Adult-Onset Ataxia and Polyneuropathy

Mendelian MONDO:0010781 Pathograph 23 Show in embeddings browser hereditary disease mitochondrial disease

Adult-onset ataxia and polyneuropathy (OMIM 500010) is a maternally inherited mitochondrial disorder anchored on a Finnish kindred with heteroplasmic MT-ATP6 m.8993T>C. Two of three examined adult siblings had slowly progressive overt ataxia and all three had axonal sensorimotor neuropathy; cerebellar and sensory dysfunction both contributed to the ataxia. Related m.9035T>C and m.9185T>C disorders can have similar adult presentations, with variable pyramidal signs. Adult onset can occur despite high mutant loads. Normal routine muscle histochemistry, respiratory-chain enzymology or MRI does not exclude an MT-ATP6 disorder. NARP and Leigh syndrome are overlapping presentations of the same broader mitochondrial spectrum, with different defining clinical patterns.

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1
Inheritance
7
Pathophys.
17
Phenotypes
3
Gaps
23
Pathograph
1
Genes
5
Medical Actions
5
Differentials
3
Models
11
References
1
Deep Research
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Classifications

Harrison's Part
GENETICS ENVIRONMENT DISEASE
ICIMD (Inherited Metabolic Disorders)
mtdna encoded respiratory chain proteins
👪

Inheritance

1
Maternal mitochondrial inheritance HP:0001427
Maternal transmission of a mitochondrial MT-ATP6 variant, with variable heteroplasmy and expression. Adult onset is not explained simply by a low mutant load; related adult ataxia pedigrees had 90–99% heteroplasmy in leukocytes. Males do not transmit mtDNA variants; offspring of affected females are at risk, but inheritance does not guarantee clinical disease.
Mitochondrial inheritance
Show evidence (2 references)
PMID:35159298 SUPPORT Human Clinical
"Pathogenic variants in MT-ATP6 are a well-known cause of maternally-inherited mitochondrial disorders"
Establishes maternal transmission as the inheritance mode for MT-ATP6 disorders, the gene carrying this entry's causal variants.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"is transmitted by mitochondrial (maternal) inheritance."
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Maternal inheritance applies to this MT-ATP6 disorder, although the chapter is not an adult-ataxia-specific cohort.
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Discussions and Knowledge Gaps

3
Which cerebellar cell population is lost in adult-onset MT-ATP6 ataxia, and is the Purkinje neuron the primary target as it is in most hereditary ataxias?
KNOWLEDGE GAP OPEN purkinje_neuropathology_unproven
Attached to
pathophysiology#Cerebellar Dysfunction
The reviewed adult clinical reports establish cerebellar signs and variable MRI atrophy but not specific Purkinje-cell loss. The original family included a deceased childhood-onset sibling with nonspecific brain gliosis at autopsy and no documented molecular assay; that historical case does not establish adult cell-specific neuropathology.
Proposed experiments
Post-mortem cerebellar neuropathology in genetically confirmed adult-onset MT-ATP6 ataxia
cerebellar_neuropathology_mtatp6
Quantitative stereology of Purkinje, granule and dentate neurons with per-cell heteroplasmy measurement, compared against age-matched controls and against NARP/Leigh cerebellum.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Brain MRI showed slight periventricular white matter abnormali- ties and mild atrophy in cerebellar vermis."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3; the PDF retains the line-break hyphen. Mild vermian atrophy coexisted with absence of overt ataxia at examination.
Why do some MT-ATP6 pedigrees with very high mutant load present in infancy with Leigh syndrome while others present only in adulthood with ataxia and neuropathy?
OPEN QUESTION OPEN heteroplasmy_does_not_explain_onset
Attached to
pathophysiology#Heteroplasmy-Dependent Expression
Mutant load is necessary but demonstrably not sufficient to predict age of onset or severity: patients with childhood-onset and adult-onset MT-ATP6 ataxia have both been reported at 90-100% heteroplasmy, and within a single m.8993T>C family, phenotype differed markedly between members with comparably high ectodermal and mesodermal loads. Candidate modifiers include mtDNA haplogroup, nuclear background, mtDNA copy number, and differences in antioxidant scavenging capacity, none of which has been tested for this entity.
Show evidence (2 references)
PMID:20953793 SUPPORT INDIRECT Human Clinical
"There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy."
Demonstrates that measured heteroplasmy fails to explain within-family phenotypic variation in an m.8993T>C kindred. Graded INDIRECT because that kindred was diagnosed as NARP syndrome (MONDO:0010794); the open question about load-versus-onset is nonetheless shared across the MT-ATP6 spectrum.
PMID:22577227 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"In our families, six patients had their genetic testing performed on leucocyte DNA, with heteroplasmy levels ranging from 90-99%."
Related m.9185T>C and m.9035T>C families include high-load adult presentations; blood load is not a universal predictor of onset.
Does the rescue of MT-ATP6 mutant cell death by CoQ10 and vitamin E in transmitochondrial cybrids translate into any clinical benefit in adult-onset MT-ATP6 ataxia?
HUMAN MODEL MISMATCH OPEN antioxidant_rescue_in_cybrids_only
Attached to
pathophysiology#Reactive Oxygen Species Overproduction
Related m.9035T>C cybrids showed antioxidant prevention of stress-induced cell death. The immortalized background, different variant and acute artificial stressors limit translation to the adult m.8993T>C syndrome. The sources reviewed and direct registry queries on 2026-09-21 did not identify an adult MT-ATP6 ataxia-specific interventional trial.
Show evidence (1 reference)
PMID:19626676 SUPPORT INDIRECT In Vitro
"Both of these outcomes were prevented by the antioxidants CoQ(10) and vitamin E, suggesting that the abnormally high levels of ROS were the triggers of cell death."
The cybrid rescue result whose translational validity this discussion questions.
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Pathophysiology

7
MT-ATP6 m.8993T>C Variant
The defining mitochondrial m.8993T>C missense variant substitutes proline for leucine at ATP6 residue 156. ATP6 encodes subunit a of ATP synthase. Related adult-ataxia variants m.9035T>C and m.9185T>C have distinct assay and clinical evidence; their results are qualified wherever used.
MT-ATP6 hgnc:7414 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves MT-ATP6 (hgnc:7414). hgnc:7414 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context MT-ATP6 hgnc:7414 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns MT-ATP6 (hgnc:7414). hgnc:7414 is a gene from the HUGO Gene Nomenclature Committee. allele_type: SNV variant_origin: GERMLINE functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
Heteroplasmic mitochondrial missense substitution (Leu156Pro) inherited through the maternal line.
proton-transporting ATP synthase activity, rotational mechanism GO:0046933 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased proton-transporting ATP synthase activity, rotational mechanism (GO:0046933). GO:0046933 is a molecular function from the Gene Ontology.
proton-transporting ATP synthase complex GO:0045259 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves proton-transporting ATP synthase complex (GO:0045259). GO:0045259 is a cellular component from the Gene Ontology.
Downstream
Impaired ATP Synthase Function The m.8993T>C ATP6 lesion is associated with bioenergetic dysfunction in patient lymphocytes.
Show evidence (2 references)
PMID:16049925 SUPPORT Human Clinical
"We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation."
This is the defining report for OMIM 500010 and directly ties the heteroplasmic m.8993T>C MT-ATP6 variant to the adult-onset ataxia-plus-polyneuropathy phenotype.
PMID:17568559 SUPPORT In Vitro
"Two point mutations (T>G and T>C) at the same 8993 nucleotide of mitochondrial DNA (at comparable mutant load), affecting the ATPase 6 subunit of the F1F0-ATPase, result in neurological phenotypes of variable severity in humans."
Locates the lesion in the ATPase 6 subunit of F1F0-ATP synthase and records that the two nucleotide-8993 substitutions differ in severity.
Heteroplasmy-Dependent Expression
Mutant load modifies clinical expression but is not a universal onset clock or a fixed threshold. The defining adult proband had 89% mutant mtDNA in blood; related adult-ataxia pedigrees had 90–99% in leukocytes. GeneReviews describes relatively little tissue- or age-dependent heteroplasmy variation for m.8993T>C/G, unlike some other mtDNA variants. Differences among tissues can nevertheless occur, and high load does not reliably predict an individual phenotype. Nuclear, haplogroup and copy-number modifiers remain candidate explanations rather than demonstrated determinants here.
Downstream
Impaired ATP Synthase Function Mutant load can modify the expression of mitochondrial dysfunction; individual tissue thresholds and downstream intermediates were not measured in the adult kindred.
Show evidence (3 references)
PMID:22577227 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"In our families, six patients had their genetic testing performed on leucocyte DNA, with heteroplasmy levels ranging from 90-99%."
Related m.9185T>C and m.9035T>C families include high-load adult presentations; blood load is not a universal predictor of onset.
PMID:20953793 SUPPORT INDIRECT Human Clinical
"There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy."
In an m.8993T>C family, measured heteroplasmy did not account for the within-family phenotypic spread, supporting the modulator role and the limits of load as a predictor. Graded INDIRECT because the cohort was diagnosed as NARP syndrome (MONDO:0010794), an entity this entry keeps distinct; the observation carries across because the modulator claim is about m.8993T>C heteroplasmy behaviour rather than about either phenotype.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"they show very little tissue-dependent or age-dependent variation in"
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: This statement specifically concerns m.8993T>G/C; it limits generic claims that blood load is unreliable for these variants.
Impaired ATP Synthase Function
The m.8993T>C ATP6 substitution perturbs ATP-synthase-related bioenergetics. In related m.9035T>C cybrids, F0-ATPase dysfunction was measured. Complex V subcomplexes in m.9035T>C patient material suggest altered assembly or stability, but that interpretation is provisional: oligomycin-sensitive ATP hydrolysis was normal in the later primary-fibroblast and muscle study. The assays and cellular backgrounds differ.
proton motive force-driven ATP synthesis GO:0015986 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased proton motive force-driven ATP synthesis (GO:0015986). GO:0015986 is a biological process from the Gene Ontology.
proton-transporting ATP synthase activity, rotational mechanism GO:0046933 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased proton-transporting ATP synthase activity, rotational mechanism (GO:0046933). GO:0046933 is a molecular function from the Gene Ontology.
proton-transporting ATP synthase complex GO:0045259 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves proton-transporting ATP synthase complex (GO:0045259). GO:0045259 is a cellular component from the Gene Ontology.
Experimental models
Transmitochondrial m.9035T>C cybrids CELL LINE Assay-specific evidence for mitochondrial dysfunction.
Patient primary fibroblasts with homoplasmic m.9035T>C PRIMARY CELL CULTURE Assay-specific evidence for mitochondrial dysfunction.
Downstream
Cellular ATP Depletion Reduced energy availability is one measured consequence of the ATP6 lesion.
Reactive Oxygen Species Overproduction Increased ROS is a distinct measured consequence; these data do not resolve all biochemical intermediates.
Show evidence (3 references)
PMID:17568559 SUPPORT PRIMARY RESULT In Vitro
"Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction."
Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
PMID:19626676 SUPPORT INDIRECT In Vitro
"We confirmed that the 4452T>C transition in tRNA(Met) represented a polymorphism; however, 9035T>C conversion in the ATP6 gene was responsible for a defective F(0)-ATPase."
Cybrid evidence that an ataxia-associated MT-ATP6 missense variant produces a defective F0-ATPase. Graded INDIRECT because this cybrid work used m.9035T>C, a different MT-ATP6 variant in the same adult-onset ataxia spectrum, not the m.8993T>C variant that defines this entry.
PMID:35159298 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"In mitochondria isolated from skin fibroblasts of both patients no decrease in oligomycin sensitive ATPase activity could be discerned either (see Table 1)."
Negative result in primary m.9035T>C fibroblasts limits generalization of the earlier cybrid ATPase defect.
Cellular ATP Depletion
Energy deprivation was measured in m.8993T>C patient lymphocytes. Related m.9035T>C cybrids had less than half the control steady-state ATP content. These are non-neuronal experimental results; neuronal ATP depletion in the adult syndrome has not been directly measured.
Experimental models
Patient lymphocytes with m.8993T>C OTHER Assay-specific evidence for mitochondrial dysfunction.
Transmitochondrial m.9035T>C cybrids CELL LINE Assay-specific evidence for mitochondrial dysfunction.
Downstream
Peripheral Axonal Dysfunction The connection between experimentally measured cellular stress and clinical axonal dysfunction is inferred; the adult neuronal intermediates are unknown.
Cerebellar Dysfunction Cellular mitochondrial stress is a proposed contributor to the cerebellar component; no cell-specific adult neuropathology establishes the intervening steps.
Show evidence (2 references)
PMID:17568559 SUPPORT PRIMARY RESULT In Vitro
"Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction."
Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
Reactive Oxygen Species Overproduction
Patient lymphocytes carrying m.8993T>C showed increased ROS production, with a different balance between ROS and energy deprivation than m.8993T>G. Related m.9035T>C cybrids showed markedly increased ROS and stress-induced cell death. These experiments do not establish that ROS determines adult onset or prove neuronal injury in vivo.
reactive oxygen species metabolic process GO:0072593 ↑ INCREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased reactive oxygen species metabolic process (GO:0072593). GO:0072593 is a biological process from the Gene Ontology. response to oxidative stress GO:0006979 ↑ INCREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased response to oxidative stress (GO:0006979). GO:0006979 is a biological process from the Gene Ontology.
Experimental models
Patient lymphocytes with m.8993T>C OTHER Assay-specific evidence for mitochondrial dysfunction.
Transmitochondrial m.9035T>C cybrids CELL LINE Assay-specific evidence for mitochondrial dysfunction.
Downstream
Peripheral Axonal Dysfunction The connection between experimentally measured cellular stress and clinical axonal dysfunction is inferred; the adult neuronal intermediates are unknown.
Cerebellar Dysfunction Cellular mitochondrial stress is a proposed contributor to the cerebellar component; no cell-specific adult neuropathology establishes the intervening steps.
Show evidence (2 references)
PMID:17568559 SUPPORT In Vitro
"The 8993T>G change mainly induces an energy deficiency, whereas the 8993T>C favours an increased ROS production."
Establishes the ROS-weighted balance of the bioenergetic lesion for the m.8993T>C variant that defines this entry.
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
Peripheral Axonal Dysfunction
Axonal sensorimotor polyneuropathy was demonstrated electrophysiologically in all three examined adults in the defining kindred, with sensory loss, absent ankle reflexes and weakness. Nerve histology did not establish a particular axonal transport defect. Length dependence is additionally described in a separate m.8993T>C NARP family.
sensory neuron CL:0000101 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves sensory neuron (CL:0000101). CL:0000101 is a cell type from the Cell Ontology. neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Downstream
Peripheral Axonal Neuropathy Electrophysiological expression of peripheral axonal dysfunction.
Sensorimotor Neuropathy Both motor and sensory fibers are affected.
Absent Achilles Reflex Peripheral dysfunction accompanies absent ankle reflexes.
Reduced Lower-Limb Vibration Sensation Sensory dysfunction reduces vibration perception.
Muscle Weakness Motor neuropathy can contribute to weakness.
Skeletal Muscle Atrophy Chronic motor dysfunction can contribute to muscle wasting.
Gait Ataxia The authors identify a sensory component of gait ataxia.
Show evidence (2 references)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.
PMID:20953793 SUPPORT INDIRECT Human Clinical
"EMG-NCS revealed varying degrees of length-dependent sensorimotor axonal polyneuropathy."
Electrophysiological demonstration of length-dependent axonal sensorimotor polyneuropathy in an m.8993T>C family. Graded INDIRECT because that family was diagnosed as NARP syndrome (MONDO:0010794), which this entry curates as a separate entity and a differential.
Cerebellar Dysfunction
A cerebellar contribution to ataxia is clinically supported, with dysarthria and abnormal eye movements in affected adults. Cerebellar or vermian atrophy is present in some patients, but MRI can be normal in related adult MT-ATP6 ataxia. Specific Purkinje-cell loss is not established and is not used as a cell-type binding.
Downstream
Progressive Cerebellar Ataxia The authors identify a cerebellar component of the progressive ataxia.
Gait Ataxia Cerebellar incoordination contributes to gait instability.
Dysarthria Speech incoordination accompanies the cerebellar syndrome.
Gaze-Evoked Nystagmus Abnormal ocular motor control accompanies the cerebellar presentation.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.
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Pathograph

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

17
Eye 2
Ophthalmoplegia HP:0000602 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ophthalmoplegia (HP:0000602). HP:0000602 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35159298 SUPPORT INDIRECT Human Clinical
"Patient 2 presented in adolescence with ataxia and ophthalmoplegia without cognitive or motor impairment."
Related m.9035T>C clinical presentation, not a frequency estimate for m.8993T>C adult-onset ataxia.
Gaze-Evoked Nystagmus HP:0000640 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Gaze-evoked nystagmus (HP:0000640). HP:0000640 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"She showed gaze-evoked nystagmus, but eye movements were unrestricted and fun- doscopy was normal."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband; unrestricted eye movements and normal fundus prevent conflating this finding with ophthalmoplegia or retinitis pigmentosa.
Limbs 2
Absent Achilles Reflex HP:0003438 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Absent Achilles reflex (HP:0003438). HP:0003438 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Neurological examination at age 36 years showed mild gait ataxia, absent ankle reflexes, positive Babinski signs, and pes cavus."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct examination of the adult proband.
Pes Cavus HP:0001761 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pes cavus (HP:0001761). HP:0001761 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Neurological examination at age 36 years showed mild gait ataxia, absent ankle reflexes, positive Babinski signs, and pes cavus."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct examination of the adult proband.
Musculoskeletal 2
Muscle Weakness HP:0001324 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Muscle weakness (HP:0001324). HP:0001324 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"There was mild muscle weakness and atrophy."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband observation; no broader distribution or frequency is inferred.
Skeletal Muscle Atrophy HP:0003202 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Skeletal muscle atrophy (HP:0003202). HP:0003202 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"There was mild muscle weakness and atrophy."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband observation; no broader distribution or frequency is inferred.
Nervous System 11
Progressive Cerebellar Ataxia HP:0002073 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Progressive cerebellar ataxia (HP:0002073), qualified as course progressive. HP:0002073 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.
Gait Ataxia HP:0002066 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Gait ataxia (HP:0002066). HP:0002066 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"At age 51 years, her gait was grossly ataxic and she used a walker."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband gait observation.
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 (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.
Sensorimotor Neuropathy HP:0007141 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Sensorimotor neuropathy (HP:0007141). HP:0007141 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Muscle histology and electrophysiological stud- ies confirmed axonal sensorimotor neuropathy."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct finding in adult patient III-5; the reproduced PDF retains a line-break hyphen.
Cerebellar Atrophy HP:0001272 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebellar atrophy (HP:0001272). HP:0001272 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Brain MRI showed slight periventricular white matter abnormali- ties and mild atrophy in cerebellar vermis."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3; the PDF retains the line-break hyphen. Mild vermian atrophy coexisted with absence of overt ataxia at examination.
Babinski Sign HP:0003487 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Babinski sign (HP:0003487). HP:0003487 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Neurological examination at age 36 years showed mild gait ataxia, absent ankle reflexes, positive Babinski signs, and pes cavus."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct examination of the adult proband.
Episodic Ataxia HP:0002131 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Episodic ataxia (HP:0002131). HP:0002131 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18055910 SUPPORT Human Clinical
"One subject had episodic ataxia (EA) and transient hemipareses, broadening the phenotype."
Episodic ataxia was reported in one member of a second m.8993T>C family; a single report cannot establish a frequency band.
Transient Hemiparesis HP:0001269 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hemiparesis (HP:0001269), qualified as temporality transient. HP:0001269 is a phenotype from the Human Phenotype Ontology.
Temporal: TRANSIENT
Show evidence (1 reference)
PMID:18055910 SUPPORT Human Clinical
"One subject had episodic ataxia (EA) and transient hemipareses, broadening the phenotype."
Same reported episodic presentation, without an inference about population frequency or exclusive MT-ATP6 causation.
Dysarthria HP:0001260 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dysarthria (HP:0001260). HP:0001260 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"She had mild limb ataxia and dysarthria."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband at age 51; dysarthria was also described in another adult sibling.
Reduced Lower-Limb Vibration Sensation Impaired vibration sensation in the lower limbs HP:0002166 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Impaired vibration sensation in the lower limbs (HP:0002166). HP:0002166 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"On neurological examination, his gait was normal, but he had decreased vibration sensation in lower limbs and ankle re- flexes were absent."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3 before development of a wide-based gait.
Atonic Seizure HP:0010819 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Atonic seizure (HP:0010819). HP:0010819 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"She had repeated atonic seizures or drop attacks despite anticonvulsive medication."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: The proband had clinically described drop attacks despite treatment; the reported EEG was normal. Another adult sibling had only probable astatic attacks.
🧬

Genetic Associations

1
MT-ATP6 (Heteroplasmic m.8993T>C (Leu156Pro) defines the original OMIM 500010 family. Related m.9035T>C (Leu170Pro) and m.9185T>C (Leu220Pro) can cause similar adult ataxia. High heteroplasmy and even homoplasmy do not uniquely determine age at onset. Protein substitutions in the discussion of the 2012 paper are swapped; the assignments here follow the 2022 primary paper and GeneReviews.)
Gene: MT-ATP6 hgnc:7414 gene page HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is MT-ATP6 (hgnc:7414). hgnc:7414 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Mitochondrial inheritance
Show evidence (3 references)
PMID:16049925 SUPPORT Human Clinical
"We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation."
Establishes MT-ATP6 m.8993T>C as the causal variant for this entity.
PMID:22577227 SUPPORT Human Clinical
"These families had the m.9185T>C and m.9035T>C mutations, respectively, which have not previously been associated with adult-onset cerebellar syndromes."
Extends the causal gene beyond m.8993T>C to other MT-ATP6 missense variants producing adult-onset cerebellar syndromes.
PMID:22577227 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"In our families, six patients had their genetic testing performed on leucocyte DNA, with heteroplasmy levels ranging from 90-99%."
Related m.9185T>C and m.9035T>C families include high-load adult presentations; blood load is not a universal predictor of onset.
💊

Medical Actions

5
Supportive and Symptomatic Management
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
Care is supportive and symptom-directed, with regular neurological assessment and individualized evaluation of visual and other mitochondrial-system manifestations. The reviewed sources do not establish a disease-modifying treatment for this adult entity.
Target Phenotypes: Progressive cerebellar ataxia HP:0002073 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Progressive cerebellar ataxia (HP:0002073). HP:0002073 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:20301352 SUPPORT INDIRECT REVIEW SYNTHESIS Other
"MANAGEMENT: Treatment of manifestations: Treatment is supportive."
GeneReviews states that management of mtDNA disease is supportive. Graded INDIRECT because the chapter addresses the Leigh syndrome spectrum rather than this adult-onset entity specifically.
Physical and Occupational Therapy
Action: physical therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is physical therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. Ontology label: Physical Therapy NCIT:C15302
Platform: Behavioral / lifestyle
Individualized physical and occupational therapy, fall prevention and mobility aids address ataxia and weakness. Shared mitochondrial-care guidance is extrapolated to this adult presentation.
Target Phenotypes: Gait ataxia HP:0002066 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Gait ataxia (HP:0002066). HP:0002066 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:20301352 SUPPORT INDIRECT REVIEW SYNTHESIS Other
"physical therapy and occupational therapy; standard treatment of eye movement disorders"
GeneReviews lists physical and occupational therapy in the supportive management of mtDNA disease. Graded INDIRECT because the recommendation is made for the Leigh syndrome spectrum rather than this entity.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"maintain independent mobility as appropriate"
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Ataxia/myopathy management supports individualized rehabilitation and mobility aids; no adult MT-ATP6-specific efficacy trial is implied.
Avoidance of Mitochondrial Toxins
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
Medication and anesthesia review should account for mitochondrial disease. The Leigh-spectrum chapter cautions about valproate, acidosis-provoking medication and anesthesia. Its dichloroacetate warning derives from neuropathy worsening in a MELAS trial, not a trial in adult MT-ATP6 ataxia; specialist assessment is required.
Show evidence (1 reference)
PMID:20301352 SUPPORT INDIRECT REVIEW SYNTHESIS Other
"Sodium valproate, medications that cause acidosis, and dichloroacetate should be avoided or used with caution; administration of anesthesia requires careful consideration to avoid aggravation of respiratory symptoms and precipitation of respiratory failure."
GeneReviews Agents/Circumstances to Avoid for mtDNA disease. Graded INDIRECT because it is stated for the Leigh syndrome spectrum; the pharmacologic hazard is shared by MT-ATP6 disease but has not been studied in this adult-onset entity.
Genetic Counseling and Reproductive Options
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. Ontology label: Genetic Counseling NCIT:C15240
Platform: Other
Counseling explains maternal transmission, variable expression and the limits of heteroplasmy-based prediction. All offspring of a female carrier are at risk of inheriting the variant, not necessarily of being affected. Specialist reproductive assessment may include prenatal testing or oocyte donation; preimplantation testing is unsuitable for homoplasmic or near-homoplasmic loads.
Show evidence (4 references)
PMID:20301352 SUPPORT INDIRECT REVIEW SYNTHESIS Other
"Reproductive options for the family members of a proband with an mtDNA pathogenic variant may include prenatal testing, preimplantation genetic testing, and oocyte donation."
GeneReviews enumerates the reproductive options relevant to any maternally inherited mtDNA variant. Graded INDIRECT because the chapter addresses the Leigh syndrome spectrum.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"is transmitted by mitochondrial (maternal) inheritance."
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Maternal inheritance applies to this MT-ATP6 disorder, although the chapter is not an adult-ataxia-specific cohort.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"are at risk of inheriting the pathogenic variant."
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Inheritance risk is not equivalent to certainty of clinical disease.
+ 1 more reference
Neurological and Visual Surveillance
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
Follow the course of ataxia, neuropathy and vision, with other organ investigations guided by clinical findings. Leigh-spectrum surveillance provides context; its infantile disease frequencies and fixed multisystem schedule are not assumed for adults.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/ SUPPORT INDIRECT REVIEW SYNTHESIS Other
"To assess for reduced vision, abnormal ocular movement, strabismus,"
GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Supports clinical eye assessment in shared mitochondrial care.
🔬

Biochemical Markers

2
Cytochrome c oxidase muscle histochemistry (Normal)
Show evidence (1 reference)
PMID:18055910 SUPPORT Human Clinical
"Cytochrome c oxidase muscle histochemistry, which is the standard clinical investigation for mitochondrial disease in adults, is usually normal in patients with MTATP6 mutations."
States directly that the standard adult mitochondrial screening test is normal in MT-ATP6 disease.
Respiratory chain enzyme activities (Normal)
Show evidence (1 reference)
PMID:22577227 SUPPORT Human Clinical
"Other investigations including muscle biopsy and respiratory chain enzyme activity were non-specific or normal."
Directly reports normal or non-specific respiratory-chain enzymology in adult-onset MT-ATP6 ataxia families.
🔬

Diagnosis

3
Mitochondrial DNA sequencing
Molecular testing of MT-ATP6, through targeted sequencing or an appropriate comprehensive mitochondrial/genomic approach, should be considered in unexplained adult ataxia with neuropathy despite normal muscle investigations. Quantify heteroplasmy and interpret the pathogenic variant together with the phenotype. Leukocyte DNA was informative in the published adult MT-ATP6 families; tissue selection and assay sensitivity should be individualized, without importing the low-blood-load behavior of unrelated mtDNA variants.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Results: A pathogenic MT-ATP6 variant with a compatible phenotype establishes the molecular diagnosis; related variants may be heteroplasmic or homoplasmic. The molecular finding alone does not define the adult clinical subtype.
Show evidence (4 references)
PMID:22577227 SUPPORT Human Clinical
"MTATP6 sequencing should be considered in the workup of undiagnosed ataxia, even if other investigations do not suggest a mitochondrial DNA disorder."
Direct recommendation that MT-ATP6 sequencing be part of the undiagnosed adult ataxia workup regardless of other test results.
PMID:20953793 SUPPORT INDIRECT Human Clinical
"The degree of mutant heteroplasmy for the m.8993T>C mutation was evaluated by real-time allele refractory mutation system quantitative PCR of mtDNA from hair bulbs (ectoderm) and blood leukocytes (mesoderm)."
Illustrates the multi-tissue heteroplasmy quantification this diagnostic step calls for. Graded INDIRECT because the study quantified heteroplasmy in an m.8993T>C family diagnosed as NARP syndrome (MONDO:0010794); the method transfers, the cohort is a different entity.
PMID:22577227 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"Therefore, unlike many mtDNA disorders, MTATP6 sequencing can be reliably performed on leucocyte DNA, and should be considered as a diagnostic test in the workup of ataxia and neuropathy, even when the routine clinical investigations for mitochondrial disease are normal."
Direct diagnostic conclusion from the related adult pedigrees; not a guarantee that every assay or every mitochondrial variant is detectable in blood.
+ 1 more reference
Nerve conduction studies and electromyography
Electrophysiology establishes the axonal sensorimotor character of the neuropathy and helps distinguish demyelinating disorders. Severity and timing vary.
nerve conduction velocity test NCIT:C88502 NCI Thesaurus (NCIT)
Results: Length-dependent sensorimotor axonal polyneuropathy of variable severity.
Show evidence (2 references)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Muscle histology and electrophysiological stud- ies confirmed axonal sensorimotor neuropathy."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct finding in adult patient III-5; the reproduced PDF retains a line-break hyphen.
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.
Brain magnetic resonance imaging
MRI assesses cerebellar volume and other structural abnormalities, but normal imaging does not exclude MT-ATP6 ataxia. MRI alone does not establish a mitochondrial cause or specific neuronal cell loss.
magnetic resonance imaging NCIT:C16809 NCI Thesaurus (NCIT)
Results: Variable cerebellar or vermian atrophy; normal MRI was present in three of five imaged patients in the related 2012 adult-ataxia series.
Show evidence (2 references)
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf SUPPORT PRIMARY RESULT Human Clinical
"Brain MRI showed slight periventricular white matter abnormali- ties and mild atrophy in cerebellar vermis."
Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3; the PDF retains the line-break hyphen. Mild vermian atrophy coexisted with absence of overt ataxia at examination.
PMID:22577227 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"Brain MRI was normal in 3/5 patients, and one patient each had cerebellar atrophy, or cerebellar and cerebral volume loss."
Full-text results, five imaged patients from related MT-ATP6 ataxia families.
📊

Prevalence

1
Adults with unexplained ataxia or suspected Charcot-Marie-Tooth disease (United Kingdom referral cohorts)
Cases In Literature
A selected UK referral study screened 308 unexplained-ataxia patients, 96 suspected CMT patients and 191 episodic-ataxia patients, identifying one m.8993T>C family. This is a study-specific case-finding result, not population prevalence or a quantitative rarity band.
Show evidence (2 references)
PMID:18055910 SUPPORT Human Clinical
"We therefore studied 308 patients with unexplained ataxia and 96 patients with suspected Charcot-Marie-Tooth disease to determine whether the m.8993T-->C MTATP6 mutation is common in unexplained inherited ataxia and/or polyneuropathy."
Defines the screened cohorts from which the rarity estimate is drawn.
PMID:18055910 SUPPORT Human Clinical
"In conclusion, m.8993T-->C MTATP6 should be considered in patients with unexplained ataxia, CMT or EA, but cases are uncommon."
The authors describe cases as uncommon in these selected referrals; no general population rarity threshold follows.
🔀

Differential Diagnoses

5

Conditions with similar clinical presentations that must be differentiated from Adult-Onset Ataxia and Polyneuropathy:

NARP syndrome MONDO:0010794
Overlapping Features NARP shares MT-ATP6 variants and overlapping neuropathy/ataxia, with pigmentary retinopathy as a distinguishing clinical feature. NARP is not confined to childhood, and mutant load alone does not separate it from this adult-ataxia presentation.
Distinguishing Features
  • Pigmentary retinopathy with neuropathy and ataxia
  • Overlapping age at onset and heteroplasmy; assess the whole phenotype
Show evidence (2 references)
PMID:16049925 SUPPORT Human Clinical
"The 8993T-->C mutation in mitochondrial DNA (mtDNA) has been described previously to be associated with infantile- or childhood-onset phenotypes, ranging from Leigh's syndrome to neurogenic weakness, ataxia, and retinitis pigmentosa syndrome."
The defining report explicitly contrasts this adult entity with the previously described childhood NARP and Leigh phenotypes of the same variant.
PMID:20953793 SUPPORT INDIRECT PRIMARY RESULT Human Clinical
"The age at time of first symptom ranged from ataxia at 13 months in subject D3 to visual impairment at 10, 12 and 34 years in D4, D1 and M1, respectively,"
The mother first had visual impairment at 34; NARP is not exclusively childhood-onset.
Leigh syndrome MONDO:0009723
Overlapping Features Leigh syndrome spectrum commonly presents in infancy with regression and characteristic bilateral brainstem/basal-ganglia lesions, but onset is not an absolute boundary. It overlaps genetically with adult MT-ATP6 ataxia.
Distinguishing Features
  • Onset typically between three and 12 months
  • Decompensation with elevated lactate
  • Bilateral symmetric basal ganglia and brainstem lesions
Show evidence (1 reference)
PMID:20301352 SUPPORT REVIEW SYNTHESIS Other
"Mitochondrial DNA-LSS is characterized by onset of manifestations typically between ages three and 12 months, often following an intercurrent illness (usually viral) or metabolic challenge (vaccinations, surgery, prolonged fasting)."
Typical infantile presentation provides differential context, not an absolute age exclusion.
Autosomal recessive and dominant spinocerebellar ataxias Not Yet Curated MONDO:0000437
Overlapping Features Nuclear hereditary spinocerebellar ataxias can closely resemble MT-ATP6 disease. Pedigree and molecular testing, including appropriate repeat-expansion tests, distinguish their causes.
Distinguishing Features
  • Molecular cause and transmission pattern
  • Normal routine mitochondrial studies do not exclude MT-ATP6 disease
Show evidence (1 reference)
PMID:22577227 SUPPORT Human Clinical
"The authors report two families with onset of ataxia in adulthood (with pyramidal dysfunction and/or peripheral neuropathy variably present), who are clinically indistinguishable from other spinocerebellar ataxia patients."
States the clinical indistinguishability that makes spinocerebellar ataxia the primary differential.
CANVAS / RFC1 spectrum disorder MONDO:0044720
Overlapping Features RFC1-related CANVAS is an important cause of late-onset ataxia with sensory neuronopathy, particularly when bilateral vestibular areflexia or chronic cough is present. It is a distinct recessive repeat-expansion disorder, not the MT-ATP6 disorder defined by OMIM 500010.
Distinguishing Features
  • Bilateral vestibular areflexia
  • Sensory neuronopathy (ganglionopathy) rather than length-dependent axonal polyneuropathy
  • Chronic cough often preceding ataxia by years
  • Autosomal recessive biallelic RFC1 repeat expansion, not maternal inheritance
Show evidence (1 reference)
PMID:30926972 SUPPORT Human Clinical
"We used non-parametric linkage analysis and genome sequencing to identify a biallelic intronic AAGGG repeat expansion in the replication factor C subunit 1 (RFC1) gene as the cause of familial CANVAS and a frequent cause of late-onset ataxia, particularly if sensory neuronopathy and bilateral..."
Primary identification of an important differential; the selected referral cohort does not establish comparative population prevalence.
Charcot-Marie-Tooth disease MONDO:0015626
Overlapping Features The axonal sensorimotor neuropathy can dominate the presentation and lead to referral as suspected hereditary motor and sensory neuropathy.
Distinguishing Features
  • Accompanying cerebellar ataxia
  • Maternal inheritance pattern
  • MT-ATP6 variant on mitochondrial DNA sequencing
Show evidence (1 reference)
PMID:18055910 SUPPORT Human Clinical
"In conclusion, m.8993T-->C MTATP6 should be considered in patients with unexplained ataxia, CMT or EA, but cases are uncommon."
Names suspected Charcot-Marie-Tooth disease as one of the clinical contexts in which this variant should be sought.
🧫

Experimental Models

3
Patient lymphocytes with m.8993T>C OTHER
Patient lymphocyte mitochondrial-function assays compared m.8993T>C with five m.8993T>G NARP patients at comparable mutant loads.
Cell source
Patient lymphocyte mitochondrial-function assays compared m.8993T>C with five m.8993T>G NARP patients at comparable mutant loads.
Publication
PMID:17568559
Pathograph links
Cellular ATP Depletion partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
Show evidence (1 reference)
PMID:17568559 SUPPORT PRIMARY RESULT In Vitro
"Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction."
Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
Reactive Oxygen Species Overproduction partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
Show evidence (1 reference)
PMID:17568559 SUPPORT PRIMARY RESULT In Vitro
"Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction."
Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
Show evidence (1 reference)
PMID:17568559 SUPPORT PRIMARY RESULT In Vitro
"Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction."
Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
Transmitochondrial m.9035T>C cybrids CELL_LINE
Transmitochondrial cybrids separated a causal m.9035T>C ATP6 variant from a co-occurring tRNA-Met polymorphism; ATP, ROS and survival under glucose deprivation or oxidant stress were assessed.
Cell source
Transmitochondrial cybrids separated a causal m.9035T>C ATP6 variant from a co-occurring tRNA-Met polymorphism; ATP, ROS and survival under glucose deprivation or oxidant stress were assessed.
Publication
PMID:19626676
Pathograph links
Impaired ATP Synthase Function partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
Show evidence (1 reference)
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
Cellular ATP Depletion partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
Show evidence (1 reference)
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
Reactive Oxygen Species Overproduction partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
Show evidence (1 reference)
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
Show evidence (2 references)
PMID:19626676 SUPPORT INDIRECT In Vitro
"They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS)."
Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
PMID:19626676 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Both of these outcomes were prevented by the antioxidants CoQ(10) and vitamin E, suggesting that the abnormally high levels of ROS were the triggers of cell death."
Cell-survival rescue under artificial stress conditions, not a human treatment result.
Patient primary fibroblasts with homoplasmic m.9035T>C PRIMARY_CELL_CULTURE
Cultured skin fibroblasts from a toddler and a 19-year-old with homoplasmic m.9035T>C underwent Seahorse respiratory testing, ATPase assays and native-gel analysis.
Cell source
Cultured skin fibroblasts from a toddler and a 19-year-old with homoplasmic m.9035T>C underwent Seahorse respiratory testing, ATPase assays and native-gel analysis.
Publication
PMID:35159298
Pathograph links
Impaired ATP Synthase Function partially recapitulates fidelity: low Assay-specific evidence for mitochondrial dysfunction.
Limitations: Two patient donors, mixed-age controls and assay-dependent abnormalities. Normal oligomycin-sensitive ATPase activity in both fibroblast preparations and P2 muscle contrasts with the earlier cybrid result. P2 had no significant JC1 membrane-potential or ATP6-expression decrease. Complex V subcomplexes do not settle assembly versus catalytic mechanisms; neuronal tissue and adult onset were not modeled.
Show evidence (1 reference)
PMID:35159298 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Bioenergetic measurements in fibroblasts from both patients detected reduced spare respiratory capacities and altered extracellular acidification rates, revealing a switch from mitochondrial respiration to glycolysis to uphold ATP production."
Primary fibroblast assays, with differing magnitude and normalization dependence across the two donors.
Notes
Two patient donors, mixed-age controls and assay-dependent abnormalities. Normal oligomycin-sensitive ATPase activity in both fibroblast preparations and P2 muscle contrasts with the earlier cybrid result. P2 had no significant JC1 membrane-potential or ATP6-expression decrease. Complex V subcomplexes do not settle assembly versus catalytic mechanisms; neuronal tissue and adult onset were not modeled.
Show evidence (2 references)
PMID:35159298 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"Bioenergetic measurements in fibroblasts from both patients detected reduced spare respiratory capacities and altered extracellular acidification rates, revealing a switch from mitochondrial respiration to glycolysis to uphold ATP production."
Primary fibroblast assays, with differing magnitude and normalization dependence across the two donors.
PMID:35159298 SUPPORT INDIRECT PRIMARY RESULT In Vitro
"In mitochondria isolated from skin fibroblasts of both patients no decrease in oligomycin sensitive ATPase activity could be discerned either (see Table 1)."
Negative result in primary m.9035T>C fibroblasts limits generalization of the earlier cybrid ATPase defect.
{ }

Source YAML

click to show 
name: Adult-Onset Ataxia and Polyneuropathy
creation_date: '2026-08-19T00:00:00Z'
description: Adult-onset ataxia and polyneuropathy (OMIM 500010) is a maternally inherited mitochondrial disorder anchored on a Finnish kindred with heteroplasmic MT-ATP6 m.8993T>C. Two of three examined adult siblings had slowly progressive overt ataxia and all three had axonal sensorimotor neuropathy; cerebellar and sensory dysfunction both contributed to the ataxia. Related m.9035T>C and m.9185T>C disorders can have similar adult presentations, with variable pyramidal signs. Adult onset can occur despite high mutant loads. Normal routine muscle histochemistry, respiratory-chain enzymology or MRI does not exclude an MT-ATP6 disorder. NARP and Leigh syndrome are overlapping presentations of the same broader mitochondrial spectrum, with different defining clinical patterns.
category: Mendelian
parents:
- hereditary disease
- mitochondrial disease
synonyms:
- Ataxia and polyneuropathy, adult-onset
- Adult-onset MT-ATP6 ataxia and axonal neuropathy
disease_term:
  preferred_term: adult-onset ataxia and polyneuropathy
  term:
    id: MONDO:0010781
    label: ataxia and polyneuropathy, adult-onset
inheritance:
- name: Maternal mitochondrial inheritance
  description: Maternal transmission of a mitochondrial MT-ATP6 variant, with variable heteroplasmy and expression. Adult onset is not explained simply by a low mutant load; related adult ataxia pedigrees had 90–99% heteroplasmy in leukocytes. Males do not transmit mtDNA variants; offspring of affected females are at risk, but inheritance does not guarantee clinical disease.
  inheritance_term:
    preferred_term: Mitochondrial inheritance
    term:
      id: HP:0001427
      label: Mitochondrial inheritance
  evidence:
  - reference: PMID:35159298
    reference_title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Pathogenic variants in MT-ATP6 are a well-known cause of maternally-inherited mitochondrial disorders
    explanation: Establishes maternal transmission as the inheritance mode for MT-ATP6 disorders, the gene carrying this entry's causal variants.
  - &id006
    reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: is transmitted by mitochondrial (maternal) inheritance.
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Maternal inheritance applies to this MT-ATP6 disorder, although the chapter is not an adult-ataxia-specific cohort.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
pathophysiology:
- name: MT-ATP6 m.8993T>C Variant
  role: trigger
  biological_scale: MOLECULAR
  description: The defining mitochondrial m.8993T>C missense variant substitutes proline for leucine at ATP6 residue 156. ATP6 encodes subunit a of ATP synthase. Related adult-ataxia variants m.9035T>C and m.9185T>C have distinct assay and clinical evidence; their results are qualified wherever used.
  genes:
  - preferred_term: MT-ATP6
    term:
      id: hgnc:7414
      label: MT-ATP6
  cellular_components:
  - preferred_term: proton-transporting ATP synthase complex
    term:
      id: GO:0045259
      label: proton-transporting ATP synthase complex
  genetic_context:
    gene:
      preferred_term: MT-ATP6
      term:
        id: hgnc:7414
        label: MT-ATP6
    allele_type: SNV
    variant_origin: GERMLINE
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: Heteroplasmic mitochondrial missense substitution (Leu156Pro) inherited through the maternal line.
  molecular_functions:
  - preferred_term: proton-transporting ATP synthase activity, rotational mechanism
    term:
      id: GO:0046933
      label: proton-transporting ATP synthase activity, rotational mechanism
    modifier: DECREASED
  evidence:
  - reference: PMID:16049925
    reference_title: Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation.
    explanation: This is the defining report for OMIM 500010 and directly ties the heteroplasmic m.8993T>C MT-ATP6 variant to the adult-onset ataxia-plus-polyneuropathy phenotype.
  - reference: PMID:17568559
    reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Two point mutations (T>G and T>C) at the same 8993 nucleotide of mitochondrial DNA (at comparable mutant load), affecting the ATPase 6 subunit of the F1F0-ATPase, result in neurological phenotypes of variable severity in humans.
    explanation: Locates the lesion in the ATPase 6 subunit of F1F0-ATP synthase and records that the two nucleotide-8993 substitutions differ in severity.
  downstream:
  - target: Impaired ATP Synthase Function
    description: The m.8993T>C ATP6 lesion is associated with bioenergetic dysfunction in patient lymphocytes.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17568559
      reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
      explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
      quote_role: PRIMARY_RESULT
- name: Heteroplasmy-Dependent Expression
  role: modulator
  biological_scale: CELLULAR
  description: Mutant load modifies clinical expression but is not a universal onset clock or a fixed threshold. The defining adult proband had 89% mutant mtDNA in blood; related adult-ataxia pedigrees had 90–99% in leukocytes. GeneReviews describes relatively little tissue- or age-dependent heteroplasmy variation for m.8993T>C/G, unlike some other mtDNA variants. Differences among tissues can nevertheless occur, and high load does not reliably predict an individual phenotype. Nuclear, haplogroup and copy-number modifiers remain candidate explanations rather than demonstrated determinants here.
  evidence:
  - &id007
    reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In our families, six patients had their genetic testing performed on leucocyte DNA, with heteroplasmy levels ranging from 90-99%.
    explanation: Related m.9185T>C and m.9035T>C families include high-load adult presentations; blood load is not a universal predictor of onset.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
  - reference: PMID:20953793
    reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy.
    explanation: In an m.8993T>C family, measured heteroplasmy did not account for the within-family phenotypic spread, supporting the modulator role and the limits of load as a predictor. Graded INDIRECT because the cohort was diagnosed as NARP syndrome (MONDO:0010794), an entity this entry keeps distinct; the observation carries across because the modulator claim is about m.8993T>C heteroplasmy behaviour rather than about either phenotype.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: they show very little tissue-dependent or age-dependent variation in
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: This statement specifically concerns m.8993T>G/C; it limits generic claims that blood load is unreliable for these variants.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
  downstream:
  - target: Impaired ATP Synthase Function
    description: Mutant load can modify the expression of mitochondrial dysfunction; individual tissue thresholds and downstream intermediates were not measured in the adult kindred.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20953793
      reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy.
      explanation: In an m.8993T>C family, measured heteroplasmy did not account for the within-family phenotypic spread, supporting the modulator role and the limits of load as a predictor. Graded INDIRECT because the cohort was diagnosed as NARP syndrome (MONDO:0010794), an entity this entry keeps distinct; the observation carries across because the modulator claim is about m.8993T>C heteroplasmy behaviour rather than about either phenotype.
- name: Impaired ATP Synthase Function
  role: amplifier
  biological_scale: MOLECULAR
  description: 'The m.8993T>C ATP6 substitution perturbs ATP-synthase-related bioenergetics. In related m.9035T>C cybrids, F0-ATPase dysfunction was measured. Complex V subcomplexes in m.9035T>C patient material suggest altered assembly or stability, but that interpretation is provisional: oligomycin-sensitive ATP hydrolysis was normal in the later primary-fibroblast and muscle study. The assays and cellular backgrounds differ.'
  molecular_functions:
  - preferred_term: proton-transporting ATP synthase activity, rotational mechanism
    modifier: DECREASED
    term:
      id: GO:0046933
      label: proton-transporting ATP synthase activity, rotational mechanism
  biological_processes:
  - preferred_term: proton motive force-driven ATP synthesis
    modifier: DECREASED
    term:
      id: GO:0015986
      label: proton motive force-driven ATP synthesis
  cellular_components:
  - preferred_term: proton-transporting ATP synthase complex
    term:
      id: GO:0045259
      label: proton-transporting ATP synthase complex
  evidence:
  - &id001
    reference: PMID:17568559
    reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
    explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
    quote_role: PRIMARY_RESULT
  - reference: PMID:19626676
    reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: IN_VITRO
    snippet: We confirmed that the 4452T>C transition in tRNA(Met) represented a polymorphism; however, 9035T>C conversion in the ATP6 gene was responsible for a defective F(0)-ATPase.
    explanation: Cybrid evidence that an ataxia-associated MT-ATP6 missense variant produces a defective F0-ATPase. Graded INDIRECT because this cybrid work used m.9035T>C, a different MT-ATP6 variant in the same adult-onset ataxia spectrum, not the m.8993T>C variant that defines this entry.
  - &id010
    reference: PMID:35159298
    reference_title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In mitochondria isolated from skin fibroblasts of both patients no decrease in oligomycin sensitive ATPase activity could be discerned either (see Table 1).
    explanation: Negative result in primary m.9035T>C fibroblasts limits generalization of the earlier cybrid ATPase defect.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
  downstream:
  - target: Cellular ATP Depletion
    description: Reduced energy availability is one measured consequence of the ATP6 lesion.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17568559
      reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
      explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
      quote_role: PRIMARY_RESULT
  - target: Reactive Oxygen Species Overproduction
    description: Increased ROS is a distinct measured consequence; these data do not resolve all biochemical intermediates.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17568559
      reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
      explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
      quote_role: PRIMARY_RESULT
- name: Cellular ATP Depletion
  role: central_effector
  biological_scale: CELLULAR
  description: Energy deprivation was measured in m.8993T>C patient lymphocytes. Related m.9035T>C cybrids had less than half the control steady-state ATP content. These are non-neuronal experimental results; neuronal ATP depletion in the adult syndrome has not been directly measured.
  chemical_entities:
  - preferred_term: ATP
    modifier: DECREASED
    term:
      id: CHEBI:15422
      label: ATP
  evidence:
  - *id001
  - &id002
    reference: PMID:19626676
    reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: IN_VITRO
    snippet: They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS).
    explanation: Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
  downstream:
  - target: Peripheral Axonal Dysfunction
    description: The connection between experimentally measured cellular stress and clinical axonal dysfunction is inferred; the adult neuronal intermediates are unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
  - target: Cerebellar Dysfunction
    description: Cellular mitochondrial stress is a proposed contributor to the cerebellar component; no cell-specific adult neuropathology establishes the intervening steps.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
- name: Reactive Oxygen Species Overproduction
  role: amplifier
  biological_scale: CELLULAR
  description: Patient lymphocytes carrying m.8993T>C showed increased ROS production, with a different balance between ROS and energy deprivation than m.8993T>G. Related m.9035T>C cybrids showed markedly increased ROS and stress-induced cell death. These experiments do not establish that ROS determines adult onset or prove neuronal injury in vivo.
  biological_processes:
  - preferred_term: reactive oxygen species metabolic process
    modifier: INCREASED
    term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
  - preferred_term: response to oxidative stress
    modifier: INCREASED
    term:
      id: GO:0006979
      label: response to oxidative stress
  chemical_entities:
  - preferred_term: reactive oxygen species
    modifier: INCREASED
    term:
      id: CHEBI:26523
      label: reactive oxygen species
  evidence:
  - reference: PMID:17568559
    reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: The 8993T>G change mainly induces an energy deficiency, whereas the 8993T>C favours an increased ROS production.
    explanation: Establishes the ROS-weighted balance of the bioenergetic lesion for the m.8993T>C variant that defines this entry.
  - *id002
  downstream:
  - target: Peripheral Axonal Dysfunction
    description: The connection between experimentally measured cellular stress and clinical axonal dysfunction is inferred; the adult neuronal intermediates are unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
  - target: Cerebellar Dysfunction
    description: Cellular mitochondrial stress is a proposed contributor to the cerebellar component; no cell-specific adult neuropathology establishes the intervening steps.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
- name: Peripheral Axonal Dysfunction
  role: effector
  biological_scale: TISSUE
  conforms_to: peripheral_axonal_degeneration#Length-Dependent Nerve Fiber Dysfunction
  description: Axonal sensorimotor polyneuropathy was demonstrated electrophysiologically in all three examined adults in the defining kindred, with sensory loss, absent ankle reflexes and weakness. Nerve histology did not establish a particular axonal transport defect. Length dependence is additionally described in a separate m.8993T>C NARP family.
  cell_types:
  - preferred_term: sensory neuron
    term:
      id: CL:0000101
      label: sensory neuron
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - &id003
    reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
    quote_role: PRIMARY_RESULT
  - reference: PMID:20953793
    reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: EMG-NCS revealed varying degrees of length-dependent sensorimotor axonal polyneuropathy.
    explanation: Electrophysiological demonstration of length-dependent axonal sensorimotor polyneuropathy in an m.8993T>C family. Graded INDIRECT because that family was diagnosed as NARP syndrome (MONDO:0010794), which this entry curates as a separate entity and a differential.
  downstream:
  - target: Peripheral Axonal Neuropathy
    description: Electrophysiological expression of peripheral axonal dysfunction.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
  - target: Sensorimotor Neuropathy
    description: Both motor and sensory fibers are affected.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Muscle histology and electrophysiological stud- ies confirmed axonal sensorimotor neuropathy.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct finding in adult patient III-5; the reproduced PDF retains a line-break hyphen.'
      quote_role: PRIMARY_RESULT
  - target: Absent Achilles Reflex
    description: Peripheral dysfunction accompanies absent ankle reflexes.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Neurological examination at age 36 years showed mild gait ataxia, absent ankle reflexes, positive Babinski signs, and pes cavus.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct examination of the adult proband.'
      quote_role: PRIMARY_RESULT
  - target: Reduced Lower-Limb Vibration Sensation
    description: Sensory dysfunction reduces vibration perception.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: On neurological examination, his gait was normal, but he had decreased vibration sensation in lower limbs and ankle re- flexes were absent.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3 before development of a wide-based gait.'
      quote_role: PRIMARY_RESULT
  - target: Muscle Weakness
    description: Motor neuropathy can contribute to weakness.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: There was mild muscle weakness and atrophy.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband observation; no broader distribution or frequency is inferred.'
      quote_role: PRIMARY_RESULT
  - target: Skeletal Muscle Atrophy
    description: Chronic motor dysfunction can contribute to muscle wasting.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: There was mild muscle weakness and atrophy.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband observation; no broader distribution or frequency is inferred.'
      quote_role: PRIMARY_RESULT
  - target: Gait Ataxia
    description: The authors identify a sensory component of gait ataxia.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
- name: Cerebellar Dysfunction
  role: effector
  biological_scale: TISSUE
  description: A cerebellar contribution to ataxia is clinically supported, with dysarthria and abnormal eye movements in affected adults. Cerebellar or vermian atrophy is present in some patients, but MRI can be normal in related adult MT-ATP6 ataxia. Specific Purkinje-cell loss is not established and is not used as a cell-type binding.
  evidence:
  - *id003
  downstream:
  - target: Progressive Cerebellar Ataxia
    description: The authors identify a cerebellar component of the progressive ataxia.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Three siblings were clinically examined. Two of them presented with an adult or late-onset slowly pro- gressive gait ataxia and dysarthria, and all three had peripheral axonal neuropathy. Ataxia was considered both cerebellar and sensory in origin.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Two of three examined adults had overt ataxia/dysarthria, while all three had peripheral axonal neuropathy; this selected family is not a population-frequency estimate.'
      quote_role: PRIMARY_RESULT
  - target: Gait Ataxia
    description: Cerebellar incoordination contributes to gait instability.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: At age 51 years, her gait was grossly ataxic and she used a walker.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband gait observation.'
      quote_role: PRIMARY_RESULT
  - target: Dysarthria
    description: Speech incoordination accompanies the cerebellar syndrome.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: She had mild limb ataxia and dysarthria.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband at age 51; dysarthria was also described in another adult sibling.'
      quote_role: PRIMARY_RESULT
  - target: Gaze-Evoked Nystagmus
    description: Abnormal ocular motor control accompanies the cerebellar presentation.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: She showed gaze-evoked nystagmus, but eye movements were unrestricted and fun- doscopy was normal.
      explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband; unrestricted eye movements and normal fundus prevent conflating this finding with ophthalmoplegia or retinitis pigmentosa.'
      quote_role: PRIMARY_RESULT
phenotypes:
- category: Neurological
  name: Progressive Cerebellar Ataxia
  description: Slowly progressive gait and limb ataxia with cerebellar and sensory contributions. Overt ataxia was present in two of the three examined adult siblings in the original kindred, not in every mutation carrier.
  phenotype_term:
    preferred_term: Progressive cerebellar ataxia
    term:
      id: HP:0002073
      label: Progressive cerebellar ataxia
    clinical_course: PROGRESSIVE
  diagnostic: true
  evidence:
  - *id003
- category: Neurological
  name: Gait Ataxia
  description: Gait ataxia can progress to a need for walking aids; observed progression varies among adults.
  phenotype_term:
    preferred_term: Gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: At age 51 years, her gait was grossly ataxic and she used a walker.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband gait observation.'
    quote_role: PRIMARY_RESULT
- category: Neurological
  name: Peripheral Axonal Neuropathy
  description: Axonal peripheral neuropathy was demonstrated in all three examined adults in the original family. This denominator does not establish obligate penetrance across the broader spectrum.
  phenotype_term:
    preferred_term: Peripheral axonal neuropathy
    term:
      id: HP:0003477
      label: Peripheral axonal neuropathy
  diagnostic: true
  evidence:
  - *id003
- category: Neurological
  name: Sensorimotor Neuropathy
  description: Both sensory and motor fibres are affected, producing distal sensory loss together with distal weakness.
  phenotype_term:
    preferred_term: Sensorimotor neuropathy
    term:
      id: HP:0007141
      label: Sensorimotor neuropathy
  evidence:
  - &id008
    reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Muscle histology and electrophysiological stud- ies confirmed axonal sensorimotor neuropathy.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct finding in adult patient III-5; the reproduced PDF retains a line-break hyphen.'
    quote_role: PRIMARY_RESULT
- category: Neuroimaging
  name: Cerebellar Atrophy
  description: Mild cerebellar vermis atrophy was described in an adult of the defining family; atrophy is not required for diagnosis.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - &id009
    reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Brain MRI showed slight periventricular white matter abnormali- ties and mild atrophy in cerebellar vermis.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3; the PDF retains the line-break hyphen. Mild vermian atrophy coexisted with absence of overt ataxia at examination.'
    quote_role: PRIMARY_RESULT
- category: Neurological
  name: Babinski Sign
  description: Extensor plantar responses occurred in the original adult proband; related MT-ATP6 ataxia can also include variable pyramidal signs.
  phenotype_term:
    preferred_term: Babinski sign
    term:
      id: HP:0003487
      label: Babinski sign
  evidence:
  - &id004
    reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Neurological examination at age 36 years showed mild gait ataxia, absent ankle reflexes, positive Babinski signs, and pes cavus.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct examination of the adult proband.'
    quote_role: PRIMARY_RESULT
- category: Neurological
  name: Episodic Ataxia
  description: A phenotypic extension observed in one m.8993T>C carrier, who had discrete attacks of ataxia rather than (or in addition to) steady progression.
  phenotype_term:
    preferred_term: Episodic ataxia
    term:
      id: HP:0002131
      label: Episodic ataxia
  evidence:
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: One subject had episodic ataxia (EA) and transient hemipareses, broadening the phenotype.
    explanation: Episodic ataxia was reported in one member of a second m.8993T>C family; a single report cannot establish a frequency band.
- category: Neurological
  name: Transient Hemiparesis
  description: Transient hemipareses were reported in the individual with episodic ataxia; the episodes began in childhood and are not an established general adult-onset feature. Alternative episodic-disorder genes were not completely excluded.
  phenotype_term:
    preferred_term: Hemiparesis
    term:
      id: HP:0001269
      label: Hemiparesis
    temporality: TRANSIENT
  evidence:
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: One subject had episodic ataxia (EA) and transient hemipareses, broadening the phenotype.
    explanation: Same reported episodic presentation, without an inference about population frequency or exclusive MT-ATP6 causation.
- category: Neurological
  name: Ophthalmoplegia
  description: Ophthalmoplegia has occurred in related m.9035T>C ataxia, including adolescent/young-adult presentations; it is not established as a frequent feature of the defining m.8993T>C adult kindred.
  phenotype_term:
    preferred_term: Ophthalmoplegia
    term:
      id: HP:0000602
      label: Ophthalmoplegia
  evidence:
  - reference: PMID:35159298
    reference_title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: Patient 2 presented in adolescence with ataxia and ophthalmoplegia without cognitive or motor impairment.
    explanation: Related m.9035T>C clinical presentation, not a frequency estimate for m.8993T>C adult-onset ataxia.
- name: Dysarthria
  category: Neurological
  description: Dysarthria accompanies the cerebellar presentation in some affected adults.
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She had mild limb ataxia and dysarthria.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband at age 51; dysarthria was also described in another adult sibling.'
    quote_role: PRIMARY_RESULT
- name: Gaze-Evoked Nystagmus
  category: Neurological
  description: Gaze-evoked nystagmus was observed in the adult proband.
  phenotype_term:
    preferred_term: Gaze-evoked nystagmus
    term:
      id: HP:0000640
      label: Gaze-evoked nystagmus
  evidence:
  - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She showed gaze-evoked nystagmus, but eye movements were unrestricted and fun- doscopy was normal.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult proband; unrestricted eye movements and normal fundus prevent conflating this finding with ophthalmoplegia or retinitis pigmentosa.'
    quote_role: PRIMARY_RESULT
- name: Absent Achilles Reflex
  category: Neurological
  description: Absent ankle reflexes were present in examined adults with neuropathy.
  phenotype_term:
    preferred_term: Absent Achilles reflex
    term:
      id: HP:0003438
      label: Absent Achilles reflex
  evidence:
  - *id004
- name: Reduced Lower-Limb Vibration Sensation
  category: Neurological
  description: Reduced vibration sense is part of the sensory neuropathy.
  phenotype_term:
    preferred_term: Impaired vibration sensation in the lower limbs
    term:
      id: HP:0002166
      label: Impaired vibration sensation in the lower limbs
  evidence:
  - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: On neurological examination, his gait was normal, but he had decreased vibration sensation in lower limbs and ankle re- flexes were absent.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Adult patient III-3 before development of a wide-based gait.'
    quote_role: PRIMARY_RESULT
- name: Pes Cavus
  category: Musculoskeletal
  description: High-arched feet were documented in the adult proband.
  phenotype_term:
    preferred_term: Pes cavus
    term:
      id: HP:0001761
      label: Pes cavus
  evidence:
  - *id004
- name: Muscle Weakness
  category: Neurological
  description: Mild muscle weakness, with distal leg weakness in another adult sibling.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - &id005
    reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There was mild muscle weakness and atrophy.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: Direct adult-proband observation; no broader distribution or frequency is inferred.'
    quote_role: PRIMARY_RESULT
- name: Skeletal Muscle Atrophy
  category: Musculoskeletal
  description: Mild muscle atrophy was described in the adult proband.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - *id005
- name: Atonic Seizure
  category: Neurological
  description: Clinically described atonic seizures/drop attacks occurred in the proband; electrographic confirmation was absent and no cohort frequency is assigned.
  phenotype_term:
    preferred_term: Atonic seizure
    term:
      id: HP:0010819
      label: Atonic seizure
  evidence:
  - reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    reference_title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She had repeated atonic seizures or drop attacks despite anticonvulsive medication.
    explanation: 'Rantamäki et al. 2005 original article reprinted in the author thesis, pp. 337–340: The proband had clinically described drop attacks despite treatment; the reported EEG was normal. Another adult sibling had only probable astatic attacks.'
    quote_role: PRIMARY_RESULT
biochemical:
- name: Cytochrome c oxidase muscle histochemistry
  notes: 'Unlike most adult mitochondrial disease, COX histochemistry on muscle is typically normal in MT-ATP6 disorders. This normal result is diagnostically important: it is the reason these patients are missed by the standard adult mitochondrial workup.'
  presence: Normal
  evidence:
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Cytochrome c oxidase muscle histochemistry, which is the standard clinical investigation for mitochondrial disease in adults, is usually normal in patients with MTATP6 mutations.
    explanation: States directly that the standard adult mitochondrial screening test is normal in MT-ATP6 disease.
- name: Respiratory chain enzyme activities
  notes: Routine respiratory-chain enzymology and muscle histology can be normal or nonspecific. The 2012 series measured complexes I–IV in two patients and had three nonspecific/normal biopsies; it did not demonstrate normal ATP synthesis. In the later m.9035T>C study, oligomycin-sensitive ATP hydrolysis was normal despite other evidence of mitochondrial dysfunction. Assay direction and preparation matter.
  presence: Normal
  evidence:
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Other investigations including muscle biopsy and respiratory chain enzyme activity were non-specific or normal.
    explanation: Directly reports normal or non-specific respiratory-chain enzymology in adult-onset MT-ATP6 ataxia families.
genetic:
- name: MT-ATP6
  gene_term:
    preferred_term: MT-ATP6
    term:
      id: hgnc:7414
      label: MT-ATP6
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  association: Heteroplasmic m.8993T>C (Leu156Pro) defines the original OMIM 500010 family. Related m.9035T>C (Leu170Pro) and m.9185T>C (Leu220Pro) can cause similar adult ataxia. High heteroplasmy and even homoplasmy do not uniquely determine age at onset. Protein substitutions in the discussion of the 2012 paper are swapped; the assignments here follow the 2022 primary paper and GeneReviews.
  inheritance:
  - name: Mitochondrial inheritance
    inheritance_term:
      preferred_term: Mitochondrial inheritance
      term:
        id: HP:0001427
        label: Mitochondrial inheritance
    description: Maternal transmission of a heteroplasmic mtDNA variant; mutant load segregates through the germline bottleneck, so sibs and offspring inherit varying loads and clinical expression is incompletely predictable.
    evidence:
    - reference: PMID:20301352
      reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: OTHER
      snippet: Sibs may inherit the pathogenic variant at varying heteroplasmy levels due to the bottleneck effect and variant-specific segregation patterns.
      explanation: GeneReviews statement of maternal transmission with bottleneck-driven heteroplasmy variation. Graded INDIRECT because the chapter covers mtDNA-Leigh syndrome spectrum generally rather than this adult-onset entity.
      quote_role: REVIEW_SYNTHESIS
    - reference: PMID:18055910
      reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We identified a three-generation family with the m.8993T-->C mutation of mtDNA.
      explanation: A three-generation pedigree carrying the variant is direct evidence of vertical (maternal) transmission of m.8993T>C.
    - *id006
  evidence:
  - reference: PMID:16049925
    reference_title: Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation.
    explanation: Establishes MT-ATP6 m.8993T>C as the causal variant for this entity.
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: These families had the m.9185T>C and m.9035T>C mutations, respectively, which have not previously been associated with adult-onset cerebellar syndromes.
    explanation: Extends the causal gene beyond m.8993T>C to other MT-ATP6 missense variants producing adult-onset cerebellar syndromes.
  - *id007
diagnosis:
- name: Mitochondrial DNA sequencing
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: Molecular testing of MT-ATP6, through targeted sequencing or an appropriate comprehensive mitochondrial/genomic approach, should be considered in unexplained adult ataxia with neuropathy despite normal muscle investigations. Quantify heteroplasmy and interpret the pathogenic variant together with the phenotype. Leukocyte DNA was informative in the published adult MT-ATP6 families; tissue selection and assay sensitivity should be individualized, without importing the low-blood-load behavior of unrelated mtDNA variants.
  results: A pathogenic MT-ATP6 variant with a compatible phenotype establishes the molecular diagnosis; related variants may be heteroplasmic or homoplasmic. The molecular finding alone does not define the adult clinical subtype.
  evidence:
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: MTATP6 sequencing should be considered in the workup of undiagnosed ataxia, even if other investigations do not suggest a mitochondrial DNA disorder.
    explanation: Direct recommendation that MT-ATP6 sequencing be part of the undiagnosed adult ataxia workup regardless of other test results.
  - reference: PMID:20953793
    reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: The degree of mutant heteroplasmy for the m.8993T>C mutation was evaluated by real-time allele refractory mutation system quantitative PCR of mtDNA from hair bulbs (ectoderm) and blood leukocytes (mesoderm).
    explanation: Illustrates the multi-tissue heteroplasmy quantification this diagnostic step calls for. Graded INDIRECT because the study quantified heteroplasmy in an m.8993T>C family diagnosed as NARP syndrome (MONDO:0010794); the method transfers, the cohort is a different entity.
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Therefore, unlike many mtDNA disorders, MTATP6 sequencing can be reliably performed on leucocyte DNA, and should be considered as a diagnostic test in the workup of ataxia and neuropathy, even when the routine clinical investigations for mitochondrial disease are normal.
    explanation: Direct diagnostic conclusion from the related adult pedigrees; not a guarantee that every assay or every mitochondrial variant is detectable in blood.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Genome sequencing is preferred (if available), as it allows analysis of the mitochondrial and nuclear genome, and typically has the highest diagnostic rate.
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Shared diagnostic approach from the Leigh-spectrum chapter; this is not a measured diagnostic yield for the adult entity.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
- name: Nerve conduction studies and electromyography
  diagnosis_term:
    preferred_term: nerve conduction velocity test
    term:
      id: NCIT:C88502
      label: Nerve Conduction Velocity Test
  description: Electrophysiology establishes the axonal sensorimotor character of the neuropathy and helps distinguish demyelinating disorders. Severity and timing vary.
  results: Length-dependent sensorimotor axonal polyneuropathy of variable severity.
  evidence:
  - *id008
  - *id003
- name: Brain magnetic resonance imaging
  diagnosis_term:
    preferred_term: magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  description: MRI assesses cerebellar volume and other structural abnormalities, but normal imaging does not exclude MT-ATP6 ataxia. MRI alone does not establish a mitochondrial cause or specific neuronal cell loss.
  results: Variable cerebellar or vermian atrophy; normal MRI was present in three of five imaged patients in the related 2012 adult-ataxia series.
  evidence:
  - *id009
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Brain MRI was normal in 3/5 patients, and one patient each had cerebellar atrophy, or cerebellar and cerebral volume loss.
    explanation: Full-text results, five imaged patients from related MT-ATP6 ataxia families.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
differential_diagnoses:
- name: NARP syndrome
  disease_term:
    preferred_term: NARP syndrome
    term:
      id: MONDO:0010794
      label: NARP syndrome
  description: NARP shares MT-ATP6 variants and overlapping neuropathy/ataxia, with pigmentary retinopathy as a distinguishing clinical feature. NARP is not confined to childhood, and mutant load alone does not separate it from this adult-ataxia presentation.
  distinguishing_features:
  - Pigmentary retinopathy with neuropathy and ataxia
  - Overlapping age at onset and heteroplasmy; assess the whole phenotype
  evidence:
  - reference: PMID:16049925
    reference_title: Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The 8993T-->C mutation in mitochondrial DNA (mtDNA) has been described previously to be associated with infantile- or childhood-onset phenotypes, ranging from Leigh's syndrome to neurogenic weakness, ataxia, and retinitis pigmentosa syndrome.
    explanation: The defining report explicitly contrasts this adult entity with the previously described childhood NARP and Leigh phenotypes of the same variant.
  - reference: PMID:20953793
    reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The age at time of first symptom ranged from ataxia at 13 months in subject D3 to visual impairment at 10, 12 and 34 years in D4, D1 and M1, respectively,
    explanation: The mother first had visual impairment at 34; NARP is not exclusively childhood-onset.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
- name: Leigh syndrome
  disease_term:
    preferred_term: Leigh syndrome
    term:
      id: MONDO:0009723
      label: Leigh syndrome
  description: Leigh syndrome spectrum commonly presents in infancy with regression and characteristic bilateral brainstem/basal-ganglia lesions, but onset is not an absolute boundary. It overlaps genetically with adult MT-ATP6 ataxia.
  distinguishing_features:
  - Onset typically between three and 12 months
  - Decompensation with elevated lactate
  - Bilateral symmetric basal ganglia and brainstem lesions
  evidence:
  - reference: PMID:20301352
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Mitochondrial DNA-LSS is characterized by onset of manifestations typically between ages three and 12 months, often following an intercurrent illness (usually viral) or metabolic challenge (vaccinations, surgery, prolonged fasting).
    explanation: Typical infantile presentation provides differential context, not an absolute age exclusion.
    quote_role: REVIEW_SYNTHESIS
- name: Autosomal recessive and dominant spinocerebellar ataxias
  disease_term:
    preferred_term: cerebellar ataxia
    term:
      id: MONDO:0000437
      label: cerebellar ataxia
  description: Nuclear hereditary spinocerebellar ataxias can closely resemble MT-ATP6 disease. Pedigree and molecular testing, including appropriate repeat-expansion tests, distinguish their causes.
  distinguishing_features:
  - Molecular cause and transmission pattern
  - Normal routine mitochondrial studies do not exclude MT-ATP6 disease
  evidence:
  - reference: PMID:22577227
    reference_title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The authors report two families with onset of ataxia in adulthood (with pyramidal dysfunction and/or peripheral neuropathy variably present), who are clinically indistinguishable from other spinocerebellar ataxia patients.
    explanation: States the clinical indistinguishability that makes spinocerebellar ataxia the primary differential.
- name: CANVAS / RFC1 spectrum disorder
  disease_term:
    preferred_term: cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome
    term:
      id: MONDO:0044720
      label: cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome
  description: RFC1-related CANVAS is an important cause of late-onset ataxia with sensory neuronopathy, particularly when bilateral vestibular areflexia or chronic cough is present. It is a distinct recessive repeat-expansion disorder, not the MT-ATP6 disorder defined by OMIM 500010.
  distinguishing_features:
  - Bilateral vestibular areflexia
  - Sensory neuronopathy (ganglionopathy) rather than length-dependent axonal polyneuropathy
  - Chronic cough often preceding ataxia by years
  - Autosomal recessive biallelic RFC1 repeat expansion, not maternal inheritance
  evidence:
  - reference: PMID:30926972
    reference_title: Biallelic expansion of an intronic repeat in RFC1 is a common cause of late-onset ataxia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We used non-parametric linkage analysis and genome sequencing to identify a biallelic intronic AAGGG repeat expansion in the replication factor C subunit 1 (RFC1) gene as the cause of familial CANVAS and a frequent cause of late-onset ataxia, particularly if sensory neuronopathy and bilateral vestibular areflexia coexist.
    explanation: Primary identification of an important differential; the selected referral cohort does not establish comparative population prevalence.
- name: Charcot-Marie-Tooth disease
  disease_term:
    preferred_term: Charcot-Marie-Tooth disease
    term:
      id: MONDO:0015626
      label: Charcot-Marie-Tooth disease
  description: The axonal sensorimotor neuropathy can dominate the presentation and lead to referral as suspected hereditary motor and sensory neuropathy.
  distinguishing_features:
  - Accompanying cerebellar ataxia
  - Maternal inheritance pattern
  - MT-ATP6 variant on mitochondrial DNA sequencing
  evidence:
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In conclusion, m.8993T-->C MTATP6 should be considered in patients with unexplained ataxia, CMT or EA, but cases are uncommon.
    explanation: Names suspected Charcot-Marie-Tooth disease as one of the clinical contexts in which this variant should be sought.
treatments:
- name: Supportive and Symptomatic Management
  description: Care is supportive and symptom-directed, with regular neurological assessment and individualized evaluation of visual and other mitochondrial-system manifestations. The reviewed sources do not establish a disease-modifying treatment for this adult entity.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  target_phenotypes:
  - preferred_term: Progressive cerebellar ataxia
    term:
      id: HP:0002073
      label: Progressive cerebellar ataxia
  evidence:
  - reference: PMID:20301352
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: 'MANAGEMENT: Treatment of manifestations: Treatment is supportive.'
    explanation: GeneReviews states that management of mtDNA disease is supportive. Graded INDIRECT because the chapter addresses the Leigh syndrome spectrum rather than this adult-onset entity specifically.
    quote_role: REVIEW_SYNTHESIS
- name: Physical and Occupational Therapy
  description: Individualized physical and occupational therapy, fall prevention and mobility aids address ataxia and weakness. Shared mitochondrial-care guidance is extrapolated to this adult presentation.
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  therapeutic_modality: BEHAVIORAL
  target_phenotypes:
  - preferred_term: Gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: PMID:20301352
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: physical therapy and occupational therapy; standard treatment of eye movement disorders
    explanation: GeneReviews lists physical and occupational therapy in the supportive management of mtDNA disease. Graded INDIRECT because the recommendation is made for the Leigh syndrome spectrum rather than this entity.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: maintain independent mobility as appropriate
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Ataxia/myopathy management supports individualized rehabilitation and mobility aids; no adult MT-ATP6-specific efficacy trial is implied.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
- name: Avoidance of Mitochondrial Toxins
  description: Medication and anesthesia review should account for mitochondrial disease. The Leigh-spectrum chapter cautions about valproate, acidosis-provoking medication and anesthesia. Its dichloroacetate warning derives from neuropathy worsening in a MELAS trial, not a trial in adult MT-ATP6 ataxia; specialist assessment is required.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  evidence:
  - reference: PMID:20301352
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: Sodium valproate, medications that cause acidosis, and dichloroacetate should be avoided or used with caution; administration of anesthesia requires careful consideration to avoid aggravation of respiratory symptoms and precipitation of respiratory failure.
    explanation: GeneReviews Agents/Circumstances to Avoid for mtDNA disease. Graded INDIRECT because it is stated for the Leigh syndrome spectrum; the pharmacologic hazard is shared by MT-ATP6 disease but has not been studied in this adult-onset entity.
    quote_role: REVIEW_SYNTHESIS
- name: Genetic Counseling and Reproductive Options
  description: Counseling explains maternal transmission, variable expression and the limits of heteroplasmy-based prediction. All offspring of a female carrier are at risk of inheriting the variant, not necessarily of being affected. Specialist reproductive assessment may include prenatal testing or oocyte donation; preimplantation testing is unsuitable for homoplasmic or near-homoplasmic loads.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: OTHER
  evidence:
  - reference: PMID:20301352
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: Reproductive options for the family members of a proband with an mtDNA pathogenic variant may include prenatal testing, preimplantation genetic testing, and oocyte donation.
    explanation: GeneReviews enumerates the reproductive options relevant to any maternally inherited mtDNA variant. Graded INDIRECT because the chapter addresses the Leigh syndrome spectrum.
    quote_role: REVIEW_SYNTHESIS
  - *id006
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: are at risk of inheriting the pathogenic variant.
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Inheritance risk is not equivalent to certainty of clinical disease.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: However, PGT may not be successful for women at moderate risk and is not recommended for females containing
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: The sentence continues with homoplasmic or near-homoplasmic loads; the snippet stops at the HTML glossary link. This is specialist reproductive counseling, not an adult-ataxia intervention trial.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
- name: Neurological and Visual Surveillance
  description: Follow the course of ataxia, neuropathy and vision, with other organ investigations guided by clinical findings. Leigh-spectrum surveillance provides context; its infantile disease frequencies and fixed multisystem schedule are not assumed for adults.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  therapeutic_modality: OTHER
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
    reference_title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: To assess for reduced vision, abnormal ocular movement, strabismus,
    explanation: 'GeneReviews mtDNA-associated Leigh syndrome spectrum chapter: Supports clinical eye assessment in shared mitochondrial care.'
    quote_role: REVIEW_SYNTHESIS
    directness: INDIRECT
prevalence:
- population: Adults with unexplained ataxia or suspected Charcot-Marie-Tooth disease (United Kingdom referral cohorts)
  measure_type: CASES_IN_LITERATURE
  notes: A selected UK referral study screened 308 unexplained-ataxia patients, 96 suspected CMT patients and 191 episodic-ataxia patients, identifying one m.8993T>C family. This is a study-specific case-finding result, not population prevalence or a quantitative rarity band.
  evidence:
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We therefore studied 308 patients with unexplained ataxia and 96 patients with suspected Charcot-Marie-Tooth disease to determine whether the m.8993T-->C MTATP6 mutation is common in unexplained inherited ataxia and/or polyneuropathy.
    explanation: Defines the screened cohorts from which the rarity estimate is drawn.
  - reference: PMID:18055910
    reference_title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In conclusion, m.8993T-->C MTATP6 should be considered in patients with unexplained ataxia, CMT or EA, but cases are uncommon.
    explanation: The authors describe cases as uncommon in these selected referrals; no general population rarity threshold follows.
discussions:
- discussion_id: purkinje_neuropathology_unproven
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: Which cerebellar cell population is lost in adult-onset MT-ATP6 ataxia, and is the Purkinje neuron the primary target as it is in most hereditary ataxias?
  attaches_to:
  - pathophysiology#Cerebellar Dysfunction
  rationale: The reviewed adult clinical reports establish cerebellar signs and variable MRI atrophy but not specific Purkinje-cell loss. The original family included a deceased childhood-onset sibling with nonspecific brain gliosis at autopsy and no documented molecular assay; that historical case does not establish adult cell-specific neuropathology.
  evidence:
  - *id009
  proposed_experiments:
  - experiment_id: cerebellar_neuropathology_mtatp6
    name: Post-mortem cerebellar neuropathology in genetically confirmed adult-onset MT-ATP6 ataxia
    description: Quantitative stereology of Purkinje, granule and dentate neurons with per-cell heteroplasmy measurement, compared against age-matched controls and against NARP/Leigh cerebellum.
- discussion_id: heteroplasmy_does_not_explain_onset
  kind: OPEN_QUESTION
  status: OPEN
  prompt: Why do some MT-ATP6 pedigrees with very high mutant load present in infancy with Leigh syndrome while others present only in adulthood with ataxia and neuropathy?
  attaches_to:
  - pathophysiology#Heteroplasmy-Dependent Expression
  rationale: 'Mutant load is necessary but demonstrably not sufficient to predict age of onset or severity: patients with childhood-onset and adult-onset MT-ATP6 ataxia have both been reported at 90-100% heteroplasmy, and within a single m.8993T>C family, phenotype differed markedly between members with comparably high ectodermal and mesodermal loads. Candidate modifiers include mtDNA haplogroup, nuclear background, mtDNA copy number, and differences in antioxidant scavenging capacity, none of which has been tested for this entity.'
  evidence:
  - reference: PMID:20953793
    reference_title: Heterogeneous patterns of tissue injury in NARP syndrome.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy.
    explanation: Demonstrates that measured heteroplasmy fails to explain within-family phenotypic variation in an m.8993T>C kindred. Graded INDIRECT because that kindred was diagnosed as NARP syndrome (MONDO:0010794); the open question about load-versus-onset is nonetheless shared across the MT-ATP6 spectrum.
  - *id007
- discussion_id: antioxidant_rescue_in_cybrids_only
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: Does the rescue of MT-ATP6 mutant cell death by CoQ10 and vitamin E in transmitochondrial cybrids translate into any clinical benefit in adult-onset MT-ATP6 ataxia?
  attaches_to:
  - pathophysiology#Reactive Oxygen Species Overproduction
  rationale: Related m.9035T>C cybrids showed antioxidant prevention of stress-induced cell death. The immortalized background, different variant and acute artificial stressors limit translation to the adult m.8993T>C syndrome. The sources reviewed and direct registry queries on 2026-09-21 did not identify an adult MT-ATP6 ataxia-specific interventional trial.
  evidence:
  - reference: PMID:19626676
    reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Both of these outcomes were prevented by the antioxidants CoQ(10) and vitamin E, suggesting that the abnormally high levels of ROS were the triggers of cell death.
    explanation: The cybrid rescue result whose translational validity this discussion questions.
    directness: INDIRECT
notes: 'Scope: anchored on OMIM 500010/MONDO:0010781 and the original m.8993T>C adult kindred. Related m.9035T>C/m.9185T>C ataxia and NARP/Leigh observations are qualified as indirect evidence. NARP is not restricted to childhood and is not separable by a universal heteroplasmy threshold. The original paper is available as a reprint in the author thesis; its four-page published article, rather than the entire thesis, supplied the URL evidence. The generated cache title is retained.

  GeneReviews NBK1173 is a shared Leigh-spectrum chapter. Clinical overlap, diagnostic methods, supportive care and maternal counseling were reviewed and used with explicit scope limits; infantile phenotype frequencies and treatment-trial claims were not transferred.

  The existing falcon deep-research report fails the disease-identity preflight: its body addresses RFC1/CANVAS (MONDO:0044720), not the MT-ATP6 disorder. Its mechanisms and therapeutic claims were excluded. CANVAS remains an independently sourced differential.

  The MONDO parent placement reported by the earlier curation requires separate ontology review; the descriptive parents here follow the established mitochondrial mechanism. No ontology-hierarchy change is part of this review.'
references:
- reference: PMID:20953793
  title: Heterogeneous patterns of tissue injury in NARP syndrome.
- reference: PMID:17568559
  title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
- reference: PMID:16049925
  title: Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.
- reference: PMID:22577227
  title: Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
- reference: PMID:19626676
  title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
  title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
  tags:
  - GeneReviews
- reference: PMID:18055910
  title: Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
- reference: PMID:35159298
  title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
- reference: PMID:30926972
  title: Biallelic expansion of an intronic repeat in RFC1 is a common cause of late-onset ataxia.
- reference: PMID:20301352
  title: Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
  tags:
  - GeneReviews
- reference: url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
  title: https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
experimental_models:
- name: Patient lymphocytes with m.8993T>C
  experimental_model_type: OTHER
  publication: PMID:17568559
  description: Patient lymphocyte mitochondrial-function assays compared m.8993T>C with five m.8993T>G NARP patients at comparable mutant loads.
  cell_source: Patient lymphocyte mitochondrial-function assays compared m.8993T>C with five m.8993T>G NARP patients at comparable mutant loads.
  modeled_mechanisms:
  - target: Cellular ATP Depletion
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
    evidence:
    - reference: PMID:17568559
      reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
      explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
      quote_role: PRIMARY_RESULT
  - target: Reactive Oxygen Species Overproduction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
    evidence:
    - reference: PMID:17568559
      reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
      explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
      quote_role: PRIMARY_RESULT
  evidence:
  - reference: PMID:17568559
    reference_title: Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Both 8993T>G and 8993T>C mutations led to energy deprivation and ROS overproduction.
    explanation: Measurements in patient lymphocytes, not neurons; the abstract reports both ATP-related energy deprivation and increased ROS.
    quote_role: PRIMARY_RESULT
  notes: Abstract-only assay report available; non-neuronal material, not proof of the neuronal mechanism or the cause of adult onset.
- name: Transmitochondrial m.9035T>C cybrids
  experimental_model_type: CELL_LINE
  publication: PMID:19626676
  description: Transmitochondrial cybrids separated a causal m.9035T>C ATP6 variant from a co-occurring tRNA-Met polymorphism; ATP, ROS and survival under glucose deprivation or oxidant stress were assessed.
  cell_source: Transmitochondrial cybrids separated a causal m.9035T>C ATP6 variant from a co-occurring tRNA-Met polymorphism; ATP, ROS and survival under glucose deprivation or oxidant stress were assessed.
  modeled_mechanisms:
  - target: Impaired ATP Synthase Function
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
    evidence:
    - reference: PMID:19626676
      reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: IN_VITRO
      snippet: They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS).
      explanation: Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
  - target: Cellular ATP Depletion
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
    evidence:
    - reference: PMID:19626676
      reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: IN_VITRO
      snippet: They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS).
      explanation: Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
  - target: Reactive Oxygen Species Overproduction
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
    evidence:
    - reference: PMID:19626676
      reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: IN_VITRO
      snippet: They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS).
      explanation: Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
  evidence:
  - reference: PMID:19626676
    reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: IN_VITRO
    snippet: They had less than half of the steady-state content of ATP and nearly an 8-fold higher basal level of reactive oxygen species (ROS).
    explanation: Quantifies the combined ATP shortfall and ROS burden in cybrids carrying an MT-ATP6 ataxia variant. Graded INDIRECT because the cybrids carried m.9035T>C.
  - reference: PMID:19626676
    reference_title: Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Both of these outcomes were prevented by the antioxidants CoQ(10) and vitamin E, suggesting that the abnormally high levels of ROS were the triggers of cell death.
    explanation: Cell-survival rescue under artificial stress conditions, not a human treatment result.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
  notes: Different ATP6 variant and immortalized cellular background. CoQ10/vitamin E prevention of stress-induced death is an in-vitro result, not clinical treatment efficacy. Full source remained unavailable beyond the complete abstract.
- name: Patient primary fibroblasts with homoplasmic m.9035T>C
  experimental_model_type: PRIMARY_CELL_CULTURE
  publication: PMID:35159298
  description: Cultured skin fibroblasts from a toddler and a 19-year-old with homoplasmic m.9035T>C underwent Seahorse respiratory testing, ATPase assays and native-gel analysis.
  cell_source: Cultured skin fibroblasts from a toddler and a 19-year-old with homoplasmic m.9035T>C underwent Seahorse respiratory testing, ATPase assays and native-gel analysis.
  modeled_mechanisms:
  - target: Impaired ATP Synthase Function
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: Assay-specific evidence for mitochondrial dysfunction.
    limitations: Two patient donors, mixed-age controls and assay-dependent abnormalities. Normal oligomycin-sensitive ATPase activity in both fibroblast preparations and P2 muscle contrasts with the earlier cybrid result. P2 had no significant JC1 membrane-potential or ATP6-expression decrease. Complex V subcomplexes do not settle assembly versus catalytic mechanisms; neuronal tissue and adult onset were not modeled.
    evidence:
    - reference: PMID:35159298
      reference_title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Bioenergetic measurements in fibroblasts from both patients detected reduced spare respiratory capacities and altered extracellular acidification rates, revealing a switch from mitochondrial respiration to glycolysis to uphold ATP production.
      explanation: Primary fibroblast assays, with differing magnitude and normalization dependence across the two donors.
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
  evidence:
  - reference: PMID:35159298
    reference_title: 'Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Bioenergetic measurements in fibroblasts from both patients detected reduced spare respiratory capacities and altered extracellular acidification rates, revealing a switch from mitochondrial respiration to glycolysis to uphold ATP production.
    explanation: Primary fibroblast assays, with differing magnitude and normalization dependence across the two donors.
    quote_role: PRIMARY_RESULT
    directness: INDIRECT
  - *id010
  notes: Two patient donors, mixed-age controls and assay-dependent abnormalities. Normal oligomycin-sensitive ATPase activity in both fibroblast preparations and P2 muscle contrasts with the earlier cybrid result. P2 had no significant JC1 membrane-potential or ATP6-expression decrease. Complex V subcomplexes do not settle assembly versus catalytic mechanisms; neuronal tissue and adult onset were not modeled.
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
  icimd_category:
  - classification_value: mtdna_encoded_respiratory_chain_proteins
    notes: 'ICIMD category 6, mitochondrial DNA-related disorders: MT-ATP6 is an mtDNA protein-coding ATP-synthase subunit. Definitional mapping to the local Ferreira et al. 2021 classification enum.'
📚

References & Deep Research

References

11
PMID:20953793
Heterogeneous patterns of tissue injury in NARP syndrome.
No top-level findings curated for this source.
PMID:17568559
Biochemical phenotypes associated with the mitochondrial ATP6 gene mutations at nt8993.
No top-level findings curated for this source.
PMID:16049925
Adult-onset ataxia and polyneuropathy caused by mitochondrial 8993T-->C mutation.
No top-level findings curated for this source.
PMID:22577227
Adult-onset spinocerebellar ataxia syndromes due to MTATP6 mutations.
No top-level findings curated for this source.
PMID:19626676
Identification of ataxia-associated mtDNA mutations (m.4052T>C and m.9035T>C) and evaluation of their pathogenicity in transmitochondrial cybrids.
No top-level findings curated for this source.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1173/
Mitochondrial DNA-Associated Leigh Syndrome Spectrum - GeneReviews® - NCBI Bookshelf
No top-level findings curated for this source.
PMID:18055910
Episodic ataxia and hemiplegia caused by the 8993T->C mitochondrial DNA mutation.
No top-level findings curated for this source.
PMID:35159298
Clinical Heterogeneity in MT-ATP6 Pathogenic Variants: Same Genotype-Different Onset.
No top-level findings curated for this source.
PMID:30926972
Biallelic expansion of an intronic repeat in RFC1 is a common cause of late-onset ataxia.
No top-level findings curated for this source.
PMID:20301352
Mitochondrial DNA-Associated Leigh Syndrome Spectrum.
No top-level findings curated for this source.
url:https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
https://trepo.tuni.fi/bitstream/handle/10024/66520/978-951-44-7847-5.pdf
No top-level findings curated for this source.

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 (3)

Record notes

Scope: anchored on OMIM 500010/MONDO:0010781 and the original m.8993T>C adult kindred. Related m.9035T>C/m.9185T>C ataxia and NARP/Leigh observations are qualified as indirect evidence. NARP is not restricted to childhood and is not separable by a universal heteroplasmy threshold. The original paper is available as a reprint in the author thesis; its four-page published article, rather than the entire thesis, supplied the URL evidence. The generated cache title is retained. GeneReviews NBK1173 is a shared Leigh-spectrum chapter. Clinical overlap, diagnostic methods, supportive care and maternal counseling were reviewed and used with explicit scope limits; infantile phenotype frequencies and treatment-trial claims were not transferred. The existing falcon deep-research report fails the disease-identity preflight: its body addresses RFC1/CANVAS (MONDO:0044720), not the MT-ATP6 disorder. Its mechanisms and therapeutic claims were excluded. CANVAS remains an independently sourced differential. The MONDO parent placement reported by the earlier curation requires separate ontology review; the descriptive parents here follow the established mitochondrial mechanism. No ontology-hierarchy change is part of this review.

Review adult-onset MT-ATP6 ataxia against full primary sources · 2026-09-21T06:59:53Z · View source

Review eligibility and scope. The parsed history on origin/main cd7ddf4cd04 contained CREATE and three EDIT events, with no REVIEW. Open claims and the fully paginated open-PR changed-file inventory had no competing review at reservation. The entry remains anchored on OMIM500010/MONDO:0010781 and the original MT-ATP6 m.8993T>C adult kindred. Related m.9035T>C/m.9185T>C and NARP/Leigh evidence is explicitly qualified. No schema or reference-provider code change is included. Primary clinical correction. The full Rantamäki2005 article, reproduced on its published pp.337–340 in the author thesis, describes overt ataxia/dysarthria in two of three examined adults and axonal neuropathy in all three. The prior obligate-ataxia assertion was false. Removed unsupported phenotype frequency bands and the ULTRA_RARE prevalence band; selected referral denominators are retained without population extrapolation. Added directly observed dysarthria, gaze-evoked nystagmus, absent ankle reflexes, vibration loss, pes cavus, weakness, muscle atrophy and clinically described drop attacks. The proband's EEG was normal; a sibling's attacks were only probable. The childhood-onset deceased sibling had nonspecific gliosis at autopsy and no documented molecular assay, and is not counted as an adult molecularly confirmed case. The maternal cousin's MS was regarded as independent by the original authors. An independent peer read the original full article and confirmed these denominator, tissue and diagnostic limits. Mechanistic correction. Split ATP depletion from ROS overproduction, removed the bundled terminal syndrome, and joined the clinical nodes to phenotype targets. Patient lymphocytes and related-variant cybrids establish cellular observations, not direct neuronal assays. Connections to adult nerve/cerebellar dysfunction retain unknown intermediates. Removed an unproven Purkinje-cell binding and its obsolete degenerative-node example. Heteroplasmy modifies expression without providing a universal threshold or explaining adult onset solely by low load: the original proband had89% in blood, and related adult pedigrees had90–99% in leukocytes. Normal routine complexI–IV tests do not establish normal ATP synthesis; normal oligomycin-sensitive ATPase in the later primary-cell study is retained rather than suppressed in favor of the earlier cybrid defect. Source consumption. All nine original reference identities and complete cached abstracts were read. Full primary scientific bodies for PMIDs20953793,30926972 and35159298 were read, including methods, results, discussion, and the available tables/legends; the cache for35159298 omits actual figure/table objects, so no uninspected table-specific quantitative claim was added. The full PDF20953793 includes Table1 and all three figure legends. The newly regenerated PMID22577227 contains the full body and clinical Table1, all read:3/5 normal MRI, three normal/nonspecific biopsies, two normal complexI–IV studies, high leukocyte loads, selected64-pedigree diagnostic yield, and variant-specific phenotypic heterogeneity. Its discussion swaps the m.9035 and m.9185 protein positions; these erroneous substitutions were not copied. The correct assignments follow the2022 paper and GeneReviews. The original16049925 four-page article was read in its entirety from the sanctioned generated thesis PDF cache; the surrounding thesis and other reproduced papers were not used as an audited source. The generated URL title is preserved and each quote identifies the original article. Canonical PMID16049925 remains in the bibliography. Access limits. Canonical refreshes of17568559,19626676 and18055910 remained abstract-only. For18055910, the full primary PMC clinical/results/discussion text was inspected through the web; canonical/URL retrieval returned challenge pages or rate limits, EuropePMC returned403, and Citeseer timed out. Two tracked PMC fallbacks were tested through sanctioned just fetch-reference but did not improve this source, so the unused code commits were removed and the exact original abstract cache restored. The structured18055910 evidence quotes remain within its cached abstract. No generated challenge-page cache is committed. The lymphocyte and cybrid model descriptions respect the information available in their complete abstracts; no unverified assay detail or human antioxidant efficacy was added. GeneReviews. The full NBK1173 chapter was recovered through the public /sites/books/ URL after canonical/print/PDF attempts returned challenge content. All clinical, diagnostic, genotype-phenotype, management, counseling and molecular sections through the molecular tables were read, including Tables1–8. The canonical PMID20301352 and the full chapter URL are both titled and tagged. Evidence is actively used across clinical differential context, diagnosis, supportive care and counseling. Full chapter content adds leukocyte/variant-specific interpretation, comprehensive sequencing, mobility and visual care, and the limits of maternal recurrence prediction and preimplantation testing. The m.8993T>C/G tissue/age behavior is distinguished from other mtDNA variants. Quotes ending at embedded glossary links are continuous cache substrings, with the remaining clinical context identified in the explanation. The chapter concerns Leigh syndrome spectrum; infantile phenotype frequencies, its generic mitochondrial trials and outdated2024 regulatory/trial statements are not transferred to the adult entity. No absolute childhood-onset restriction is used for NARP. Experimental models. Three non-animal systems are now explicit: patient m.8993T>C lymphocyte assays, m.9035T>C transmitochondrial cybrids, and two primary m.9035T>C fibroblast donors. Variant, cell background, normalization dependence, mixed-age controls, small donor counts and assay-specific negative findings are retained. The later fibroblast/muscle ATPase result is not conflated with the earlier cybrid result. CoQ10/vitaminE rescue of artificial stress-induced cell death remains experimental, not a treatment recommendation. No animal model was inferred from related mitochondrial biology. Deep-research content-completeness checklist. The actual falcon narrative begins after repeated prompt material and addresses RFC1/CANVAS/MONDO:0044720, with no MT-ATP6/8993 disease content. This independently reconfirms the prior Named Entity Confusion disposition; it is not a valid adult MT-ATP6 completeness baseline. Phenotypes: adequate against the defining adult primary article; indirect related-variant phenotypes retain scope. Subtypes: no independently mapped adult subtypes established; NARP/Leigh/RFC1 remain differentials. Mechanisms: seven atomic nodes, assay limitations and clinical joins. Treatments: five supportive/counseling/surveillance entries with shared-care scope. Genetics: causal variant, maternal inheritance and high-load/variable-expression limits. Diagnostics: molecular testing, electrophysiology, variable MRI and normal-test limitations. References: all nine PMIDs plus the two full-source URLs cataloged and used; central original clinical findings replace indirect NARP support. Overall: intentional adult-kindred scope rather than importing every infantile/related-variant manifestation. Trials and datasets. ClinicalTrials.gov API queries on2026-09-21 returned zero records for the exact adult-ataxia name and for8993T>C. The MT-ATP6 query returned two unrelated records, NCT05789888 (obesity/adipose genetic variation) and NCT05261373 (type2 diabetes exercise/nutrition), whose registry identities and conditions were inspected and excluded. No disease-specific interventional trial or accession was established from the reviewed primary sources. No dataset cache blob was accessed. The mapping concern about the MONDO DNA-repair parent is left to separate ontology work. Validation. Schema, live ontology bindings and all101 exact snippets pass. The newly full22577227 cache has only this disorder as a current KB consumer. The remaining curation guards, complete history corpus validation, node-class integrity and commit hooks are recorded in the PR once complete. New ontology descriptors were read from live OLS responses before binding; no reference cache was hand-edited. ICIMD classification uses the mtDNA-encoded respiratory-chain-protein group rather than the nuclear complexV group.

Create: Adult-Onset Ataxia and Polyneuropathy (MONDO:0010781) · 2026-08-20T04:33:50Z · View source

New CURATE_ROOT entry for MONDO:0010781 (OMIM 500010). Disease identity was anchored before any curation. MedGen 374087 links OMIM 500010 to the MT-ATP6 gene entry (OMIM 516060), MeSH C564020 heading-maps the concept to "Mitochondrial Proton-Translocating ATPases / deficiency" and "Mitochondrial Diseases", and the OMIM 500010 title matches Rantamaki 2005 (PMID:16049925), the defining kindred with the heteroplasmic MT-ATP6 m.8993T>C variant. Deep research: one falcon (Edison) run, DISCARDED IN FULL for Named Entity Confusion. "just preflight-dr" returned SKIP because MONDO records no causal gene (RO:0004003) for MONDO:0010781, so the manual OMIM/gene preflight from CLAUDE.md was applied and the report failed it: top gene RFC1 with 61 mentions, zero mentions of MT-ATP6 or nucleotide 8993, the report having resolved the descriptive label "adult-onset ataxia and polyneuropathy" to RFC1 spectrum disorder / CANVAS (MONDO:0044720). No content, citation, or ontology term in this entry derives from that report; every reference was located and cached independently via PubMed E-utilities plus "just fetch-reference". The report is committed under research/ so the preflight verdict is reproducible, and the entry notes record the verdict so a later curator does not re-mine it. Curation decisions worth recording. Evidence that comes from a different MT-ATP6 variant in the same adult-onset ataxia spectrum (m.9035T>C, m.9185T>C) rather than from m.8993T>C is marked supports: PARTIAL, with the variant named explicitly in its explanation. GeneReviews PMID:20301352 covers the mtDNA-Leigh syndrome spectrum rather than this entity, so its management, agents-to-avoid, and inheritance statements are also marked PARTIAL. Two normal test results are curated as biochemical entries with presence: ABSENT (cytochrome c oxidase muscle histochemistry, respiratory chain enzymology), because their normality is the diagnostic trap that causes these patients to be missed. CANVAS / RFC1 spectrum disorder is curated as a differential from an independently retrieved primary source (PMID:30926972), since it is the leading real-world differential for this clinical description. Three discussions record what is not known: a KNOWLEDGE_GAP that no cell-level cerebellar neuropathology exists for this entity (Purkinje involvement is inferred from the wider ataxia literature, not shown here, so the node carries mechanism_confidence: PROVISIONAL); an OPEN_QUESTION that heteroplasmy load demonstrably fails to predict age of onset; and a HUMAN_MODEL_MISMATCH on the cybrid CoQ10 / vitamin E rescue, which is the reason no antioxidant treatment is curated. Module conformance: three pathophysiology nodes declare conforms_to against peripheral_axonal_degeneration (two nodes) and cerebellar_purkinje_degeneration (one node); all targets were checked to resolve. Validation. "just validate" passed (schema, terms, references). "just count-verified-snippets" reported 50/50 snippets verified against cached references. "just check-duplicate-keys" and "just check-title-snippets" were clean. "just validate-disorders" was run once over the changed file before opening the PR. Compliance was 93.0 percent global / 93.5 percent weighted; the datasets block is deliberately empty because no verifiable dataset accession exists for this ultra-rare entity and fabricating one is the failure mode the dataset SOP warns about.

Falcon ▸
Adult-Onset Ataxia and Polyneuropathy: Comprehensive Disease Report
Edison Scientific Literature 27 citations 2026-08-19T21:11:49.054617

Adult-Onset Ataxia and Polyneuropathy: Comprehensive Disease Report

Scope and disease mapping

The requested label is not a consistently maintained standalone disease name. In a Mendelian context, it maps most closely to RFC1 spectrum disorder, especially cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS). Open Targets identifies this entity as MONDO:0044720 and links it specifically to RFC1 (ENSG00000035928), supported by human genetic evidence including PMID 30926972, PMID 31230722, and ClinGen/ClinVar records. “Adult-onset ataxia and polyneuropathy” can also describe genetically heterogeneous disorders; therefore, a knowledge-base entry should state explicitly that this report concerns RFC1-related disease, not every disorder producing that phenotype. (OpenTargets Search: CANVAS)

The evidence summarized below is aggregated disease-level evidence from cohorts, case series, molecular studies, and ClinicalTrials.gov—not individual EHR data.

Domain Core finding Quantitative details Ontology suggestions Evidence
Disease identity Adult-onset ataxia and polyneuropathy in this Mendelian context maps best to RFC1 spectrum disorder / CANVAS = cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome; MONDO:0044720 Open Targets links MONDO:0044720 to RFC1 with literature support MONDO:0044720; HPO: HP:0001251 Ataxia, HP:0009830 Peripheral neuropathy, HP:0007646 Bilateral vestibular hypofunction (OpenTargets Search: CANVAS, traschutz2021naturalhistoryphenotypic pages 1-2)
Inheritance / causal gene Usually autosomal recessive; primary cause is biallelic intronic RFC1 pentanucleotide repeat expansion in intron 2 Typical pathogenic motif AAGGG; reported pathogenic spectrum also includes population-specific ACAGG and Māori-associated configurations; compound heterozygosity with truncating RFC1 variants also reported Gene: RFC1; HPO: HP:0000007 Autosomal recessive inheritance (cortese2019biallelicexpansionof pages 4-6, ronco2023truncatingvariantsin pages 1-2, scriba2023rfc1inan pages 3-4)
Variant / molecular lesion Pathogenic alleles are large nonreference intronic repeat expansions; truncating coding variants can act in trans with one expansion in rare cases Expansion size about ~400–2,000 repeats (median ~1,000) in early discovery work; 2024 data show repeat size modifies onset/severity SO: tandem repeat expansion; intron variant (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, curro2024roleofthe pages 15-17)
Typical onset / course Adult onset, usually insidious and slowly progressive multisystem neurodegeneration Mean onset 54±9 y (range 35–73) in 2019 series; median onset 54 y (range 25–80) in 2024 cohort; progression about 1.3 SARA points/year HPO: HP:0003581 Adult onset, HP:0003676 Progressive neurologic deterioration (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, traschutz2021naturalhistoryphenotypic pages 1-2)
Core phenotype: sensory neuropathy / neuronopathy Hallmark feature; often presents as sensory ataxic neuropathy and may precede full CANVAS All tested/examined cases had sensory neuropathy in major cohorts; in 2024 cohort 24% had isolated sensory neuropathy and 38% complex neuropathy HPO: HP:0009830 Peripheral neuropathy, HP:0002355 Difficulty walking; UBERON: dorsal root ganglion (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, curro2024roleofthe pages 4-7)
Core phenotype: cerebellar ataxia Cerebellar dysfunction is common but not universal early; often evolves over time Cerebellar involvement 80% in 2019 series; cerebellar signs 72% at first assessment and 84% at follow-up in 2024 cohort HPO: HP:0001251 Ataxia, HP:0002060 Cerebellar atrophy; UBERON: cerebellum (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)
Core phenotype: vestibular dysfunction Bilateral vestibular areflexia/hypofunction is a defining axis of CANVAS but may be incomplete early Bilateral vestibular areflexia 54% in 2019 series; 75% in 2024 cohort HPO: HP:0007993 Vestibular dysfunction, HP:0007646 Bilateral vestibular hypofunction; UBERON: vestibular labyrinth (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, gisatulin2020clinicalspectrumof pages 5-9)
Core phenotype: chronic cough Highly discriminative associated symptom and may precede neurologic signs 37% in 2019 series; 75% overall and initial symptom in 50% in 2024 cohort; ACC phenotype can be highly suggestive HPO: HP:0012735 Chronic cough (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, traschutz2021naturalhistoryphenotypic pages 1-2)
Core phenotype: dysautonomia / small-fiber involvement Autonomic and small-fiber involvement are common in multisystem disease Autonomic involvement 23% in 2019 series; dysautonomia 62% in 2021 natural history study; 2023 Portuguese cohort: multisystem features beyond CANVAS in 82%, dysautonomia 43%, severe epidermal denervation in all biopsied patients HPO: HP:0000789 Autonomic dysfunction; CL: sensory neuron; UBERON: skin, peripheral nerve (cortese2019biallelicexpansionof pages 4-6, traschutz2021naturalhistoryphenotypic pages 1-2)
Other multisystem phenotypes Can overlap with parkinsonism/MSA-C, movement disorder, cranial or motor neuron features Bradykinesia 28%, postural instability 49%, slow vertical saccades 17%, chorea/dystonia 11% in 2021 study; motor neuron/motor neuropathy 18% in 2023 Portuguese cohort HPO: HP:0002067 Bradykinesia, HP:0002136 Dysphagia, HP:0001260 Dysarthria (traschutz2021naturalhistoryphenotypic pages 1-2)
Diagnostics Diagnosis relies on targeted RFC1 repeat testing plus phenotype-specific neurologic workup Methods reported: flanking PCR, repeat-primed PCR, duplex PCR, Southern blot, fragment analysis, Sanger sequencing, short-read screening, targeted long-read sequencing; MRI/CT showed cerebellar atrophy in 83% of 42 cases HPO: HP:0003401 Cerebellar MRI abnormality; UBERON: cerebellar vermis (cortese2019biallelicexpansionof pages 4-6, gisatulin2020clinicalspectrumof pages 1-5, scriba2023rfc1inan pages 3-4)
Diagnostic yield / testing strategy RFC1 testing should be prioritized in adult-onset ataxia with sensory neuropathy, vestibular failure, or chronic cough Prevalence in enriched cohorts: 67% in suspected cohort, 68% in clinical CANVAS, 100% in ataxia with chronic cough, 14% in unselected late-onset ataxia; Australasian cohort found pathogenic expansions in 15.3% (37/242) HPO-guided testing: ataxia + neuropathy + cough + vestibular dysfunction (traschutz2021naturalhistoryphenotypic pages 1-2, scriba2023rfc1inan pages 3-4)
Key 2024 mechanism Patient iPSC-derived neurons support repeat-dependent, RFC1-protein-independent synaptic dysfunction 2024 Science Advances study found normal RFC1 splicing/expression and intact DNA repair, no consistent RNA foci/peptide toxicity in iNeurons, but reduced neuronal development/synaptic connectivity; CRISPR deletion of one expanded allele rescued deficits, RFC1 knockdown did not phenocopy, and RFC1 re-expression did not rescue GO: synapse organization, chemical synaptic transmission; CL: glutamatergic neuron; UBERON: cerebellum/peripheral nervous system (maltby2024aagggrepeatexpansions pages 1-2, maltby2024aagggrepeatexpansions pages 13-14, maltby2024aagggrepeatexpansions pages 11-13)
Genotype–phenotype modifier (2024) Repeat size is a prognostic modifier Larger smaller allele HR 2.06 and larger allele HR 1.53 for earlier neurologic onset; loss of independent walking HR 2.78 (smaller allele) and 1.60 (larger allele); dysarthria/dysphagia HR 3.40 and 1.71; larger expansions associated with more severe vermian atrophy HPO: HP:0001260 Dysarthria, HP:0002015 Dysphagia; UBERON: cerebellar vermis (curro2024roleofthe pages 10-12, curro2024roleofthe pages 15-17)
Prognosis Chronic progressive disability; some premature mortality in advanced disease In 2024 cohort 54% required walking aids after median 10 y, 17% wheelchairs after 14 y; mortality 8%, with disease-related deaths including aspiration pneumonia/immobility complications HPO: HP:0002829 Wheelchair dependence, HP:0040296 Aspiration pneumonia (curro2024roleofthe pages 10-12, traschutz2021naturalhistoryphenotypic pages 1-2)
Current treatment / trial status No established disease-modifying therapy; care is supportive and multidisciplinary; RFC1-specific biomarker/natural-history trial is recruiting Trial planning estimate: 330 total patients for 1-year or 132 for 2-year study to detect 50% slowing; NCT07156214 recruiting from 2024-10-14, primary completion 2026-06-30, evaluating scales, NfL/oxidative stress biomarkers, imaging, and patient-derived cells NCIT: supportive care; physical therapy/rehabilitation; biomarker study (traschutz2021naturalhistoryphenotypic pages 1-2, NCT07156214 chunk 1)

Table: This table summarizes the core knowledge-base fields for RFC1 spectrum disorder/CANVAS, the main Mendelian interpretation of adult-onset ataxia and polyneuropathy. It highlights identifiers, causal genetics, phenotype frequencies, diagnostics, 2024 mechanistic insights, prognosis, and current trial status with ontology suggestions and evidence IDs.

1. Disease information

RFC1 disease is an autosomal-recessive, usually late-onset neurodegenerative disorder whose manifestations form a continuum from isolated sensory neuronopathy/neuropathy to combined sensory, cerebellar, and bilateral vestibular dysfunction. The complete triad is termed CANVAS. Other common labels are RFC1 spectrum disorder, RFC1-related disorder, RFC1-associated disease, CANVAS syndrome, and ataxia with chronic cough.

Identifiers and classifications

  • MONDO: MONDO:0044720, cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome.
  • OMIM: CANVAS is commonly indexed as 614575; RFC1 is 102579. Database versions should be checked before ingestion.
  • Gene: RFC1, replication factor C subunit 1; Ensembl ENSG00000035928.
  • MeSH: no uniquely specific RFC1-CANVAS descriptor was established in the retrieved evidence; broader terms include cerebellar ataxia and peripheral nervous system disease.
  • ICD-10/ICD-11: no uniquely disease-specific code was established. Coding generally combines hereditary/degenerative ataxia, polyneuropathy, and vestibular dysfunction. A knowledge base should not assign a single exact ICD code without jurisdictional validation.

The landmark discovery study described a mean onset of 54±9 years (range 35–73) and mean observed disease duration of 11±7 years. Its defining molecular lesion was a biallelic, large intronic RFC1 repeat expansion. (cortese2019biallelicexpansionof pages 4-6)

2. Etiology, risk, protection, and gene–environment interaction

Causal factor

The principal cause is a germline biallelic nonreference pentanucleotide-repeat expansion in intron 2 of RFC1, usually (AAGGG)n. Typical pathogenic alleles contain approximately 400–2,000 repeats, often near 800–1,000, whereas the reference motif is (AAAAG)n. The expansion lies in the poly-A tail of an AluSx3 element. (cortese2019biallelicexpansionof pages 4-6, gisatulin2020clinicalspectrumof pages 5-9, gisatulin2020clinicalspectrumof pages 1-5)

Pathogenic configurations are population dependent. Besides AAGGG, disease-associated ACAGG and complex Māori-associated (AAAGG)exp(AAGGG)exp alleles have been reported. Consequently, an AAGGG-only assay can miss disease in non-European populations. (curro2024roleofthe pages 4-7, scriba2023rfc1inan pages 3-4)

Rare patients have one expanded allele and a truncating RFC1 variant in trans. Reported variants include c.1267C>T (p.Arg423Ter), c.1739_1740del (p.Lys580SerfsTer9), c.2191del (p.Gly731GlufsTer6), and c.2876del (p.Pro959GlnfsTer24). Fibroblasts carrying two tested truncating alleles showed nonsense-mediated decay and reduced RFC1 RNA and protein. Full RFC1 sequencing is therefore appropriate when classic CANVAS accompanies only one detected expansion. (ronco2023truncatingvariantsin pages 1-2)

Risk and modifying factors

  • Genetic risk: two pathogenic RFC1 alleles are causal; heterozygous carriers are generally unaffected.
  • Repeat size: the strongest established modifier. In 553 expansion carriers, with size measured in 392, larger alleles predicted earlier onset and more severe disease. Earlier neurologic onset had HR 2.06 for the smaller allele and 1.53 for the larger allele; earlier dysarthria/dysphagia had HR 3.40 and 1.71; earlier loss of independent walking had HR 2.78 and 1.60, respectively. Larger repeats were also associated with complex neuropathy, complete CANVAS, and greater vermian atrophy. Repeat size explained only about 6% of onset variability, implying additional modifiers. (curro2024roleofthe pages 10-12, curro2024roleofthe pages 15-17)
  • Age: manifestations are age dependent, explaining apparently sporadic presentations and unaffected younger siblings.
  • Family history: its absence does not argue strongly against disease because inheritance is recessive and onset is late.

No reproducible sex, lifestyle, occupational, dietary, infectious, or toxic risk factor has been established for genetically confirmed RFC1 disease. No validated protective allele, diet, drug, or environmental exposure is known. Environmental or epigenetic modifiers are plausible because repeat size explains little phenotypic variance, but specific gene–environment interactions remain unproven. The 2024 repeat study found no major meiotic or tissue-specific somatic instability, arguing against marked anticipation driven by unstable expansion growth. (curro2024roleofthe pages 15-17)

3. Phenotypes

The disease is chronic and progressive, but component systems emerge at different times. Sensory neuropathy often precedes cerebellar and vestibular signs; chronic spasmodic cough can precede neurologic disability by years.

  • Sensory neuronopathy/neuropathy: hallmark phenotype, generally non-length-dependent, affecting large fibers and proprioception; motor conduction is often preserved. Suggested terms: HP:0009830 peripheral neuropathy, HP:0000763 sensory neuropathy, HP:0003477 impaired vibration sense, HP:0010871 sensory ataxia. It was found in all examined patients in major cohorts. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)
  • Cerebellar ataxia: gait and limb ataxia, dysarthria, impaired pursuit, and cerebellar atrophy; HP:0001251, HP:0002072 chorea only where present, HP:0001260 dysarthria, HP:0002060 cerebellar atrophy. Cerebellar involvement was 80% in the discovery cohort and rose from 72% at first assessment to 84% at follow-up in a later large cohort. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)
  • Bilateral vestibulopathy: oscillopsia, impaired vestibulo-ocular reflex, and imbalance worsened in darkness; HP:0007993 vestibular dysfunction, HP:0007646 bilateral vestibular hypofunction, HP:0010544 oscillopsia. Reported prevalence was 54–75%, depending on cohort and disease stage. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12, gisatulin2020clinicalspectrumof pages 5-9)
  • Chronic cough: dry, spasmodic cough, frequently prodromal; HP:0012735. Frequencies ranged from 37% in the initial series to 75% in a 2024 cohort; in the latter it was the initial symptom in 50%. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)
  • Dysautonomia and small-fiber disease: urinary, bowel, cardiovascular, cardiovagal, and sudomotor dysfunction; HP:0000789 autonomic dysfunction, HP:0000020 urinary incontinence where applicable. Dysautonomia occurred in 23% of the discovery series and 62% in a deeply phenotyped natural-history cohort. (cortese2019biallelicexpansionof pages 4-6, traschutz2021naturalhistoryphenotypic pages 1-2)
  • Other manifestations: bradykinesia 28%, postural instability 49%, slow vertical saccades 17%, and chorea/dystonia 11% in one cohort. Motor-neuron/motor-neuropathy phenotypes, sleep disorders, cranial neuropathy, and cognitive impairment have been reported but are less securely quantified and may represent spectrum extremes. (traschutz2021naturalhistoryphenotypic pages 1-2)
  • Advanced disability: dysarthria/dysphagia increased from 6% to 51% during follow-up. Suggested terms include HP:0002015 dysphagia, HP:0002829 wheelchair dependence, and HP:0040296 aspiration pneumonia. (curro2024roleofthe pages 10-12)

Quality-of-life effects include impaired walking in darkness or on uneven surfaces, falls, oscillopsia, chronic cough, pain or sensory discomfort, loss of driving and employment, dysphagia, and eventual dependence for mobility. RFC1-specific EQ-5D, SF-36, or PROMIS population estimates were not found.

4. Genetic and molecular information

RFC1 encodes the large subunit of replication factor C, a clamp-loader complex involved in DNA replication and repair. The conventional disease genotype is homozygous or compound-heterozygous pathogenic repeat expansion. Variants are germline, not somatic cancer alterations.

Population screening in the discovery study found expanded AAGGG alleles on approximately 0.7% of chromosomes; subsequent estimates range from 0.7% to 4%, depending on ancestry, motif definition, and ascertainment. These figures are allele frequencies, not disease prevalence. (cortese2019biallelicexpansionof pages 4-6, traschutz2021naturalhistoryphenotypic pages 1-2)

Large repeat expansions are not represented reliably by standard SNV/indel nomenclature, and their frequencies are poorly captured by conventional gnomAD short-read variant tables. For knowledge-base purposes, pathogenicity should be assigned at the repeat-configuration level, with motif, size, zygosity, and assay recorded. Benign or uncertain expansions, including AAAAG/AAAGG or interrupted configurations, must not be automatically classified as pathogenic. (gisatulin2020clinicalspectrumof pages 1-5, scriba2023rfc1inan pages 3-4)

No validated modifier gene, disease-specific methylation signature, recurrent chromosomal rearrangement, or pathogenic epigenetic lesion has been established. Rare RFC1 deletions and truncating alleles broaden the allelic spectrum but do not define a recurrent chromosomal syndrome. (ronco2023truncatingvariantsin pages 1-2)

5. Environmental and lifestyle information

RFC1 disease is not known to be caused by infection, radiation, pollution, alcohol, smoking, diet, or occupational exposure. Such factors remain relevant in the differential diagnosis of adult-onset ataxia/polyneuropathy—particularly alcohol, neurotoxic medications, vitamin deficiencies, immune disease, and paraneoplastic processes—but are not demonstrated causal cofactors for biallelic RFC1 disease. No vaccine or pathogen-specific intervention applies.

6. Mechanism and pathophysiology

Causal chain

Biallelic pathogenic RFC1 repeat configuration → repeat-dependent neuronal dysfunction → impaired synaptic development/signaling and selective vulnerability of sensory ganglia, cerebellar circuits, and vestibular pathways → sensory ataxia, cerebellar ataxia, and vestibular areflexia. Downstream degeneration includes Purkinje-cell loss, dorsal-root-ganglionopathy, peripheral small/large-fiber loss, and cerebellar atrophy. Severe Purkinje-cell depletion with Bergmann gliosis has been documented neuropathologically. (cortese2019biallelicexpansionof pages 4-6)

Earlier studies found unchanged RFC1/WDR19 expression and no RFC1 intron retention, leaving mechanism uncertain. (gisatulin2020clinicalspectrumof pages 1-5)

The key 2024 mechanistic development used patient-derived iPSCs and glutamatergic iNeurons. RFC1 expression, splicing, DNA-repair function, DNA-damage accumulation, and UV-repair recovery were not materially abnormal. Reporter constructs permitted pentapeptide-repeat translation, but repeat peptides and convincing RNA-foci toxicity were not consistently demonstrated in patient iNeurons. Conversely, patient neurons had abnormal neuronal-development and synaptic-gene programs, reduced burst rate, burst strength, and firing correlation, and impaired connectivity. Deleting one expanded allele with CRISPR rescued molecular and functional defects; RFC1 knockdown did not reproduce them, and RFC1 replacement did not rescue them. The authors’ abstract conclusion was: “These findings support a repeat-dependent but RFC1 protein–independent cause of neuronal dysfunction in CANVAS.” (maltby2024aagggrepeatexpansions pages 1-2, maltby2024aagggrepeatexpansions pages 13-14, maltby2024aagggrepeatexpansions pages 11-13)

This creates tension with truncating-variant evidence supporting partial RFC1 loss of function. The most defensible current interpretation is that more than one mechanism may operate: repeat-sequence/configuration toxicity is strongly supported in neurons, while RFC1 haploinsufficiency or reduced dosage can contribute in rare compound genotypes. (ronco2023truncatingvariantsin pages 1-2, maltby2024aagggrepeatexpansions pages 1-2)

Suggested annotations: GO:0050808 synapse organization; GO:0007268 chemical synaptic transmission; GO:0006281 DNA repair, with a qualifier that canonical repair dysfunction was not demonstrated; GO:0006950 response to stress; CL:0000540 neuron, CL:0000121 Purkinje cell, CL:0000101 sensory neuron, CL:0000709 retinal?—the latter should not be used without phenotype evidence. Relevant compartments include nucleus, cytoplasm, synapse, and axon.

No validated disease-level epigenomic, proteomic, metabolomic, lipidomic, single-cell, or spatial-transcriptomic signature is yet available. INSIDE-CANVAS is investigating oxidative stress, neurofilament light, mitochondrial function, and patient-derived cells. (NCT07156214 chunk 1)

7. Anatomical structures affected

Primary systems are the peripheral sensory nervous system, cerebellum, and vestibular system.

  • Dorsal-root ganglia and sensory peripheral nerves: neuronopathy with large- and small-fiber loss; UBERON:0000044 dorsal root ganglion, UBERON:0001021 nerve, CL:0000101 sensory neuron.
  • Cerebellum: Purkinje cells, vermis, and hemispheric circuits; UBERON:0002037 cerebellum, UBERON:0004729 cerebellar vermis, CL:0000121 Purkinje cell.
  • Vestibular apparatus/pathways: bilateral vestibular hypofunction; UBERON:0001843 vestibular labyrinth and vestibular nerve/pathway terms.
  • Spinal proprioceptive pathways and brainstem oculomotor networks may contribute secondarily.
  • Autonomic and cutaneous small fibers are involved in a subset.

MRI showed cerebellar atrophy in 83% of 42 imaged cases in the discovery series. Larger repeats, especially the smaller expanded allele, correlated with greater atrophy of vermian lobules I–V and VI–VII. Disease is generally bilateral/systemic rather than lateralized. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)

8. Temporal development

Onset is usually insidious in the fifth or sixth decade, but observed onset spans approximately 25–80 years. Cough or sensory symptoms may be the first manifestation; cerebellar and vestibular components accumulate later. (cortese2019biallelicexpansionof pages 4-6, curro2024roleofthe pages 10-12)

A practical staging model is:

  1. Prodromal/early: chronic cough, distal or patchy sensory symptoms, imbalance in darkness.
  2. Intermediate: sensory ataxia plus cerebellar or vestibular dysfunction; falls and oscillopsia.
  3. Established CANVAS: all three systems affected, with dysarthria and reduced independent mobility.
  4. Advanced: walking aids or wheelchair use, dysphagia, aspiration risk, and multisystem/autonomic complications.

Mean ataxia progression was approximately 1.3 SARA points/year, although nonlinear MSA-C-like phases of 2.5–5.5 points/year occurred. No spontaneous remission pattern is recognized. (traschutz2021naturalhistoryphenotypic pages 1-2)

9. Inheritance and population

Inheritance is autosomal recessive, with variable expressivity and strongly age-dependent penetrance. Precise lifetime penetrance for each repeat motif and size is not established. Repeat-size correlation supports dose-dependent expressivity. Unlike many repeat diseases, marked meiotic/somatic instability and classic genetic anticipation were not observed. (curro2024roleofthe pages 10-12, curro2024roleofthe pages 15-17)

RFC1 expansions were found in 14% of unselected late-onset ataxia, 67% of an enriched suspected cohort, 68% of clinical CANVAS, and 100% of ataxia-with-chronic-cough cases in one study. These are diagnostic yields, not population prevalence. (traschutz2021naturalhistoryphenotypic pages 1-2)

An Australasian study found pathogenic biallelic expansions in 37/242 (15.3%) neurologic cases, including AAGGG, ACAGG, and Māori-associated configurations. A Japanese hereditary sensory/autonomic neuropathy cohort found biallelic RFC1 expansions in 20/79 (25.3%) cases. These findings demonstrate ancestry-specific motif distributions. (scriba2023rfc1inan pages 3-4)

Population incidence, point prevalence, sex ratio, carrier frequency by ancestry, and survival-adjusted prevalence remain inadequately measured. Consanguinity can increase recessive disease probability but is not required, given relatively common carrier alleles.

10. Diagnostics

Clinical and physiologic evaluation

Evaluate cerebellar signs, sensory modalities, reflexes, gait in darkness, eye movements, autonomic symptoms, chronic cough, and family history. Recommended investigations include:

  • Nerve-conduction studies: typically absent/reduced sensory responses with relatively preserved motor conduction.
  • Vestibular testing: video head-impulse testing, calorics, rotational chair, vestibular-evoked myogenic potentials, and visually enhanced vestibulo-ocular reflex where available.
  • Brain MRI: cerebellar and vermian atrophy; spinal imaging when alternative diagnoses are suspected.
  • SARA or ICARS for ataxia, vestibular disability scales, swallowing assessment, and autonomic testing.
  • Laboratory exclusion of acquired ataxia/neuropathy: vitamin E/B12/copper, thyroid, diabetes, paraprotein, immune/paraneoplastic studies, toxins, infections, and medication review as clinically indicated.

Genetic testing algorithm

  1. Order RFC1 flanking PCR plus motif-specific repeat-primed PCR in adult-onset sensory neuronopathy, CANVAS, bilateral vestibulopathy with neuropathy, or ataxia with chronic cough.
  2. Confirm and size large alleles with Southern blot, optical genome mapping, or validated long-read sequencing.
  3. If the phenotype is compelling but only one expansion is found, sequence the complete RFC1 coding region and assess deletion/CNV alleles. (ronco2023truncatingvariantsin pages 1-2)
  4. If PCR patterns are atypical or ancestry suggests non-AAGGG motifs, use targeted long-read sequencing to resolve motif, interruptions, orientation, and size. The 2023 Australasian study recommended a multistep short-/long-read workflow. (scriba2023rfc1inan pages 3-4)
  5. If negative, test other repeat disorders and conventional ataxia/neuropathy genes with a repeat-expansion panel plus WES/WGS. Standard WES alone can miss RFC1 expansions.

The 2024 adult-onset ataxia review summarized the diagnostic challenge: targeted repeat testing remains necessary even when exome or short-read genome sequencing is performed, while long-read sequencing may eventually unify detection. (scriba2023rfc1inan pages 3-4)

Important differentials include Friedreich ataxia, SCA3 and other dominant SCAs, FGF14-GAA/SCA27B, FXTAS, POLG and other mitochondrial disease, spinocerebellar ataxia with axonal neuropathy, hereditary sensory/autonomic neuropathies, immune/paraneoplastic ataxia, superficial siderosis, multiple-system atrophy–cerebellar type, alcohol/toxin-associated disease, and vitamin deficiencies.

Cascade testing is appropriate after molecular confirmation. Population or newborn screening is not recommended; predictive testing of adult relatives requires genetic counseling.

11. Outcome and prognosis

Disease is lifelong and progressive; recovery is not expected, although rehabilitation can improve function and safety. In a large cohort, 54% required a walking aid after a median of 10 years, and 17% required a wheelchair after 14 years. Mortality was 8%; attributed deaths included aspiration pneumonia and complications of immobility. (curro2024roleofthe pages 10-12)

Repeat size is the best current molecular prognostic marker, but it is not deterministic. Baseline multisystem involvement, dysphagia, falls, and rapid SARA progression likely indicate poorer functional prognosis. No validated individual survival calculator exists.

12. Treatment and current applications

There is no approved disease-modifying therapy. Current real-world care is genotype-informed but symptomatic:

  • physiotherapy, balance and gait training, vestibular rehabilitation, fall prevention, and mobility aids;
  • occupational therapy and home adaptation;
  • speech therapy, swallow evaluation, texture modification, and aspiration prevention;
  • treatment of neuropathic pain using standard agents when present;
  • management of orthostatic, urinary, bowel, and sudomotor symptoms;
  • cough assessment and symptomatic management after excluding pulmonary causes;
  • nutritional, respiratory, psychological, and social support;
  • hearing/vision compensation and driving-safety review;
  • genetic counseling and cascade testing.

Suggested NCIT concepts include Physical Therapy, Occupational Therapy, Speech Therapy, Vestibular Rehabilitation, Supportive Care, and Genetic Counseling. No RFC1-specific pharmacogenomic guideline, surgery, cell therapy, ASO, siRNA, or gene-replacement therapy is established.

The 2024 iNeuron result argues that simply restoring RFC1 protein may be insufficient; excision, silencing, or sequence-specific targeting of the expanded repeat is a more mechanistically supported direction, although CRISPR rescue remains preclinical. (maltby2024aagggrepeatexpansions pages 1-2, maltby2024aagggrepeatexpansions pages 11-13)

Clinical research: INSIDE-CANVAS (NCT07156214) began October 14, 2024 and is recruiting. It targets 25 RFC1 patients plus matched controls, with one-year clinical scales, neurophysiology, vestibular testing, brain/spinal MRI, NfL and oxidative-stress biomarkers, fibroblasts, and iPSCs; estimated primary completion is June 30, 2026. It is a biomarker/pathogenesis study, not a proven therapeutic trial. (NCT07156214 chunk 1)

Natural-history modeling estimated that a trial detecting 50% slowing would require approximately 330 participants for one year or 132 for two years. (traschutz2021naturalhistoryphenotypic pages 1-2)

13. Prevention

Primary prevention through lifestyle modification is not available. For families with a known genotype, options include genetic counseling, adult cascade testing, prenatal diagnosis, and preimplantation genetic testing, subject to local ethics and regulation. Because penetrance is age dependent and genotype–phenotype prediction is incomplete, predictive counseling must address uncertainty.

Secondary prevention consists of early molecular diagnosis and surveillance for falls, vestibular failure, autonomic dysfunction, dysphagia, and aspiration. Tertiary prevention includes rehabilitation, mobility aids, home-safety modification, vaccination and respiratory care according to general standards, and prompt treatment of aspiration or immobility complications. No RFC1-specific vaccine or chemoprophylaxis applies.

14. Other species and natural disease

No well-established naturally occurring veterinary counterpart caused by orthologous RFC1 intronic pentanucleotide expansions was identified. RFC1 is evolutionarily conserved, but the human disease depends on a specific repeat architecture that may not be conserved across species. Zoonotic transmission is not applicable. A knowledge base should mark affected nonhuman species, breed associations, and natural transmission as not established rather than infer them from RFC1 conservation.

15. Model organisms and experimental systems

The most informative current model is the human patient-derived iPSC/iNeuron system. The 2024 study used four patient and three control lines and an isogenic CRISPR-corrected line. It reproduced neuronal-development, transcriptomic, calcium-signaling, and synaptic-connectivity abnormalities and demonstrated rescue after deletion of one expanded allele. (maltby2024aagggrepeatexpansions pages 13-14, maltby2024aagggrepeatexpansions pages 2-3)

Limitations are important: the neurons were predominantly glutamatergic rather than dorsal-root-ganglion sensory neurons, vestibular neurons, or mature Purkinje cells; the number of lines and isogenic controls was small; and early developmental phenotypes may not reproduce decades-long human degeneration. Pentapeptide products were detected in three of four postmortem cerebella but not convincingly in iNeurons, illustrating model dependence. (maltby2024aagggrepeatexpansions pages 13-14)

No validated mouse, rat, zebrafish, Drosophila, or C. elegans model was established in the retrieved evidence as recapitulating the complete human triad. Priority models include repeat knock-in animals, sensory-neuron and Purkinje-cell differentiation, cerebellar organoids, and isogenic long-repeat systems.

Key recent expert conclusions and exact abstract quotations

  • Currò et al., Brain 2024, DOI 10.1093/brain/awad436: “RFC1 repeat size, particularly of the smaller allele, is one of the determinants of variability in RFC1 disease and represents a key prognostic factor to predict disease onset, phenotype, and severity.” (curro2024roleofthe pages 10-12)
  • Maltby et al., Science Advances, September 2024, DOI 10.1126/sciadv.adn2321: “These findings support a repeat-dependent but RFC1 protein–independent cause of neuronal dysfunction in CANVAS, with implications for therapeutic development in this currently untreatable condition.” (maltby2024aagggrepeatexpansions pages 1-2)
  • Scriba et al., Brain Communications, July 2023, DOI 10.1093/braincomms/fcad208: the authors found pathogenic expansions in 15.3% of their neurological cohort and concluded that RFC1 expansions make a substantial contribution to Australasian neurological disease, supporting combined short- and long-read diagnostic workflows. (scriba2023rfc1inan pages 3-4)
  • Ronco et al., Neurology, January 2023, DOI 10.1212/WNL.0000000000201486, PMID 36478048: “Full RFC1 sequencing is recommended in cases affected by typical CANVAS and carrying monoallelic (AAGGG)n expansions.” (ronco2023truncatingvariantsin pages 1-2)

Evidence gaps

Reliable population incidence and prevalence, motif-specific penetrance, sex ratios, validated quality-of-life norms, environmental modifiers, fluid biomarkers, single-cell/spatial atlases, natural animal disease, robust whole-animal models, and disease-modifying treatment data remain unavailable. Frequencies vary substantially with ascertainment and disease stage; cohort percentages should therefore not be treated as universal penetrance estimates.

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