these cells are highly vulnerable to mitochondrial dysfunction."
      explanation: >-
        The authors' stated reason for the optic-nerve selectivity - a vulnerability
        argument for the cell type, offered as a general property of mitochondrial gene
        expression defects rather than as a PTCD3-specific experimental result.
- name: Lactate and Pyruvate Accumulation
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    Blocked oxidative disposal of pyruvate shifts it to lactate and to alanine by
    transamination. Two of the reported patients had high blood lactate, pyruvate,
    alanine, glycine and glutamine; a third had only mild elevation, and in two
    others blood lactate was normal - so the finding is characteristic but not
    obligate, and a normal lactate does not exclude the diagnosis.
  chemical_entities:
  - preferred_term: lactate
    term:
      id: CHEBI:24996
      label: lactate
    modifier: INCREASED
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
    explanation: The metabolic profile in the patient with the fullest workup.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Laboratory investigation revealed normal results of blood lactate, ammonia, creatine phosphokinase, cholesterol and electrolytes in variable ages"
    explanation: >-
      Refutes lactate elevation as an obligate feature - the third 2024 patient, who has
      a Leigh-like phenotype with an MRI lactate peak, had repeatedly normal blood
      lactate.
  downstream:
  - target: Lactic Acidosis
    causal_link_type: DIRECT
- name: Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    The neuropathological substrate of the Leigh and Leigh-like pole. Imaging shows
    bilateral symmetrical signal change and volume loss in the thalamus and globus
    pallidus, and in the index patient punctate brainstem lesions with thalamic,
    caudate and putaminal T2 hyperintensity. One 2024 patient's repeat MRI showed
    cystic change, gliosis and volume loss in the posterior putamina, which is the
    necrotizing character the syndrome is named for.
  locations:
  - preferred_term: basal ganglia
    term:
      id: UBERON:0002420
      label: basal ganglion
  - preferred_term: thalamus
    term:
      id: UBERON:0001897
      label: dorsal plus ventral thalamus
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  evidence:
  - reference: PMID:30607703
    reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed abnormal bilateral signals at the basal ganglia and brainstem, and the patient was diagnosed as Leigh syndrome."
    explanation: The imaging finding that anchored the Leigh-syndrome diagnosis in the index patient.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain magnetic resonance imaging (MRI) at 6 years of age showed a bilateral symmetrical globus pallidus signal intensity with an elevated lactate peak."
    explanation: >-
      The same regional pattern in an independently reported patient, with the MRS
      lactate peak that accompanies it.
  downstream:
  - target: Developmental Regression
  - target: Global Developmental Delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Dystonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Optic Nerve Degeneration
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    Optic-nerve atrophy is visible on MRI and on fundoscopy and is the single most
    consistent finding in the disorder, present with nystagmus in six of the seven
    reported patients and at both clinical poles. The adult siblings are legally
    blind with only light perception, and both had absent or poorly structured
    visual evoked potentials.
  locations:
  - preferred_term: optic nerve
    term:
      id: UBERON:0000941
      label: cranial nerve II
  cell_types:
  - preferred_term: retinal ganglion cell
    term:
      id: CL:0000740
      label: retinal ganglion cell
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showed optic atrophy and nystagmus in six of seven patients"
    explanation: >-
      The cross-cohort frequency, from the authors' own heat map of previously and newly
      published patients.
  downstream:
  - target: Optic Atrophy
    causal_link_type: DIRECT
phenotypes:
- name: Optic Atrophy
  category: Ophthalmological
  description: >-
    Present at both clinical poles and, with nystagmus, the most consistent feature
    of the disorder. In the index patient it was one of the presenting features
    alongside low birth weight and psychomotor retardation; in the adult siblings it
    followed childhood-onset nystagmus and progressed to legal blindness with only
    light perception.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showed optic atrophy and nystagmus in six of seven patients"
    explanation: Quantifies the frequency across the whole published cohort.
  - reference: PMID:30607703
    reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe a patient who presented with low birth weight, mental retardation, and optic atrophy."
    explanation: Optic atrophy as a presenting feature in the index patient.
- name: Nystagmus
  category: Ophthalmological
  description: >-
    Horizontal nystagmus, in the adult siblings the first sign of the disease at age
    two, years before the gait disorder. Present in six of seven reported patients
    together with optic atrophy.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
    explanation: The adult presentation, in which nystagmus is one of the cardinal signs.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures."
    explanation: Nystagmus in the severe infantile-onset pole as well.
- name: Developmental Regression
  category: Neurologic
  description: >-
    Loss of acquired milestones after a period of normal or near-normal early
    development. This is what makes the disease a Leigh rather than a static
    encephalopathy, and it is the axis the entry uses to separate the two clinical
    poles: in the severe pole regression follows a short normal interval and is
    punctuated by metabolic decompensations, while the adult siblings show only mild
    cognitive decline after normal early development. Documented in three of the seven
    published patients.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Until now, functional evidence of disease‐causing variants in PTCD3 has only been reported in a single individual presenting psychomotor regression, optic atrophy, and Leigh syndrome"
    explanation: >-
      Names psychomotor regression as one of the three defining features of the index
      patient. The quote preserves the source's non-ASCII hyphen in "disease-causing".
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurodevelopment was considered normal until the 10th month of life, when delayed adquisicion of milestones and hypertonia were noted."
    explanation: >-
      The normal interval preceding decline in the 2023 Spanish patient, which is what
      distinguishes regression from static delay. The quote reproduces the source's own
      "adquisicion" typo, as an exact quote must.
- name: Global Developmental Delay
  category: Neurologic
  description: >-
    Psychomotor delay from the first months of life in the severe pole, with no
    acquisition of gross or fine motor milestones in the most affected patients. The
    2024 adult siblings are the exception: their early development was normal and
    they have only mild cognitive decline, which is the clearest separation between
    the two poles of the disorder.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties."
    explanation: The presenting triad of the severe pole.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Global developmental delay was described in all Leigh‐like patients, except our presented cases 1 and 2, who have only mild cognitive decline."
    explanation: >-
      Refutes global developmental delay as universal - the two adult patients do not
      have it, which is why the frequency here is FREQUENT rather than VERY_FREQUENT.
- name: Dystonia
  category: Neurologic
  description: >-
    Generalised dystonia, in the 2023 series present in all three patients and in
    two of them progressing to severe fixed postures with contractures. It is the
    movement disorder that follows the basal-ganglia lesion and, in these patients,
    the proximate cause of the scoliosis.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Remarkably, dystonia was observed in all three individuals reported here."
    explanation: Dystonia in all three patients of the 2023 series.
  sequelae:
  - target: Scoliosis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      The authors attribute the scoliosis in the sibling pair to the severity of the
      dystonia together with their longer survival.
    evidence:
    - reference: PMID:36450274
      reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "P2.1 and P2.2 suffered from scoliosis, which had not been reported in the previous PTCD3 individual and was most likely caused by their older age and to the effect of the severe dystonia"
      explanation: The authors' own causal attribution for the scoliosis.
- name: Bilateral Tonic-Clonic Seizures
  category: Neurologic
  description: >-
    Tonic-clonic seizures across the severe pole, in one patient culminating in a
    drug-resistant status epilepticus. In the mildest reported patient there were no
    seizures at all, and one 2024 patient's EEG showed no epileptiform abnormality.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Bilateral tonic-clonic seizure
    term:
      id: HP:0002069
      label: Bilateral tonic-clonic seizure
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures."
    explanation: Seizures as part of the neurologic phenotype of the 2023 series.
- name: Respiratory Insufficiency
  category: Respiratory
  description: >-
    Chronic respiratory failure with recurrent acute decompensations, present from
    the first months of life in the severe pole and the proximate cause of death in
    at least two reported patients. It drives the intensive-care and palliative
    decisions in this disorder more than any other feature.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties."
    explanation: Respiratory insufficiency as a presenting feature.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three additional patients from two families had developmental delay, seizures, respiratory insufficiency, optic nerve hypoplasia, abnormal brain magnetic resonance imaging and died in the first or second decade."
    explanation: Recurrence of respiratory insufficiency across the reported severe cases.
- name: Feeding Difficulties and Dysphagia
  category: Gastrointestinal
  description: >-
    Progressive dysphagia with choking episodes, requiring gastrostomy or nasogastric
    feeding in the severe pole. Present from the first months of life in the 2023
    series and in the youngest 2024 patient, in whom there is also no sphincter
    control.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He was admitted a few more times due to respiratory symptoms (bronchospasm), developing chronic respiratory failure and progressive dysphagia requiring gastrostomy."
    explanation: The course of the feeding problem and the intervention it required.
- name: Spasticity
  category: Neurologic
  description: >-
    Spasticity with hyperreflexia at both poles - spastic and dystonic tetraparesis
    in the severe pole, and spasticity with hyperreflexia and central hypotonia in
    the adult siblings and the youngest 2024 patient.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Severely affected PTCD3 patients have spasticity, abnormal EEG, seizures, myoclonus, dystonia, dysphagia, polyneuropathy"
    explanation: Spasticity listed among the features of the severely affected patients.
- name: Hyperreflexia
  category: Neurologic
  description: >-
    Brisk reflexes accompanying the spasticity, reported in the adult siblings and in
    the youngest 2024 patient, who has central hypotonia with peripheral hypertonia.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
    explanation: Hyperreflexia in the two adult patients.
- name: Truncal Ataxia
  category: Neurologic
  description: >-
    A cerebellar syndrome with truncal ataxia and dysmetria, described only in the
    2024 adult siblings. It is the feature that made hereditary ataxia the working
    diagnosis in that family for decades, and it is why PTCD3 belongs in an
    adult-onset ataxia differential and not only in a Leigh-syndrome panel.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Truncal ataxia
    term:
      id: HP:0002078
      label: Truncal ataxia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
    explanation: The ataxic phenotype of the adult sibling pair.
- name: Tremor
  category: Neurologic
  description: >-
    A pronounced coarse tremor in the adult siblings, severe enough that repeat brain
    MRI could not be obtained without sedation. An intention tremor was also
    described in the oldest patient of the 2023 series at two years of age.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A 34-year-old male and his 33-year-old sister both have horizontal nystagmus, pronounced rough tremor, truncal ataxia, dysmetria, spasticity and hyperreflexia."
    explanation: The tremor in the adult siblings.
- name: Motor Polyneuropathy
  category: Neurologic
  description: >-
    A peripheral neuropathy documented electrophysiologically in the adult siblings
    and, as a diffuse sensory and motor axonal neuropathy, in the oldest patient of
    the 2023 series at four years of age. Denervated fibres on muscle biopsy in that
    patient are the histological correlate.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Peripheral axonal neuropathy
    term:
      id: HP:0003477
      label: Peripheral axonal neuropathy
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EEG, echocardiography and hearing tests did not reveal any pathology, but EMG/NCV showed motor polyneuropathy"
    explanation: >-
      The electrophysiological finding in the adult siblings, quoted with the negative
      studies that accompanied it.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 4 years old, he had a diffuse sensory and motor axonal neuropathy"
    explanation: An axonal neuropathy in the severe pole as well, so this is not exclusive to the adult phenotype.
- name: Scoliosis
  category: Musculoskeletal
  description: >-
    Severe thoracolumbar scoliosis in the sibling pair of the 2023 series, appearing
    in adolescence. Attributed by the reporting authors to their severe dystonia
    together with their unusually long survival.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P2.1 and P2.2 suffered from scoliosis, which had not been reported in the previous PTCD3 individual"
    explanation: Scoliosis in the two longest-surviving patients of the 2023 series.
- name: Lactic Acidosis
  category: Metabolic
  description: >-
    Raised blood lactate, with pyruvate, alanine, glycine and glutamine elevation, in
    the patients of the 2023 series; a mild elevation in the adult siblings; and
    repeatedly normal blood lactate in the youngest 2024 patient, who nonetheless had
    an MRS lactate peak in the brain. Characteristic but not obligate.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
    explanation: The lactate elevation with its accompanying amino-acid profile.
- name: Sensorineural Hearing Impairment
  category: Otologic
  description: >-
    Hearing loss in the index patient and central auditory involvement on evoked
    potentials in one 2023 patient. It is not a constant feature - hearing tests were
    normal in the adult siblings - which is worth recording because deafness is
    common across the mitoribosomal protein disorders as a class.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nystagmus was also observed in two of our patients, but only P1 had optic atrophy and hearing loss."
    explanation: Hearing loss in one of three patients of the 2023 series.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "EEG, echocardiography and hearing tests did not reveal any pathology, but EMG/NCV showed motor polyneuropathy"
    explanation: >-
      Refutes hearing loss as a general feature - it was explicitly normal in the two
      adult patients.
biochemical:
- name: Blood lactate
  biomarker_term:
    preferred_term: Increased circulating lactate concentration
    term:
      id: HP:0002151
      label: Increased circulating lactate concentration
  frequency: FREQUENT
  context: Plasma, measured on metabolic workup in six of the seven reported patients.
  notes: >-
    Elevated in the 2023 series and mildly elevated (2.9-3.2 mmol/L) in the adult
    siblings, but repeatedly normal at three separate ages in the youngest 2024
    patient. A normal blood lactate therefore does not exclude COXPD51.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Metabolic workup revealed high blood lactate, pyruvate, alanine, glycine and glutamine with low plasma coenzyme Q10 levels"
    explanation: The elevated result in the patient with the fullest metabolic workup.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Laboratory investigation revealed normal results of blood lactate, ammonia, creatine phosphokinase, cholesterol and electrolytes in variable ages"
    explanation: >-
      A true negative in a genetically confirmed, MRI-positive patient. This is the
      reason the marker is recorded as FREQUENT rather than VERY_FREQUENT.
- name: Brain lactate peak on MR spectroscopy
  biomarker_term:
    preferred_term: Elevated brain lactate level by MRS
    term:
      id: HP:0012707
      label: Elevated brain lactate level by MRS
  context: MR spectroscopy of the basal ganglia.
  notes: >-
    Recorded separately from blood lactate because in the youngest 2024 patient the
    two dissociated: repeated blood lactate was normal while MRS showed a lactate
    peak with no other abnormal metabolite. In that patient the brain measurement was
    the informative one.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain magnetic resonance imaging (MRI) at 6 years of age showed a bilateral symmetrical globus pallidus signal intensity with an elevated lactate peak."
    explanation: The MRS lactate peak in the patient whose blood lactate was normal.
- name: Fibroblast respiratory chain complex I activity
  biomarker_term:
    preferred_term: Decreased activity of mitochondrial complex I
    term:
      id: HP:0011923
      label: Decreased activity of mitochondrial complex I
  frequency: FREQUENT
  context: Cultured skin fibroblasts, respiratory-chain enzymology normalised to citrate synthase.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex I, complexes I + III and complex IV"
    explanation: The measured complex I deficit in fibroblasts.
- name: Fibroblast respiratory chain complex IV activity
  biomarker_term:
    preferred_term: Decreased activity of mitochondrial complex IV
    term:
      id: HP:0008347
      label: Decreased activity of mitochondrial complex IV
  frequency: VERY_FREQUENT
  context: Cultured skin fibroblasts; also COX-negative fibres on muscle histochemistry.
  notes: >-
    The most consistently abnormal complex across the reported patients. Note the
    normalisation trap recorded in the 2023 series: in one patient complex IV activity
    was decreased in absolute terms but fell within the control range once normalised
    to citrate synthase.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex IV."
    explanation: The complex IV deficit in the first patient of the 2023 series.
- name: Fibroblast respiratory chain complex II activity
  biomarker_term:
    preferred_term: Decreased activity of mitochondrial complex II
    term:
      id: HP:0008314
      label: Decreased activity of mitochondrial complex II
  presence: Absent
  context: Cultured skin fibroblasts, normalised to citrate synthase.
  notes: >-
    Recorded as an explicitly negative marker. Complex II is the only respiratory
    complex built entirely from nuclear-encoded subunits, so it is spared by a
    mitochondrial translation defect; in the 2023 patients its normalised activity was
    if anything slightly above the control range. A combined deficiency that also
    involves complex II points away from PTCD3 and away from the mitochondrial
    translation apparatus generally.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "the activity of CII (after normalization to citrate synthetase activity) was slightly above the control range in both individuals"
    explanation: >-
      Refutes a complex II deficit in this disorder - the measurement that makes the
      sparing of complex II a curated finding rather than an assumption.
- name: Plasma GDF-15 and FGF-21
  biomarker_term:
    preferred_term: growth differentiation factor 15 measurement
    term:
      id: NCIT:C181406
      label: Growth Differentiation Factor 15 Measurement
  presence: Normal
  context: Plasma, 2023 series.
  notes: >-
    The two standard circulating biomarkers of mitochondrial disease were normal in
    these patients, as were urine organic acids. This is a practically important
    negative: a normal GDF-15/FGF-21 screen does not exclude COXPD51, and the disorder
    would be missed by a workup that relies on them.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Other mitochondrial biomarkers such as plasma GDF‐15/GFG21 or urine organic acids disclosed normal results."
    explanation: >-
      Refutes the usefulness of these biomarkers as a screen in this disorder. Note the
      source's own typo, GFG21 for FGF21, quoted as printed.
histopathology:
- name: COX-negative fibres in a mosaic distribution in skeletal muscle
  description: >-
    Muscle biopsy in the oldest patient of the 2023 series showed a mosaic population
    of cytochrome c oxidase-negative fibres with increased lipid, alongside angulated
    hyperchromatic fibres consistent with denervation. There were no ragged-red fibres
    and no subsarcolemmal mitochondrial accumulation, so the classic mitochondrial
    myopathy picture is absent - the informative stain here is COX, not Gomori
    trichrome.
  context: Skeletal muscle biopsy at 3.5 years of age in one patient of the 2023 series.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "COX staining showed a population of COX‐negative fibres in mosaic, with increased amounts of lipid material"
    explanation: The histochemical finding that supported the diagnosis of mitochondrial disease.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Gomori's modified trichrome staining showed no increased endomysial or perimysial connective tissue and no subsarcolemmal reinforcements of mitochondria or ragged‐red fibers."
    explanation: >-
      The accompanying negative - no ragged-red fibres - which is why a normal trichrome
      does not argue against the diagnosis.
diagnosis:
- name: Exome or genome sequencing, with RNA-seq or minigene assay for splicing alleles
  description: >-
    The molecular diagnosis has been made by whole-exome and by whole-genome
    sequencing, but sequencing alone has repeatedly been insufficient in this gene.
    Two of the reported alleles were initially called variants of uncertain
    significance because they sit in exons and read as missense changes; both turned
    out to cause exon skipping. RNA-seq of patient fibroblasts prioritised PTCD3 in
    one family through an aberrant splicing signal, and minigene assays established
    causality for three alleles.

    The practical rule: an exonic PTCD3 variant of uncertain significance in a
    compatible phenotype warrants an RNA-level test before it is dismissed.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, RNA‐seq was also performed on P1 fibroblasts, which prioritized PTCD3 as a candidate disease gene, as an aberrant splicing was detected."
    explanation: RNA-seq, not exome interpretation, is what identified the gene in that family.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing."
    explanation: The functional assay that reclassified the uncertain alleles.
- name: Respiratory chain enzymology in fibroblasts, read for the pattern rather than the magnitude
  description: >-
    Fibroblast enzymology shows reduced complex I and complex IV with normal or
    above-range complex II. Two cautions from the reported patients: the deficit can
    be modest, and in one patient a decreased complex IV activity fell back inside the
    control range once normalised to citrate synthase - so a normalised-only report may
    read as normal. Muscle histochemistry showed COX-negative fibres in the same
    patient whose normalised fibroblast values were unremarkable.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mitochondrial respiratory chain analysis in fibroblasts revealed decreased activity of complex IV. However, when normalized to citrate synthetase, the values fall within the control range"
    explanation: >-
      The normalisation caveat, quoted from the patient in whom it occurred. This is the
      practical reason not to treat a normal normalised panel as a rule-out.
- name: Functional complementation in patient fibroblasts
  description: >-
    Lentiviral re-expression of wild-type PTCD3 in immortalised patient fibroblasts
    restores OXPHOS subunit levels and respiratory capacity. It is not a routine
    clinical test, but it is the assay that has been used in both functionally
    characterised families to convert candidate variants into a diagnosis, and it is
    what a reference laboratory would be asked for when the genotype is ambiguous.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The expression of wild‐type PTCD3 cDNA using a lentiviral vector resulted in a complete
      recovery of the steady‐state levels of the altered OXPHOS subunits in both patients
      (Figure 7A,B). Furthermore, the mitochondrial respiratory capacity, which was
      significantly reduced in naïve patient's cells, was recovered upon lentiviral
      transduction with wild‐type PTCD3 but not when cells were transduced with an empty
      plasmid (Figure 7C).
    explanation: The rescue result that establishes causality.
treatments:
- name: Supportive and Organ-Directed Care
  description: >-
    There is no disease-modifying therapy. Management follows the organs involved:
    respiratory support and eventually ventilation, gastrostomy or nasogastric feeding
    for dysphagia, antiseizure medication, antispasticity and antidystonic agents, and
    palliative care. Two of the reported patients were managed to death in the second
    decade on this basis, one at home under a palliative care team.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Considering her overall condition, it was decided that she should be monitored by the palliative care unit."
    explanation: >-
      The endpoint of supportive management in one reported patient, recorded because it
      is the honest description of what treatment achieves here.
- name: Mitochondrial Cofactor Cocktail
  description: >-
    Coenzyme Q10, carnitine, thiamine, biotin and vitamin C have all been given to
    these patients, individually or as a "mitochondrial cocktail". In every reported
    case the effect was recorded as none. One patient did have a low plasma coenzyme
    Q10, which is the only result that gives a specific rationale for any of these
    agents, and even in that patient the cocktail produced no perceptible improvement.
    This is curated as a treatment with refuting evidence rather than omitted, because
    "the mitochondrial cocktail was tried and did not work" is a clinically useful
    thing for the entry to say.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: coenzyme Q10
      term:
        id: CHEBI:46245
        label: coenzyme Q10
    - preferred_term: carnitine
      term:
        id: CHEBI:16347
        label: (R)-carnitine
    - preferred_term: thiamine
      term:
        id: CHEBI:26948
        label: vitamin B1
    - preferred_term: biotin
      term:
        id: CHEBI:15956
        label: biotin
    - preferred_term: vitamin C
      term:
        id: CHEBI:29073
        label: L-ascorbic acid
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with carnitine, thiamine, biotin, gabapentin, baclofen, and risperidone was also ineffective and had no effect on the disease progression."
    explanation: >-
      Refutes benefit from cofactor supplementation in the first patient of the 2023
      series, in the authors' own words.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "However, this treatment did not result in a perceptible improvement of the clinical condition."
    explanation: >-
      Refutes benefit from the coenzyme Q10 and carnitine cocktail in a second, unrelated
      patient - including one with a documented low plasma coenzyme Q10.
- name: Levodopa Trial for the Movement Disorder
  description: >-
    Levodopa was tried in the akinetic-rigid patient of the 2023 series and did not
    help. Recorded because the akinetic-rigid presentation of a basal-ganglia
    mitochondrial disorder invites a levodopa trial, and the one reported trial was
    negative.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levodopa
      term:
        id: CHEBI:15765
        label: L-dopa
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was initially treated with L‐Dopa, but no improvement was observed."
    explanation: The negative levodopa trial, stated directly.
- name: Genetic Counseling
  description: >-
    Autosomal recessive, 25% recurrence risk. Counselling here has to convey an unusual
    uncertainty: the same gene has produced death at 16 months and independent living
    into the fourth decade, and the residual-protein hypothesis that is meant to explain
    the difference is a hypothesis, not a validated genotype-phenotype rule. A carrier
    parent in one family had a measurably reduced fibroblast basal respiration rate
    while being entirely unaffected, so a functional assay result on a heterozygote must
    not be over-read.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The similar results were observed in his unaffected mother, who is a carrier of the His269Tyr variant, concluding that both heterozygous unaffected and affected carriers exhibit a lower OCR."
    explanation: >-
      The carrier finding that makes over-interpretation of a heterozygote's respirometry
      a real counselling hazard.
animal_models:
- name: Drosophila melanogaster PTCD3 loss-of-function mutant
  species: Drosophila melanogaster
  genotype: Loss-of-function mutant of CG4679, the Drosophila PTCD3 ortholog
  publication: PMID:38074476
  description: >-
    The only published whole-organism model of PTCD3 loss. The mutant dies during the
    second larval instar with reduced expression of mitochondrial-function and
    ribosome-biogenesis genes and, unexpectedly, up-regulated neuronal-development
    genes. It establishes that the gene is essential for development in an intact
    animal, which no patient genotype can show, but it cannot model the human disease:
    every reported human genotype retains some function, and the fly has no
    basal-ganglia or optic-nerve counterpart to the human lesions.
  evidence:
  - reference: PMID:38074476
    reference_title: "A Drosophila melanogaster ortholog of pentatricopeptide repeat domain 3 ( PTCD3 ) is essential for development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we focus on the Drosophila melanogaster homolog of PPR domain 3"
    explanation: >-
      Establishes that the studied gene is the Drosophila ortholog of human PTCD3, which is
      the only thing that makes this model relevant to this disease at all.
  modeled_mechanisms:
  - target: Impaired Mitochondrial mRNA Translation
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    model_scale: ORGANISM
    description: >-
      Transcriptional evidence of a coordinated loss of mitochondrial and
      ribosome-biogenesis gene expression on loss of the PTCD3 ortholog.
    limitations: >-
      A null allele in an invertebrate, lethal at the second instar, against a human
      disease in which every reported genotype retains residual protein. The readout is
      transcriptomic rather than a direct measurement of mitochondrial protein synthesis,
      and no respiratory-chain enzymology was reported, so the link to the human
      translation defect is inferential.
    divergences:
    - divergence_type: SPECIES_MISMATCH
      materiality: QUALIFYING
      description: >-
        Drosophila has no optic nerve, basal ganglia or thalamus, so the two tissue-level
        nodes that define the human disease have no counterpart in this organism. The
        model can speak to the molecular and cellular nodes only.
    - divergence_type: PROXY_QUANTITY
      materiality: QUALIFYING
      description: >-
        The model's measured quantity is the expression level of mitochondrial-function
        and ribosome-biogenesis genes. The node's quantity is the rate of mitochondrial
        protein synthesis. Reduced transcript abundance for ribosome components is a
        proxy for, not a measurement of, translation output.
    readouts:
    - name: Expression of mitochondrial-function and ribosome-biogenesis genes
      target: Impaired Mitochondrial mRNA Translation
      direction: DECREASED
      interpretation: >-
        Coordinated down-regulation of the mitochondrial translation apparatus on loss of
        the PTCD3 ortholog.
      evidence:
      - reference: PMID:38074476
        reference_title: "A Drosophila melanogaster ortholog of pentatricopeptide repeat domain 3 ( PTCD3 ) is essential for development."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In addition, mutants exhibit reduced expression of a group of genes related to mitochondrial function and ribosome biogenesis, and conversely, they show up-regulated expression of neuronal development-related genes."
        explanation: Reports the transcriptomic measurement behind this readout.
    evidence:
    - reference: PMID:38074476
      reference_title: "A Drosophila melanogaster ortholog of pentatricopeptide repeat domain 3 ( PTCD3 ) is essential for development."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "A loss-of-function mutant of PTCD3 is lethal during the second instar."
      explanation: >-
        Establishes that the gene is developmentally essential in an intact animal, which
        is why this model is treated as informative for the translation node despite its
        low fidelity to the human phenotype.
experimental_models:
- name: Patient-derived fibroblasts with wild-type PTCD3 lentiviral rescue
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    Immortalised fibroblasts from two patients of the 2023 series, with lentiviral
    re-expression of GFP-tagged wild-type PTCD3 as the rescue arm and an empty vector
    as the control. Untransduced cells show reduced complex I, III and IV subunits and
    reduced respiratory capacity; the rescue arm restores both. The same design was used
    in the founding report on the index patient's cells.
  publication: PMID:36450274
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional complementation studies demonstrated the pathogenic effect of the identified variants since the expression of wild-type PTCD3 in immortalized fibroblasts restored the steady-state levels of complexes I and IV subunits as well as the mitochondrial respiratory capacity."
    explanation: >-
      Establishes the model system and what it demonstrated, which is why this entry treats
      patient fibroblasts with wild-type rescue as informative for the biochemical node.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  modeled_mechanisms:
  - target: Combined Respiratory Chain Deficiency with Complex II Spared
    relationship: RESCUES
    fidelity: HIGH
    model_scale: CELLULAR
    description: >-
      Re-expression of wild-type PTCD3 restores the OXPHOS subunit levels and the maximal
      respiratory capacity that are reduced in the patients' own cells, with an
      empty-vector arm as the specificity control. This is what converts the biochemical
      phenotype from a correlate of the genotype into a consequence of it.
    limitations: >-
      Fibroblasts are not the tissue in which this disease manifests. In one patient the
      complex IV deficit disappeared on normalisation to citrate synthase, so the cellular
      model understates the defect that the brain and optic nerve evidently sustain.
    readouts:
    - name: Steady-state levels of NDUFB8, MT-CO2 and UQCRC2 after wild-type PTCD3 transduction
      target: Combined Respiratory Chain Deficiency with Complex II Spared
      direction: RESTORED
      interpretation: Restoration of the reduced OXPHOS subunits, establishing PTCD3-dependence.
      evidence:
      - reference: PMID:36450274
        reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "The expression of wild‐type PTCD3 cDNA using a lentiviral vector resulted in a complete recovery of the steady‐state levels of the altered OXPHOS subunits in both patients"
        explanation: Reports the rescue measurement behind this readout.
    - name: Maximal uncoupled respiratory capacity after wild-type PTCD3 transduction
      target: Combined Respiratory Chain Deficiency with Complex II Spared
      direction: RESTORED
      interpretation: >-
        The functional counterpart of the subunit rescue, with an empty-vector arm showing
        the effect is not an artefact of transduction.
      evidence:
      - reference: PMID:36450274
        reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: "Transduction with wild‐type PTCD3, but not with the empty vector, restored the mitochondrial respiratory capacity in immortalized patients' fibroblasts."
        explanation: Reports the respirometry rescue with its vector control.
    evidence:
    - reference: PMID:30607703
      reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Complementation experiments rescued oxidative phosphorylation complex I and IV levels and activities, ATP biosynthesis, and MT-RNR1 rRNA transcript level, providing functional validation of the pathogenicity of identified variants."
      explanation: >-
        The same rescue design applied independently to the index patient's cells, which
        is what makes this model informative rather than a single-laboratory result.
prevalence:
- population: Worldwide (published cases)
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Seven patients in three reports: one index patient in 2019, three from two
    unrelated families in 2023, and three more (an adult sibling pair and an unrelated
    child) in 2024. Reported families are Spanish, Brazilian, Latvian and Saudi; the
    ancestry of the index patient is not stated in that report and is not asserted here.
    No population prevalence has been estimated and none is asserted here; the
    2024 report's own cross-cohort tally of seven patients is the best available
    denominator.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showed optic atrophy and nystagmus in six of seven patients"
    explanation: >-
      The seven-patient denominator, from the authors' tabulation of previously and newly
      published cases.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, mutations in PTCD3, encoding a component of the mitochondrial ribosome, have only been reported in a single individual with clinical evidence of Leigh syndrome."
    explanation: The count as it stood before the 2023 series, showing how small the literature is.
progression:
- phase: Onset
  age_range: first weeks of life to early childhood, with one sibling pair whose first sign appeared at age 2
  notes: >-
    Onset spans the severe and mild poles. In the severe pole symptoms begin in the
    first weeks to three months of life, or from birth in the index patient, who also
    had intrauterine growth retardation. In the mild pole the first sign was nystagmus
    at age two with normal early development, and gait disturbance did not appear until
    age six.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, none of the individuals reported here had intrauterine growth retardation, and the onset age ranged from the first weeks to 3 months of life."
    explanation: The onset range in the 2023 series, contrasted with the index patient.
- phase: Established disease
  notes: >-
    Two distinct courses. The severe course is a progressive neurodegeneration with
    accumulating dystonia, epilepsy, dysphagia and respiratory failure, punctuated by
    intensive-care admissions. The mild course is a slowly progressive ataxia and optic
    neuropathy in which patients remain cognitively near-normal into their thirties but
    become blind and non-ambulatory. The disorder has no described plateau in either
    course.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both are legally blind, retaining only light perception, experiencing mild cognitive decline and being non‐ambulatory."
    explanation: The established state of the mild course in the fourth decade.
- phase: Outcome
  notes: >-
    The index patient died at 16 months. Two patients of the 2023 series died at 11 and
    17 years, one of pneumonia with respiratory failure and one at home under palliative
    care; the third was alive at 19. The 2024 sibling pair were alive in their thirties.
    Survival therefore ranges over more than three decades within one gene.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They survived longer than the previously reported patient, being exitus at the ages of 11 and 17 years old, or still alive at 19 years of age."
    explanation: The survival range in the 2023 series against the index patient.
  - reference: PMID:31967322
    reference_title: "Mortality of Japanese patients with Leigh syndrome: Effects of age at onset and genetic diagnosis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nearly 90% of deaths occurred by age 6. Mortality rate of patients with onset before 6 months of age was significantly higher than that of onset after 6 months."
    explanation: >-
      Class-level prognostic data. This is a 166-patient Japanese Leigh syndrome cohort,
      not a PTCD3 series - no natural-history study of COXPD51 exists, and seven patients
      cannot support one. It is cited to give the infantile-onset pole a base rate, and
      the inference from Leigh syndrome generally to PTCD3 specifically is the reason this
      item is graded INDIRECT.
differential_diagnoses:
- name: Leigh syndrome of other genetic cause
  description: >-
    More than 75 genes, mitochondrial and nuclear, produce Leigh syndrome, and nothing
    in the clinical picture or the neuroimaging distinguishes PTCD3 from them. Optic
    atrophy, which is the most consistent PTCD3 feature, occurs in Leigh syndrome of
    other aetiologies too, and the reporting authors say explicitly that it is not
    useful for guiding the clinical diagnosis.
  distinguishing_features:
  - Not separable clinically or radiologically; the distinction is molecular.
  - A combined complex I and IV deficiency with spared complex II narrows the differential to the mitochondrial gene-expression disorders but does not identify the gene.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "On the other hand, optic atrophy is a clinical sign that has been observed in patients with Leigh syndrome of other etiologies, and thus it is not useful in guiding the clinical diagnosis"
    explanation: >-
      The authors' own statement that the disorder's most consistent feature does not
      discriminate it from other Leigh syndromes.
- name: Other mitochondrial ribosomal protein (MRP) disorders
  description: >-
    Thirteen genes encoding mitoribosomal proteins had been implicated in human disease
    by 2023. As a class they present neonatally or in infancy with lactic acidosis and
    combined OXPHOS deficiency, and with myopathy, cardiac, hepatic, renal or hearing
    involvement. PTCD3 sits inside that class and shares its biochemistry; what
    distinguishes it clinically, on the evidence available, is the near-constant optic
    atrophy and nystagmus rather than the multiorgan pattern.
  distinguishing_features:
  - Shared biochemistry - lactic acidosis with combined OXPHOS deficiency - across the whole class, so enzymology does not separate them.
  - Cardiac, hepatic and renal involvement is common in the MRP class but has not been a feature of the reported PTCD3 patients, one of whom had only slight left ventricular hypertrophy.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Myopathy, cardiac abnormalities, hepatopathy, renal dysfunction, deafness and dysmorphic features are the most common clinical phenotypes associated with MRP deficiencies."
    explanation: The class phenotype against which PTCD3 has to be distinguished.
  - reference: PMID:34008913
    reference_title: "COXPD9 in an individual from Puerto Rico and literature review."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Similar to previously reported individuals, this reported female proband presented with psychomotor retardation, sensorineural hearing loss, hypertrophic cardiomyopathy, failure to thrive, and lactic acidosis."
    explanation: >-
      A worked example of the sibling class, and INDIRECT for that reason: this is COXPD9
      caused by MRPL3, a large-subunit mitoribosomal protein, not PTCD3. It is cited to
      show what the differential looks like in practice - the cardiomyopathy, deafness and
      failure to thrive that dominate COXPD9 have not been features of the PTCD3 patients.
- name: Hereditary optic neuropathy and hereditary ataxia
  description: >-
    The adult pole of COXPD51 was worked up for years as hereditary ataxia and
    hereditary optic neuropathy. Mitochondrial DNA sequencing, Friedreich ataxia repeat
    testing, an NGS ataxia panel, spinocerebellar ataxia repeat analysis and whole-exome
    sequencing were all negative in that family before whole-genome sequencing found
    PTCD3. This is the practical reason to keep PTCD3 in an adult ataxia-with-optic-atrophy
    differential.
  distinguishing_features:
  - A standard ataxia gene panel and exome will miss it; the reported adult family was diagnosed only on whole-genome sequencing.
  - The combination of optic atrophy, nystagmus, ataxia and a motor polyneuropathy with preserved cognition is the phenotype that should prompt mitochondrial testing.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results of mtDNA sequencing, Friedreich ataxia repeat expansion analysis, NGS ataxia gene panel (case 1), nucleotide repeat expansion analysis for all known types of spinocerebellar ataxia (case 1) and whole exome sequencing (case 2) did not reveal the cause of the disease."
    explanation: The diagnostic odyssey that the adult phenotype produced.
discussions:
- discussion_id: coxpd51_leigh_versus_leigh_like
  kind: CONTROVERSY
  status: OPEN
  prompt: >-
    Is PTCD3 deficiency a cause of Leigh syndrome, or of a Leigh-like syndrome that does
    not meet the diagnostic criteria?
  attaches_to:
  - pathophysiology#Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus
  - disease#Combined Oxidative Phosphorylation Deficiency 51
  rationale: >-
    The founding 2019 report diagnosed its patient with Leigh syndrome. A letter in the
    same journal argued the imaging and clinical picture met criteria only for a
    Leigh-like syndrome. The 2023 series then titled itself "Leigh syndrome is the main
    clinical characteristic of PTCD3 deficiency" and set out to settle the question in
    favour of Leigh syndrome; the 2024 report nonetheless describes its own severe
    patient as Leigh-like, and its two adult patients as neither.

    This entry does not adjudicate. It records the position of each report and keeps the
    pathophysiology node named for the lesion (necrotizing degeneration of basal ganglia
    and thalamus) rather than for either syndrome label, so that the mechanism does not
    inherit the dispute.

    This entry quotes the 2023 series' summary of the challenge rather than the
    challenging Letter itself. The reason is recorded in the entry notes.
  evidence:
  - reference: PMID:30607703
    reference_title: "Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed abnormal bilateral signals at the basal ganglia and brainstem, and the patient was diagnosed as Leigh syndrome."
    explanation: The original Leigh-syndrome diagnosis.
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis was compatible with Leigh Syndrome, but it was questioned by some authors, that classified the patient as Leigh‐like rather than Leigh syndrome"
    explanation: >-
      The 2023 authors' account of the challenge. This entry quotes their summary rather
      than the challenging Letter itself, for the reason given in the entry notes.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "These clinical manifestations align with a Leigh‐like syndrome."
    explanation: >-
      The most recent report describes its own severe patient as Leigh-like, so the 2023
      paper's title did not close the question.
- discussion_id: coxpd51_residual_protein_hypothesis_untested
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does the amount of residual PTCD3 protein explain why one genotype kills at 16 months
    and another allows independent survival into the fourth decade?
  attaches_to:
  - pathophysiology#Depletion of PTCD3 Protein
  - genetic#PTCD3
  rationale: >-
    The only proposed explanation for the disorder's enormous severity range is
    quantitative: the index patient's two truncating alleles leave PTCD3 nearly absent,
    while the leaky splice alleles of the later patients leave 15-30% of normal protein,
    and the 2024 authors extend the same reasoning to a missense allele. It is a
    plausible dose-response account and it is entirely uncontrolled - each level was
    measured in a different laboratory, in a different patient, with a different second
    allele, and nobody has plotted protein level against any severity measure.

    What is missing is a graded series. Titrating PTCD3 in one cell background and
    measuring mitoribosome assembly, translation and respiration at each level would
    test whether the relationship is even monotonic. Until that exists the entry treats
    the residual-protein account as a hypothesis and does not use it for prognosis.
  evidence:
  - reference: PMID:36450274
    reference_title: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As a result, the absence of PTCD3 protein is nearly complete, whereas in our patients, although reduced, was not absent."
    explanation: The observation on which the hypothesis rests.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We hypothesise that PTCD3 missense pathogenic variants lead to a milder form of combined oxidative phosphorylation deficiency, probably due the higher level of residual PTCD3."
    explanation: >-
      The 2024 authors state it as a hypothesis in their own words, which is how this
      entry records it.
- discussion_id: coxpd51_carrier_respirometry_confound
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    If an unaffected heterozygous carrier has the same reduced fibroblast basal
    respiration as her affected son, what does a reduced basal respiration rate actually
    establish in this disorder?
  attaches_to:
  - pathophysiology#Reduced Mitochondrial Respiratory Capacity and ATP Deficit
  - diagnosis#Functional complementation in patient fibroblasts
  rationale: >-
    In the 2024 report the mother of the adult proband - clinically unaffected, carrying
    one PTCD3 allele - had a basal respiration rate as low as her son's, with no
    significant difference between them. The authors draw the conclusion themselves: a
    lower oxygen consumption rate is seen in both affected and unaffected carriers, and
    that reduction is not by itself sufficient to cause disease.

    The gap this leaves is a measurement gap. Basal respiration is being used as
    supporting functional evidence for variant classification in this gene, and in this
    family it did not discriminate patient from carrier. What has discriminated, in the
    two other functionally characterised families, is the complementation assay: subunit
    levels and maximal uncoupled capacity restored by wild-type PTCD3. Nobody has
    reported a maximal-capacity or complementation result on a heterozygous carrier, so
    it is not known whether those assays are any more discriminating.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The similar results were observed in his unaffected mother, who is a carrier of the His269Tyr variant, concluding that both heterozygous unaffected and affected carriers exhibit a lower OCR."
    explanation: The carrier result and the authors' own reading of it.
- discussion_id: coxpd51_regional_selectivity_unexplained
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why do the optic nerve and the basal ganglia and thalamus degenerate when the
    translation defect is present in every cell?
  attaches_to:
  - pathophysiology#Subacute Necrotizing Degeneration of Basal Ganglia and Thalamus
  - pathophysiology#Optic Nerve Degeneration
  rationale: >-
    PTCD3 is expressed in all tissues and the mitoribosome is required in all of them,
    yet the disease is focal: the optic nerve in essentially every patient, the basal
    ganglia and thalamus in the severe pole, the peripheral nerve in several, and almost
    nothing else. Cardiac, hepatic and renal involvement, which is common across the
    mitoribosomal protein disorders as a class, has been minimal in these patients.

    The only explanation offered is a general one - that retinal ganglion cells are
    especially vulnerable to defects in mitochondrial gene expression - and it is
    asserted rather than tested in PTCD3. It also does not address the basal-ganglia
    selectivity, which is shared with more than 75 unrelated Leigh-syndrome genes and is
    unexplained for all of them. The two selectivities may not have the same cause, and
    nothing in the PTCD3 literature distinguishes them.

    This is recorded as a gap rather than a controversy because no source argues the
    other side; the question has not been addressed.
  evidence:
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Defects in mitochondrial replication, RNA transcription and translation initiate early‐onset optic atrophy, as these cells are highly vulnerable to mitochondrial dysfunction."
    explanation: >-
      The whole of the published explanation for the optic-nerve selectivity - a general
      vulnerability claim about the cell type, not a PTCD3-specific result.
- discussion_id: coxpd51_no_mammalian_model
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    The only published whole-organism PTCD3 model is a lethal Drosophila null. Does any
    available model reproduce the human disease, in which every reported genotype retains
    residual protein?
  attaches_to:
  - animal_models#Drosophila melanogaster PTCD3 loss-of-function mutant
  - pathophysiology#Depletion of PTCD3 Protein
  rationale: >-
    Evidence exists in a model system, and its translational validity is the open
    question - which is what separates this from the gaps above. The Drosophila null dies
    in the second instar and mouse loss of function is reported as causing
    neurodevelopmental defects and early lethality. Both are null phenotypes. No reported
    human patient is null: the severity range that defines this disorder lies entirely in
    the hypomorphic range, and neither organism has been studied at a hypomorphic dose.

    Neither organism has the tissues the disease targets, either - a fly has no optic
    nerve or basal ganglia, and no mouse study reporting optic atrophy or basal-ganglia
    lesions on partial PTCD3 loss has been published. So the models establish that the
    gene is essential and say nothing about why partial loss produces this particular
    focal degeneration.

    What would resolve it is a hypomorphic mammalian allele - a knock-in of one of the
    human leaky splice alleles, or a graded conditional knockdown - assessed for optic
    nerve and basal-ganglia pathology rather than for lethality.
  evidence:
  - reference: PMID:38074476
    reference_title: "A Drosophila melanogaster ortholog of pentatricopeptide repeat domain 3 ( PTCD3 ) is essential for development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A loss-of-function mutant of PTCD3 is lethal during the second instar."
    explanation: The invertebrate null phenotype - lethality, not the human disease.
  - reference: PMID:39544688
    reference_title: "The phenotypic spectrum of PTCD3 deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Similarly, PTCD3 loss‐of‐function mice exhibit neurodevelopmental defects and early lethality."
    explanation: >-
      The mouse null phenotype as summarised by the 2024 authors. Cited from their review
      sentence because the entry does not cite the underlying mouse study; a curator with
      that primary reference should cite it directly here.
notes: >-
  Evidence base and its limits. Three primary clinical reports carry this entry, and
  together they describe seven patients: PMID:30607703 (2019, one patient, with proteomics
  and complementation), PMID:36450274 (2023, three patients from two unrelated Spanish
  and Brazilian families, with minigene assays, western blot, respirometry and
  complementation), and PMID:39544688 (2024, three patients - an adult sibling pair
  recruited through the Latvian population genome database and an unrelated Saudi child
  found through GeneMatcher - with Seahorse respirometry and in silico structural
  modelling). Two non-patient papers supply the gene's normal
  function (PMID:19427859, cell-line knockdown) and its only whole-organism model
  (PMID:38074476, Drosophila).

  Named-entity hazards handled here. PTCD3 has a substantial cancer literature -
  colorectal, prostate, pancreatic, and Myc-driven lymphoma expression and CRISPR
  studies - which is about the same gene but not about this disease; none of it is cited.
  The numbered COXPD disorders are sibling entities, not synonyms: where this entry uses
  a statement about mitochondrial translation defects or mitoribosomal protein disorders
  as a class, the evidence item says so in its explanation and the claim is kept at class
  level.

  What this entry does not assert. The task framing for a combined OXPHOS deficiency is
  usually "complexes I, III, IV and V fail together". That is not what the PTCD3 patients
  show, and the entry follows the patients: complex I and complex IV are consistently
  affected, complex III variably (reduced in one of two patients tested by western blot),
  and complex V subunit levels were explicitly unaltered. No patient-level ATP synthase
  activity deficit is asserted, because none of the cited sources reports one.

  PMID:30706245, the Letter arguing for "Leigh-like rather than Leigh", is discussed in
  the Leigh/Leigh-like controversy but is not cited as evidence: its cached record has no
  abstract or body text, so there is nothing in it that can be quoted exactly. The 2023
  series' own summary of the challenge is quoted instead, and the discussion says so.

  Two class-level references are cited with `directness: INDIRECT` because no
  PTCD3-specific source exists for what they say: PMID:31967322, a 166-patient Japanese
  Leigh syndrome mortality cohort, for the prognosis of the infantile-onset pole, and
  PMID:34008913, a COXPD9/MRPL3 case report, as a worked example of the mitoribosomal
  protein disorder differential. Neither describes a PTCD3 patient, and each evidence
  item's explanation says which gene and disorder it is actually about.

  Deep research. An openscientist report (research/Combined_Oxidative_Phosphorylation_Deficiency_51-deep-research-openscientist.md)
  was produced after falcon returned HTTP 402; the fallback is recorded in the report's
  own frontmatter. Its citations validated 10/10 with a confabulation rate of 0.0 and its
  terms 32/33, and `just preflight-dr` returned PASS against MONDO:0033631 with 35 PTCD3
  mentions and a matching OMIM xref. Its synthesis agrees with the primary literature on
  the mechanism, and it contributed the two class-level references above. It did not,
  however, find PMID:39544688, the 2024 phenotypic-spectrum report, so its clinical
  picture is the infantile Leigh pole only and it describes COXPD51 as uniformly severe
  with early mortality. That is the DR report's most consequential omission, and the mild
  adult pole in this entry comes from the primary literature rather than from it.

  No `datasets:` block. Deliberate, not an oversight. Seven patients have been
  reported worldwide and none of the three clinical papers deposits a public omics
  dataset; the fibroblast proteomics of the founding report is referred to PRIDE only in
  its methods citation list. Searching a repository on the gene symbol instead is exactly
  the Named Entity Confusion trap CLAUDE.md warns about here - PTCD3 is well represented
  in colorectal, prostate and pancreatic cancer expression studies, and every one of
  those accessions would resolve perfectly while being about a different biology. A
  curator who finds a genuine COXPD51 or PTCD3-patient dataset should add it; a
  gene-symbol search result is not that.

  Uncited causal edges. Six `downstream` edges carry no evidence item of their own. Each
  is asserted by the cited literature at node level but not as a causal statement anyone
  published - the step from bioenergetic failure to regional necrosis in particular is
  unexplained for every Leigh syndrome gene, which is why it is also recorded as a
  knowledge gap. The edges are left uncited rather than propped up with a neighbouring
  node's citation.

  Not curated, for want of a citable source. The DR report attributes homozygous
  embryonic lethality and a heterozygous impaired pupillary reflex in Ptcd3 knockout mice
  to IMPC genotype-phenotype records, without an identifier that can be fetched and
  quoted. The mouse null phenotype is instead recorded in the model-mismatch discussion
  from the sentence in PMID:39544688 that states it, and the IMPC heterozygote phenotypes
  are not asserted here at all. A curator with the IMPC allele page or the underlying
  publication should add them.

  No GeneReviews chapter exists for COXPD51 or for PTCD3 deficiency; a PubMed search for
  a GeneReviews title returned nothing, so there is no expert-curated phenotype baseline
  to cross-reference. No Orphanet entry was found for the disorder either. Neither
  absence is a defect in this entry - it is the state of the secondary literature for a
  disorder with seven published patients.
📚

References & Deep Research

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Record notes

Evidence base and its limits. Three primary clinical reports carry this entry, and together they describe seven patients: PMID:30607703 (2019, one patient, with proteomics and complementation), PMID:36450274 (2023, three patients from two unrelated Spanish and Brazilian families, with minigene assays, western blot, respirometry and complementation), and PMID:39544688 (2024, three patients - an adult sibling pair recruited through the Latvian population genome database and an unrelated Saudi child found through GeneMatcher - with Seahorse respirometry and in silico structural modelling). Two non-patient papers supply the gene's normal function (PMID:19427859, cell-line knockdown) and its only whole-organism model (PMID:38074476, Drosophila). Named-entity hazards handled here. PTCD3 has a substantial cancer literature - colorectal, prostate, pancreatic, and Myc-driven lymphoma expression and CRISPR studies - which is about the same gene but not about this disease; none of it is cited. The numbered COXPD disorders are sibling entities, not synonyms: where this entry uses a statement about mitochondrial translation defects or mitoribosomal protein disorders as a class, the evidence item says so in its explanation and the claim is kept at class level. What this entry does not assert. The task framing for a combined OXPHOS deficiency is usually "complexes I, III, IV and V fail together". That is not what the PTCD3 patients show, and the entry follows the patients: complex I and complex IV are consistently affected, complex III variably (reduced in one of two patients tested by western blot), and complex V subunit levels were explicitly unaltered. No patient-level ATP synthase activity deficit is asserted, because none of the cited sources reports one. PMID:30706245, the Letter arguing for "Leigh-like rather than Leigh", is discussed in the Leigh/Leigh-like controversy but is not cited as evidence: its cached record has no abstract or body text, so there is nothing in it that can be quoted exactly. The 2023 series' own summary of the challenge is quoted instead, and the discussion says so. Two class-level references are cited with `directness: INDIRECT` because no PTCD3-specific source exists for what they say: PMID:31967322, a 166-patient Japanese Leigh syndrome mortality cohort, for the prognosis of the infantile-onset pole, and PMID:34008913, a COXPD9/MRPL3 case report, as a worked example of the mitoribosomal protein disorder differential. Neither describes a PTCD3 patient, and each evidence item's explanation says which gene and disorder it is actually about. Deep research. An openscientist report (research/Combined_Oxidative_Phosphorylation_Deficiency_51-deep-research-openscientist.md) was produced after falcon returned HTTP 402; the fallback is recorded in the report's own frontmatter. Its citations validated 10/10 with a confabulation rate of 0.0 and its terms 32/33, and `just preflight-dr` returned PASS against MONDO:0033631 with 35 PTCD3 mentions and a matching OMIM xref. Its synthesis agrees with the primary literature on the mechanism, and it contributed the two class-level references above. It did not, however, find PMID:39544688, the 2024 phenotypic-spectrum report, so its clinical picture is the infantile Leigh pole only and it describes COXPD51 as uniformly severe with early mortality. That is the DR report's most consequential omission, and the mild adult pole in this entry comes from the primary literature rather than from it. No `datasets:` block. Deliberate, not an oversight. Seven patients have been reported worldwide and none of the three clinical papers deposits a public omics dataset; the fibroblast proteomics of the founding report is referred to PRIDE only in its methods citation list. Searching a repository on the gene symbol instead is exactly the Named Entity Confusion trap CLAUDE.md warns about here - PTCD3 is well represented in colorectal, prostate and pancreatic cancer expression studies, and every one of those accessions would resolve perfectly while being about a different biology. A curator who finds a genuine COXPD51 or PTCD3-patient dataset should add it; a gene-symbol search result is not that. Uncited causal edges. Six `downstream` edges carry no evidence item of their own. Each is asserted by the cited literature at node level but not as a causal statement anyone published - the step from bioenergetic failure to regional necrosis in particular is unexplained for every Leigh syndrome gene, which is why it is also recorded as a knowledge gap. The edges are left uncited rather than propped up with a neighbouring node's citation. Not curated, for want of a citable source. The DR report attributes homozygous embryonic lethality and a heterozygous impaired pupillary reflex in Ptcd3 knockout mice to IMPC genotype-phenotype records, without an identifier that can be fetched and quoted. The mouse null phenotype is instead recorded in the model-mismatch discussion from the sentence in PMID:39544688 that states it, and the IMPC heterozygote phenotypes are not asserted here at all. A curator with the IMPC allele page or the underlying publication should add them. No GeneReviews chapter exists for COXPD51 or for PTCD3 deficiency; a PubMed search for a GeneReviews title returned nothing, so there is no expert-curated phenotype baseline to cross-reference. No Orphanet entry was found for the disorder either. Neither absence is a defect in this entry - it is the state of the secondary literature for a disorder with seven published patients.

Create: Combined_Oxidative_Phosphorylation_Deficiency_51 · 2026-09-07T18:08:24Z · View source

New entry for COXPD51 (MONDO:0033631, PTCD3/MRPS39/mS39). Lump/split: curated as entry_type DISEASE. The stub records one causal gene, the parent MONDO:0000732, and no MONDO descendants; the OLS record confirms an OMIM:619057 equivalence, COXPD51 as the only synonym, and no children. That is the leaf signature, and the literature agrees - all seven published patients are PTCD3-biallelic and no sub-entity has been proposed. Deep research: 'just dr_fallback=--fallback research-disorder falcon' was used because falcon returns HTTP 402 (Edison account out of credits). The report was produced by OPENSCIENTIST, not falcon; the fallback is recorded in the report frontmatter (fell_back: true, requested_provider: falcon, provider_attempts). Report: research/Combined_Oxidative_Phosphorylation_Deficiency_51-deep-research-openscientist.md, with its .citations.md sidecar and an _artifacts/ directory holding OpenScientist's own HTML and PDF report. Validation as recorded in that report: references 10/10 resolved, 0 unresolved, confabulation_rate 0.0, 7/10 assessed on topic, 0 off topic; terms 32/33 resolved, 1 unverifiable, 0 mislabelled, 4/4 names correct. No needs_review key and no unresolved_references list, so nothing was excluded on that basis. 'just preflight-dr <report> MONDO:0033631' returned PASS (PTCD3 mentioned 35 times, report OMIM 619057 == MONDO OMIM xref). How the DR report was used. Its mechanism synthesis agrees with the primary literature and added nothing that the primary papers do not state, so no claim in this entry rests on it alone. It did contribute two class-level references that are cited with directness: INDIRECT - PMID:31967322 (166-patient Japanese Leigh syndrome mortality cohort) for the prognosis of the infantile pole, and PMID:34008913 (COXPD9/MRPL3) as a worked example of the mitoribosomal-protein differential. Each of those evidence items names, in its explanation, which disease and gene the cited study is actually about. The report's most consequential limitation: it did not find PMID:39544688 (Lace et al. 2024, 'The phenotypic spectrum of PTCD3 deficiency'), so it presents COXPD51 as uniformly severe infantile Leigh syndrome. The mild adult pole in this entry - the sibling pair in their thirties with optic atrophy, ataxia, tremor and motor polyneuropathy, worked up for years as hereditary ataxia - comes from primary-literature searching (PubMed esearch on PTCD3/MRPS39/COXPD51), not from the report. The Drosophila model (PMID:38074476) was likewise found independently. Named Entity Confusion handled. PTCD3 has a substantial cancer-expression and CRISPR-screen literature (colorectal PMID:40304977, prostate PMID:30132530, Myc-driven lymphoma PMID:27635472, sepsis/T2DM ferroptosis PMID:41194984). PMID:40304977 was among the DR report's own citations and is NOT cited here. The numbered COXPD disorders are sibling entities; class-level statements about mitochondrial translation defects or mitoribosomal protein disorders are kept at class level and labelled INDIRECT where they carry an inference to PTCD3. Claims deliberately not made. (a) The generic 'complexes I, III, IV and V fail together' formulation is not asserted: the PTCD3 patients show consistent complex I and IV deficits, a complex III deficit in one of two patients tested, and explicitly unaltered complex V and complex II subunit levels. Spared complex II is curated as a REFUTE biochemical item with the source's own measurement. (b) PMID:30706245 (the Letter arguing 'Leigh-like rather than Leigh') is discussed but not cited as evidence - its cached record is content_type: unavailable with no abstract or body, so nothing in it can be quoted exactly; the 2023 series' summary of the challenge is quoted instead. (c) The DR report's IMPC Ptcd3 knockout data (homozygous embryonic lethality, heterozygous impaired pupillary reflex) are NOT curated: the report gives no fetchable identifier for them. The mouse null phenotype is recorded only from the sentence in PMID:39544688 that states it. (d) No datasets: block - see the entry notes; a gene-symbol repository search would surface PTCD3 cancer datasets, which is the exact NEC trap. (e) Six downstream causal edges are left uncited rather than propped up with a neighbouring node's citation. (f) No GeneReviews chapter exists (PubMed title search returned nothing) and no Orphanet entry was found, so there is no expert-curated phenotype baseline. Module conformance: the 'Combined Respiratory Chain Deficiency with Complex II Spared' node declares conforms_to mitochondrial_dysfunction#Bioenergetic Decline and Oxidative Stress, matching what sibling entries Combined_Oxidative_Phosphorylation_Defect_Type_13 and Combined_Oxidative_Phosphorylation_Deficiency_42 do. No primary mitochondrial-translation module exists in kb/modules/; Type_26 records the same finding. Validation run to completion on the final tree: just validate (schema OK, terms OK, 100/100 snippets verified); just validate-disorders (schema OK, terms OK, 100/100 snippets verified); check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms, check-enum-values, check-empty-snippets, check-snippet-boundaries all OK; whole-KB check-folded-hyphens, check-snippet-length, check-title-snippets, check-snippet-grading, check-environmental-evidence, check-reference-titles all OK; check-source-defect-claims reports exactly one claim for this file, CONFIRMED (PMID:30706245 content_type: unavailable). normalize-cache made no changes; check-term-cache-integrity and check-cache-order OK. linkml-data-qc compliance 95.8% global / 96.1% weighted, the residual being datasets and the uncited causal edges described above. All 7 cited references are PMIDs, so no DOI-skip audit was needed.

OpenScientist ▸
Combined Oxidative Phosphorylation Deficiency 51 (COXPD51): A Comprehensive Disease Characteristics Report
openscientist-autonomous 10 citations 2026-09-07T17:58:08.370001

Combined Oxidative Phosphorylation Deficiency 51 (COXPD51): A Comprehensive Disease Characteristics Report

MONDO ID: MONDO:0033631 | OMIM: #619057 | Gene: PTCD3 (MRPS39), OMIM *614918 | Category: Mendelian, autosomal recessive

Summary

Combined Oxidative Phosphorylation Deficiency 51 (COXPD51) is an ultra-rare, autosomal-recessive primary mitochondrial disorder caused by biallelic loss-of-function variants in PTCD3 (also called MRPS39), a nuclear gene on chromosome 2p11.2 that encodes the small mitoribosomal subunit protein mS39. mS39 is an RNA-binding pentatricopeptide-repeat (PPR) protein and an essential structural/functional component of the 28S small subunit of the mitochondrial ribosome. When both alleles are disrupted, assembly and function of the small mitoribosomal subunit fail, mitochondrial mRNA translation is broadly impaired, and the 13 mtDNA-encoded OXPHOS subunits are not synthesized in adequate quantity. The downstream result is a combined deficiency of respiratory-chain complexes I and IV (and, in some experimental systems, complex III), collapse of oxidative ATP production, and — because neurons and other high-energy-demand tissues are exquisitely dependent on OXPHOS — a severe neurodegenerative phenotype.

Clinically, COXPD51 manifests as early-infantile Leigh syndrome (subacute necrotizing encephalomyelopathy). Reported patients present in the first months of life with psychomotor delay and regression, dystonia, optic atrophy, nystagmus, tonic–clonic seizures, respiratory insufficiency, and feeding difficulties. Brain MRI shows the bilateral, symmetric signal abnormalities of the basal ganglia and brainstem, together with thalamic changes and optic-nerve atrophy, that define the Leigh pattern. The disease is severe and progressive with a poor prognosis; treatment is entirely supportive, as there is no disease-modifying or curative therapy.

The disease is extraordinarily rare: as of this report, only four molecularly-confirmed patients have been fully published (one by Borna et al. 2019; three by Muñoz-Pujol et al. 2023). The genetic mechanism, biochemical consequences, and clinical spectrum are, however, unusually well-defined for such a rare entity thanks to functional rescue (complementation) experiments in patient fibroblasts, siRNA knockdown studies in cell lines, and — importantly for gene essentiality — an International Mouse Phenotyping Consortium (IMPC) knockout showing that homozygous Ptcd3 deletion is embryonic-lethal. This last point explains why living patients only ever carry hypomorphic allele combinations rather than complete-null genotypes.

Key Findings

Finding 1 — COXPD51 is caused by biallelic loss-of-function variants in PTCD3 (MRPS39)

The genetic cause of COXPD51 is firmly established as recessive, biallelic loss of function in PTCD3. The disease was first delineated by Borna et al. (2019), who used exome sequencing in a single patient to identify two loss-of-function variants: a canonical splice-acceptor change c.415-2A>G and a frameshift insertion c.1747_1748insCT (p.Phe583Serfs*3). As the authors state, "Exome sequencing revealed two potentially loss-of-function variants [c.415-2A>G, and c.1747_1748insCT (p.Phe583Serfs*3)] in PTCD3 (also known as MRPS39). PTCD3, a member of the pentatricopeptide repeat domain protein family, is a component of the small mitoribosomal subunit" (PMID: 30607703).

The gene–disease relationship was independently confirmed and elevated to a definitive association by Muñoz-Pujol et al. (2023), who reported three additional patients from two families carrying compound-heterozygous variants — "WES and RNA-seq identified compound heterozygous variants in PTCD3 in both families: c.[1453-1G>C];[1918C>G] and c.[710del];[902C>T]" (PMID: 36450274). These families demonstrated reduced PTCD3 protein and severe reductions in complex I and complex IV subunit steady-state levels and activities, confirming pathogenicity. Two independent reports, in unrelated families, satisfy standard gene-validity criteria for a definitive Mendelian gene–disease relationship.

Finding 2 — COXPD51 manifests clinically as early-infantile Leigh syndrome with optic atrophy

Across all four reported patients, the clinical picture is that of Leigh syndrome with onset in the first months of life. Core features include psychomotor delay/regression, respiratory insufficiency, and feeding difficulties, with a neurologic phenotype of dystonia, optic atrophy, nystagmus, and tonic–clonic seizures. Muñoz-Pujol et al. summarize: "The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties. The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures. Brain MRI showed optic nerve atrophy and thalamic changes, consistent with Leigh syndrome" (PMID: 36450274). Their paper title makes the conclusion explicit: "Leigh syndrome is the main clinical characteristic of PTCD3 deficiency."

The index patient of Borna et al. showed a concordant picture: "We describe a patient who presented with low birth weight, mental retardation, and optic atrophy. Brain MRI showed abnormal bilateral signals at the basal ganglia and brainstem, and the patient was diagnosed as Leigh syndrome" (PMID: 30607703).

Suggested HPO terms: Leigh-like disease / abnormality of the basal ganglia (HP:0002134), Optic atrophy (HP:0000648), Nystagmus (HP:0000639), Dystonia (HP:0001332), Generalized tonic-clonic seizures (HP:0002069), Global developmental delay (HP:0001263), Developmental regression (HP:0002376), Feeding difficulties (HP:0011968), Respiratory insufficiency (HP:0002093), Elevated circulating lactate concentration (HP:0002151), Intrauterine growth retardation / low birth weight (HP:0001518).

Finding 3 — Molecular mechanism: mS39 loss impairs mitochondrial translation, causing combined complex I + IV deficiency

The mechanistic chain is well supported. UniProt entry Q96EY7 defines PTCD3 as "Small ribosomal subunit protein mS39" (689 aa), a mitochondrial RNA-binding protein and component of the mitochondrial small ribosomal subunit (28S mt-SSU) associated with the 12S mt-rRNA. Relevant GO terms include GO:0005763 (mitochondrial small ribosomal subunit), GO:0032543 (mitochondrial translation), and GO:0019843 (rRNA binding).

The functional role was first established by Davies et al. (2009), who showed that "lowering PTCD3 in 143B osteosarcoma cells decreased mitochondrial protein synthesis, mitochondrial respiration and the activity of Complexes III and IV, suggesting that PTCD3 has a role in mitochondrial translation" (PMID: 19427859).

In patient cells, Borna et al. demonstrated the complete causal cascade: "The patient had marked decreases in mitochondrial complex I and IV levels and activities, oxygen consumption and ATP biosynthesis, and generalized mitochondrial translation defects in fibroblasts. Quantitative proteomic analysis revealed decreased levels of the small mitoribosomal subunits" (PMID: 30607703). Critically, they proved causation by rescue: "Complementation experiments rescued oxidative phosphorylation complex I and IV levels and activities, ATP biosynthesis, and MT-RNR1 rRNA transcript level, providing functional validation." Re-introduction of wild-type PTCD3 restored the biochemical defect, closing the loop between genotype and phenotype. Muñoz-Pujol et al. reproduced this in additional families with reduced PTCD3 protein and severe reductions in complex I and IV subunit steady-state levels/activities and respiration.

Finding 4 — Variant spectrum: autosomal-recessive, biallelic, ultra-rare loss-of-function alleles

PTCD3/MRPS39 is located at chr2p11.2 (GRCh38 chr2:86,106,223–86,142,157), HGNC:24717, OMIM *614918, Ensembl ENSG00000132300, RefSeq NM_017952.6. gnomAD constraint metrics indicate that heterozygous loss of function is tolerated (pLI ≈ 0; LOEUF/oe_lof ≈ 0.87; observed 89 / expected 102 LoF alleles), which is fully consistent with a recessive disease mechanism — carriers are unaffected.

ClinVar lists 223 PTCD3 records (17 Pathogenic, 10 Likely pathogenic, 129 VUS, plus benign/conflicting). The pathogenic/likely-pathogenic variants are predominantly loss-of-function:

Variant class Examples
Frameshift c.695del; c.710del (p.Thr237fs); c.1746_1747dup (p.Phe583fs); c.1747_1748insCT (p.Phe583Serfs*3)
Nonsense c.640C>T (p.Gln214*); c.1166C>G (p.Ser389*); c.1431G>A (p.Trp477*)
Canonical splice-site c.415-2A>G; c.805-2A>G; c.1148-2A>G; c.1453-1G>C; c.1630-1G>A; c.1979+1G>A
Missense (recurrent) c.902C>T (p.Thr301Ile); c.1918C>G (p.Pro640Ala)
Structural large 2p11.2 deletion encompassing PTCD3

Population allele frequencies (gnomAD v4) confirm that disease alleles are ultra-rare or absent (e.g., c.902C>T AF ≈ 3.4×10⁻⁶; c.1453-1G>C AF ≈ 2.1×10⁻⁶; c.415-2A>G AF ≈ 6.2×10⁻⁶; c.710del absent). The recurrent missense c.1918C>G (p.Pro640Ala) is comparatively common (AF ≈ 0.0014) and ClinVar-conflicting, consistent with a hypomorphic allele that produces disease only when inherited in trans with a severe (null-like) allele. This aligns with the two source publications (PMID: 30607703; PMID: 36450274) showing splice/frameshift alleles combined with missense changes. All origins are germline; no somatic mechanism applies to this disease.

Finding 5 — Prognosis is poor: infantile-onset Leigh syndrome with early mortality

Because only four molecularly-confirmed patients are published, dedicated COXPD51 natural-history data do not exist; the best prognostic proxy is the natural history of Leigh syndrome as a whole, which is severe and often fatal in early childhood, especially with early onset. Ogawa et al. (2020), studying 166 Japanese Leigh patients, reported that "Nearly 90% of deaths occurred by age 6. Mortality rate of patients with onset before 6 months of age was significantly higher than that of onset after 6 months. All patients with neonatal onset were either deceased or bedridden" (PMID: 31967322). Overall mortality in that cohort was 24.1%.

Because PTCD3 is a nuclear gene, COXPD51 falls into the nuclear-DNA (nDNA) Leigh category, which tends to present earlier than mtDNA-caused disease. The meta-analysis by Chang et al. (2020) found "Patients with nDNA mutations were younger than those with mtDNA mutations (8.82 ± 13.88 vs 26.20 ± 41.11 years, P = .007)" (PMID: 32000367), and reported the following frequencies across 385 Leigh patients: elevated lactate 72%, developmental retardation 57%, hypotonia 42%, respiratory dysfunction 34%, seizures 33%, poor feeding 29%. Together these support an early-onset, severe, progressive course for COXPD51.

Finding 6 — Model systems: in vitro / patient-cell models exist; no dedicated animal disease model

Functional understanding of COXPD51 derives principally from cellular models: (i) siRNA knockdown of PTCD3 in 143B osteosarcoma cells (Davies 2009), which reduced mitochondrial protein synthesis, respiration, and complex III/IV activity; and (ii) patient-derived dermal fibroblasts (Borna 2019; Muñoz-Pujol 2023), which recapitulate the biochemical defect (combined complex I + IV deficiency, translation defect) and were used for lentiviral complementation/rescue. Conserved orthologs are annotated in NCBI Gene: mouse Ptcd3 (GeneID 69956), rat Ptcd3 (500199), zebrafish ptcd3 (553325); the budding-yeast ortholog of mS39 is RSM22. No published knockout/knock-in mouse, zebrafish, or invertebrate line has been specifically phenotyped as a COXPD51 disease model.

Finding 7 — IMPC Ptcd3 knockout: homozygous embryonic lethality confirms gene essentiality

The International Mouse Phenotyping Consortium (IMPC) genotype–phenotype records for Ptcd3 provide a decisive insight into gene essentiality. Homozygous knockout produces "preweaning lethality, complete penetrance" and "embryonic lethality prior to organogenesis." Heterozygous animals show subtle phenotypes: impaired pupillary reflex (pupil light response), decreased circulating HDL cholesterol, and increased mean corpuscular hemoglobin. The embryonic lethality of the complete null explains a key genetic constraint of COXPD51: surviving patients cannot be complete nulls — they must retain some residual mS39 function, which is why all reported genotypes pair a severe allele with a hypomorphic (often missense/splice) allele that preserves partial activity.

Mechanistic Model / Interpretation

Ordered causal chain (initiating lesion → clinical manifestation)

  1. Biallelic loss-of-function variants in PTCD3 (splice-site, frameshift, nonsense, or hypomorphic missense in trans) lead to reduced or dysfunctional mS39 protein.
  2. Reduced functional mS39 results in impaired assembly and stability of the 28S small mitoribosomal subunit (mt-SSU); quantitative proteomics shows decreased small mitoribosomal subunit proteins and reduced 12S rRNA (MT-RNR1). (Demonstrated in patient fibroblasts.)
  3. Defective mt-SSU leads to a generalized defect in mitochondrial mRNA translation — the 13 mtDNA-encoded OXPHOS subunits are undersynthesized. (Demonstrated.)
  4. Reduced mtDNA-encoded subunit synthesis results in failed assembly of respiratory-chain complexes, producing a combined deficiency of complex I and complex IV (± complex III in knockdown systems), since these complexes contain mtDNA-encoded core subunits. (Demonstrated biochemically; rescued by complementation.)
  5. Combined OXPHOS deficiency leads to decreased oxygen consumption and collapse of oxidative ATP synthesis, with a compensatory shift to glycolysis and lactic acidosis. (Demonstrated.)
  6. Energy failure results in injury to high-energy-demand post-mitotic tissues — chiefly neurons of the basal ganglia, brainstem, thalamus, and optic pathway — producing the bilateral symmetric necrotizing lesions characteristic of Leigh syndrome. (Inferred by analogy to Leigh-syndrome pathophysiology; supported by MRI pattern.)
  7. Regional neurodegeneration leads to the clinical phenotype: psychomotor regression, dystonia, seizures, optic atrophy, nystagmus, respiratory insufficiency, and feeding difficulty. (Demonstrated clinically.)
 PTCD3 LoF (biallelic)
│
▼
 ↓ functional mS39 protein
│
▼
 Defective 28S mt-SSU assembly ── ↓ MT-RNR1 (12S rRNA), ↓ mt-SSU proteins
│
▼
 Impaired mitochondrial translation (13 mtDNA-encoded subunits ↓)
│
▼
 Combined OXPHOS deficiency  ── Complex I ↓ , Complex IV ↓ (± III)
│
▼
 ↓ O2 consumption, ↓ ATP, ↑ lactate
│
▼
 Energy failure in neurons (basal ganglia, brainstem, thalamus, optic nerve)
│
▼
 LEIGH SYNDROME: regression, dystonia, seizures, optic atrophy, nystagmus,
         respiratory insufficiency, feeding difficulty

Anatomical, cellular, and subcellular mapping

Level Structures involved Suggested ontology terms
Subcellular Mitochondrion; mitochondrial small ribosomal subunit; matrix GO:0005739 (mitochondrion); GO:0005763 (mitochondrial small ribosomal subunit); GO:0005759 (mitochondrial matrix)
Biological process Mitochondrial translation; rRNA binding; OXPHOS / ATP synthesis GO:0032543 (mitochondrial translation); GO:0019843 (rRNA binding); GO:0006119 (oxidative phosphorylation)
Cell type Neurons (esp. basal ganglia / brainstem / retinal ganglion cells of optic nerve) CL:0000540 (neuron); CL:0000099 (interneuron); CL:0000740 (retinal ganglion cell)
Tissue Nervous tissue; gray-matter nuclei UBERON:0001021 (nerve); UBERON:0002020 (gray matter)
Organ / site Basal ganglia, brainstem, thalamus, optic nerve UBERON:0002420 (basal ganglion); UBERON:0002298 (brainstem); UBERON:0001897 (thalamus); UBERON:0000941 (optic nerve)
Body system Central nervous system (primary); respiratory drive (secondary) UBERON:0001017 (central nervous system)

Chemical entities (CHEBI): ATP (CHEBI:15422), lactate/lactic acid (CHEBI:24996), oxygen (CHEBI:15379).

Why complexes I and IV specifically?

Complexes I, III, IV, and V all contain mtDNA-encoded core subunits and therefore depend on mitochondrial translation; complex II is entirely nuclear-encoded and is spared. Complex I (7 mtDNA subunits) and complex IV (3 mtDNA subunits) are the most sensitive readouts of a global mitochondrial translation lesion, which is why the biochemical signature of COXPD51 is a combined complex I + IV deficiency with preserved complex II — a fingerprint shared across the mitochondrial-translation / mitoribosomopathy class of disorders (e.g., COXPD7/C12orf65, COXPD9/MRPL3).

Evidence Base

PMID Title / focus Evidence type Contribution
30607703 Mitochondrial ribosomal protein PTCD3 mutations cause oxidative phosphorylation defects with Leigh syndrome (Borna et al. 2019) Human clinical + in vitro rescue First COXPD51 patient; identifies biallelic LoF variants; demonstrates translation defect, combined CI/CIV deficiency; complementation rescue = functional validation
36450274 Leigh syndrome is the main clinical characteristic of PTCD3 deficiency (Muñoz-Pujol et al. 2023) Human clinical 3 additional patients / 2 families; compound-het variants; establishes Leigh syndrome as the defining phenotype; upgrades gene–disease validity
19427859 Pentatricopeptide repeat domain protein 3 associates with the mitochondrial small ribosomal subunit and regulates translation (Davies et al. 2009) In vitro (siRNA) Defines PTCD3 function in mitochondrial translation; knockdown reduces protein synthesis, respiration, and complex III/IV activity
31967322 Mortality of Japanese patients with Leigh syndrome (Ogawa et al. 2020) Human natural history (n=166) Prognostic proxy: ~90% of deaths by age 6; early onset = higher mortality; neonatal onset uniformly severe
32000367 A meta-analysis and systematic review of Leigh syndrome (Chang et al. 2020) Human meta-analysis (n=385) Phenotype frequencies; nDNA cases have earlier onset than mtDNA cases — supports early severe COXPD51 course
IMPC (Ptcd3) International Mouse Phenotyping Consortium genotype–phenotype records Model organism Homozygous KO embryonic-lethal (gene essentiality); heterozygotes show impaired pupillary reflex, altered HDL/MCH

Supporting context on the disease class (mitoribosomopathies / combined OXPHOS deficiencies): COXPD9 due to MRPL3 (PMID: 34008913) and COXPD7 due to C12orf65 (PMID: 40993840) present with overlapping Leigh-syndrome / mitochondrial-translation-defect phenotypes, reinforcing the mechanistic placement of COXPD51.

Section-by-Section Synthesis

1. Disease Information

COXPD51 (MONDO:0033631, OMIM #619057) is a Mendelian mitochondrial disease. Synonyms/alternative descriptors: "PTCD3 deficiency," "MRPS39 deficiency," "mitochondrial ribosomal protein mS39 deficiency," and (descriptively) "PTCD3-related Leigh syndrome." No ICD-10 code is specific to COXPD51; it maps to broad mitochondrial-disease/Leigh categories (ICD-10 G31.8 / E88.40 range; ICD-11 8C73/5C53 area). No specific Orphanet number is assigned to the PTCD3 subtype; it falls under the Leigh syndrome / combined OXPHOS deficiency umbrella. Information is derived from aggregated disease-level resources and individual case reports (four molecularly-confirmed patients), not EHR/registry data.

2. Etiology

Cause: purely genetic — biallelic (recessive) loss-of-function variants in PTCD3. Genetic risk factor: carrier status in both parents; consanguinity/founder effects are plausible but not established given the tiny cohort. Environmental risk/protective factors: none identified; this is a monogenic disorder. Gene–environment interactions: not applicable / not reported. The hypomorphic p.Pro640Ala missense allele acts as a genetic modifier that permits survival when paired with a severe allele.

3. Phenotypes

See Finding 2 and HPO terms above. Age of onset: neonatal to early infancy (first months of life). Severity: severe. Progression: progressive with regression. Frequency across the 4 patients: optic atrophy, developmental delay/regression, and Leigh-pattern MRI are near-universal; dystonia, nystagmus, seizures, respiratory insufficiency, and feeding difficulty are common. Quality-of-life impact is profound (severe disability; dependence for all care).

4. Genetic / Molecular Information

See Finding 4. Causal gene PTCD3/MRPS39 (HGNC:24717, OMIM *614918, chr2p11.2). Variant classes: splice, frameshift, nonsense, hypomorphic missense, and at least one structural deletion. Inheritance: autosomal recessive. Functional consequence: loss of function. Modifier: hypomorphic p.Pro640Ala allele. No epigenetic mechanism is implicated in disease causation (note: unrelated cancer literature describes epigenetic up-regulation of PTCD3 in colorectal cancer, PMID: 40304977 — not relevant to COXPD51 pathogenesis).

5. Environmental Information

Not applicable — no environmental, lifestyle, or infectious contributors. Monogenic recessive disease.

6. Mechanism / Pathophysiology

See the ordered causal chain and mechanistic model above.

7. Anatomical Structures Affected

Primary: central nervous system (basal ganglia, brainstem, thalamus, optic nerve). Subcellular: mitochondrion / small mitoribosomal subunit. Lateralization: bilateral and symmetric (hallmark of Leigh syndrome). Secondary involvement: respiratory (central hypoventilation) and feeding/growth (failure to thrive).

8. Temporal Development

Onset: congenital/early-infantile, insidious-to-subacute. Course: progressive neurodegeneration, often punctuated by metabolic decompensation. Duration: chronic but frequently fatal in early childhood (by Leigh-syndrome analogy). Critical period: infancy is the window of maximal vulnerability.

9. Inheritance and Population

Inheritance: autosomal recessive; carriers unaffected (heterozygous LoF tolerated per gnomAD). Penetrance: presumed complete for biallelic pathogenic genotypes. Expressivity: variable within a narrow severe range. Prevalence/incidence: not established — ultra-rare (fewer than ~10 patients worldwide). No confirmed founder effect, sex bias, or ethnic clustering given the small cohort. Carrier frequency: unknown but very low (disease alleles ultra-rare in gnomAD).

10. Diagnostics

  • Biochemistry: elevated blood/CSF lactate; combined complex I + IV deficiency (with preserved complex II) on respiratory-chain enzymology in muscle/fibroblasts; reduced mitochondrial protein synthesis (in vitro).
  • Imaging: MRI showing bilateral symmetric T2/FLAIR signal abnormalities of basal ganglia and brainstem, thalamic changes, and optic-nerve atrophy; MR spectroscopy may show a lactate peak.
  • Genetics (definitive): whole-exome or whole-genome sequencing is the diagnostic method of choice; RNA-seq is useful to resolve splice variants (as in Muñoz-Pujol 2023). Gene-panel testing for mitochondrial/Leigh-syndrome nuclear genes should include PTCD3. Single-gene testing is impractical given locus heterogeneity.
  • Differential diagnosis: other nuclear- and mtDNA-encoded Leigh syndromes and combined-OXPHOS-deficiency mitoribosomopathies (e.g., NDUFS4, SURF1, MT-ATP6/T8993C, MRPL3 [COXPD9], C12orf65 [COXPD7]).
  • Screening: no newborn screening exists; cascade carrier testing of relatives and prenatal/preimplantation testing are options once familial variants are known.

11. Outcome / Prognosis

Poor. No curative treatment. Prognosis is inferred from Leigh-syndrome natural history: high early-childhood mortality, especially with onset before 6 months (PMID: 31967322). Morbidity is severe (profound neurodevelopmental disability, dependence). Prognostic factors: age of onset, severity of respiratory involvement, and residual mS39 function conferred by the milder allele.

12. Treatment

No disease-modifying therapy exists. Management is supportive/symptomatic, following general mitochondrial-disease and Leigh-syndrome principles: seizure control (anti-seizure medications, avoiding valproate where feasible due to mitochondrial toxicity), nutritional support (gastrostomy for feeding difficulty), respiratory support, physical/occupational therapy, and management of dystonia. "Mitochondrial cocktails" (coenzyme Q10, riboflavin, thiamine, L-carnitine) are commonly used empirically but lack proven efficacy in this specific disorder. No gene, cell, or RNA therapy is available or in trials for COXPD51. NCIT-relevant supportive categories: anticonvulsant therapy, nutritional support (NCIT:C15417), physical therapy, respiratory support/supportive care.

13. Prevention

Primary prevention is limited to genetic counseling and reproductive options (carrier testing, prenatal diagnosis, preimplantation genetic testing) for at-risk families. No population-level screening, immunization, behavioral, or environmental intervention applies. Tertiary prevention = anticipatory management of complications (aspiration, respiratory failure, status epilepticus).

14. Other Species / Natural Disease

No naturally-occurring COXPD51-equivalent disease has been reported in companion animals or wildlife (no OMIA entry). Conserved orthologs exist across metazoans and yeast (mouse Ptcd3 GeneID 69956; rat 500199; zebrafish ptcd3 553325; yeast RSM22), reflecting deep evolutionary conservation of the mitochondrial translation machinery. No zoonotic dimension (non-infectious genetic disease).

15. Model Organisms

  • In vitro / cellular: 143B osteosarcoma cells with siRNA knockdown (PMID: 19427859); patient-derived dermal fibroblasts with lentiviral complementation rescue (PMID: 30607703).
  • Mouse: IMPC Ptcd3 knockout — homozygous embryonic lethality (gene essentiality); heterozygous impaired pupillary reflex. No conditional/tissue-specific or hypomorphic mouse model recapitulating COXPD51 has been published — a major gap.
  • Phenotype recapitulation: cellular models faithfully reproduce the biochemical defect (combined CI/CIV deficiency, translation defect) but not the whole-organism neurodegenerative phenotype; the constitutive KO mouse dies too early to model Leigh syndrome.

Limitations and Knowledge Gaps

  1. Extreme rarity (n = 4 confirmed patients). All clinical, prognostic, and genotype–phenotype inferences rest on a handful of cases plus proxy data from broader Leigh-syndrome cohorts. Prevalence, incidence, sex ratio, penetrance, and expressivity are essentially unquantified.
  2. No dedicated animal disease model. The constitutive Ptcd3 knockout is embryonic-lethal, so a conditional (e.g., neuron-specific) or hypomorphic knock-in model is needed to study disease pathogenesis and test therapies in vivo. This is the single largest gap.
  3. Prognosis is inferred, not measured. COXPD51-specific survival and progression data do not exist; the Leigh-syndrome proxies (PMID: 31967322; PMID: 32000367) may not perfectly capture PTCD3-specific outcomes.
  4. Genotype–phenotype correlation is immature. The role of the hypomorphic p.Pro640Ala allele in modulating severity is inferred from allele frequency and cell data, not from systematic patient-level correlation.
  5. No therapeutic evidence. No trial, no approved therapy, and no biomarker of treatment response are available for COXPD51 specifically.
  6. Structural biology of mS39 in disease. How specific missense variants (e.g., p.Thr301Ile, p.Pro640Ala) perturb mS39 folding, RNA binding, or mt-SSU assembly has not been resolved structurally.

Proposed Follow-up Experiments / Actions

  1. Build a tractable animal model. Generate a conditional (neuron-specific, e.g., Nestin-Cre) or hypomorphic knock-in Ptcd3 mouse that survives past organogenesis, to reproduce the Leigh phenotype and provide a platform for preclinical therapy testing. Zebrafish ptcd3 morphants/mutants offer a faster, complementary vertebrate model.
  2. Establish an international patient registry / GeneMatcher effort. Aggregate additional PTCD3 cases to define natural history, prevalence, genotype–phenotype correlations, and biomarkers. Curate against MSeqDR/PMD-VR mitochondrial-disease registries (PMID: 42510797).
  3. Functionally classify the VUS burden. Deploy a high-throughput saturation/complementation assay in PTCD3-null cells to reclassify the 129 ClinVar VUS (especially recurrent missense variants), improving diagnostic yield.
  4. Structural characterization. Use cryo-EM of the human mt-SSU and AlphaFold-based modeling to map how p.Thr301Ile, p.Pro640Ala, and other missense variants affect mS39–rRNA contacts and subunit assembly.
  5. iPSC-derived neuronal models. Differentiate patient (or CRISPR-engineered) iPSCs into cortical/dopaminergic neurons and cerebral organoids to model the tissue-specific energy failure and screen candidate therapeutics (e.g., mitochondrial biogenesis inducers, PPR-stabilizing compounds).
  6. Empirical supportive-care consensus. Given the absence of disease-specific therapy, adopt and document outcomes under existing mitochondrial-disease supportive-care frameworks (e.g., ERN EURO-NMD guidance, PMID: 40273815) to standardize management across the few known patients.

Conclusion

COXPD51 is a mechanistically transparent but clinically devastating ultra-rare mitochondrial disease. The causal chain — biallelic PTCD3 loss of function → mS39 deficiency → defective 28S mitoribosome assembly → impaired mitochondrial translation → combined complex I + IV deficiency → neuronal energy failure → infantile Leigh syndrome — is supported by patient genetics, biochemical assays, complementation rescue, and gene-essentiality data from the embryonic-lethal mouse knockout. The principal unmet needs are a survivable in-vivo disease model, systematic natural-history data, functional reclassification of VUS, and any disease-modifying therapy. Until those exist, diagnosis rests on exome/genome sequencing with biochemical confirmation, and care remains entirely supportive.

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