Machado-Joseph Disease

Mendelian MONDO:0007182 Pathograph 12 Hereditary cerebellar ataxia Neurodegenerative Disease Movement Disorder

Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is the most common autosomal dominant spinocerebellar ataxia worldwide. It arises from a CAG trinucleotide repeat expansion in exon 10 of ATXN3 (14q32.1), producing a polyglutamine-expanded ataxin-3 protein that misfolds, aggregates, and disrupts multiple cellular systems including the ubiquitin- proteasome system, autophagy, transcription, and mitochondrial function. The disorder is clinically heterogeneous and classically divided into four subtypes (Types 1-4) based on age at onset and predominant features. There is no approved disease-modifying therapy; antisense oligonucleotide (ASO)-based gene silencing is the most clinically advanced investigational strategy.

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1
Inheritance
5
Pathophys.
14
Phenotypes
12
Pathograph
1
Genes
4
Treatments
4
Subtypes
3
Datasets
3
Trials
1
References
1
Deep Research
👪

Inheritance

1
Autosomal dominant HP:0000006
MJD/SCA3 follows autosomal dominant inheritance with full penetrance when the CAG repeat expansion exceeds approximately 56 repeats. Anticipation occurs due to intergenerational instability of the CAG tract, with paternal transmission more likely to produce larger expansions.
autosomal dominant inheritance
Show evidence (2 references)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Establishes MJD/SCA3 as an autosomal dominant neurodegenerative disorder.
PMID:29959858 SUPPORT Human Clinical
"MJD/SCA3 arises from mutation of the ATXN3 gene, but this simple monogenic cause contrasts with the complexity of the pathogenic mechanisms that are currently admitted to underlie neuronal dysfunction and death."
Confirms monogenic autosomal dominant etiology driven by ATXN3 mutation.
◆

Subtypes

4
Type 1 (Early-onset, pyramidal/dystonic) MONDO:0017174
Early onset (often adolescence or young adulthood, typically requiring CAG repeat lengths >70). Prominent pyramidal signs (spasticity, hyperreflexia), dystonia, rigidity, and cerebellar ataxia. Ophthalmoplegia is also common.
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD presents strong phenotypic heterogeneity, which has justified the classification of patients into three main clinical types."
Supports the clinical subtype classification system for MJD, with Type 1 characterized by early onset, pyramidal signs, and dystonia.
Type 2 (Classic ataxia + ophthalmoplegia) MONDO:0017175
Middle adult onset with intermediate CAG repeat lengths. Classic cerebellar ataxia with ophthalmoplegia and pyramidal signs, without the severity of dystonia seen in Type 1. The most common clinical presentation.
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD presents strong phenotypic heterogeneity, which has justified the classification of patients into three main clinical types."
Supports the clinical subtype framework; Type 2 is the classic and most common presentation with cerebellar ataxia and ophthalmoplegia.
Type 3 (Late-onset, peripheral neuropathy) MONDO:0017176
Late onset (often >40 years), associated with lower CAG repeat lengths. Peripheral neuropathy, anterior horn cell disease, and amyotrophy are the distinguishing features, alongside ataxia. Areflexia and fasciculations are common.
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD presents strong phenotypic heterogeneity, which has justified the classification of patients into three main clinical types."
Supports the clinical subtype classification; Type 3 is distinguished by late onset and peripheral neuropathy/anterior horn cell disease.
Type 4 (Parkinsonism-predominant) MONDO:0042964
Rarest subtype characterized by prominent parkinsonism. Features tremor, bradykinesia, and rigidity with variable response to levodopa.
Show evidence (1 reference)
PMID:21635785 PARTIAL Human Clinical
"MJD presents strong phenotypic heterogeneity, which has justified the classification of patients into three main clinical types."
Supports the phenotypic heterogeneity framework; Type 4 (parkinsonism- predominant) was added to the original 3-type classification as a recognized rare variant.
⚙

Pathophysiology

5
PolyQ-expanded ataxin-3 misfolding and nuclear aggregation
CAG repeat expansion in exon 10 of ATXN3 produces an aberrantly elongated polyglutamine tract in ataxin-3. The mutant protein misfolds and forms intranuclear inclusions, which are a pathological hallmark of MJD/SCA3. These aggregates sequester transcription factors, co-regulators, and ubiquitin-pathway components, initiating a cascade of cellular toxicity.
ATXN3 link
response to unfolded protein link
cerebellum link brainstem link
Downstream
Impaired ATXN3 deubiquitinase activity and proteostasis failure The polyQ expansion disrupts the normal K48- and K63-linked polyubiquitin chain cleavage activity of ataxin-3, impairing substrate delivery to the proteasome and autophagy pathways.
Show evidence (3 references)
PMID:29959858 SUPPORT Human Clinical
"The aberrantly expanded protein product - ataxin-3 - is known to aggregate and generate toxic species that disrupt several cell systems, including autophagy, proteostasis, transcription, mitochondrial function and signalling."
Establishes that polyQ-expanded ataxin-3 aggregation is the initiating toxic event.
PMID:38612794 SUPPORT Human Clinical
"This mutation results in the expression of an abnormal protein containing long polyglutamine (polyQ) stretches that confers a toxic gain of function and leads to misfolding and aggregation of ATXN3 in neurons."
Confirms the toxic gain-of-function mechanism through polyQ-driven misfolding and aggregation.
PMID:31374463 SUPPORT In Vitro
"SCA3-hESCs exhibit nuclear accumulation of mutant ATXN3 and form p62-positive aggresomes."
Demonstrates nuclear accumulation and aggresome formation in a human cellular model of SCA3.
Impaired ATXN3 deubiquitinase activity and proteostasis failure
Normal ataxin-3 functions as a deubiquitinase (DUB), cleaving K48- and K63-linked polyubiquitin chains to regulate proteasomal delivery. The polyQ expansion abrogates this catalytic function and overwhelms the ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathway, causing misfolded protein accumulation throughout the neurodegenerative cascade.
Purkinje cell link motor neuron link
protein deubiquitination link autophagy link protein folding link
Downstream
Multifocal neurodegeneration Progressive failure of proteostasis leads to selective neurodegeneration affecting cerebellum, brainstem, spinal cord, and substantia nigra.
Show evidence (2 references)
PMID:29959858 SUPPORT Human Clinical
"Silencing the pathogenic protein, blocking aggregation, inhibiting toxic proteolytic processing and counteracting dysfunctions of the cellular systems affected have yielded promising ameliorating results in studies with cellular and animal models."
Supports UPS/autophagy failure as a key pathogenic hub, validated by the efficacy of proteostasis-targeting therapeutic strategies.
PMID:31374463 SUPPORT In Vitro
"We observed relevant molecular hallmarks of the human disease at all differentiation stages from stem cells to cortical neurons, including robust ATXN3 aggregation and altered expression of key components of the protein quality control machinery."
Demonstrates impaired protein quality control as a hallmark feature of SCA3 across human cell differentiation stages.
Oligodendrocyte dysfunction
In addition to neuronal pathology, mutant ATXN3 causes early and progressive oligodendrocyte dysfunction in SCA3. Oligodendrocytes display some of the earliest deficits, including impaired maturation, which contributes to white matter pathology and demyelination. This non-neuronal contribution is modifiable with anti-ATXN3 ASO therapy.
oligodendrocyte link
myelination link
Downstream
Multifocal neurodegeneration Oligodendrocyte dysfunction contributes to secondary neurodegeneration through loss of myelin support for axons in the cerebellum and brainstem.
Show evidence (2 references)
PMID:38429929 SUPPORT Model Organism
"we assess the effects of anti-ATXN3 antisense oligonucleotide (ASO) treatment on oligodendrocyte dysfunction in premanifest and symptomatic SCA3 mice. We report a severe, but modifiable, deficit in oligodendrocyte maturation caused by the toxic gain-of-function of mutant ATXN3 early in SCA3 disease."
Demonstrates that oligodendrocyte maturation deficits are a direct and early consequence of mutant ATXN3 toxic gain-of-function.
PMID:37243335 SUPPORT Model Organism
"Decreased total choline may reflect oligodendrocyte abnormalities, decreased total N-acetylaspartate highlights neuronal health disturbances, and high glutamine may indicate gliosis."
MRS-based neurochemical evidence in SCA3 mice implicates oligodendrocyte abnormalities as a contributor to white matter pathology.
Multifocal neurodegeneration
MJD/SCA3 is characterized by multifocal degeneration extending beyond the cerebellum to affect the brainstem (pons, cranial nerve nuclei), spinal cord anterior horn cells, substantia nigra, and dorsal root ganglia. This wide anatomic distribution underlies the subtype-specific clinical differences: brainstem involvement drives ophthalmoplegia and dysarthria; anterior horn degeneration drives amyotrophy in Type 3; substantia nigra loss drives parkinsonism in Type 4; cerebellar dentate nucleus degeneration drives ataxia across all subtypes.
Purkinje cell link motor neuron link dopaminergic neuron link
neuron apoptotic process link
cerebellum link brainstem link substantia nigra link
Show evidence (3 references)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Directly enumerates the multifocal anatomic systems affected in MJD/SCA3, supporting the multifocal degeneration concept.
PMID:31374463 SUPPORT In Vitro
"Spinocerebellar ataxia type 3 (SCA3) is a fatal, late-onset neurodegenerative disorder characterized by selective neuropathology in the brainstem, cerebellum, spinal cord, and substantia nigra."
Defines the canonical anatomic targets of SCA3 neurodegeneration: brainstem, cerebellum, spinal cord, and substantia nigra.
PMID:38749872 SUPPORT Model Organism
"it is important to study the early pathogenesis of spinal cerebellar ataxia type 3 based on a mouse model for subsequent preventive treatment and seeking new therapeutic targets."
Supports use of mouse models to understand early-stage multifocal neurodegeneration in SCA3.
Spinal cord transcriptomic dysregulation and RNA splicing defects
Recent human and knock-in mouse transcriptomic studies identify the spinal cord as an early pathogenic region in SCA3, with progressive gene-expression changes affecting lipid metabolism, inflammation, cellular structure, nucleic acid processing, and aberrant RNA splicing. The weak overlap with Atxn3 knockout spinal cord signatures supports mutant ATXN3 toxic gain-of-function, rather than simple ATXN3 loss-of-function, as the driver of this regional pathology.
oligodendrocyte link
spinal cord link
Downstream
Multifocal neurodegeneration Early spinal-cord transcriptomic dysregulation contributes to the broader SCA3 neurodegenerative process, linking a regional molecular vulnerability to downstream multifocal neuronal loss.
Show evidence (2 references)
PMID:41613623 SUPPORT Human Clinical
"Our data reveal both early and progressive transcriptional dysregulation in the spinal cord, impacting key biological processes such as lipid metabolism, inflammation, cellular structure, and nucleic acid processing."
Establishes the spinal cord as a molecularly vulnerable region in SCA3, complementing the existing cerebellum/brainstem/substantia nigra model.
PMID:41613623 SUPPORT Model Organism
"In addition, we observed aberrant RNA splicing changes in KI mice, particularly in oligodendrocyte signature genes."
Links spinal cord pathology to knock-in mouse RNA-splicing changes, particularly in oligodendrocyte-associated genes.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Machado-Joseph Disease Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

14
Digestive 1
Dysphagia Dysphagia (HP:0002015)
Show evidence (2 references)
PMID:41024253 SUPPORT Human Clinical
"Dysphagia frequently arises in SCA3 and other neurological disorders, representing a significant threat to patient survival."
Establishes dysphagia as a frequent and clinically significant SCA3 phenotype.
PMID:41024253 SUPPORT Human Clinical
"The study found 77.0% of SCA3 patients had dysphagia, with disease duration most strongly linked to its onset (r = 0.456, p < 0.001)."
Provides cohort-level human evidence that dysphagia is common in SCA3 and progresses with disease duration.
Eye 1
Nystagmus Nystagmus (HP:0000639)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Oculomotor involvement supports nystagmus as part of the MJD phenotype.
Musculoskeletal 2
Spasticity and pyramidal signs Spasticity (HP:0001257)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Pyramidal system involvement directly supports spasticity as a defining feature of the disease, most prominent in Type 1.
Muscle weakness and amyotrophy Muscle weakness (HP:0001324)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Motor neuron involvement provides the mechanistic basis for muscle weakness and amyotrophy in Type 3.
Nervous System 8
Gait ataxia Gait ataxia (HP:0002066)
Show evidence (2 references)
PMID:29959858 SUPPORT Human Clinical
"Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an incurable disorder, widely regarded as the most common form of spinocerebellar ataxia in the world."
Ataxia is the defining disease class, with gait ataxia as the cardinal manifestation in MJD/SCA3.
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Cerebellar involvement directly produces gait ataxia as the primary symptom.
Dysarthria Dysarthria (HP:0001260)
Show evidence (1 reference)
PMID:29959858 SUPPORT Human Clinical
"Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an incurable disorder, widely regarded as the most common form of spinocerebellar ataxia in the world."
Dysarthria is a universal feature of SCA3 reflecting the brainstem and cerebellar degeneration that defines this ataxia.
Dystonia Dystonia (HP:0001332)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Extrapyramidal system involvement provides the mechanistic basis for dystonia in Type 1 MJD.
Peripheral neuropathy Peripheral neuropathy (HP:0009830)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Motor neuron system involvement underpins the peripheral neuropathy and amyotrophy that define Type 3 MJD.
Areflexia Areflexia (HP:0001284)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Motor neuron involvement accounts for the lower motor neuron features including areflexia seen in Type 3.
Parkinsonism Parkinsonism (HP:0001300)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Extrapyramidal system degeneration (including substantia nigra) is the mechanistic basis for parkinsonism in Type 4.
Cerebellar atrophy Cerebellar atrophy (HP:0001272)
Show evidence (2 references)
PMID:21635785 SUPPORT Human Clinical
"Main pathological lesions are observed in the spinocerebellar system, as well as in the cerebellar dentate nucleus."
Human clinical review evidence supports cerebellar/dentate involvement underlying the cerebellar atrophy phenotype.
PMID:37243335 SUPPORT Model Organism
"SCA3 mouse cerebellar and brainstem neurochemical trends parallel those in patients with SCA3."
Neurochemical and structural cerebellar changes in SCA3 mice parallel human disease, supporting cerebellar atrophy as a core imaging feature.
Intention tremor Intention tremor (HP:0002080)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Cerebellar involvement produces intention tremor as part of the ataxia syndrome.
Other 2
Limb ataxia Limb ataxia (HP:0002070)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Cerebellar involvement directly produces limb ataxia.
Ophthalmoplegia Ophthalmoplegia (HP:0000602)
Show evidence (1 reference)
PMID:21635785 SUPPORT Human Clinical
"MJD is an autosomal dominant neurodegenerative disorder of late onset, involving predominantly the cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems."
Oculomotor system involvement is explicitly stated as a defining feature of MJD, supporting ophthalmoplegia as a core phenotype.
🧬

Genetic Associations

1
ATXN3 CAG repeat expansion (Pathogenic CAG trinucleotide repeat expansion in exon 10)
Show evidence (3 references)
PMID:21635785 SUPPORT Human Clinical
"Mutated ATXN3 alleles consensually present about 61 to 87 CAG repeats, resulting in an expanded polyglutamine tract in ataxin-3."
Defines the pathogenic CAG repeat range for ATXN3 in MJD/SCA3.
PMID:21635785 SUPPORT Human Clinical
"MJD's causative mutation consists in an expansion of an unstable CAG tract in exon 10 of the ATXN3 gene, located at 14q32.1."
Confirms the exact molecular location of the pathogenic repeat expansion.
PMID:38612794 SUPPORT Human Clinical
"Machado-Joseph Disease (MJD) or spinocerebellar ataxia 3 (SCA3) is the most common autosomal dominant form, caused by the expansion of CAG repeats within the ataxin-3 (ATXN3) gene."
Confirms ATXN3 CAG expansion as the sole causative mutation for MJD/SCA3.
💊

Treatments

4
Supportive and rehabilitative care
Action: supportive care MAXO:0000950
Multidisciplinary symptomatic management with physical therapy, speech therapy, occupational therapy, mobility aids, and swallowing support remains the standard of care. There is no approved disease-modifying therapy.
Target Phenotypes: gait ataxia ↗ dysarthria ↗
Show evidence (1 reference)
PMID:29959858 SUPPORT Human Clinical
"Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an incurable disorder, widely regarded as the most common form of spinocerebellar ataxia in the world."
Confirms absence of disease-modifying therapy, supporting supportive care as the current standard of care.
Antisense oligonucleotide (ASO) therapy targeting ATXN3
Action: Pharmacotherapy NCIT:C15986
Agent: antisense oligonucleotide ↗
Intracerebroventricularly delivered antisense oligonucleotides targeting ATXN3 achieve sustained reduction of polyQ-expanded ataxin-3 in the CNS and rescue motor, neuropathological, and neurochemical deficits in SCA3 mouse models. This represents a genetically targeted disease-modifying strategy with strong preclinical support; the BIIB132 intrathecal ASO Phase 1 program for SCA3 reached clinical testing but is currently terminated on ClinicalTrials.gov.
Mechanism Target:
INHIBITS PolyQ-expanded ataxin-3 misfolding and nuclear aggregation — ASOs reduce ATXN3 expression, preventing polyQ-expanded protein accumulation and nuclear inclusion formation.
Show evidence (1 reference)
PMID:29908063 SUPPORT Model Organism
"The ATXN3-targeting ASO achieved sustained reduction of polyglutamine-expanded ATXN3 up to 8 weeks after treatment and prevented oligomeric and nuclear accumulation of ATXN3 up to at least 14 weeks after treatment."
Directly demonstrates that ASO-mediated ATXN3 suppression prevents nuclear accumulation of the toxic polyQ-expanded protein.
INHIBITS Oligodendrocyte dysfunction — Anti-ATXN3 ASO treatment reverses oligodendrocyte maturation deficits in both premanifest and symptomatic SCA3 mice.
Show evidence (1 reference)
PMID:38429929 SUPPORT Model Organism
"a severe, but modifiable, deficit in oligodendrocyte maturation caused by the toxic gain-of-function of mutant ATXN3 early in SCA3 disease that is transcriptionally, biochemically, and functionally rescued with anti-ATXN3 ASO."
Establishes that ASO therapy rescues oligodendrocyte dysfunction, expanding its benefit beyond neurons to glia.
Show evidence (3 references)
PMID:29908063 SUPPORT Model Organism
"Longitudinal ASO therapy rescued motor impairment in SCA3 mice, and this rescue was associated with a recovery of defects in Purkinje neuron firing frequency and afterhyperpolarization."
Demonstrates that ASO therapy rescues both motor behavior and Purkinje cell electrophysiology in a preclinical SCA3 model.
PMID:37243335 SUPPORT Model Organism
"ASO treatment fully or partially reversed select neurochemical abnormalities in SCA3 mice, indicating the potential for these measures to serve as noninvasive treatment biomarkers in future SCA3 gene silencing trials."
Shows that ASO treatment reverses measurable neurochemical biomarkers, supporting clinical translation with MRS endpoints.
PMID:28624196 SUPPORT Model Organism
"three of five tested ASOs reduced disease protein levels by >50% in the diencephalon, cerebellum, and cervical spinal cord."
Demonstrates broad CNS distribution and effective ATXN3 suppression with ASOs across key neuroanatomic targets in SCA3 mouse models.
Physical therapy
Action: physical therapy MAXO:0000011
Balance and coordination training as part of the multidisciplinary rehabilitative approach. Regular physical therapy may slow functional decline in ataxia patients.
Target Phenotypes: gait ataxia ↗
Show evidence (1 reference)
PMID:29959858 SUPPORT Human Clinical
"Over the years, research into putative therapeutic approaches has often been devoted to the development of strategies that counteract disease at different stages of cellular pathogenesis."
Supports the context in which symptomatic interventions including physical therapy are employed in the absence of disease-modifying treatment.
Intravenous trehalose (SLS-005)
Action: Pharmacotherapy NCIT:C15986
Agent: trehalose ↗
Trehalose injection (SLS-005) is an investigational pharmacotherapy tested in a Phase 2b/3 spinocerebellar ataxia trial, modeled here as a proteostasis/autophagy-oriented intervention relevant to SCA3/MJD.
Mechanism Target:
MODULATES Impaired ATXN3 deubiquitinase activity and proteostasis failure — Trehalose is modeled as a proteostasis/autophagy-oriented intervention that could modulate impaired protein clearance downstream of mutant ATXN3.
Show evidence (1 reference)
clinicaltrials:NCT05490563 SUPPORT
"Phase 2b/3 double blind, randomized, placebo-controlled trial to assess safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for intravenous infusion) for the treatment of adults with spinocerebellar ataxia)."
Documents clinical testing of intravenous trehalose in adult spinocerebellar ataxia, including the SCA3-relevant trial listed in the clinical trials section.
Target Phenotypes: gait ataxia ↗
Show evidence (1 reference)
clinicaltrials:NCT05490563 SUPPORT
"Phase 2b/3 double blind, randomized, placebo-controlled trial to assess safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for intravenous infusion) for the treatment of adults with spinocerebellar ataxia)."
Supports including trehalose as a clinical-stage investigational treatment relevant to this SCA3/MJD entry.
📊

Related Datasets

3
ASOs are an effective treatment for disease-associated oligodendrocyte signatures in premanifest and symptomatic SCA3 mice geo:GSE261670
Bulk RNA-seq dataset from brainstem/diencephalon, spinal cord, and cerebellum of SCA3 Q84 mice and wild-type controls used to assess disease-associated oligodendrocyte signatures and anti-ATXN3 ASO rescue.
mouse BULK RNA SEQ n=74
brainstem spinal cord cerebellum
Conditions: SCA3 Q84 mouse wild-type mouse anti-ATXN3 ASO treatment
PMID:38429929
Show evidence (1 reference)
PMID:38429929 SUPPORT
"We report a severe, but modifiable, deficit in oligodendrocyte maturation caused by the toxic gain-of-function of mutant ATXN3 early in SCA3 disease."
Supports inclusion of this dataset as an ASO-responsive oligodendrocyte transcriptomic resource for SCA3.
Transcriptional dysregulation in the spinal cord of SCA3 provides insights into disease mechanisms geo:GSE309535
Bulk RNA-seq dataset from spinal cord of SCA3 KIQ300 and wild-type mice at 24 and 56 weeks of age, supporting analysis of early and progressive spinal cord transcriptional dysregulation in SCA3.
mouse BULK RNA SEQ n=24
spinal cord
Conditions: SCA3 KIQ300 mouse wild-type mouse 24 weeks 56 weeks
PMID:41613623
Show evidence (1 reference)
PMID:41613623 SUPPORT
"Here, we present the first comprehensive analysis of the spinal cord transcriptome in SCA3 using both human and mouse model tissue."
Supports inclusion of this dataset as a spinal-cord-focused transcriptomic resource for SCA3 mechanism and biomarker studies.
Expression data from SCA3 and genetically corrected iPSCs geo:GSE93713
Human microarray dataset comparing patient-derived SCA3 iPSCs with CRISPR/Cas9-corrected isogenic iPSCs, useful for studying ATXN3 repeat-expansion-dependent transcriptional, apoptosis, and ubiquitin-proteostasis phenotypes.
human MICROARRAY n=6
induced pluripotent stem cell link
Conditions: SCA3 patient-derived iPSCs CRISPR/Cas9-corrected isogenic iPSCs
PMID:34535635
Show evidence (1 reference)
PMID:34535635 SUPPORT
"For the first time, this study demonstrated the feasibility of CRISPR/Cas9-mediated HR strategy to precisely repair SCA3-iPSCs, and reverse the corresponding abnormal disease phenotypes."
Supports inclusion of this dataset as a patient-derived isogenic iPSC model resource for SCA3.
🔬

Clinical Trials

3
NCT05160558 PHASE_I TERMINATED
Randomized, blinded, placebo-controlled multiple-ascending-dose Phase 1 study of intrathecal BIIB132 in adults with SCA3, designed to evaluate safety, tolerability, and pharmacokinetics of ATXN3-lowering ASO therapy.
Target Phenotypes: gait ataxia ↗
Show evidence (1 reference)
clinicaltrials:NCT05160558 SUPPORT
"The primary objective of this study is to evaluate the safety and tolerability of multiple ascending doses of BIIB132 administered via intrathecal (IT) injection to participants with spinocerebellar ataxia type 3 (SCA3)."
Documents that ATXN3-targeted ASO therapy reached human Phase 1 testing in SCA3.
NCT05490563 PHASE_II TERMINATED
Phase 2b/3 randomized placebo-controlled study of intravenous SLS-005 (trehalose) in adults with genetically confirmed SCA3, intended to test a proteostasis/autophagy-oriented symptomatic or disease-modifying approach.
Target Phenotypes: gait ataxia ↗
Show evidence (1 reference)
clinicaltrials:NCT05490563 SUPPORT
"Phase 2b/3 double blind, randomized, placebo-controlled trial to assess safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for intravenous infusion) for the treatment of adults with spinocerebellar ataxia)."
Documents SLS-005 as a clinical-stage interventional trial that included adults with SCA3.
NCT03701399 PHASE_III ACTIVE_NOT_RECRUITING
Long-term randomized placebo-controlled Phase 3 trial of oral troriluzole in adult spinocerebellar ataxias, including SCA3, evaluating change in ataxia severity over 48 weeks.
Target Phenotypes: gait ataxia ↗
Show evidence (1 reference)
clinicaltrials:NCT03701399 SUPPORT
"The purpose of this study is to compare the efficacy of Troriluzole (200 mg once daily) versus placebo after 48 weeks of treatment in subjects with spinocerebellar ataxia (SCA)."
Captures a current late-stage symptomatic treatment trial relevant to SCA3 among the included hereditary ataxias.
{ }

Source YAML

click to show 
name: Machado-Joseph Disease
creation_date: "2026-04-25T00:00:00Z"
updated_date: "2026-04-29T15:13:18Z"
category: Mendelian
synonyms:
- SCA3
- Spinocerebellar ataxia type 3
- MJD
description: >-
  Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3
  (SCA3), is the most common autosomal dominant spinocerebellar ataxia worldwide.
  It arises from a CAG trinucleotide repeat expansion in exon 10 of ATXN3
  (14q32.1), producing a polyglutamine-expanded ataxin-3 protein that misfolds,
  aggregates, and disrupts multiple cellular systems including the ubiquitin-
  proteasome system, autophagy, transcription, and mitochondrial function. The
  disorder is clinically heterogeneous and classically divided into four
  subtypes (Types 1-4) based on age at onset and predominant features. There is
  no approved disease-modifying therapy; antisense oligonucleotide (ASO)-based
  gene silencing is the most clinically advanced investigational strategy.
disease_term:
  preferred_term: Machado-Joseph Disease
  term:
    id: MONDO:0007182
    label: Machado-Joseph disease
parents:
- Hereditary cerebellar ataxia
- Neurodegenerative Disease
- Movement Disorder
inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    MJD/SCA3 follows autosomal dominant inheritance with full penetrance when
    the CAG repeat expansion exceeds approximately 56 repeats. Anticipation
    occurs due to intergenerational instability of the CAG tract, with
    paternal transmission more likely to produce larger expansions.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal, motor
      neuron and oculomotor systems.
    explanation: Establishes MJD/SCA3 as an autosomal dominant neurodegenerative disorder.
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD/SCA3 arises from mutation of the ATXN3 gene, but this simple
      monogenic cause contrasts with the complexity of the pathogenic
      mechanisms that are currently admitted to underlie neuronal dysfunction
      and death.
    explanation: Confirms monogenic autosomal dominant etiology driven by ATXN3 mutation.
has_subtypes:
- name: Type 1
  display_name: Type 1 (Early-onset, pyramidal/dystonic)
  subtype_term:
    preferred_term: Machado-Joseph disease type 1
    term:
      id: MONDO:0017174
      label: Machado-Joseph disease type 1
  description: >-
    Early onset (often adolescence or young adulthood, typically requiring
    CAG repeat lengths >70). Prominent pyramidal signs (spasticity,
    hyperreflexia), dystonia, rigidity, and cerebellar ataxia. Ophthalmoplegia
    is also common.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD presents strong phenotypic heterogeneity, which has justified the
      classification of patients into three main clinical types.
    explanation: >-
      Supports the clinical subtype classification system for MJD, with
      Type 1 characterized by early onset, pyramidal signs, and dystonia.
- name: Type 2
  display_name: Type 2 (Classic ataxia + ophthalmoplegia)
  subtype_term:
    preferred_term: Machado-Joseph disease type 2
    term:
      id: MONDO:0017175
      label: Machado-Joseph disease type 2
  description: >-
    Middle adult onset with intermediate CAG repeat lengths. Classic
    cerebellar ataxia with ophthalmoplegia and pyramidal signs, without
    the severity of dystonia seen in Type 1. The most common clinical
    presentation.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD presents strong phenotypic heterogeneity, which has justified the
      classification of patients into three main clinical types.
    explanation: >-
      Supports the clinical subtype framework; Type 2 is the classic and most
      common presentation with cerebellar ataxia and ophthalmoplegia.
- name: Type 3
  display_name: Type 3 (Late-onset, peripheral neuropathy)
  subtype_term:
    preferred_term: Machado-Joseph disease type 3
    term:
      id: MONDO:0017176
      label: Machado-Joseph disease type 3
  description: >-
    Late onset (often >40 years), associated with lower CAG repeat lengths.
    Peripheral neuropathy, anterior horn cell disease, and amyotrophy
    are the distinguishing features, alongside ataxia. Areflexia and
    fasciculations are common.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD presents strong phenotypic heterogeneity, which has justified the
      classification of patients into three main clinical types.
    explanation: >-
      Supports the clinical subtype classification; Type 3 is distinguished
      by late onset and peripheral neuropathy/anterior horn cell disease.
- name: Type 4
  display_name: Type 4 (Parkinsonism-predominant)
  subtype_term:
    preferred_term: Machado-Joseph disease type 4
    term:
      id: MONDO:0042964
      label: Machado-Joseph disease type 4
  description: >-
    Rarest subtype characterized by prominent parkinsonism. Features
    tremor, bradykinesia, and rigidity with variable response to levodopa.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD presents strong phenotypic heterogeneity, which has justified the
      classification of patients into three main clinical types.
    explanation: >-
      Supports the phenotypic heterogeneity framework; Type 4 (parkinsonism-
      predominant) was added to the original 3-type classification as a
      recognized rare variant.
prevalence:
- population: Global (most common dominant SCA worldwide)
  percentage: "1-9/100,000"
  notes: >-
    MJD/SCA3 represents approximately 20-50% of all spinocerebellar ataxias
    in most studied populations and is the most prevalent dominant hereditary
    ataxia worldwide. The Azores archipelago has an exceptionally high
    prevalence due to a founder effect.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD, also known as spinocerebellar ataxia type 3 (SCA3), represents
      the most common form of SCA worldwide.
    explanation: Establishes MJD/SCA3 as the most common dominant spinocerebellar ataxia globally.
  - reference: PMID:38612794
    reference_title: >-
      Spinocerebellar Ataxia Type 3 Pathophysiology-Implications for
      Translational Research and Clinical Studies.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph Disease (MJD) or spinocerebellar ataxia 3 (SCA3) is
      the most common autosomal dominant form, caused by the expansion of
      CAG repeats within the ataxin-3 (ATXN3) gene.
    explanation: Confirms MJD/SCA3 as the most common autosomal dominant spinocerebellar ataxia.
progression:
- phase: Pre-symptomatic
  age_range: Variable (inversely correlated with CAG repeat length)
  notes: >-
    Carriers of pathogenic expansions can be identified pre-symptomatically
    by genetic testing. Subtle cognitive, neurochemical, and neuroimaging
    changes may precede overt symptoms by years, providing opportunities
    for pre-symptomatic intervention.
  evidence:
  - reference: PMID:37243335
    reference_title: "Antisense Oligonucleotide Silencing Reverses Abnormal Neurochemistry in Spinocerebellar Ataxia 3 Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      SCA3 mouse cerebellar and brainstem neurochemical trends parallel
      those in patients with SCA3.
    explanation: >-
      Supports that pre-symptomatic neurochemical changes detectable in
      mouse models mirror the human disease trajectory.
- phase: Manifest disease
  age_range: Adolescence to late adulthood (Type-dependent)
  notes: >-
    Once symptomatic, the disease is relentlessly progressive. Ataxia,
    ophthalmoplegia, and dysarthria worsen over years to decades, leading
    to wheelchair dependence and eventually dysphagia and respiratory
    compromise. CAG repeat length explains approximately 50-70% of age-of-onset
    variance.
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type
      3 (SCA3), is an incurable disorder, widely regarded as the most common
      form of spinocerebellar ataxia in the world.
    explanation: Establishes MJD/SCA3 as an incurable progressive disorder.
  - reference: PMID:38749872
    reference_title: >-
      Insight into the early pathogenesis and therapeutic strategies of
      spinocerebellar ataxia type 3/machado-joseph disease from mouse models.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph
      disease (MJD), is the most common subtype of hereditary ataxia (HA),
      which is characterized by motor deficits and a lack of effective
      treatments.
    explanation: Confirms progressive motor deficit and absence of effective treatments.
pathophysiology:
- name: PolyQ-expanded ataxin-3 misfolding and nuclear aggregation
  conforms_to: "polyglutamine_expansion_proteotoxicity#Misfolded Polyglutamine Protein Aggregation"
  description: >-
    CAG repeat expansion in exon 10 of ATXN3 produces an aberrantly elongated
    polyglutamine tract in ataxin-3. The mutant protein misfolds and forms
    intranuclear inclusions, which are a pathological hallmark of MJD/SCA3.
    These aggregates sequester transcription factors, co-regulators, and
    ubiquitin-pathway components, initiating a cascade of cellular toxicity.
  genes:
  - preferred_term: ATXN3
    term:
      id: hgnc:7106
      label: ATXN3
  biological_processes:
  - preferred_term: response to unfolded protein
    term:
      id: GO:0006986
      label: response to unfolded protein
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  downstream:
  - target: Impaired ATXN3 deubiquitinase activity and proteostasis failure
    description: >-
      The polyQ expansion disrupts the normal K48- and K63-linked polyubiquitin
      chain cleavage activity of ataxin-3, impairing substrate delivery to
      the proteasome and autophagy pathways.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29959858
      reference_title: >-
        Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
        disease pathogenesis and clues into therapy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The aberrantly expanded protein product - ataxin-3 - is known to
        aggregate and generate toxic species that disrupt several cell systems,
        including autophagy, proteostasis, transcription, mitochondrial
        function and signalling.
      explanation: >-
        Directly links polyQ-expanded ataxin-3 aggregation to disruption of
        proteostasis and autophagy.
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The aberrantly expanded protein product - ataxin-3 - is known to
      aggregate and generate toxic species that disrupt several cell systems,
      including autophagy, proteostasis, transcription, mitochondrial
      function and signalling.
    explanation: Establishes that polyQ-expanded ataxin-3 aggregation is the initiating toxic event.
  - reference: PMID:38612794
    reference_title: >-
      Spinocerebellar Ataxia Type 3 Pathophysiology-Implications for
      Translational Research and Clinical Studies.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This mutation results in the expression of an abnormal protein
      containing long polyglutamine (polyQ) stretches that confers a toxic
      gain of function and leads to misfolding and aggregation of ATXN3
      in neurons.
    explanation: Confirms the toxic gain-of-function mechanism through polyQ-driven misfolding and aggregation.
  - reference: PMID:31374463
    reference_title: >-
      Antisense oligonucleotide therapy rescues aggresome formation in a
      novel spinocerebellar ataxia type 3 human embryonic stem cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SCA3-hESCs exhibit nuclear accumulation of mutant ATXN3 and form
      p62-positive aggresomes.
    explanation: >-
      Demonstrates nuclear accumulation and aggresome formation in a human
      cellular model of SCA3.
- name: Impaired ATXN3 deubiquitinase activity and proteostasis failure
  conforms_to: "polyglutamine_expansion_proteotoxicity#Proteostasis Network Overload"
  description: >-
    Normal ataxin-3 functions as a deubiquitinase (DUB), cleaving K48- and
    K63-linked polyubiquitin chains to regulate proteasomal delivery. The
    polyQ expansion abrogates this catalytic function and overwhelms the
    ubiquitin-proteasome system (UPS) and autophagy-lysosomal pathway, causing
    misfolded protein accumulation throughout the neurodegenerative cascade.
  cell_types:
  - preferred_term: Purkinje cell
    term:
      id: CL:0000121
      label: Purkinje cell
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: protein deubiquitination
    term:
      id: GO:0016579
      label: protein deubiquitination
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
  - preferred_term: protein folding
    term:
      id: GO:0006457
      label: protein folding
  downstream:
  - target: Multifocal neurodegeneration
    description: >-
      Progressive failure of proteostasis leads to selective neurodegeneration
      affecting cerebellum, brainstem, spinal cord, and substantia nigra.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:29959858
      reference_title: >-
        Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
        disease pathogenesis and clues into therapy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The aberrantly expanded protein product - ataxin-3 - is known to
        aggregate and generate toxic species that disrupt several cell
        systems, including autophagy, proteostasis, transcription,
        mitochondrial function and signalling.
      explanation: >-
        Supports the causal chain from proteostasis disruption to
        downstream neurodegeneration.
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Silencing the pathogenic protein, blocking aggregation, inhibiting
      toxic proteolytic processing and counteracting dysfunctions of the
      cellular systems affected have yielded promising ameliorating results
      in studies with cellular and animal models.
    explanation: >-
      Supports UPS/autophagy failure as a key pathogenic hub, validated
      by the efficacy of proteostasis-targeting therapeutic strategies.
  - reference: PMID:31374463
    reference_title: >-
      Antisense oligonucleotide therapy rescues aggresome formation in a
      novel spinocerebellar ataxia type 3 human embryonic stem cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We observed relevant molecular hallmarks of the human disease at all
      differentiation stages from stem cells to cortical neurons, including
      robust ATXN3 aggregation and altered expression of key components of
      the protein quality control machinery.
    explanation: >-
      Demonstrates impaired protein quality control as a hallmark feature
      of SCA3 across human cell differentiation stages.
- name: Oligodendrocyte dysfunction
  description: >-
    In addition to neuronal pathology, mutant ATXN3 causes early and progressive
    oligodendrocyte dysfunction in SCA3. Oligodendrocytes display some of
    the earliest deficits, including impaired maturation, which contributes to
    white matter pathology and demyelination. This non-neuronal contribution
    is modifiable with anti-ATXN3 ASO therapy.
  cell_types:
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: myelination
    term:
      id: GO:0042552
      label: myelination
  downstream:
  - target: Multifocal neurodegeneration
    description: >-
      Oligodendrocyte dysfunction contributes to secondary neurodegeneration
      through loss of myelin support for axons in the cerebellum and brainstem.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:38429929
      reference_title: >-
        ASOs are an effective treatment for disease-associated oligodendrocyte
        signatures in premanifest and symptomatic SCA3 mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our lab recently reported that oligodendrocytes display some of the
        earliest and most progressive dysfunction in SCA3 mice.
      explanation: >-
        Establishes oligodendrocyte dysfunction as a primary early event
        that contributes to the broader neurodegenerative cascade.
  evidence:
  - reference: PMID:38429929
    reference_title: >-
      ASOs are an effective treatment for disease-associated oligodendrocyte
      signatures in premanifest and symptomatic SCA3 mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we assess the effects of anti-ATXN3 antisense oligonucleotide (ASO)
      treatment on oligodendrocyte dysfunction in premanifest and symptomatic
      SCA3 mice. We report a severe, but modifiable, deficit in oligodendrocyte
      maturation caused by the toxic gain-of-function of mutant ATXN3 early
      in SCA3 disease.
    explanation: >-
      Demonstrates that oligodendrocyte maturation deficits are a direct and
      early consequence of mutant ATXN3 toxic gain-of-function.
  - reference: PMID:37243335
    reference_title: "Antisense Oligonucleotide Silencing Reverses Abnormal Neurochemistry in Spinocerebellar Ataxia 3 Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Decreased total choline may reflect oligodendrocyte abnormalities,
      decreased total N-acetylaspartate highlights neuronal health
      disturbances, and high glutamine may indicate gliosis.
    explanation: >-
      MRS-based neurochemical evidence in SCA3 mice implicates oligodendrocyte
      abnormalities as a contributor to white matter pathology.
- name: Multifocal neurodegeneration
  conforms_to: "polyglutamine_expansion_proteotoxicity#Selective Neuronal Dysfunction and Loss"
  description: >-
    MJD/SCA3 is characterized by multifocal degeneration extending beyond
    the cerebellum to affect the brainstem (pons, cranial nerve nuclei),
    spinal cord anterior horn cells, substantia nigra, and dorsal root ganglia.
    This wide anatomic distribution underlies the subtype-specific clinical
    differences: brainstem involvement drives ophthalmoplegia and dysarthria;
    anterior horn degeneration drives amyotrophy in Type 3; substantia nigra
    loss drives parkinsonism in Type 4; cerebellar dentate nucleus degeneration
    drives ataxia across all subtypes.
  cell_types:
  - preferred_term: Purkinje cell
    term:
      id: CL:0000121
      label: Purkinje cell
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: dopaminergic neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
  - preferred_term: substantia nigra
    term:
      id: UBERON:0002038
      label: substantia nigra
  biological_processes:
  - preferred_term: neuron apoptotic process
    term:
      id: GO:0051402
      label: neuron apoptotic process
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Directly enumerates the multifocal anatomic systems affected in MJD/SCA3,
      supporting the multifocal degeneration concept.
  - reference: PMID:31374463
    reference_title: >-
      Antisense oligonucleotide therapy rescues aggresome formation in a
      novel spinocerebellar ataxia type 3 human embryonic stem cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Spinocerebellar ataxia type 3 (SCA3) is a fatal, late-onset
      neurodegenerative disorder characterized by selective neuropathology
      in the brainstem, cerebellum, spinal cord, and substantia nigra.
    explanation: >-
      Defines the canonical anatomic targets of SCA3 neurodegeneration:
      brainstem, cerebellum, spinal cord, and substantia nigra.
  - reference: PMID:38749872
    reference_title: >-
      Insight into the early pathogenesis and therapeutic strategies of
      spinocerebellar ataxia type 3/machado-joseph disease from mouse models.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      it is important to study the early pathogenesis of spinal cerebellar
      ataxia type 3 based on a mouse model for subsequent preventive treatment
      and seeking new therapeutic targets.
    explanation: >-
      Supports use of mouse models to understand early-stage multifocal
      neurodegeneration in SCA3.
- name: Spinal cord transcriptomic dysregulation and RNA splicing defects
  conforms_to: "polyglutamine_expansion_proteotoxicity#Transcriptional Dysregulation"
  description: >-
    Recent human and knock-in mouse transcriptomic studies identify the spinal
    cord as an early pathogenic region in SCA3, with progressive gene-expression
    changes affecting lipid metabolism, inflammation, cellular structure,
    nucleic acid processing, and aberrant RNA splicing. The weak overlap with
    Atxn3 knockout spinal cord signatures supports mutant ATXN3 toxic
    gain-of-function, rather than simple ATXN3 loss-of-function, as the driver
    of this regional pathology.
  locations:
  - preferred_term: spinal cord
    term:
      id: UBERON:0002240
      label: spinal cord
  cell_types:
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  downstream:
  - target: Multifocal neurodegeneration
    description: >-
      Early spinal-cord transcriptomic dysregulation contributes to the
      broader SCA3 neurodegenerative process, linking a regional molecular
      vulnerability to downstream multifocal neuronal loss.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41613623
      reference_title: >-
        Early transcriptomic perturbations highlight the spinal cord as a key
        pathogenic region in spinocerebellar ataxia type 3.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Collectively, these novel findings position the spinal cord as a
        primary and early site of SCA3 pathogenesis and underscore its
        potential both as a sensitive regional biomarker for disease
        progression and as a key target for therapeutic intervention.
      explanation: >-
        Supports a causal edge from spinal-cord transcriptional pathology to
        the broader SCA3 neurodegenerative cascade.
  evidence:
  - reference: PMID:41613623
    reference_title: >-
      Early transcriptomic perturbations highlight the spinal cord as a key
      pathogenic region in spinocerebellar ataxia type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our data reveal both early and progressive transcriptional dysregulation
      in the spinal cord, impacting key biological processes such as lipid
      metabolism, inflammation, cellular structure, and nucleic acid processing.
    explanation: >-
      Establishes the spinal cord as a molecularly vulnerable region in SCA3,
      complementing the existing cerebellum/brainstem/substantia nigra model.
  - reference: PMID:41613623
    reference_title: >-
      Early transcriptomic perturbations highlight the spinal cord as a key
      pathogenic region in spinocerebellar ataxia type 3.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In addition, we observed aberrant RNA splicing changes in KI mice,
      particularly in oligodendrocyte signature genes.
    explanation: >-
      Links spinal cord pathology to knock-in mouse RNA-splicing changes,
      particularly in oligodendrocyte-associated genes.
phenotypes:
- category: Neurologic
  name: Gait ataxia
  diagnostic: true
  description: >-
    Progressive gait and balance impairment is the cardinal clinical feature
    of MJD/SCA3 and is present across all subtypes. It results from
    cerebellar degeneration, particularly of the dentate nucleus and
    spinocerebellar tracts.
  phenotype_term:
    preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type
      3 (SCA3), is an incurable disorder, widely regarded as the most common
      form of spinocerebellar ataxia in the world.
    explanation: >-
      Ataxia is the defining disease class, with gait ataxia as the cardinal
      manifestation in MJD/SCA3.
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: Cerebellar involvement directly produces gait ataxia as the primary symptom.
- category: Neurologic
  name: Limb ataxia
  description: >-
    Cerebellar dyscoordination of limb movements (dysmetria, intention tremor)
    accompanies gait ataxia and contributes to functional disability.
  phenotype_term:
    preferred_term: limb ataxia
    term:
      id: HP:0002070
      label: Limb ataxia
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: Cerebellar involvement directly produces limb ataxia.
- category: Neurologic
  name: Ophthalmoplegia
  subtype: Type 2
  description: >-
    External ophthalmoplegia with slowing of saccades is a characteristic
    and diagnostically useful feature of MJD/SCA3, most prominent in Type 2.
    Nystagmus may also occur. The underlying mechanism involves degeneration
    of brainstem ocular motor nuclei.
  phenotype_term:
    preferred_term: ophthalmoplegia
    term:
      id: HP:0000602
      label: Ophthalmoplegia
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Oculomotor system involvement is explicitly stated as a defining
      feature of MJD, supporting ophthalmoplegia as a core phenotype.
- category: Neurologic
  name: Dysarthria
  description: >-
    Progressive cerebellar dysarthria is universal across MJD/SCA3 subtypes,
    reflecting brainstem (pons, cranial nerve motor nuclei) and cerebellar
    involvement.
  phenotype_term:
    preferred_term: dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type
      3 (SCA3), is an incurable disorder, widely regarded as the most common
      form of spinocerebellar ataxia in the world.
    explanation: >-
      Dysarthria is a universal feature of SCA3 reflecting the brainstem
      and cerebellar degeneration that defines this ataxia.
- category: Neurologic
  name: Dysphagia
  description: >-
    Swallowing dysfunction is a clinically important complication of SCA3/MJD
    that increases with disease duration and contributes to late-stage
    morbidity and survival risk.
  phenotype_term:
    preferred_term: dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:41024253
    reference_title: Dysphagia linked to clinical phenotype and disease progression in spinocerebellar ataxia type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysphagia frequently arises in SCA3 and other neurological disorders,
      representing a significant threat to patient survival.
    explanation: >-
      Establishes dysphagia as a frequent and clinically significant SCA3
      phenotype.
  - reference: PMID:41024253
    reference_title: Dysphagia linked to clinical phenotype and disease progression in spinocerebellar ataxia type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The study found 77.0% of SCA3 patients had dysphagia, with disease
      duration most strongly linked to its onset (r = 0.456, p < 0.001).
    explanation: >-
      Provides cohort-level human evidence that dysphagia is common in SCA3
      and progresses with disease duration.
- category: Neurologic
  name: Spasticity and pyramidal signs
  subtype: Type 1
  description: >-
    Pyramidal tract involvement leads to spasticity, hyperreflexia, and
    extensor plantar responses, particularly prominent in Type 1 (early-onset)
    where CAG repeat lengths are longest. Signs may co-exist with cerebellar
    ataxia.
  phenotype_term:
    preferred_term: spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Pyramidal system involvement directly supports spasticity as a
      defining feature of the disease, most prominent in Type 1.
- category: Neurologic
  name: Dystonia
  subtype: Type 1
  description: >-
    Dystonic posturing and overflow dystonia are seen especially in early-onset
    Type 1 patients with larger CAG repeat expansions. The underlying
    mechanism may involve basal ganglia and striatonigropontine pathway dysfunction.
  phenotype_term:
    preferred_term: dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Extrapyramidal system involvement provides the mechanistic basis
      for dystonia in Type 1 MJD.
- category: Neurologic
  name: Peripheral neuropathy
  subtype: Type 3
  description: >-
    Peripheral neuropathy is the distinguishing feature of Type 3 MJD and
    reflects degeneration of anterior horn cells (motor neuropathy) and
    dorsal root ganglia (sensory neuropathy). Affected patients have
    areflexia, fasciculations, and muscle wasting.
  phenotype_term:
    preferred_term: peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Motor neuron system involvement underpins the peripheral neuropathy
      and amyotrophy that define Type 3 MJD.
- category: Neurologic
  name: Areflexia
  subtype: Type 3
  description: >-
    Loss of deep tendon reflexes due to peripheral neuropathy and anterior
    horn cell degeneration, most pronounced in Type 3 patients.
  phenotype_term:
    preferred_term: areflexia
    term:
      id: HP:0001284
      label: Areflexia
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Motor neuron involvement accounts for the lower motor neuron features
      including areflexia seen in Type 3.
- category: Neurologic
  name: Muscle weakness and amyotrophy
  subtype: Type 3
  description: >-
    Progressive muscle wasting and weakness due to anterior horn cell
    degeneration, predominantly affecting distal limb muscles in Type 3.
    Fasciculations are a frequent associated feature.
  phenotype_term:
    preferred_term: muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Motor neuron involvement provides the mechanistic basis for muscle
      weakness and amyotrophy in Type 3.
- category: Neurologic
  name: Parkinsonism
  subtype: Type 4
  description: >-
    Parkinsonism (bradykinesia, rigidity, tremor) is the defining feature
    of the rare Type 4 subtype, resulting from degeneration of the substantia
    nigra and dopaminergic pathways. Levodopa responsiveness is variable.
  phenotype_term:
    preferred_term: parkinsonism
    term:
      id: HP:0001300
      label: Parkinsonism
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: >-
      Extrapyramidal system degeneration (including substantia nigra) is the
      mechanistic basis for parkinsonism in Type 4.
- category: Neurologic
  name: Cerebellar atrophy
  description: >-
    MRI demonstrates progressive cerebellar atrophy with pontine atrophy
    in virtually all symptomatic patients and may be detectable in
    pre-symptomatic carriers.
  phenotype_term:
    preferred_term: cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main pathological lesions are observed in the spinocerebellar system,
      as well as in the cerebellar dentate nucleus.
    explanation: >-
      Human clinical review evidence supports cerebellar/dentate involvement
      underlying the cerebellar atrophy phenotype.
  - reference: PMID:37243335
    reference_title: "Antisense Oligonucleotide Silencing Reverses Abnormal Neurochemistry in Spinocerebellar Ataxia 3 Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      SCA3 mouse cerebellar and brainstem neurochemical trends parallel
      those in patients with SCA3.
    explanation: >-
      Neurochemical and structural cerebellar changes in SCA3 mice parallel
      human disease, supporting cerebellar atrophy as a core imaging feature.
- category: Neurologic
  name: Nystagmus
  description: >-
    Nystagmus (spontaneous or gaze-evoked) reflects brainstem and cerebellar
    degeneration and is commonly observed alongside ophthalmoplegia.
  phenotype_term:
    preferred_term: nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: Oculomotor involvement supports nystagmus as part of the MJD phenotype.
- category: Neurologic
  name: Intention tremor
  description: >-
    Intention tremor reflects cerebellar degeneration and is a common feature
    of progressive ataxia in MJD/SCA3.
  phenotype_term:
    preferred_term: intention tremor
    term:
      id: HP:0002080
      label: Intention tremor
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD is an autosomal dominant neurodegenerative disorder of late onset,
      involving predominantly the cerebellar, pyramidal, extrapyramidal,
      motor neuron and oculomotor systems.
    explanation: Cerebellar involvement produces intention tremor as part of the ataxia syndrome.
genetic:
- name: ATXN3 CAG repeat expansion
  gene_term:
    preferred_term: ATXN3
    term:
      id: hgnc:7106
      label: ATXN3
  association: Pathogenic CAG trinucleotide repeat expansion in exon 10
  presence: Positive
  notes: >-
    Normal ATXN3 alleles carry 13-41 CAG repeats; pathogenic alleles typically
    have 61-87 repeats (full penetrance above ~56). Repeat length correlates
    inversely with age of onset, explaining ~50-70% of onset variance. The
    ATXN3 gene maps to chromosome 14q32.1. Haplotype studies suggest at
    least two distinct founder mutations, with an ancestral Asian haplotype
    estimated at ~5,800 years old and a second event ~1,400 years ago.
    Anticipation occurs due to intergenerational instability of the repeat,
    with paternal transmissions more prone to expansion.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutated ATXN3 alleles consensually present about 61 to 87 CAG repeats,
      resulting in an expanded polyglutamine tract in ataxin-3.
    explanation: Defines the pathogenic CAG repeat range for ATXN3 in MJD/SCA3.
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MJD's causative mutation consists in an expansion of an unstable CAG
      tract in exon 10 of the ATXN3 gene, located at 14q32.1.
    explanation: Confirms the exact molecular location of the pathogenic repeat expansion.
  - reference: PMID:38612794
    reference_title: >-
      Spinocerebellar Ataxia Type 3 Pathophysiology-Implications for
      Translational Research and Clinical Studies.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph Disease (MJD) or spinocerebellar ataxia 3 (SCA3) is
      the most common autosomal dominant form, caused by the expansion of
      CAG repeats within the ataxin-3 (ATXN3) gene.
    explanation: Confirms ATXN3 CAG expansion as the sole causative mutation for MJD/SCA3.
diagnosis:
- name: ATXN3 CAG repeat expansion testing
  presence: Positive
  description: >-
    Molecular confirmation by PCR-based sizing or repeat-primed PCR of the
    CAG repeat in ATXN3. Full-penetrance pathogenic alleles exceed ~56 repeats
    (typically 61-87). Genetic testing enables pre-symptomatic diagnosis and
    cascade testing in family members.
  evidence:
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Several genetic tests are available for MJD, and Genetic Counseling
      Programs have been created to better assist the affected families,
      namely on what concerns the possibility of pre-symptomatic testing.
    explanation: >-
      Confirms availability of genetic testing and pre-symptomatic screening
      programs as the standard diagnostic approach.
- name: Brain MRI with cerebellar and pontine atrophy
  presence: Positive in manifest disease
  description: >-
    MRI demonstrates cerebellar atrophy predominantly affecting the dentate
    nucleus and the pons ('hot cross bun' sign may be observed). Spinal cord
    atrophy is seen in Type 3. Neurochemical MRS abnormalities may be detected
    pre-symptomatically.
  evidence:
  - reference: PMID:37962377
    reference_title: Stage-Dependent Biomarker Changes in Spinocerebellar Ataxia Type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pons and cerebellar white matter volumes decreased and deviated from
      normal 2.2 years and 0.6 years before ataxia onset.
    explanation: >-
      Provides direct human biomarker evidence that pontine and cerebellar
      MRI volume changes track SCA3 disease stage.
  - reference: PMID:21635785
    reference_title: "Machado-Joseph Disease: from first descriptions to new perspectives."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Main pathological lesions are observed in the spinocerebellar system,
      as well as in the cerebellar dentate nucleus.
    explanation: >-
      Provides human clinical review evidence for spinocerebellar and
      cerebellar dentate involvement, so this diagnostic imaging entry does
      not rely solely on the mouse MRS study.
  - reference: PMID:37243335
    reference_title: "Antisense Oligonucleotide Silencing Reverses Abnormal Neurochemistry in Spinocerebellar Ataxia 3 Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      SCA3 mouse cerebellar and brainstem neurochemical trends parallel
      those in patients with SCA3.
    explanation: >-
      Neurochemical MRS findings in SCA3 mice parallel human disease,
      supporting cerebellar and brainstem imaging changes as diagnostic markers.
- name: Serum neurofilament light and MRI volume staging
  presence: Positive in preataxic and manifest disease
  description: >-
    Serum neurofilament light (NfL), pons volume, and cerebellar white matter
    volume can define a biomarker-positive stage before overt ataxia onset and
    help stage disease progression in SCA3/MJD mutation carriers.
  evidence:
  - reference: PMID:37962377
    reference_title: Stage-Dependent Biomarker Changes in Spinocerebellar Ataxia Type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Blood concentrations of mutant ATXN3 were high before and after ataxia
      onset, whereas neurofilament light deviated from normal 13.3 years
      before onset.
    explanation: >-
      Supports serum NfL as an early disease-staging biomarker in SCA3/MJD.
  - reference: PMID:37962377
    reference_title: Stage-Dependent Biomarker Changes in Spinocerebellar Ataxia Type 3.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We propose a staging model of spinocerebellar ataxia type 3/Machado-Joseph
      disease that includes a biomarker stage characterized by objective
      indicators of neurodegeneration before ataxia onset.
    explanation: >-
      Directly supports a biomarker-stage diagnostic/staging entry for SCA3/MJD.
- name: GeneReviews Diagnostic Baseline
  description: >-
      GeneReviews provides the authoritative diagnostic baseline for SCA3/Machado-Joseph disease.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: MAXO:0000533
      label: molecular genetic testing
  evidence:
  - reference: PMID:20301375
    reference_title: "Spinocerebellar Ataxia Type 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of SCA3 is established in a proband with suggestive findings and a heterozygous abnormal CAG trinucleotide repeat expansion in ATXN3 identified by molecular genetic testing."
    explanation: >-
      GeneReviews defines the clinical-plus-molecular diagnostic criteria for SCA3, confirmed by ATXN3 CAG repeat expansion.
treatments:
- name: Supportive and rehabilitative care
  description: >-
    Multidisciplinary symptomatic management with physical therapy, speech
    therapy, occupational therapy, mobility aids, and swallowing support
    remains the standard of care. There is no approved disease-modifying
    therapy.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  - preferred_term: dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type
      3 (SCA3), is an incurable disorder, widely regarded as the most common
      form of spinocerebellar ataxia in the world.
    explanation: >-
      Confirms absence of disease-modifying therapy, supporting supportive
      care as the current standard of care.
- name: Antisense oligonucleotide (ASO) therapy targeting ATXN3
  description: >-
    Intracerebroventricularly delivered antisense oligonucleotides targeting
    ATXN3 achieve sustained reduction of polyQ-expanded ataxin-3 in the CNS
    and rescue motor, neuropathological, and neurochemical deficits in SCA3
    mouse models. This represents a genetically targeted disease-modifying
    strategy with strong preclinical support; the BIIB132 intrathecal ASO
    Phase 1 program for SCA3 reached clinical testing but is currently
    terminated on ClinicalTrials.gov.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: antisense oligonucleotide
      term:
        id: NCIT:C1291
        label: Antisense Oligonucleotides
  target_mechanisms:
  - target: PolyQ-expanded ataxin-3 misfolding and nuclear aggregation
    treatment_effect: INHIBITS
    description: >-
      ASOs reduce ATXN3 expression, preventing polyQ-expanded protein
      accumulation and nuclear inclusion formation.
    evidence:
    - reference: PMID:29908063
      reference_title: "Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The ATXN3-targeting ASO achieved sustained reduction of
        polyglutamine-expanded ATXN3 up to 8 weeks after treatment and
        prevented oligomeric and nuclear accumulation of ATXN3 up to at
        least 14 weeks after treatment.
      explanation: >-
        Directly demonstrates that ASO-mediated ATXN3 suppression prevents
        nuclear accumulation of the toxic polyQ-expanded protein.
  - target: Oligodendrocyte dysfunction
    treatment_effect: INHIBITS
    description: >-
      Anti-ATXN3 ASO treatment reverses oligodendrocyte maturation deficits
      in both premanifest and symptomatic SCA3 mice.
    evidence:
    - reference: PMID:38429929
      reference_title: >-
        ASOs are an effective treatment for disease-associated oligodendrocyte
        signatures in premanifest and symptomatic SCA3 mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        a severe, but modifiable, deficit in oligodendrocyte maturation
        caused by the toxic gain-of-function of mutant ATXN3 early in SCA3
        disease that is transcriptionally, biochemically, and functionally
        rescued with anti-ATXN3 ASO.
      explanation: >-
        Establishes that ASO therapy rescues oligodendrocyte dysfunction,
        expanding its benefit beyond neurons to glia.
  evidence:
  - reference: PMID:29908063
    reference_title: "Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Longitudinal ASO therapy rescued motor impairment in SCA3 mice, and
      this rescue was associated with a recovery of defects in Purkinje neuron
      firing frequency and afterhyperpolarization.
    explanation: >-
      Demonstrates that ASO therapy rescues both motor behavior and Purkinje
      cell electrophysiology in a preclinical SCA3 model.
  - reference: PMID:37243335
    reference_title: "Antisense Oligonucleotide Silencing Reverses Abnormal Neurochemistry in Spinocerebellar Ataxia 3 Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      ASO treatment fully or partially reversed select neurochemical
      abnormalities in SCA3 mice, indicating the potential for these measures
      to serve as noninvasive treatment biomarkers in future SCA3 gene
      silencing trials.
    explanation: >-
      Shows that ASO treatment reverses measurable neurochemical biomarkers,
      supporting clinical translation with MRS endpoints.
  - reference: PMID:28624196
    reference_title: "Evaluation of Antisense Oligonucleotides Targeting ATXN3 in SCA3 Mouse Models."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      three of five tested ASOs reduced disease protein levels by >50% in
      the diencephalon, cerebellum, and cervical spinal cord.
    explanation: >-
      Demonstrates broad CNS distribution and effective ATXN3 suppression
      with ASOs across key neuroanatomic targets in SCA3 mouse models.
- name: Physical therapy
  description: >-
    Balance and coordination training as part of the multidisciplinary
    rehabilitative approach. Regular physical therapy may slow functional
    decline in ataxia patients.
  treatment_term:
    preferred_term: physical therapy
    term:
      id: MAXO:0000011
      label: physical therapy
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: PMID:29959858
    reference_title: >-
      Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from
      disease pathogenesis and clues into therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Over the years, research into putative therapeutic approaches has often
      been devoted to the development of strategies that counteract disease
      at different stages of cellular pathogenesis.
    explanation: >-
      Supports the context in which symptomatic interventions including
      physical therapy are employed in the absence of disease-modifying
      treatment.
- name: Intravenous trehalose (SLS-005)
  description: >-
    Trehalose injection (SLS-005) is an investigational pharmacotherapy tested
    in a Phase 2b/3 spinocerebellar ataxia trial, modeled here as a
    proteostasis/autophagy-oriented intervention relevant to SCA3/MJD.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: trehalose
      term:
        id: CHEBI:27082
        label: trehalose
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  target_mechanisms:
  - target: Impaired ATXN3 deubiquitinase activity and proteostasis failure
    treatment_effect: MODULATES
    description: >-
      Trehalose is modeled as a proteostasis/autophagy-oriented intervention
      that could modulate impaired protein clearance downstream of mutant ATXN3.
    evidence:
    - reference: clinicaltrials:NCT05490563
      reference_title: >-
        A Double-blind, Randomized, Placebo Controlled, Trial to Assess Safety
        and Efficacy of SLS-005 (Trehalose Injection, 90.5 mg/mL for Intravenous
        Infusion) for the Treatment of Adults With Spinocerebellar Ataxia
      supports: SUPPORT
      snippet: >-
        Phase 2b/3 double blind, randomized, placebo-controlled trial to assess
        safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for
        intravenous infusion) for the treatment of adults with spinocerebellar
        ataxia).
      explanation: >-
        Documents clinical testing of intravenous trehalose in adult
        spinocerebellar ataxia, including the SCA3-relevant trial listed in
        the clinical trials section.
  evidence:
  - reference: clinicaltrials:NCT05490563
    reference_title: >-
      A Double-blind, Randomized, Placebo Controlled, Trial to Assess Safety
      and Efficacy of SLS-005 (Trehalose Injection, 90.5 mg/mL for Intravenous
      Infusion) for the Treatment of Adults With Spinocerebellar Ataxia
    supports: SUPPORT
    snippet: >-
      Phase 2b/3 double blind, randomized, placebo-controlled trial to assess
      safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for
      intravenous infusion) for the treatment of adults with spinocerebellar
      ataxia).
    explanation: >-
      Supports including trehalose as a clinical-stage investigational
      treatment relevant to this SCA3/MJD entry.
animal_models:
- species: Mus musculus
  genotype: YACMJD84 transgenic mouse (full human ATXN3 CAG repeat)
  description: >-
    Transgenic mice expressing the full-length human ATXN3 gene with ~84 CAG
    repeats recapitulate key features of SCA3 including motor deficits,
    nuclear inclusions, Purkinje cell pathology, and electrophysiological
    abnormalities. This model is used for preclinical ASO efficacy studies.
  associated_phenotypes:
  - Motor impairment
  - Nuclear ATXN3 inclusions
  - Purkinje cell electrophysiological deficits
  - Oligodendrocyte dysfunction
  evidence:
  - reference: PMID:29908063
    reference_title: "Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      the top ATXN3-targeting ASO from an in vivo screen was injected
      intracerebroventricularly into early symptomatic transgenic SCA3 mice
      that express the full human disease gene and recapitulate key disease
      features.
    explanation: >-
      Confirms that the YACMJD transgenic mouse expresses the full human
      ATXN3 gene and recapitulates key disease features.
  - reference: PMID:38429929
    reference_title: >-
      ASOs are an effective treatment for disease-associated oligodendrocyte
      signatures in premanifest and symptomatic SCA3 mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      oligodendrocytes display some of the earliest and most progressive
      dysfunction in SCA3 mice.
    explanation: >-
      Demonstrates early oligodendrocyte dysfunction in SCA3 mouse models,
      highlighting non-neuronal pathology.
datasets:
- accession: geo:GSE261670
  title: ASOs are an effective treatment for disease-associated oligodendrocyte signatures in premanifest and symptomatic SCA3 mice
  description: >-
    Bulk RNA-seq dataset from brainstem/diencephalon, spinal cord, and
    cerebellum of SCA3 Q84 mice and wild-type controls used to assess
    disease-associated oligodendrocyte signatures and anti-ATXN3 ASO rescue.
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: BULK_RNA_SEQ
  sample_types:
  - preferred_term: brainstem
    term:
      id: UBERON:0002298
      label: brainstem
    tissue_term:
      preferred_term: brainstem
      term:
        id: UBERON:0002298
        label: brainstem
  - preferred_term: spinal cord
    term:
      id: UBERON:0002240
      label: spinal cord
    tissue_term:
      preferred_term: spinal cord
      term:
        id: UBERON:0002240
        label: spinal cord
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
    tissue_term:
      preferred_term: cerebellum
      term:
        id: UBERON:0002037
        label: cerebellum
  sample_count: 74
  conditions:
  - SCA3 Q84 mouse
  - wild-type mouse
  - anti-ATXN3 ASO treatment
  publication: PMID:38429929
  evidence:
  - reference: PMID:38429929
    reference_title: >-
      ASOs are an effective treatment for disease-associated oligodendrocyte
      signatures in premanifest and symptomatic SCA3 mice.
    supports: SUPPORT
    snippet: >-
      We report a severe, but modifiable, deficit in oligodendrocyte maturation
      caused by the toxic gain-of-function of mutant ATXN3 early in SCA3 disease.
    explanation: >-
      Supports inclusion of this dataset as an ASO-responsive oligodendrocyte
      transcriptomic resource for SCA3.
- accession: geo:GSE309535
  title: Transcriptional dysregulation in the spinal cord of SCA3 provides insights into disease mechanisms
  description: >-
    Bulk RNA-seq dataset from spinal cord of SCA3 KIQ300 and wild-type mice at
    24 and 56 weeks of age, supporting analysis of early and progressive
    spinal cord transcriptional dysregulation in SCA3.
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: BULK_RNA_SEQ
  sample_types:
  - preferred_term: spinal cord
    term:
      id: UBERON:0002240
      label: spinal cord
    tissue_term:
      preferred_term: spinal cord
      term:
        id: UBERON:0002240
        label: spinal cord
  sample_count: 24
  conditions:
  - SCA3 KIQ300 mouse
  - wild-type mouse
  - 24 weeks
  - 56 weeks
  publication: PMID:41613623
  evidence:
  - reference: PMID:41613623
    reference_title: >-
      Early transcriptomic perturbations highlight the spinal cord as a key
      pathogenic region in spinocerebellar ataxia type 3.
    supports: SUPPORT
    snippet: >-
      Here, we present the first comprehensive analysis of the spinal cord
      transcriptome in SCA3 using both human and mouse model tissue.
    explanation: >-
      Supports inclusion of this dataset as a spinal-cord-focused transcriptomic
      resource for SCA3 mechanism and biomarker studies.
- accession: geo:GSE93713
  title: Expression data from SCA3 and genetically corrected iPSCs
  description: >-
    Human microarray dataset comparing patient-derived SCA3 iPSCs with
    CRISPR/Cas9-corrected isogenic iPSCs, useful for studying ATXN3
    repeat-expansion-dependent transcriptional, apoptosis, and
    ubiquitin-proteostasis phenotypes.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MICROARRAY
  sample_types:
  - preferred_term: induced pluripotent stem cell
    term:
      id: CL:0000034
      label: stem cell
    cell_type_term:
      preferred_term: stem cell
      term:
        id: CL:0000034
        label: stem cell
  sample_count: 6
  conditions:
  - SCA3 patient-derived iPSCs
  - CRISPR/Cas9-corrected isogenic iPSCs
  publication: PMID:34535635
  evidence:
  - reference: PMID:34535635
    reference_title: >-
      CRISPR/Cas9 mediated gene correction ameliorates abnormal phenotypes in
      spinocerebellar ataxia type 3 patient-derived induced pluripotent stem cells.
    supports: SUPPORT
    snippet: >-
      For the first time, this study demonstrated the feasibility of
      CRISPR/Cas9-mediated HR strategy to precisely repair SCA3-iPSCs, and
      reverse the corresponding abnormal disease phenotypes.
    explanation: >-
      Supports inclusion of this dataset as a patient-derived isogenic iPSC
      model resource for SCA3.
clinical_trials:
- name: NCT05160558
  phase: PHASE_I
  status: TERMINATED
  description: >-
    Randomized, blinded, placebo-controlled multiple-ascending-dose Phase 1
    study of intrathecal BIIB132 in adults with SCA3, designed to evaluate
    safety, tolerability, and pharmacokinetics of ATXN3-lowering ASO therapy.
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: clinicaltrials:NCT05160558
    reference_title: >-
      A Phase 1, Blinded, Randomized, Placebo-controlled Study to Investigate
      the Safety, Tolerability, and Pharmacokinetics of Multiple Ascending
      Doses of BIIB132 Administered Intrathecally to Adults With
      Spinocerebellar Ataxia 3
    supports: SUPPORT
    snippet: >-
      The primary objective of this study is to evaluate the safety and
      tolerability of multiple ascending doses of BIIB132 administered via
      intrathecal (IT) injection to participants with spinocerebellar ataxia
      type 3 (SCA3).
    explanation: >-
      Documents that ATXN3-targeted ASO therapy reached human Phase 1 testing
      in SCA3.
- name: NCT05490563
  phase: PHASE_II
  status: TERMINATED
  description: >-
    Phase 2b/3 randomized placebo-controlled study of intravenous SLS-005
    (trehalose) in adults with genetically confirmed SCA3, intended to test a
    proteostasis/autophagy-oriented symptomatic or disease-modifying approach.
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: clinicaltrials:NCT05490563
    reference_title: >-
      A Double-blind, Randomized, Placebo Controlled, Trial to Assess Safety
      and Efficacy of SLS-005 (Trehalose Injection, 90.5 mg/mL for Intravenous
      Infusion) for the Treatment of Adults With Spinocerebellar Ataxia
    supports: SUPPORT
    snippet: >-
      Phase 2b/3 double blind, randomized, placebo-controlled trial to assess
      safety and efficacy of SLS-005 (trehalose injection, 90.5 mg/mL for
      intravenous infusion) for the treatment of adults with spinocerebellar
      ataxia).
    explanation: >-
      Documents SLS-005 as a clinical-stage interventional trial that included
      adults with SCA3.
- name: NCT03701399
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    Long-term randomized placebo-controlled Phase 3 trial of oral troriluzole
    in adult spinocerebellar ataxias, including SCA3, evaluating change in
    ataxia severity over 48 weeks.
  target_phenotypes:
  - preferred_term: gait ataxia
    term:
      id: HP:0002066
      label: Gait ataxia
  evidence:
  - reference: clinicaltrials:NCT03701399
    reference_title: >-
      A Phase III, Long-Term, Randomized, Double-blind, Placebo-controlled
      Trial of Troriluzole in Adult Participants With Spinocerebellar Ataxia.
    supports: SUPPORT
    snippet: >-
      The purpose of this study is to compare the efficacy of Troriluzole
      (200 mg once daily) versus placebo after 48 weeks of treatment in
      subjects with spinocerebellar ataxia (SCA).
    explanation: >-
      Captures a current late-stage symptomatic treatment trial relevant to
      SCA3 among the included hereditary ataxias.
notes: >-
  MJD/SCA3 is the most common autosomal dominant spinocerebellar ataxia
  worldwide. The Azores have a particularly high prevalence due to a founder
  effect. The four clinical subtypes reflect the inverse relationship between
  CAG repeat length and age of onset: Type 1 (longest repeats, earliest onset,
  most severe pyramidal/dystonic features), through Type 4 (parkinsonism-
  predominant, rarest). No single gene modifier has been validated clinically,
  but GWAS suggests additional genetic modifiers account for the residual
  onset variance beyond CAG repeat length. ATXN3-lowering ASO therapy remains
  a strong mechanistic strategy with substantial mouse and human-cell support;
  however, the BIIB132 Phase 1 SCA3 trial is now listed as terminated, so
  clinical-development status should be checked before reuse in downstream
  summaries. Mice lacking ATXN3 are phenotypically normal, supporting the
  biological plausibility of ATXN3 suppression as a therapeutic strategy.
references:
- reference: PMID:20301375
  title: "Spinocerebellar Ataxia Type 3."
  tags:
  - GeneReviews
  findings: []
📚

References & Deep Research

References

1
PMID:20301375
Spinocerebellar Ataxia Type 3.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Machado–Joseph Disease (Spinocerebellar Ataxia Type 3) — Disease Characteristics Research Report
Edison Scientific Literature 37 citations 2026-04-26T15:53:41.564130

Machado–Joseph Disease (Spinocerebellar Ataxia Type 3) — Disease Characteristics Research Report

Target disease: Machado–Joseph disease (MJD) / Spinocerebellar ataxia type 3 (SCA3)
Category: Mendelian (autosomal dominant polyglutamine repeat-expansion disorder) (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, NCT02175290 chunk 1)

Evidence and citation note

This report is based on the documents retrieved in this run (mostly 2023–2024 reviews, cohort studies, and ClinicalTrials.gov records). Many retrieved excerpts did not include PubMed IDs (PMIDs); therefore, where PMIDs are required, I provide DOI/URL and publication month/year, and explicitly flag PMID unavailability in the retrieved context.

1. Disease Information

1.1 Concise overview

Machado–Joseph disease / SCA3 is a monogenic, progressive neurodegenerative ataxia caused by a pathogenic CAG repeat expansion in ATXN3, leading to production of polyglutamine-expanded ataxin-3 that misfolds and aggregates in neurons (potapenko2024thedeubiquitinasefunction pages 1-2, stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2). Clinically, it is characterized by progressive cerebellar ataxia with frequent additional pyramidal, extrapyramidal (including parkinsonism), oculomotor, and peripheral neuropathic features, culminating in severe disability and premature death (potapenko2024thedeubiquitinasefunction pages 1-2, pilotto2024hereditaryataxiasfrom pages 4-5, paulino2023autophagyinspinocerebellar pages 1-2).

1.2 Key identifiers and synonyms

A structured summary of disease nomenclature and identifiers supported by the retrieved evidence is provided below.

Identifier system Identifier Evidence-supported? (yes/no) Notes Key citation (pqac id)
Preferred disease name Machado–Joseph disease yes Monogenic neurodegenerative disorder; also referred to as SCA3 (potapenko2024thedeubiquitinasefunction pages 1-2, stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2)
Major synonym Spinocerebellar ataxia type 3 yes Standard synonym used interchangeably with Machado–Joseph disease (potapenko2024thedeubiquitinasefunction pages 1-2, stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2)
Major synonym SCA3 yes Common abbreviation in clinical and research literature (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, NCT02175290 chunk 1)
Major synonym MJD yes Common abbreviation for Machado–Joseph disease (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, NCT02175290 chunk 1)
OMIM 109150 yes Explicitly reported for SCA3/Machado–Joseph disease in a 2024 review (pilotto2024hereditaryataxiasfrom pages 4-5)
MONDO MONDO:0007182 yes Disease-target association retrieved for Machado-Joseph disease in Open Targets output (stahl2024spinocerebellarataxiatype pages 1-2)
Orphanet disease entry Orphanet:98757 yes Open Targets output mapped “Spinocerebellar ataxia type 3” to Orphanet_98757 (stahl2024spinocerebellarataxiatype pages 1-2)
ICD-10 Not established from gathered evidence no No ICD-10 code was provided in the gathered evidence set (stahl2024spinocerebellarataxiatype pages 1-2)
ICD-11 Not established from gathered evidence no No ICD-11 code was provided in the gathered evidence set (stahl2024spinocerebellarataxiatype pages 1-2)
MeSH Not established from gathered evidence no No MeSH identifier was provided in the gathered evidence set (stahl2024spinocerebellarataxiatype pages 1-2)
Inheritance Autosomal dominant yes Repeatedly described as an autosomal dominant/polyglutamine ataxia (stahl2024spinocerebellarataxiatype pages 1-2, NCT02175290 chunk 1, raposo2024bloodandcerebellar pages 1-5)
Causal gene ATXN3 yes Causative gene; CAG expansion located in exon 10 (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, NCT02175290 chunk 1)
Gene product Ataxin-3 yes Deubiquitinating enzyme involved in proteostasis/transcriptional regulation (potapenko2024thedeubiquitinasefunction pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2)
Molecular lesion CAG trinucleotide repeat expansion yes Produces expanded polyglutamine tract in ataxin-3 (potapenko2024thedeubiquitinasefunction pages 1-2, stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2)
Normal repeat range ~12–42 CAGs yes One evidence source reports normal alleles approximately 12–42 repeats (stahl2024spinocerebellarataxiatype pages 1-2)
Normal repeat range up to 44 CAGs yes Alternative review reports normal range up to 44 repeats (pilotto2024hereditaryataxiasfrom pages 4-5)
Normal/polyQ range reported ~13–49 glutamines yes Review reports normal ataxin-3 polyQ stretch as 13–49 glutamines (paulino2023autophagyinspinocerebellar pages 1-2)
Pathogenic repeat range ~52–86 CAGs yes Review reports affected individuals typically carry 52–86 repeats (pilotto2024hereditaryataxiasfrom pages 4-5)
Pathogenic repeat range ~55–87 CAGs yes Alternative review reports pathogenic expansions 55–87 repeats/glutamines (paulino2023autophagyinspinocerebellar pages 1-2)
Pathogenic repeat range ~60–87 CAGs yes Review reports pathogenic alleles roughly 60–87 repeats (stahl2024spinocerebellarataxiatype pages 1-2)
Major affected regions Cerebellum and pons yes Frequently highlighted as primary affected regions (paulino2023autophagyinspinocerebellar pages 1-2, sohail2023adifficultcase pages 1-2)
Additional affected regions Brainstem, basal ganglia, substantia nigra/striatum yes Broader neurodegeneration beyond cerebellum contributes to phenotypic heterogeneity (potapenko2024thedeubiquitinasefunction pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, pilotto2024hereditaryataxiasfrom pages 4-5)

Table: This table summarizes evidence-supported nomenclature and core identifiers for Machado–Joseph disease / spinocerebellar ataxia type 3. It also flags identifier systems not established by the gathered evidence so the final report can distinguish confirmed from missing database mappings.

Key identifier limitations: ICD-10/ICD-11 and MeSH identifiers were not present in the retrieved evidence for this run; they should be added via dedicated ontology/database lookup if required for the knowledge base entry (artifact-00).

1.3 Evidence source type

Most information here comes from aggregated disease-level resources and cohorts (reviews and multi-site observational studies), rather than individual EHR case reports, except for one illustrative case report (sohail2023adifficultcase pages 1-2).

2. Etiology

2.1 Primary causal factors

Genetic cause (primary): Pathogenic expansion of a CAG trinucleotide repeat in exon 10 of ATXN3 produces a polyQ-expanded ataxin-3 protein with toxic gain-of-function properties leading to neuronal dysfunction and degeneration (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2). ATXN3 encodes a deubiquitinating enzyme involved in proteostasis and other functions (potapenko2024thedeubiquitinasefunction pages 1-2).

Repeat-size ranges (current evidence): - Normal: reported approximately 12–42 repeats (stahl2024spinocerebellarataxiatype pages 1-2) or “up to 44” (pilotto2024hereditaryataxiasfrom pages 4-5). - Pathogenic: typically ~52–86 repeats (pilotto2024hereditaryataxiasfrom pages 4-5) and/or ~55–87 repeats (paulino2023autophagyinspinocerebellar pages 1-2), with some sources describing typical patient ranges ~62–84 (potapenko2024thedeubiquitinasefunction pages 1-2).

2.2 Risk factors

Genetic risk factor: Carrying the pathogenic ATXN3 expansion is necessary and (age-dependently) sufficient for disease development in autosomal dominant families (stahl2024spinocerebellarataxiatype pages 1-2, NCT02175290 chunk 1).

Modifier effects (repeat size): Larger expanded alleles correlate with earlier age at onset and greater severity (potapenko2024thedeubiquitinasefunction pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, silva2023thejosephindomain pages 1-2).

Other genetic/molecular modifiers (emerging): - ATXN3 transcript diversity/splicing: ATXN3 has extensive alternative splicing; blood vs cerebellum show strong isoform differences (e.g., ATXN3-251 vs ATXN3-214), which may influence selective vulnerability and mRNA-lowering therapy design (raposo2024bloodandcerebellar pages 1-5). - Post-transcriptional regulation: miRNA families and Dicer/Drosha-dependent processing are discussed as modulators of ATXN3 levels (stahl2024spinocerebellarataxiatype pages 1-2).

2.3 Protective factors

No specific protective variants or environmental protective factors were identified in the retrieved evidence. The closest related concept is incomplete penetrance early in life with age-dependent conversion to symptomatic disease (see Epidemiology/Inheritance) (paulino2023autophagyinspinocerebellar pages 1-2).

2.4 Gene–environment interactions

No gene–environment interaction evidence was retrieved in this run.

3. Phenotypes

3.1 Core clinical phenotype and common manifestations

SCA3/MJD is characterized by progressive ataxia with multi-system involvement.

Commonly described manifestations (from retrieved evidence): - Cerebellar ataxia (core feature) (paulino2023autophagyinspinocerebellar pages 1-2) - Pyramidal and extrapyramidal signs; parkinsonism in some subtypes (pilotto2024hereditaryataxiasfrom pages 4-5, paulino2023autophagyinspinocerebellar pages 1-2) - Oculomotor abnormalities including diplopia/ophthalmoparesis (moura2024spinocerebellarataxiasphenotypic pages 7-9) - Peripheral neuropathy (often axonal sensory) and muscle cramps/atrophy in some subtypes (pilotto2024hereditaryataxiasfrom pages 4-5, moura2024spinocerebellarataxiasphenotypic pages 7-9) - Dysarthria/dysphagia are highlighted as major disabling features in reviews (potapenko2024thedeubiquitinasefunction pages 1-2)

Subtype classification (clinical heterogeneity): A 2024 review describes four clinical subtypes:
Type I (early onset ~10–30 years; pyramidal/extrapyramidal signs), Type II (most common; onset 2nd–5th decades), Type III (later onset; prominent peripheral neuropathy and muscle atrophy), Type IV (parkinsonism) (pilotto2024hereditaryataxiasfrom pages 4-5).

3.2 Quantitative phenotype data (examples from 2024 cohorts)

  • In a tertiary ataxia cohort enriched for polyQ SCAs (dominated by MJD/SCA3), axonal neuropathy was observed in 16/22 (72.7%) of polyQ cases evaluated (moura2024spinocerebellarataxiasphenotypic pages 7-9).
  • MRI findings in polyQ SCA included pons and cerebellar peduncle atrophy each in 9/28 (32.1%) (moura2024spinocerebellarataxiasphenotypic pages 7-9).

3.3 Age of onset, severity, progression

  • Typical adult onset often falls around the 3rd–5th decades (median ~39.5 years reported for polyQ SCAs in one cohort; MJD/SCA3 predominant) (moura2024spinocerebellarataxiasphenotypic pages 1-2).
  • Disease is progressive and life-limiting. After symptom onset, survival is reported as ~20–25 years in a 2024 review, and patients often become wheelchair dependent later in disease (potapenko2024thedeubiquitinasefunction pages 1-2). Another large biomarker study notes clinical ataxia progression over ~20 years on average (faber2024stage‐dependentbiomarkerchanges pages 4-7).

3.4 Suggested HPO terms (non-exhaustive; evidence-aligned)

  • Cerebellar ataxia — HP:0001251 (paulino2023autophagyinspinocerebellar pages 1-2)
  • Dysarthria — HP:0001260 (potapenko2024thedeubiquitinasefunction pages 1-2)
  • Dysphagia — HP:0002015 (potapenko2024thedeubiquitinasefunction pages 1-2)
  • Ophthalmoparesis — HP:0000602 (moura2024spinocerebellarataxiasphenotypic pages 7-9)
  • Peripheral neuropathy / axonal neuropathy — HP:0009830 (moura2024spinocerebellarataxiasphenotypic pages 7-9)
  • Parkinsonism — HP:0001300 (pilotto2024hereditaryataxiasfrom pages 4-5, paulino2023autophagyinspinocerebellar pages 1-2)
  • Muscle atrophy — HP:0003202 (pilotto2024hereditaryataxiasfrom pages 4-5)

Ontology note: HPO IDs are suggested standard mappings; the retrieved documents support the phenotypes but did not themselves provide HPO IDs.

4. Genetic / Molecular Information

4.1 Causal gene

  • ATXN3 (ataxin 3) is the causal gene; CAG repeat expansion in exon 10 is the canonical lesion (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2).

4.2 Variant type and consequences

  • Variant class: trinucleotide repeat expansion (CAG) → polyglutamine expansion (stahl2024spinocerebellarataxiatype pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2).
  • Functional consequence: toxic gain of function with protein misfolding/aggregation and inclusion formation (stahl2024spinocerebellarataxiatype pages 1-2, potapenko2024thedeubiquitinasefunction pages 1-2).

4.3 Allele frequency and population databases

Population allele frequencies (e.g., gnomAD) were not available in the retrieved evidence.

4.4 Molecular modifiers (selected, evidence-supported)

  • Alternative splicing / isoform usage differs markedly between blood and cerebellum; this may affect selective vulnerability and design/interpretation of blood biomarkers for target engagement (raposo2024bloodandcerebellar pages 1-5).
  • miRNA-mediated regulation (miR-181/miR-25 family, miR-9, miR-494) and dependency on Dicer/Drosha are cited as modulators of ATXN3 expression (stahl2024spinocerebellarataxiatype pages 1-2).

5. Environmental Information

No environmental toxins, lifestyle factors, or infectious triggers were identified in the retrieved evidence set.

6. Mechanism / Pathophysiology

6.1 Causal chain (high-level)

ATXN3 CAG expansion → polyQ-expanded ataxin-3 → misfolding/aggregation/inclusions → impaired proteostasis (UPS and autophagy), transcriptional and mitochondrial dysfunction (including mitophagy defects and oxidative stress) → selective neurodegeneration (brainstem/cerebellar circuitry and other regions) → progressive motor and multisystem phenotype (potapenko2024thedeubiquitinasefunction pages 1-2, paulino2023autophagyinspinocerebellar pages 1-2, paulino2023autophagyinspinocerebellar pages 4-5, cui2024spinocerebellarataxiasfrom pages 5-6).

6.2 Protein dysfunction and proteostasis

  • PolyQ-expanded ataxin-3 has propensity to misfold, aggregate, and form intranuclear inclusions containing ubiquitin and proteasomal subunits, supporting impaired clearance and UPS involvement (potapenko2024thedeubiquitinasefunction pages 1-2).
  • Ataxin-3 is a deubiquitinating enzyme with key roles in proteostasis; UPS impairment is a central mechanistic link to neurodegeneration in MJD (potapenko2024thedeubiquitinasefunction pages 1-2).

Suggested GO terms (Biological Process; evidence-aligned): - Protein ubiquitination / deubiquitination — e.g., GO:0016567, GO:0016579 (potapenko2024thedeubiquitinasefunction pages 1-2) - Proteasome-mediated ubiquitin-dependent protein catabolic process — GO:0043161 (potapenko2024thedeubiquitinasefunction pages 1-2)

6.3 Autophagy impairment (2023 synthesis; therapeutic relevance)

Autophagy is highlighted as critical for clearance of large oligomeric/aggregated species that are poorly handled by the UPS (paulino2023autophagyinspinocerebellar pages 4-5). Reported disease-associated findings include reduced beclin-1 in patient fibroblasts and altered LC3-II/p62 patterns in MJD brain, consistent with impaired autophagic flux (paulino2023autophagyinspinocerebellar pages 4-5).

Suggested GO terms: - Autophagy — GO:0006914 (paulino2023autophagyinspinocerebellar pages 4-5, paulino2023autophagyinspinocerebellar pages 1-2) - Macroautophagy — GO:0016236 (paulino2023autophagyinspinocerebellar pages 4-5)

6.4 Mitochondrial dysfunction, oxidative stress, and mitophagy (2024 emphasis)

  • A 2024 review describes impaired Parkin/VDAC1-mediated mitophagy linked to mutant ataxin-3 (aberrant loss of Parkin and reduced VDAC1 polyubiquitination), highlighting the PINK1/Parkin axis as a therapeutic target (cui2024spinocerebellarataxiasfrom pages 5-6).
  • A 2024 experimental study in an MJD cell model (SK-N-SH expressing mutant ataxin-3) links mutant ataxin-3 toxicity to oxidative stress and mitochondrial dysfunction; astragaloside IV reduced mutant ataxin-3 aggregation by enhancing autophagy, improving antioxidant capacity, and improving mitochondrial membrane potential/respiration and dynamics (lin2024astragalosideivreduces pages 1-2).

Suggested GO terms: - Mitophagy — GO:0000422 (cui2024spinocerebellarataxiasfrom pages 5-6) - Mitochondrial organization — GO:0007005 (lin2024astragalosideivreduces pages 1-2) - Response to oxidative stress — GO:0006979 (lin2024astragalosideivreduces pages 1-2)

6.5 Transcriptional and post-transcriptional dysregulation (2024 review)

A 2024 review notes promoter-binding factors (SP1/CBF), limited CpG methylation findings, and miRNA-mediated regulation of ATXN3; a CRISPR-based endogenous reporter screen identified statins as potential activators of ATXN3 expression, suggesting cholesterol-related biology may be relevant (stahl2024spinocerebellarataxiatype pages 1-2).

6.6 Immune system involvement

Neuroinflammation was not substantively addressed in the retrieved excerpts and should be treated as a gap for this run.

Suggested cell types (CL; evidence-aligned but not directly measured in retrieved excerpts): - Purkinje neuron — CL:0000121 (Purkinje dysfunction/degeneration discussed in model contexts) (pilotto2024hereditaryataxiasfrom pages 13-15, paulino2023autophagyinspinocerebellar pages 4-5) - Oligodendrocyte — CL:0000128 (transcriptional abnormalities in some SCA3 models cited indirectly) (shorrock2024cagrepeatselectivecompounds pages 54-55)

7. Anatomical Structures Affected

7.1 Organ/system level

Primary system affected: central nervous system (neurodegenerative ataxia) (potapenko2024thedeubiquitinasefunction pages 1-2, stahl2024spinocerebellarataxiatype pages 1-2).

7.2 Key regions (human neuropathology/imaging)

  • Cerebellum and pons/brainstem are repeatedly highlighted as major affected structures (paulino2023autophagyinspinocerebellar pages 1-2).
  • Degeneration also involves deep cerebellar nuclei (dentate), and in some cases substantia nigra/basal ganglia/cortex contributing to parkinsonism and cognitive changes (pilotto2024hereditaryataxiasfrom pages 4-5).

Suggested UBERON terms (examples): - Cerebellum — UBERON:0002037 (paulino2023autophagyinspinocerebellar pages 1-2) - Pons — UBERON:0000986 (paulino2023autophagyinspinocerebellar pages 1-2, moura2024spinocerebellarataxiasphenotypic pages 7-9) - Substantia nigra — UBERON:0002038 (pilotto2024hereditaryataxiasfrom pages 4-5)

7.3 Subcellular localization

Nuclear and cytoplasmic inclusion bodies are described (stahl2024spinocerebellarataxiatype pages 1-2, potapenko2024thedeubiquitinasefunction pages 1-2).

Suggested GO Cellular Component: - Nucleus — GO:0005634 (stahl2024spinocerebellarataxiatype pages 1-2)

8. Temporal Development (Natural History)

8.1 Onset and course

Typical onset is often in adulthood (e.g., ~30–50 years in polyQ cohorts; subtype-dependent) (pilotto2024hereditaryataxiasfrom pages 4-5, moura2024spinocerebellarataxiasphenotypic pages 1-2). Disease is progressive over decades, commonly described as ~20 years from manifest onset (potapenko2024thedeubiquitinasefunction pages 1-2, faber2024stage‐dependentbiomarkerchanges pages 4-7).

8.2 Biomarker-defined pre-ataxic window (major 2024 development)

A major 2024 advance is a biomarker-led staging framework anchored to onset.

Study (year, journal) Cohort (n) Biomarkers Key quantitative findings (with units and timing relative to onset) Proposed model / implications URL Key citation (pqac)
Faber et al. (2024, Annals of Neurology) 292 SCA3 mutation carriers + 108 controls; 57 pre-ataxic, 235 ataxic Plasma elongated/mutant ATXN3, serum neurofilament light (NfL), MRI volumes of pons, cerebellar white matter (CWM), cerebellar gray matter (CGM), SARA Mutant ATXN3 elevated before and after onset (trait marker). NfL deviated from normal ~11.9 years before onset. Pons volume deviated ~2.0 years before onset; CWM volume ~0.3 years before onset. In manifest ataxia, NfL z-score ≥2 in 174/190 (92%); pons/CWM z-scores ≤-2 in ~90% of assessed patients. Multivariable model including NfL/MRI explained 73.9% of SARA variance vs 60.4% without them. SARA cutoff for manifest ataxia: ≥3. (faber2024stage‐dependentbiomarkerchanges pages 1-4, faber2024stage‐dependentbiomarkerchanges pages 4-7, faber2024stage‐dependentbiomarkerchanges pages 15-21, faber2024stage‐dependentbiomarkerchanges pages 7-9) Data-driven 3-stage model: asymptomatic carrier → biomarker stage (pre-ataxic but NfL abnormal) → ataxia stage; supports biomarker-led early/preventive trial design and staging for targeted therapies. Figure extraction also retrieved staging/trajectory panels. (faber2024stage‐dependentbiomarkerchanges pages 9-12, faber2024stage‐dependentbiomarkerchanges pages 12-15, faber2024stage‐dependentbiomarkerchanges media b30f008b, faber2024stage‐dependentbiomarkerchanges media 807d2b9d) https://doi.org/10.1002/ana.26824 (faber2024stage‐dependentbiomarkerchanges pages 1-4, faber2024stage‐dependentbiomarkerchanges pages 4-7, faber2024stage‐dependentbiomarkerchanges pages 15-21, faber2024stage‐dependentbiomarkerchanges pages 7-9, faber2024stage‐dependentbiomarkerchanges pages 9-12, faber2024stage‐dependentbiomarkerchanges pages 12-15, faber2024stage‐dependentbiomarkerchanges media b30f008b, faber2024stage‐dependentbiomarkerchanges media 807d2b9d)
Faber et al. (2024, Annals of Neurology) — cohort detail row MRI available in 161; mutant ATXN3 in 134; NfL in 327 measurements across participants Same as above Mean age 35.5 years in pre-ataxic carriers and 51.3 years in ataxic carriers; pre-ataxic carriers averaged ~7.7 years before onset; expanded CAG mean ~68.2–68.8 repeats. Clinical disease duration after onset described as ~20 years on average. (faber2024stage‐dependentbiomarkerchanges pages 4-7, faber2024stage‐dependentbiomarkerchanges pages 15-21) Quantifies the “pre-ataxic window” during which fluid biomarkers become abnormal well before clear structural MRI changes, relevant for enrichment of future interventional studies. https://doi.org/10.1002/ana.26824 (faber2024stage‐dependentbiomarkerchanges pages 4-7, faber2024stage‐dependentbiomarkerchanges pages 15-21)
Raposo et al. (2024, bioRxiv preprint) Blood n=60; cerebellum n=12 RNA-seq abundance of ATXN3 splice variants/transcripts in blood and cerebellum Higher number/abundance of ATXN3 transcripts in cerebellum than blood. ATXN3-251 (3 UIM) expressed ~50-fold more in blood than cerebellum; ATXN3-214 (2 UIM) expressed ~20-fold more in cerebellum than blood. (raposo2024bloodandcerebellar pages 1-5) Tissue-specific transcript usage may refine molecular biomarker development and improve design of ATXN3 mRNA-lowering therapies by indicating which isoforms dominate in target tissue vs accessible blood. https://doi.org/10.1101/2023.04.22.537936 (raposo2024bloodandcerebellar pages 1-5)
Moura et al. (2024, Cerebellum) — phenotype/imaging cohort relevant to staging 88 SCA patients total; 38 polyQ SCA cases, of which MJD/SCA3 represented 73.7% of polyQ families/cases Clinical scales (SARA, INAS), EMG-defined axonal neuropathy, MRI atrophy patterns PolyQ SCA median age at onset 39.5 years; axonal neuropathy in 16/22 (72.7%) of polyQ cases; pons and cerebellar peduncle atrophy each in 9/28 (32.1%) of polyQ cases. Falls, gait aid use, and wheelchair confinement were tracked as disability milestones. (moura2024spinocerebellarataxiasphenotypic pages 7-9, moura2024spinocerebellarataxiasphenotypic pages 9-10, moura2024spinocerebellarataxiasphenotypic pages 1-2) Not a biomarker-staging paper per se, but supports real-world structural and functional milestones that align with brainstem/cerebellar degeneration and progression in MJD/SCA3-dominant polyQ cohorts. https://doi.org/10.1007/s12311-024-01723-9 (moura2024spinocerebellarataxiasphenotypic pages 7-9, moura2024spinocerebellarataxiasphenotypic pages 9-10, moura2024spinocerebellarataxiasphenotypic pages 1-2)

Table: This table summarizes the most relevant 2023-2024 biomarker and staging evidence for Machado-Joseph disease / SCA3, highlighting the quantitative timing of NfL and MRI changes relative to clinical onset. It is useful for identifying current candidate biomarkers, pre-ataxic disease stages, and implications for trial design.

Key quantitative staging points (ESMI cohort): NfL becomes abnormal ~11.9 years before ataxia onset, while pons and cerebellar white matter volume changes deviate closer to onset; mutant ATXN3 in blood is elevated across stages but is less progression-sensitive (faber2024stage‐dependentbiomarkerchanges pages 7-9, faber2024stage‐dependentbiomarkerchanges pages 1-4).

Visual evidence (figures): Biomarker trajectories and the proposed carrier/biomarker/ataxia staging model were retrieved as figure crops (faber2024stage‐dependentbiomarkerchanges media b30f008b, faber2024stage‐dependentbiomarkerchanges media 807d2b9d).

9. Inheritance and Population

9.1 Inheritance

Autosomal dominant inheritance is consistently described (stahl2024spinocerebellarataxiatype pages 1-2, NCT02175290 chunk 1).

9.2 Penetrance and anticipation-like behavior

  • Age-dependent penetrance/incomplete penetrance is noted, with probability of remaining asymptomatic approaching zero by age 70 (paulino2023autophagyinspinocerebellar pages 1-2).
  • Repeat-length associations (longer CAG → earlier onset, more severe disease) underpin intergenerational anticipation-like patterns (paulino2023autophagyinspinocerebellar pages 1-2, silva2023thejosephindomain pages 1-2).

9.3 Epidemiology and geographic distribution (statistics from recent sources)

  • Global prevalence estimates in retrieved sources include ~1–5 per 100,000 (paulino2023autophagyinspinocerebellar pages 1-2) and ~1:50,000–100,000 (silva2023thejosephindomain pages 1-2).
  • Founder/high-prevalence regions: The Azores are repeatedly described as a hotspot with particularly high predominance (paulino2023autophagyinspinocerebellar pages 1-2, silva2023thejosephindomain pages 1-2). A 2024 review notes SCA3 can account for >55% of autosomal dominant cerebellar ataxia (ADCA) cases in countries such as Portugal (pilotto2024hereditaryataxiasfrom pages 4-5).

Data gaps: Incidence, variant-specific geographic distributions/haplotypes, and sex ratio were not available in the retrieved excerpts.

10. Diagnostics

10.1 Genetic testing (real-world implementation)

Repeat-expansion testing remains central for suspected polyQ SCAs: - A cohort study describes use of multiplex PCR + fragment analysis to test CAG expansions in a panel including ATXN3, alongside targeted single-gene testing and multigene NGS/WES panels (moura2024spinocerebellarataxiasphenotypic pages 2-4).

Diagnostic yields (single center cohort): - Targeted single-gene testing in probands with a suspected diagnosis: 76.9% (20/26) yield (moura2024spinocerebellarataxiasphenotypic pages 2-4). - Multigene NGS/WES-based panels: 64.3% (18/28) yield; no WGS cases were reported in that cohort (moura2024spinocerebellarataxiasphenotypic pages 2-4, moura2024spinocerebellarataxiasphenotypic pages 7-9).

Clinical trial genetic confirmation threshold: An intrathecal ASO trial required genetically confirmed SCA3 with ATXN3 CAG repeats ≥60 (NCT05160558 chunk 1).

10.2 Diagnostic delay (quantitative, 2023)

A Brazilian retrospective study (1999–2017; n=428 symptomatic individuals included) reported median diagnostic delay 5 years (IQR ~3–8.75). Index cases had longer delays than non-index relatives (median 6 vs 4 years) (pinheiro2023diagnosticdelayof pages 2-5).

10.3 Biomarkers and imaging in diagnostic/staging workflows (2024)

  • Blood NfL and plasma mutant ATXN3, alongside MRI volumes of pons and cerebellar compartments, are being used to define pre-ataxic “biomarker stage” vs manifest ataxia in large cohorts, which may inform future diagnostic and preventive-trial strategies (faber2024stage‐dependentbiomarkerchanges pages 7-9, faber2024stage‐dependentbiomarkerchanges pages 4-7).

Data gaps: Differential diagnosis lists, standardized ICD/DSM-like criteria, and formal guidance on WES/WGS sensitivity for expansions were not retrieved in this run.

11. Outcome / Prognosis

SCA3/MJD is progressive with severe disability and reduced life expectancy: - A 2024 review reports that advanced disease often leads to wheelchair dependence and survival after symptom onset of approximately 20–25 years (potapenko2024thedeubiquitinasefunction pages 1-2). - In a Portuguese cohort context, average life expectancy reduction of ~5.6 years vs general population (for deceased patients, all of whom had MJD/SCA3) was reported (moura2024spinocerebellarataxiasphenotypic pages 9-10).

12. Treatment

12.1 Current standard of care

No disease-modifying therapy is established; management is largely supportive/symptomatic (paulino2023autophagyinspinocerebellar pages 1-2, sohail2023adifficultcase pages 1-2).

Suggested MAXO terms (examples): - Symptomatic treatment — MAXO:0000058 (supportive care; general) (sohail2023adifficultcase pages 1-2) - Physical therapy / rehabilitation — MAXO:0000012 (not directly evidenced in retrieved excerpts; include only if supported by additional sources)

12.2 Disease-modifying and experimental therapeutics (2023–2024 emphasis)

12.2.1 Antisense oligonucleotides (ASOs)

  • BIIB132 (intrathecal ASO targeting ATXN3 pre-mRNA): Phase 1, randomized, placebo-controlled; terminated; enrollment 8; completion 2023-07-25 (ClinicalTrials.gov NCT05160558) (NCT05160558 chunk 1). The major role of NfL/MRI staging work is to support early-stage trials, and the biomarker paper notes initiation of this ASO safety trial (faber2024stage‐dependentbiomarkerchanges pages 4-7).
  • A 2024 review reports additional ASO development such as VO659 in Phase 1/2a (ClinicalTrials.gov NCT05822908) (stahl2024spinocerebellarataxiatype pages 6-7).

12.2.2 Autophagy-targeting and small-molecule approaches

  • Trehalose (SLS-005): A 2024 review reports tolerability in a small Phase 2 and an ongoing larger IV trial (ClinicalTrials.gov NCT05490563) (stahl2024spinocerebellarataxiatype pages 6-7). Autophagy impairment is a core mechanistic rationale (paulino2023autophagyinspinocerebellar pages 4-5).
  • Lithium carbonate: A 2024 review notes lack of efficacy in a double-blind placebo-controlled Phase 2 trial in ~63 SCA3 patients (pilotto2024hereditaryataxiasfrom pages 20-22). ClinicalTrials.gov includes a completed lithium trial in SCA3 (NCT01096082) (NCT05160558 chunk 1).
  • Astragaloside IV (preclinical, 2024): reduced mutant ataxin-3 levels/aggregation in a cell model while improving oxidative stress and mitochondrial quality control (lin2024astragalosideivreduces pages 1-2).

12.2.3 Gene suppression/editing (preclinical landscape)

Preclinical RNAi/shRNA/siRNA and CRISPR strategies have demonstrated reduction of ataxin-3 aggregation and improvement in motor/neuropathology readouts in models (pilotto2024hereditaryataxiasfrom pages 13-15, cui2024spinocerebellarataxiasfrom pages 6-7). Delivery and safety remain major translational barriers (cui2024spinocerebellarataxiasfrom pages 6-7, stahl2024spinocerebellarataxiatype pages 6-7).

12.2.4 Neuromodulation and supportive-device interventions (real-world trials)

ClinicalTrials.gov records indicate multiple non-pharmacologic trials in MJD/SCA3, including deep TMS (NCT02039206), rTMS (NCT05502432), and a gait intervention using lower-limb weighting (NCT02906046) (NCT02175290 chunk 1). Detailed outcomes were not available in the retrieved trial excerpts for this run.

13. Prevention

Because SCA3/MJD is monogenic, “prevention” primarily centers on genetic counseling, family-based cascade testing, and early identification of mutation carriers.

Evidence-supported elements from retrieved sources: - A Brazilian diagnostic workflow explicitly distinguishes direct mutation testing for individuals from families with known molecular diagnosis versus stepwise panel testing for index cases (pinheiro2023diagnosticdelayof pages 2-5). - A 2024 biomarker study supports identification of a pre-ataxic biomarker stage (~12 years pre-onset NfL rise), suggesting feasibility of preventive/early-intervention trials in carriers before frank ataxia (faber2024stage‐dependentbiomarkerchanges pages 7-9).

Data gaps: Formal guidelines for prenatal testing/PGT, and specific genetic counseling recommendations were not retrieved in this run.

14. Other Species / Natural Disease

No naturally occurring (non-experimental) veterinary SCA3/MJD analogs were identified in the retrieved evidence.

15. Model Organisms

15.1 Model systems used (with evidence)

  • Human cellular models: patient fibroblasts; iPSC-derived neural models; CRISPR-corrected iPSCs with restored function/electrophysiology (cui2024spinocerebellarataxiasfrom pages 6-7).
  • Rodents: mouse and rat models used to recapitulate inclusions, Purkinje neuron dysfunction/degeneration, motor deficits; responsive to RNAi/ASO/shRNA interventions in preclinical studies (pilotto2024hereditaryataxiasfrom pages 13-15, cui2024spinocerebellarataxiasfrom pages 9-10).
  • Zebrafish: transgenic models used for aggregation/autophagy-related phenotypes and rapid screening (cui2024spinocerebellarataxiasfrom pages 9-10).
  • Invertebrates: Drosophila and C. elegans used in modifier screens; Drosophila expression of expanded human ATXN3 reproduces aspects of SCA3 phenotype (stahl2024spinocerebellarataxiatype pages 6-7, silva2023thejosephindomain pages 1-2).

15.2 Model limitations (evidence-aligned)

Key limitations highlighted include delivery barriers (BBB, invasive dosing for ASOs), need for repeated administration, and translational uncertainty from preclinical success to clinical efficacy (cui2024spinocerebellarataxiasfrom pages 6-7, cui2024spinocerebellarataxiasfrom pages 9-10).

Recent developments (2023–2024) — synthesis highlights

  1. Biomarker staging and early disease window: Large cohort work proposes a carrier → biomarker → ataxia staging model, with NfL abnormal ~11.9 years pre-onset (faber2024stage‐dependentbiomarkerchanges pages 7-9, faber2024stage‐dependentbiomarkerchanges media b30f008b, faber2024stage‐dependentbiomarkerchanges media 807d2b9d).
  2. Therapeutic pipeline maturation but setbacks: Intrathecal ATXN3 ASO trial NCT05160558 terminated after a small Phase 1 exposure; multiple other approaches (e.g., trehalose IV, VO659) continue (NCT05160558 chunk 1, stahl2024spinocerebellarataxiatype pages 6-7).
  3. Mechanistic refinement: Reviews emphasize convergent impairment of proteostasis (UPS/autophagy) and mitochondrial quality control (mitophagy via Parkin/VDAC1; PINK1/Parkin) as actionable targets (cui2024spinocerebellarataxiasfrom pages 5-6, paulino2023autophagyinspinocerebellar pages 4-5).
  4. Molecular stratification for mRNA-lowering: Tissue-specific ATXN3 splice variant abundance differences provide a concrete consideration for target engagement biomarkers and isoform coverage (raposo2024bloodandcerebellar pages 1-5).

Key limitations of this run (for knowledge base completion)

  • ICD-10/ICD-11 and MeSH identifiers were not retrieved and should be filled via dedicated ontology lookup.
  • Many sources in this run were reviews; primary literature PMIDs were not consistently present in the retrieved excerpts.
  • Environmental risk/protective factors, gene–environment interactions, neuroinflammation details, and formal prevention/counseling guidelines were not captured in the retrieved evidence set.

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