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Classifications

Harrison's Part

Mechanistic Nosology

👪

Inheritance

2

Autosomal dominant inheritance HP:0000006

SCA48 segregates as an autosomal dominant trait: heterozygous STUB1 variants cosegregate with disease across multiple generations in independent pedigrees. Penetrance is incomplete and age-dependent, and de novo variants occur, so a negative family history does not exclude the diagnosis. This is the dominant counterpart of the recessive STUB1 disorder SCAR16 / Gordon Holmes syndrome, and dominant and recessive variants produce indistinguishable in vitro defects.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:30381368 SUPPORT Human Clinical

"Since recessive mutations in STUB1 gene have been previously associated with SCAR16, these findings suggest a previously undescribed SCA locus (SCA48; MIM# 618093)."

The discovery study reports a heterozygous, cosegregating STUB1 variant and explicitly distinguishes the new dominant locus from the previously known recessive SCAR16 disorder.

PMID:32211513 SUPPORT Human Clinical

"This study confirms a dominant inheritance pattern in STUB1-ataxia in addition to a recessive one and documents its association with cognitive and behavioral disability, including autism."

Independent replication in two further families confirms that dominant inheritance coexists with the recessive pattern for the same gene.

De novo variant occurrence HP:0003745

SCA48 can arise from a de novo heterozygous STUB1 variant in a patient with no family history, so the absence of an affected parent does not exclude the diagnosis.

Sporadic

Show evidence (1 reference)

PMID:35398354 SUPPORT Human Clinical

"Here we have identified a novel, de novo mutation in STUB1 in a patient with SCA48 encoding for an A52G point mutation in the tetratricopeptide repeat domain of CHIP."

A de novo TPR-domain STUB1 variant in an SCA48 patient establishes that the disorder occurs sporadically as well as by transmission. Graded HUMAN_CLINICAL because the quoted claim is a patient genetic observation, even though the rest of this paper is biochemistry.

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Mechanistic Hypotheses

2

SCA48 as a monogenic STUB1 disorder

sca48_monogenic CANONICAL

Evidence balance 4 support

A heterozygous pathogenic STUB1 variant is by itself sufficient to cause the SCA48 phenotype. Multiple independent series report probands with the complete clinical picture - ataxia, dysarthria, cerebellar atrophy and cognitive impairment - and TBP repeat lengths within the normal range.

Show evidence (4 references)

PMID:36422518 SUPPORT Human Clinical

"Importantly, 13 STUB1 probands presenting with the full SCA48 clinical phenotype had normal TBP37-39 alleles, excluding digenic inheritance as the sole mode."

Thirteen probands with normal TBP alleles and the full phenotype directly establish that STUB1 alone suffices.

PMID:38973070 SUPPORT Human Clinical

"SCA48 is predominantly a monogenic disorder, because most patients carried an isolated, heterozygous STUB1 variant and presented with the typical combined phenotype of ataxia and cognitive dysfunction."

An independent 21-patient cohort reaches the same conclusion.

PMID:39680235 SUPPORT Human Clinical

"Our cases lacked pathological TBP expansions and provide additional evidence that STUB1 (SCA48) can manifest as a monogenic disease."

Three further unrelated probands with normal TBP repeats support the monogenic model.

+ 1 more reference

Obligate digenic TBP/STUB1 inheritance

sca48_tbp_digenic ⚠ DEPRECATED

⚠ Overturned model — shown for reference, not as current mechanism

DisMech records superseded hypotheses explicitly rather than deleting them, so that claims still circulating in reviews, textbooks and older diagnostic criteria can be checked against an assessment. This model is not part of the disease mechanism DisMech asserts.

Citation volume does not decide standing here. A hypothesis may retain more supporting than refuting citations simply because the supporting literature accumulated for decades before the refutation landed; where the two conflict, DisMech follows the more recent and more direct evidence. Supporting citations below are retained for the historical record.

Evidence balance 1 support 1 refute

The competing model held that SCA48 is not a monogenic entity but the digenic product of a heterozygous STUB1 variant plus an intermediate-length TBP expansion, with neither genotype pathogenic alone. This was a serious proposal supported by near-complete co-occurrence in one cohort. It is recorded as rejected in its strong form: probands with the full phenotype and normal TBP alleles exclude obligate digenic inheritance. The weaker modifier claim survives and is curated in the "TBP Intermediate Repeat Expansion as a Genetic Modifier" pathophysiology node.

Show evidence (2 references)

PMID:34906452 SUPPORT Human Clinical

"TBP41-46 expansions and STUB1 variants cosegregate in all affected family members, whereas the presence of either TBP41-46 expansions or STUB1 variants individually was never associated with the disease."

The observation on which the digenic hypothesis rested, quoted from the paper that proposed it.

PMID:36422518 REFUTE Human Clinical

"Importantly, 13 STUB1 probands presenting with the full SCA48 clinical phenotype had normal TBP37-39 alleles, excluding digenic inheritance as the sole mode."

Direct refutation of obligate digenic inheritance in a cohort assembled to test it.

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Discussions and Knowledge Gaps

2

How large is the TBP modifier effect on SCA48 penetrance, and does it extend to other repeat loci?

KNOWLEDGE GAP OPEN sca48-tbp-modifier-magnitude

Attached to

pathophysiology#TBP Intermediate Repeat Expansion as a Genetic Modifier

The modifier reading of the STUB1/TBP interaction is well supported, but its magnitude is not quantified: there is no penetrance estimate stratified by TBP repeat length, variant domain, age and sex. The same cohort that reported the 7% yield also reported second hits in AFG3L2 and PRKCG in three families and a 70% female excess, neither of which has been replicated. Until these are quantified, prognostic counselling for a STUB1-positive individual rests on cohort-level associations rather than an individual risk estimate.

Proposed experiments

Genotype-curated SCA48 penetrance registry with TBP sizing

exp_sca48_penetrance_registry

Prospective, genotype-curated multicentre registry with TBP repeat sizing on all STUB1 variant carriers, including asymptomatic relatives, powered to estimate age-specific penetrance stratified by TBP repeat length, CHIP domain and sex, with independent replication of the reported female excess and of the AFG3L2/PRKCG second hits.

Decision criterion

An age-specific penetrance curve that separates by TBP repeat length with non-overlapping confidence intervals would establish the magnitude of the modifier effect; overlapping curves would place an upper bound on it.

Show evidence (1 reference)

PMID:32713943 SUPPORT Human Clinical

"This screening of STUB1 variants revealed new features: (1) the majority of patients were women (70%) and (2) "second hits" in AFG3L2, PRKCG, and TBP were detected in three families suggesting synergic effects."

Source of the unreplicated sex ratio and additional candidate modifier loci that this gap asks to be quantified or refuted.

Does CHIP-dependent mitophagy dysregulation contribute to Purkinje cell loss in human SCA48?

KNOWLEDGE GAP OPEN sca48-mitophagy-human-relevance

Attached to

pathophysiology#Dysregulated PINK1/Parkin-Mediated Mitophagy

CHIP negatively regulates PINK1/Parkin mitophagy and disease-associated CHIP variants dysregulate it in cell culture and in C. elegans neurons, but no human SCA48 tissue has been examined for mitophagy or mitochondrial pathology. The node is therefore recorded with PROVISIONAL confidence and an indirect downstream edge. A comparable candidate mechanism - impaired heat-shock response - was tested in SCAR16 (biallelic) patient iPSC-derived neurons against isogenic STUB1-null controls and did not survive, which is the cautionary precedent here.

Proposed experiments

Mitophagy flux in SCA48 patient iPSC-derived Purkinje-like neurons

exp_sca48_mitophagy_human_neurons

Measure mitophagy flux, PINK1/Parkin recruitment and mitochondrial morphology in iPSC-derived Purkinje-like neurons from patients carrying dominant SCA48 STUB1 variants against isogenic corrected controls, and stain the existing SCA48 autopsy cerebellum series for mitochondrial and PINK1/Parkin pathology.

Decision criterion

A mitophagy defect present in patient neurons but absent from isogenic controls, and corroborated in autopsy tissue, would move this node from PROVISIONAL to ESTABLISHED; a null result matching the heat-shock-response precedent would justify removing the node.

Show evidence (1 reference)

PMID:33097556 SUPPORT In Vitro

"Furthermore, STUB1(-/-) neurons generated by CRISPR/Cas9-mediated genome editing from an isogenic healthy control line showed a similar HSR to patients."

The precedent for the caution: a plausible CHIP-linked mechanism failed when tested in the right cell type with isogenic controls. The patient lines were SCAR16 (biallelic), so the precedent bears on CHIP biology generally rather than on SCA48 zygosity specifically.

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Pathophysiology

8

CHIP Loss of Function from Heterozygous STUB1 Variants

The initiating lesion is a heterozygous germline pathogenic STUB1 variant. STUB1 encodes CHIP, a 35 kDa cytosolic protein whose N-terminal tetratricopeptide-repeat (TPR) domain binds the HSC70/HSP70 chaperones and whose C-terminal U-box recruits E2 ubiquitin-conjugating enzymes. Missense, nonsense, frameshift, splice and in-frame deletion variants are distributed across the coding sequence with no hotspot. The functional consequence is domain-dependent rather than uniform: TPR-domain variants retain intrinsic ligase activity but lose HSP70 binding and protein stability, while U-box variants abolish ligase activity, oligomerise abnormally and only partly impair co-chaperone function. Dominant SCA48 variants and recessive SCAR16 variants produce biochemically indistinguishable defects in vitro, which is why the two disorders form a continuous clinical spectrum rather than two mechanisms.

STUB1 hgnc:11427

ubiquitin protein ligase activity GO:0061630 ↓ DECREASED Hsp70 protein binding GO:0030544 ↓ DECREASED

Animal models

transgenic expression of human CHIP p.Ala52Gly Caenorhabditis elegans Caenorhabditis elegans recapitulates Expression of the human CHIP A52G SCA48 variant causes neurodegeneration in an intact organism.

Downstream

Impaired Chaperone-Assisted Protein Quality Control Loss of TPR-mediated chaperone engagement and/or U-box-mediated E2 recruitment removes CHIP from the chaperone-to-proteasome hand-off.

Dysregulated PINK1/Parkin-Mediated Mitophagy CHIP normally restrains PINK1/Parkin-mediated mitophagy; disease variants dysregulate this branch independently of the aggregation arm.

Show evidence (5 references)

PMID:30381368 SUPPORT Human Clinical

"Among the candidate variants, only the frameshift heterozygous c.823_824delCT STUB1 (p.L275Dfs*16) pathogenic variant cosegregated with the disease."

Identifies the initiating molecular lesion: a single heterozygous STUB1 frameshift variant cosegregating with SCA48 in the discovery pedigree.

PMID:42567515 SUPPORT In Vitro

"TPR variants retained intrinsic ligase activity but showed significantly reduced HSP70 binding, impaired substrate ubiquitination, and decreased stability. Conversely, U-box variants abolished ligase function, promoted the formation of high-molecular-weight oligomers, and often increased CHIP..."

Systematic biochemical analysis of 13 SCA48 variants shows that the molecular consequence is domain-dependent, splitting the initiating lesion into a chaperone-binding arm and a ligase arm.

PMID:42567515 SUPPORT Human Clinical

"Meta-analysis of 87 SCA48 patients linked TPR-like biochemical signatures to upper motor neuron involvement and U-box-like profiles to prominent dysarthria."

The first reported genotype-phenotype signal in SCA48: which CHIP domain the variant hits tracks with which clinical features dominate. This supersedes the earlier position that no genotype-phenotype correlation exists, and is the source of the upper-motor-neuron phenotype curated below. Graded HUMAN_CLINICAL because the quoted claim is a meta-analysis of patient phenotypes, not the paper's biochemistry.

+ 2 more references

Impaired Chaperone-Assisted Protein Quality Control

CHIP is the physical link between the cytosolic chaperone machinery and the ubiquitin-proteasome system. Through its TPR domain it binds HSC70 and HSP70 and attenuates their folding cycle; through its U-box it acts as a bona fide E3 ubiquitin ligase, recruiting UBCH5-family E2 enzymes and ubiquitinating chaperone-bound clients so that terminally misfolded proteins are routed to the proteasome instead of being refolded indefinitely. Loss of CHIP function therefore removes the triage step of cytosolic protein quality control. Loss of Chip ubiquitin ligase activity in zebrafish reduces total brain 26S proteasome activity, showing that the proteasomal arm is degraded in vivo and not only in reconstituted assays.

protein ubiquitination GO:0016567 ↓ DECREASED proteasome-mediated ubiquitin-dependent protein catabolic process GO:0043161 ↓ DECREASED protein quality control for misfolded or incompletely synthesized proteins GO:0006515 ↓ DECREASED

ubiquitin protein ligase activity GO:0061630 ↓ DECREASED protein-folding chaperone binding GO:0051087 ↓ DECREASED

Animal models

stub1 mutant with truncated Chip U-box domain Danio rerio Danio rerio recapitulates Truncating the Chip U-box abolishes ubiquitination of Hsc70 and of Chip itself and lowers whole-brain 26S proteasome activity, reproducing the molecular lesion of U-box SCA48 variants.

Downstream

Accumulation of Misfolded Client Proteins and Neuronal Inclusions Undegraded chaperone clients accumulate and aggregate; in cellular models of SCA48 variants this includes tau and alpha-synuclein.

Show evidence (4 references)

PMID:10330192 SUPPORT In Vitro

"In vitro binding assays demonstrated direct interactions between CHIP and both Hsc70 and Hsp70, and complexes containing CHIP and Hsc70 were identified in immunoprecipitates of human skeletal muscle cells in vivo."

Establishes the baseline biology this node depends on: CHIP is a direct HSC70/HSP70-binding co-chaperone.

PMID:11557750 SUPPORT In Vitro

"we demonstrate that CHIP possesses intrinsic E3 ubiquitin ligase activity and promotes ubiquitylation. This activity is dependent on the carboxyl-terminal U-box."

Establishes the second half of the baseline biology: the U-box confers genuine E3 ubiquitin ligase activity, the function lost in U-box SCA48 variants.

PMID:35398354 SUPPORT In Vitro

"CHIP is known to regulate proteostasis by recruiting chaperones via a N-terminal tetratricopeptide repeat domain and recruiting E2 ubiquitin-conjugating enzymes via a C-terminal U-box domain. These interactions allow CHIP to mediate the ubiquitination of chaperone-bound, misfolded proteins to..."

States the coupling of the chaperone machinery to the proteasome that this node describes, in the specific context of SCA48.

+ 1 more reference

Dysregulated PINK1/Parkin-Mediated Mitophagy

CHIP acts as a negative regulator of PINK1/Parkin-mediated mitophagy, promoting PINK1 degradation and limiting Parkin recruitment to stressed mitochondria. Disease-associated CHIP variants dysregulate this pathway in cell culture and in C. elegans neurons, giving a parallel branch of mitochondrial quality control alongside the aggregation branch. This arm is mechanistically plausible for SCA48 but has not been demonstrated in human SCA48 tissue, so it is recorded as a provisional mechanism.

mitophagy GO:0000423 ↕ DYSREGULATED

Downstream

Cerebellar Purkinje Cell Degeneration Loss of mitochondrial quality control is proposed to contribute to neuronal vulnerability in CHIP-associated disease. The link to Purkinje cell loss in SCA48 specifically is inferred, not demonstrated.

Show evidence (1 reference)

PMID:39117117 SUPPORT In Vitro

"Here, we demonstrate that CHIP acts as a negative regulator of the PTEN-induced kinase 1 (PINK1)/Parkin-mediated mitophagy pathway, promoting the degradation of PINK1, impairing Parkin translocation to the mitochondria, and suppressing mitophagy in response to mitochondrial stress."

Defines the normal regulatory relationship whose loss constitutes this node.

Accumulation of Misfolded Client Proteins and Neuronal Inclusions

Failure of CHIP-mediated triage leaves misfolded chaperone clients undegraded. In cellular models of SCA48 variants this produces accumulation of tau and alpha-synuclein with caspase-3 activation and apoptosis. In patients, the corresponding pathology is ubiquitin- and p62-positive neuronal inclusions, which are found in the cerebellum, neocortex and brainstem and are regarded as a pathological hallmark of the disease. Cortical neurons derived from patient iPSCs show dysfunctional protein (re)folding and elevated basal oxidative stress, while the same study found that impaired heat-shock response - an earlier candidate mechanism - was not specific to mutant cells. Those patient lines came from the recessive (SCAR16) end of the STUB1 spectrum, so the finding is carried here on the strength of the shared molecular lesion rather than observed in SCA48 patients directly.

protein refolding GO:0042026 ↓ DECREASED

inclusion body GO:0016234

cerebellum UBERON:0002037

Downstream

Peripheral neuropathy Where peripheral involvement is reported, failed proteostasis in peripheral neurons is the presumed route. No study establishes the intermediate steps, and two cohorts report no peripheral involvement at all, so this edge is speculative and deliberately uncited.

Cerebellar Purkinje Cell Degeneration Accumulated misfolded protein and inclusion pathology in a cell type with high proteostatic demand drives Purkinje cell dysfunction and loss.

Show evidence (5 references)

PMID:32337344 SUPPORT Human Clinical

"Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem."

Human neuropathology in three heterozygous STUB1 cases documents the protein-inclusion pathology this node asserts, and its anatomical distribution.

PMID:32337344 SUPPORT Human Clinical

"The presence of intranuclear inclusions is a pathologic hallmark of the disease."

States that inclusion pathology is a defining feature of SCA48 rather than an incidental finding.

PMID:34565360 SUPPORT In Vitro

"leading to neuronal accumulation of tau and α-synuclein, caspase-3 activation, and promoting cellular apoptosis through a dominant-negative pathogenic effect"

Identifies the specific accumulating clients and the downstream apoptotic response in a neuronal model of an SCA48 variant.

+ 2 more references

Cerebellar Purkinje Cell Degeneration

The Purkinje cell is the selectively vulnerable cell type in SCA48. Human neuropathology in heterozygous STUB1 patients shows marked to massive Purkinje cell loss, most severe in the vermis and substantial in the hemispheres, with strikingly little pathology elsewhere in one series and no atrophy of pons, hippocampus or cerebral cortex in another. A second cell-autonomous abnormality is loss of the normal polarised somatodendritic distribution of CHIP within surviving Purkinje cells, with aberrant protein in the distal dendritic arbor. A zebrafish chip U-box truncation reproduces the cellular phenotype - reduced Purkinje cell number and soma size and disorganised dendrites - without gross cerebellar atrophy.

cerebellar Purkinje cell CL:0000121

neuron apoptotic process GO:0051402 ↑ INCREASED

cerebellar cortex UBERON:0002129

Animal models

stub1 mutant with truncated Chip U-box domain Danio rerio Danio rerio recapitulates

Downstream

Cerebellar Atrophy and Dentate Nucleus Involvement Progressive Purkinje cell loss is the cellular substrate of the macroscopic cerebellar atrophy seen on MRI.

Show evidence (3 references)

PMID:32713943 SUPPORT Human Clinical

"We report neuropathological findings of a STUB1 heterozygous patient, showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex."

Human autopsy in a heterozygous (i.e. SCA48, not SCAR16) patient localises the degeneration to Purkinje cells with a vermian gradient.

PMID:32211513 SUPPORT Human Clinical

"The normal pattern of polarized somatodendritic STUB1 protein expression in PCs was lost, resulting in aberrant STUB1 localization in the distal PC dendritic arbors."

Adds a cell-autonomous subcellular abnormality in surviving Purkinje cells, indicating the degeneration is not only a loss of cell number.

PMID:34630034 SUPPORT INDIRECT Model Organism

"In contrast to SCAR16/SCA48 patients, no gross cerebellar atrophy was evident in mutant fish, however, these fish displayed reduced numbers and sizes of Purkinje cell bodies and abnormal organization of Purkinje cell dendrites."

A vertebrate model reproduces the Purkinje cell phenotype but not the gross atrophy. Recorded as INDIRECT because it corroborates the cellular claim through a non-human system while marking the limit of the model.

Cerebellar Atrophy and Dentate Nucleus Involvement

At tissue level, SCA48 produces cerebellar atrophy involving both vermis and hemispheres with a postero-lateral hemispheric predominance, accompanied in around 90% of patients by T2-weighted hyperintensity of both dentate nuclei; the combination is described as the "crab sign". The topography is not uniform over time. In the discovery pedigree, presymptomatic carriers already had focal atrophy restricted to the vermis, paravermis and the medial parts of lobules VI and VII - cerebellar territories serving cognition and emotion - before any ataxia, with later spread to the whole cerebellum. This staged topography is what makes the cognitive-affective syndrome precede the motor syndrome.

cerebellum UBERON:0002037 dentate nucleus UBERON:0002132 cerebellar vermis UBERON:0004720

Downstream

Disruption of Cerebello-Cerebral Motor and Cognitive Circuits Loss of cerebellar cortical output and dentate/efferent pathway involvement corrupts the cerebellar contribution to both motor and cognitive-affective circuits.

Cerebellar atrophy The tissue-level volume loss is what is observed clinically as cerebellar atrophy on MRI.

Show evidence (3 references)

PMID:32285148 SUPPORT Human Clinical

"Atrophy of the cerebellum was present in all cases, involving both the vermis and the hemispheres, but particularly affecting the postero-lateral portions of the cerebellar hemispheres."

Defines the tissue-level topography of atrophy in a dedicated SCA48 imaging series.

PMID:32285148 SUPPORT Human Clinical

"In all patients, with the exception of only one subject (90.0% of the cases), a T2WI hyperintensity of both dentate nuclei was found."

Documents dentate nucleus involvement and quantifies it, supporting the inclusion of the dentate nucleus as an affected structure.

PMID:30381368 SUPPORT Human Clinical

"Three presymptomatic patients showed focal cerebellar atrophy in the vermian, paravermian, and the medial part of cerebellar lobes VI and VII, suggesting that cerebellar atrophy preceded the ataxia, and that the neurodegeneration begins in cerebellar areas related to cognition and emotion,..."

Establishes the staged topography - cognitive/affective cerebellar territories first, whole cerebellum later - that this node asserts.

Disruption of Cerebello-Cerebral Motor and Cognitive Circuits

The clinical syndrome follows from the loss of cerebellar output to both motor and associative/limbic cerebro-cerebellar loops. The motor loop failure produces gait and limb ataxia, dysarthria, dysmetria and tremor; the cognitive-affective loop failure produces the cerebellar cognitive-affective syndrome - a predominantly frontal/dysexecutive picture with behavioural and psychiatric change that can present years before ataxia. FDG-PET in SCA48 families shows glucose hypometabolism not only in cerebellum but also in striatum and cerebral cortex, consistent with remote (diaschisis-like) effects on connected forebrain territories and matching the extrapyramidal features seen clinically.

cerebellum UBERON:0002037

Downstream

Ataxia

Dysarthria

Cerebellar cognitive-affective syndrome

Dysmetria

Dysphagia

Abnormal conjugate eye movement

Cognitive impairment

Depression

Anxiety

Behavioural and personality change

Psychiatric symptoms

Upper motor neuron involvement

Urinary symptoms

Seizure

Tremor

Parkinsonism

Chorea

Dystonia

Show evidence (2 references)

PMID:31126790 SUPPORT Human Clinical

"MRI showed a significant cerebellar atrophy, coupled to a T2-weighted hyperintensity affecting the dentate nuclei and extending to the middle cerebellar peduncles, whereas FDG-PET studies revealed glucose hypometabolism in cerebellum, striatum, and cerebral cortex."

Functional imaging shows the cerebellar lesion is accompanied by hypometabolism in connected striatal and cortical territories, which is the circuit-level disruption this node describes.

PMID:30381368 SUPPORT Human Clinical

"Six patients fully developed cognitive-affective and complete motor cerebellar syndrome associated with vermian and hemispheric cerebellar atrophy, suggesting a continuum from a dysexecutive syndrome slowly evolving to a complete and severe CCAS with late truncal ataxia."

Describes the dual motor and cognitive-affective output failure, and its temporal ordering, that this node is asserting.

TBP Intermediate Repeat Expansion as a Genetic Modifier

Intermediate-length CAG/CAA repeat expansions in TBP (roughly 40-49 repeats), which are themselves incompletely penetrant for SCA17, co-occur with heterozygous STUB1 variants far more often than chance. The original interpretation was digenic inheritance - TBP41-46 alleles and STUB1 variants cosegregating, with neither genotype alone associated with disease - and this reading questioned whether SCA48 exists as a monogenic entity at all. Subsequent work resolved the question in favour of a modifier model rather than obligate digenic inheritance: probands with the full SCA48 phenotype and normal TBP alleles exclude digenic inheritance as the sole mode, while longer TBP repeats predict more cognitive impairment and faster progression. Patients carrying both genotypes have a more severe, fully penetrant multidomain ataxia-dementia phenotype with reduced cerebellar and brainstem volumes. This node therefore modifies the severity and penetrance of the main chain rather than initiating it.

TBP hgnc:11588

Downstream

Disruption of Cerebello-Cerebral Motor and Cognitive Circuits Co-inherited intermediate TBP expansions increase the penetrance and severity of the SCA48 phenotype, particularly its cognitive component, rather than causing a separate disease process.

Show evidence (6 references)

PMID:34906452 SUPPORT Human Clinical

"All except 1 (30/31) of the index cases with TBP41-46 alleles carried a heterozygous pathogenic variant in the STUB1 gene associated with spinocerebellar ataxias SCAR16 (autosomal recessive) and SCA48 (autosomal dominant)."

Documents the strong non-random co-occurrence of intermediate TBP alleles with STUB1 variants that motivated the digenic hypothesis.

PMID:34906452 REFUTE Human Clinical

"raise questions on the existence of SCA48 as a monogenic disease with crucial implications for diagnosis and counseling"

Recorded as REFUTE because this sentence argues against the modifier framing this node asserts - the authors read the same STUB1/TBP interaction as obligate digenic inheritance rather than as modification of a monogenic disorder. It is kept on the node so the position the later literature had to answer is visible here; the digenic reading itself is curated under the sca48_tbp_digenic hypothesis.

PMID:36422518 SUPPORT Human Clinical

"We show that intermediate TBP40-49 alleles act as disease modifiers of SCA48 rather than a STUB1/TBP digenic model."

The direct answer to the digenic hypothesis from the same kind of cohort: the interaction is modifier, not obligate digenic.

+ 3 more references

✶

Histopathology

2

Purkinje cell loss with vermian predominance

Post-mortem examination in heterozygous STUB1 patients shows marked to massive Purkinje cell loss, most severe in the vermis and substantial in the hemispheres, with little or no involvement of pons, hippocampus or cerebral cortex on gross and microscopic assessment. Term-binding note: NCIT:C120874 (Degeneration and Atrophy) is generic, but it is the most specific term available under the Histopathology Result branch that the schema draws on - NCIT's only cell-loss-specific terms are for sensory hair cells and corneal endothelium. preferred_term carries the cell type.

Show evidence (2 references)

PMID:32713943 SUPPORT Human Clinical

"showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex"

Autopsy findings in a heterozygous STUB1 patient define the histopathological signature and its anatomical selectivity.

PMID:32211513 SUPPORT Human Clinical

"Unique neuropathologic examination of the 4 brains showed the marked loss of Purkinje cells (PCs) without microscopic evidence of significant pathology outside the cerebellum."

Four independent brains confirm selective Purkinje cell loss as the histopathological substrate.

Ubiquitin/p62-positive neuronal inclusions

Ubiquitin- and p62-immunoreactive neuronal inclusions, including intranuclear inclusions, are found in cerebellum, neocortex and brainstem and are regarded as a pathological hallmark of SCA48. Tau pathology was additionally present in one of three examined cases.

Show evidence (1 reference)

PMID:32337344 SUPPORT Human Clinical

"Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem. In addition, tau pathology was present in 1 case."

Documents the inclusion pathology, its distribution and the variable tau co-pathology in a heterozygous STUB1 pedigree.

⬡

Pathograph

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Phenotypes

21

Digestive 1

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:39680235 SUPPORT INDIRECT Human Clinical

"Reported clinical syndromes include gait ataxia, dysarthria, dysphagia, and oculomotor abnormalities, as well as cognitive affective symptoms, such as language impairment, depression, anxiety."

Lists dysphagia among the reported clinical features of SCA48. Recorded as INDIRECT because this sentence is the paper's introductory synthesis of prior SCA48 case reports rather than an observation in its own three probands.

Genitourinary 1

Urinary symptoms Urinary urgency HP:0000012

Show evidence (1 reference)

PMID:31126790 SUPPORT Human Clinical

"variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"

Urinary symptoms are listed among the variable features of the SCA48 syndrome in two independent families.

Musculoskeletal 1

Upper motor neuron involvement Hypertonia HP:0001276

Show evidence (4 references)

PMID:39680235 SUPPORT Human Clinical

"All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms."

Hypertonia is reported in all three probands of this TBP-negative SCA48 series, establishing pyramidal involvement as part of the phenotype.

PMID:42567515 SUPPORT Human Clinical

"Meta-analysis of 87 SCA48 patients linked TPR-like biochemical signatures to upper motor neuron involvement"

An 87-patient meta-analysis reports upper motor neuron involvement in SCA48 and ties it to TPR-domain variants.

PMID:32713943 SUPPORT Human Clinical

"Pyramidal signs were reported in 43% of patients."

The largest STUB1 cohort reports pyramidal signs in 43% of patients, which is the strongest single argument that pyramidal involvement belongs in the SCA48 phenotype. No frequency band is asserted on the phenotype because a second cohort reports the sign as absent.

+ 1 more reference

Nervous System 15

Ataxia VERY_FREQUENT HP:0001251

Course: PROGRESSIVE Onset: ADULT; 17-74y

Show evidence (3 references)

PMID:31571321 SUPPORT Human Clinical

"All our SCA48 patients had cerebellar ataxia and dysarthria associated with cerebellar atrophy on brain magnetic resonance imaging; of note, many cases were also associated with parkinsonism, chorea and dystonia."

Cerebellar ataxia was present in all 11 patients across eight independent SCA48 index families (11/11 = 100%), which is the derived count supporting the VERY_FREQUENT band (80-100%).

PMID:39680235 SUPPORT Human Clinical

"All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms. Age of onset varied from 34 to 65 years of age."

Confirms the slowly progressive course and adult onset in an independent, TBP-negative case series, and is the source of the 34-65 year onset range recorded in the onset notes.

PMID:32713943 SUPPORT Human Clinical

"STUB1 variants were detected in 50 patients. Age at onset and severity were remarkably variable."

The largest cohort documents the variability of age at onset and severity that qualifies the adult-onset label.

Dysarthria VERY_FREQUENT HP:0001260

Show evidence (1 reference)

PMID:31571321 SUPPORT Human Clinical

"All our SCA48 patients had cerebellar ataxia and dysarthria associated with cerebellar atrophy on brain magnetic resonance imaging"

Dysarthria co-occurred with ataxia in all 11 SCA48 patients across eight index families (11/11 = 100%), which is the derived count supporting the VERY_FREQUENT band (80-100%).

Cognitive impairment FREQUENT HP:0100543

Course: PROGRESSIVE

Show evidence (2 references)

PMID:32713943 SUPPORT Human Clinical

"Cognitive impairment, predominantly frontal syndrome, was observed in 54% of STUB1 variant carriers, including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia."

Direct quantitative support for both the phenotype and the FREQUENT band: 54% falls in the 30-79% range.

PMID:32211513 SUPPORT Human Clinical

"Cerebellar atrophy on imaging and cognitive deficits often preceded ataxia."

Confirms cognitive impairment as a core, often pre-ataxic feature in an independent dominant STUB1 cohort.

Behavioural and personality change Personality changes HP:0000751

Show evidence (1 reference)

PMID:32337344 SUPPORT Human Clinical

"Patients presented with adult-onset gait disturbance (ataxia or parkinsonism), combined with prominent cognitive decline and behavioral changes."

Behavioural change is documented as a presenting feature in a large heterozygous STUB1 pedigree.

Psychiatric symptoms Atypical behavior HP:0000708

Show evidence (2 references)

PMID:39680235 SUPPORT Human Clinical

"All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms."

Psychiatric symptoms were present in all three probands of this series alongside the motor and cognitive features.

PMID:31126790 SUPPORT Human Clinical

"We describe a complex syndrome characterized by ataxia and cognitive-psychiatric disorder in all cases, variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy."

Cognitive-psychiatric disorder was present in all eight patients from two independent families.

Tremor HP:0001337

Show evidence (1 reference)

PMID:39680235 SUPPORT Human Clinical

"We highlight the importance of tremor as part of the clinical phenotype including upper limb rest tremor and Parkinsonian signs."

A case series dedicated to this feature establishes tremor, including rest tremor, as part of the SCA48 phenotype.

Parkinsonism HP:0001300

Show evidence (2 references)

PMID:31571321 SUPPORT Human Clinical

"of note, many cases were also associated with parkinsonism, chorea and dystonia"

Parkinsonism was a recurring associated feature across eight SCA48 families.

PMID:32337344 SUPPORT Human Clinical

"Patients presented with adult-onset gait disturbance (ataxia or parkinsonism)"

Shows parkinsonism can be the presenting form of the gait disorder, not merely an add-on sign.

Chorea HP:0002072

Show evidence (1 reference)

PMID:31126790 SUPPORT Human Clinical

"variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"

Chorea is listed among the extrapyramidal features variably present in SCA48 patients from two families.

Dystonia HP:0001332

Show evidence (1 reference)

PMID:31571321 SUPPORT Human Clinical

"many cases were also associated with parkinsonism, chorea and dystonia"

Dystonia recurs across the eight-family SCA48 cohort.

Peripheral neuropathy HP:0009830

Show evidence (3 references)

PMID:39680235 SUPPORT INDIRECT Human Clinical

"Rarer clinical features including chorea, Parkinsonism, dystonia, peripheral neuropathies, and epilepsy have been reported."

Places peripheral neuropathy among the rarer reported SCA48 features. INDIRECT because it summarises prior reports rather than this series' own probands.

PMID:32713943 REFUTE Human Clinical

"There was no wasting or sensory loss."

The 50-carrier cohort found no wasting or sensory loss, which contradicts peripheral involvement as a general SCA48 feature. Kept so the disagreement between cohorts is visible on the phenotype rather than resolved by curator preference.

PMID:31571321 REFUTE Human Clinical

"definite signs of pyramidal tract dysfunction and peripheral nervous system involvement were absent"

A second cohort independently reports absent peripheral nervous system involvement.

Depression HP:0000716

Show evidence (1 reference)

PMID:39680235 SUPPORT INDIRECT Human Clinical

"cognitive affective symptoms, such as language impairment, depression, anxiety"

Names depression among the cognitive-affective symptoms reported in SCA48. INDIRECT because the sentence summarises prior case reports rather than this series' own probands.

Anxiety HP:0000739

Show evidence (1 reference)

PMID:39680235 SUPPORT INDIRECT Human Clinical

"cognitive affective symptoms, such as language impairment, depression, anxiety"

Names anxiety among the cognitive-affective symptoms reported in SCA48. INDIRECT because the sentence summarises prior case reports rather than this series' own probands.

Cerebellar atrophy HP:0001272

Course: PROGRESSIVE

Show evidence (2 references)

PMID:32285148 SUPPORT Human Clinical

"Atrophy of the cerebellum was present in all cases, involving both the vermis and the hemispheres"

Cerebellar atrophy was present in all ten patients of a dedicated SCA48 imaging series.

PMID:32211513 SUPPORT Human Clinical

"Cerebellar atrophy on imaging and cognitive deficits often preceded ataxia."

Documents that the atrophy is detectable before the motor phenotype declares itself.

Seizure HP:0001250

Show evidence (1 reference)

PMID:31126790 SUPPORT Human Clinical

"variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"

Epilepsy is reported as a variable feature in these SCA48 families.

Autism HP:0000717

Show evidence (1 reference)

PMID:32211513 SUPPORT Human Clinical

"documents its association with cognitive and behavioral disability, including autism"

Autism is explicitly reported among the behavioural manifestations of dominant STUB1-ataxia in this study.

Other 3

Cerebellar cognitive-affective syndrome Impaired executive functioning HP:0033051

Course: PROGRESSIVE

Show evidence (2 references)

PMID:30381368 SUPPORT Human Clinical

"To describe a new spinocerebellar ataxia (SCA48) characterized by early cerebellar cognitive-affective syndrome (CCAS) and late-onset SCA."

The defining study frames early CCAS with late ataxia as the characteristic pairing of the disorder.

PMID:31741143 SUPPORT Human Clinical

"CCAS is a prominent and often early feature of SCA48 which may be followed years after the onset of the disease by other complex neurological signs and symptoms."

Independent replication of the temporal ordering in an unrelated (Turkish) family.

Dysmetria HP:0001310

Show evidence (1 reference)

PMID:32713943 SUPPORT Human Clinical

"Neurological examination revealed an ataxic gait, dysmetria of the upper limbs, and cerebellar dysarthria."

Examination findings in the index case of family AAD-541, a heterozygous STUB1 p.Y49C carrier with dominant transmission, so this is an SCA48 and not a SCAR16 observation. That family also carries a candidate AFG3L2 second hit, which the entry records as an open question about modifier loci; it does not affect the presence of the cerebellar sign.

Abnormal conjugate eye movement HP:0000549

Show evidence (2 references)

PMID:32713943 SUPPORT Human Clinical

"Diplopia, ptosis, nystagmus, or saccadic pursuit was sometimes present but ophthalmoplegia was rare."

Cohort-level examination findings across 50 STUB1 variant carriers give both the range of oculomotor signs and the qualifier that they are intermittent, which is why no frequency is asserted.

PMID:39680235 SUPPORT INDIRECT Human Clinical

"Reported clinical syndromes include gait ataxia, dysarthria, dysphagia, and oculomotor abnormalities"

Independent confirmation that oculomotor abnormalities are part of the reported SCA48 spectrum. INDIRECT because the sentence summarises prior reports rather than this series' own probands.

🧬

Genetic Associations

2

STUB1 heterozygous pathogenic variants (Causative heterozygous pathogenic variants)

Gene: STUB1 hgnc:11427 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal dominant inheritance

Show evidence (3 references)

PMID:30381368 SUPPORT Human Clinical

"Among the candidate variants, only the frameshift heterozygous c.823_824delCT STUB1 (p.L275Dfs*16) pathogenic variant cosegregated with the disease."

The founding genetic observation: a single heterozygous STUB1 variant cosegregating with SCA48.

PMID:34565360 SUPPORT Human Clinical

"We identified a novel heterozygous frameshift variant, c.832del (p.Glu278fs), in STUB1 in two patients from the same family."

Independent identification of a novel heterozygous U-box frameshift variant in an SCA48 family, illustrating allelic heterogeneity.

PMID:39707479 SUPPORT Human Clinical

"Here, we reported a Chinese SCA48 family exhibited typical features and defined a novel missense mutation STUB1 c.755A>C (CHIP p. Y252S) through whole-exome sequencing."

Extends the reported allelic and geographic spectrum with a functionally characterised missense variant.

TBP intermediate CAG/CAA repeat expansion (modifier) (Modifier of penetrance and severity, not an independent cause of SCA48)

Gene: TBP hgnc:11588 relationship_type: MODIFIER variant_origin: GERMLINE

Show evidence (2 references)

PMID:36422518 SUPPORT Human Clinical

"We show that intermediate TBP40-49 alleles act as disease modifiers of SCA48 rather than a STUB1/TBP digenic model. This distinction from what has been proposed before has crucial consequences for genetic counseling in SCA48."

Establishes the modifier relationship_type used here and states its counselling consequence.

PMID:36422518 SUPPORT Human Clinical

"STUB1 variants were found in half of the TBP40-49 cohort. Mirroring this finding, TBP40-49 alleles were detected in 40% of STUB1 probands."

Quantifies the reciprocal co-occurrence that makes TBP sizing clinically worth doing in STUB1 probands.

💊

Medical Actions

5

Multidisciplinary Supportive Care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

No disease-modifying therapy exists for SCA48, and no SCA48-specific interventional trial has been reported. Management is symptomatic and coordinated across neurology, clinical genetics, rehabilitation, neuropsychology/psychiatry, speech-language pathology and dietetics. Expert consensus for degenerative cerebellar disorders is that no medication has been shown to be effective outside episodic ataxia type 2, so pharmacological trials should be framed as symptomatic and individualised rather than disease-modifying.

Show evidence (1 reference)

PMID:24222635 SUPPORT Other

"There is consensus that up to date, no medication has been proven effective."

Expert consensus across degenerative cerebellar ataxias establishes the absence of proven pharmacotherapy, which is the premise of a supportive management strategy.

Physiotherapy and Coordinative Training

Action: Physical Therapy NCIT:C15302

Physiotherapy is the mainstay of treatment for degenerative cerebellar ataxia, together with occupational therapy and speech therapy. A meta-analysis of 18 randomised trials in degenerative cerebellar ataxia found a significant reduction in SARA score with physiotherapy, with multi-aspect, balance and aerobic training each showing effects; the certainty of evidence was low and no trial was SCA48-specific, so this is generalised from the degenerative-ataxia population.

Target Phenotypes: Cerebellar ataxia HP:0001251

Show evidence (2 references)

PMID:24222635 SUPPORT Other

"As such, all authors agreed that the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy."

Expert consensus identifies physiotherapy as the mainstay of management for this class of disorder.

PMID:39866519 SUPPORT INDIRECT Human Clinical

"Overall, physiotherapy significantly reduced SARA scores (MD = -1.41, [95% CI: -2.16, -0.66])"

Quantifies the effect in the degenerative-ataxia population. Recorded as INDIRECT because the pooled trials were not SCA48-specific, and the review itself reports a serious risk of bias and low certainty of evidence.

Speech and Swallowing Therapy

Action: speech and swallowing therapy Ontology label: Speech Language Therapy NCIT:C159273

Speech therapy addresses the cerebellar dysarthria that is present in essentially all SCA48 patients, and swallowing assessment becomes relevant as the disease advances.

Target Phenotypes: Dysarthria HP:0001260 Dysphagia HP:0002015

Show evidence (1 reference)

PMID:24222635 SUPPORT Other

"the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy"

Speech therapy is named among the consensus mainstays of management for degenerative cerebellar ataxia.

Occupational Therapy

Action: occupational therapy Ontology label: Occupational Therapy NCIT:C121351

Occupational therapy supports activities of daily living, home safety and fall prevention as gait ataxia, tremor and dysmetria progress.

Show evidence (1 reference)

PMID:24222635 SUPPORT Other

"the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy"

Occupational therapy is named among the consensus mainstays of management.

Genetic Counselling and Cascade Testing

Action: Genetic Counseling NCIT:C15240

Counselling must cover the 50% transmission risk, the incomplete and age-dependent penetrance of heterozygous STUB1 variants, the possibility of de novo occurrence, and the effect of TBP repeat length on expected penetrance and severity. Because TBP and STUB1 alleles segregate independently, recurrence-risk calculation and predictive testing in families carrying both must account for that independence.

Show evidence (2 references)

PMID:36799493 SUPPORT Human Clinical

"The identification of the complex SCATBP/STUB1 phenotype may impact on diagnosis and genetic counseling in the families with both hereditary and sporadic ataxia. The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests."

States the specific counselling complication that this treatment entry exists to capture.

PMID:36422518 SUPPORT Human Clinical

"This distinction from what has been proposed before has crucial consequences for genetic counseling in SCA48."

Confirms that the modifier-versus-digenic resolution changes what families are told.

🔬

Diagnosis

1

STUB1 sequencing with parallel TBP repeat sizing

Diagnosis rests on identifying a heterozygous pathogenic STUB1 variant in a patient with a compatible progressive ataxia-plus-cognitive phenotype and cerebellar atrophy on MRI. Because STUB1 is a conventional (non-repeat) gene it is missed by the repeat-expansion panels used first-line in dominant ataxia, so it must be covered by a sequencing panel or exome/genome test. TBP CAG/CAA repeat length should be sized in parallel: it alters expected penetrance, severity and recurrence-risk counselling even though it is not required for the diagnosis.

Show evidence (2 references)

PMID:31571321 SUPPORT Human Clinical

"Molecular screening was performed in a cohort of 235 unrelated patients with adult-onset, autosomal dominant (17) or sporadic (218) cerebellar ataxia, negative for pathological trinucleotide expansions in the common SCAs, FRDA and FXTAS loci, by using targeted multigene panels or whole-exome sequencing."

Describes the diagnostic route by which SCA48 is actually found - sequencing after negative repeat-expansion testing.

PMID:36799493 SUPPORT Human Clinical

"The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests."

Supports sizing TBP alongside STUB1 for counselling purposes.

🩻

Imaging Findings

2

Dentate nucleus T2 hyperintensity with postero-lateral cerebellar atrophy (crab sign)

The most specific imaging feature of SCA48 is bilateral T2-weighted hyperintensity of the dentate nuclei combined with atrophy predominantly of the postero-lateral cerebellar hemispheres; the two together were likened to a crab and named the "crab sign". Supratentorial volume loss and signal change are typically absent. In a separate series the dentate signal change extended into the middle cerebellar peduncles. Term-binding caveat: HPO has no dentate-nucleus signal-intensity term (it has thalamic, brainstem and basal-ganglia siblings), so this finding is bound to the morphology term HP:0100321, which is a different kind of claim from a T2 signal abnormality; preferred_term carries the intended meaning.

Mri Bilateral

Abnormal dentate nucleus morphology HP:0100321 dentate nucleus UBERON:0002132

Show evidence (3 references)

PMID:32285148 SUPPORT Human Clinical

"We propose that the association of such signal change, along with the atrophy of the lateral portion of the cerebellar hemispheres, resembled the appearance of a crab, and therefore, we propose the "crab sign" as a neuroradiological sign present in SCA48 patients."

Names and defines the composite imaging sign in the series that described it.

PMID:32285148 SUPPORT Human Clinical

"In SCA48 patients, no meaningful supratentorial changes were found, both in terms of volume loss or MRI signal changes."

Supports the negative half of the imaging pattern, which is part of what makes the sign discriminating.

PMID:31126790 SUPPORT Human Clinical

"MRI showed a significant cerebellar atrophy, coupled to a T2-weighted hyperintensity affecting the dentate nuclei and extending to the middle cerebellar peduncles"

Independent replication of the dentate signal abnormality with extension into the middle cerebellar peduncles.

Cerebellar atrophy in presymptomatic carriers

Focal atrophy of the vermis, paravermis and medial lobules VI-VII is detectable in presymptomatic STUB1 variant carriers, before motor ataxia. These are the cerebellar territories serving cognition and emotion, which is why the cognitive-affective syndrome precedes the motor syndrome. This has practical consequences: it defines an imaging-detectable prodromal window that any future disease-modifying therapy would likely need to target.

Mri Focal

Cerebellar vermis atrophy HP:0006855 cerebellar vermis UBERON:0004720

Show evidence (1 reference)

PMID:30381368 SUPPORT Human Clinical

"Three presymptomatic patients showed focal cerebellar atrophy in the vermian, paravermian, and the medial part of cerebellar lobes VI and VII, suggesting that cerebellar atrophy preceded the ataxia"

Directly documents presymptomatic focal cerebellar atrophy and its topography in variant carriers.

📊

Prevalence

2

Index cerebellar ataxia cases, mostly with dominant inheritance (SPATAX network, 440 index cases)

Unknown Not yet documented

STUB1 variants were detected in 50 patients across the 440 index cases, an implication of 7% among dominantly inherited cerebellar ataxias. This is a diagnostic yield in a selected cohort, not a population prevalence. No population prevalence, incidence or carrier frequency for SCA48 has been established; the figure is recorded because it is the best available measure of how often SCA48 is encountered among dominant ataxias. measure_type is UNKNOWN because diagnostic yield is not one of the enumerated epidemiological measures.

Show evidence (1 reference)

PMID:32713943 SUPPORT Human Clinical

"Our results reveal an unexpectedly frequent (7%) implication of STUB1 among dominantly inherited cerebellar ataxias, and suggest that the penetrance of STUB1 variants could be modulated by other factors, including sex and variants in other ataxia-related genes."

Source of the 7% figure and of the accompanying caution that penetrance is modulated by other factors.

Unrelated patients with adult-onset dominant or sporadic cerebellar ataxia negative for common repeat expansions (Italy, 235 patients)

Unknown Not yet documented

SCA48 accounted for 3.4% (8/235) of the cohort. Diagnostic yield, not population prevalence. The yield rises to 23.5% (4/17) when only familial cases are considered, illustrating how strongly the figure depends on cohort ascertainment.

Show evidence (1 reference)

PMID:31571321 SUPPORT Human Clinical

"giving an estimated overall frequency of 3.4% (8/235) for SCA48 in our study cohort, rising to 23.5% (4/17) when considering only familial cases"

Provides both the overall and familial-only diagnostic yields quoted in the notes.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Spinocerebellar Ataxia 48:

SCAR16 / Gordon Holmes syndrome (biallelic STUB1) MONDO:0008935

Overlapping Features The allelic autosomal recessive STUB1 disorder, curated in this knowledge base as Cerebellar Ataxia-Hypogonadism Syndrome. It shares the ataxia, cognitive dysfunction, hyperkinetic movement disorder and epilepsy of SCA48, so the two form a continuous clinical spectrum rather than separable syndromes.

Distinguishing Features

SCAR16 is biallelic and typically earlier in onset, with spastic ataxia, peripheral neuropathy and hypogonadotropic hypogonadism; SCA48 is heterozygous, adult-onset, and defined by the cerebellar cognitive-affective syndrome, with pyramidal and peripheral nervous system signs conspicuously absent in some cohorts. Hypogonadism is rare in SCA48 - the eight-family Italian series reported it in one patient, in whom it was accompanied by other autoimmune endocrine dysfunction.

Show evidence (3 references)

PMID:32342324 SUPPORT Other

"SCAR16 is characterized by early onset spastic ataxia and a wide disease spectrum, including cognitive dysfunction, hyperkinetic disorders, epilepsy, peripheral neuropathy, and hypogonadism."

Characterises the recessive counterpart and the features that pull a case towards it.

PMID:32342324 SUPPORT Other

"The overlap of several clinical signs between SCAR16 and SCA48 indicates the presence of a continuous clinical spectrum among recessively and dominantly inherited mutations of STUB1."

States the continuity of the two entities, which is why zygosity rather than phenotype alone settles the distinction.

PMID:31571321 SUPPORT Human Clinical

"CCAS also occurred frequently, whereas definite signs of pyramidal tract dysfunction and peripheral nervous system involvement were absent. One SCA48 patient presented with hypogonadism, associated with other autoimmune endocrine dysfunctions."

Supports both distinguishing points: absent pyramidal/peripheral signs in this SCA48 cohort, and hypogonadism as a single-patient exception.

Spinocerebellar ataxia 17 (TBP)

Overlapping Features SCA17 is caused by fully penetrant TBP CAG/CAA expansions above 49 repeats and is the principal Huntington-disease-like SCA. It is the critical differential because intermediate TBP alleles sit at the interface between the two disorders.

Distinguishing Features

SCA17 with TBP>=47 alleles is a monogenic dominant disorder; intermediate TBP40-49 alleles are incompletely penetrant and their carriers usually also carry a STUB1 variant. Patients with both genotypes have more severe multidomain dementia and greater cerebellar and brainstem volume loss than those with fully expanded TBP alleles alone.

Show evidence (2 references)

PMID:34906452 SUPPORT Human Clinical

"demonstrate a dual inheritance pattern for SCA17, which is a monogenic dominant disorder for TBP≥47 alleles and a digenic TBP/STUB1 disease (SCA17-DI) for intermediate expansions"

Defines the repeat-length boundary that separates monogenic SCA17 from the STUB1-associated intermediate-allele form.

PMID:36799493 SUPPORT Human Clinical

"SCATBP/STUB1 patients had multi-domain dementia with a more severe impairment in respect to patient carrying only fully expanded SCA17 alleles."

Supports the severity distinction between the combined genotype and monogenic SCA17.

Multiple system atrophy, cerebellar type (MSA-C) Not Yet Curated MONDO:0016418

Overlapping Features Sporadic adult-onset cerebellar ataxia with parkinsonism and urinary symptoms is the MSA-C presentation, and it overlaps closely with the SCA48 phenotype set. Most SCA48 patients reach genetic testing only after repeat-expansion panels come back negative, so MSA-C is a realistic competing label at that point.

Distinguishing Features

MSA-C is a sporadic synucleinopathy with prominent autonomic failure and a median survival of 8-10 years; SCA48 is dominantly inherited, slowly progressive over decades, and is defined by the cerebellar cognitive-affective syndrome rather than by dysautonomia. Dentate T2 hyperintensity with postero-lateral hemispheric atrophy (the crab sign) and a family history point to SCA48; a STUB1 variant settles it.

Show evidence (2 references)

PMID:42501123 SUPPORT Other

"Multiple system atrophy (MSA) is a rare and rapidly progressive neurodegenerative disorder characterized by a variable combination of autonomic failure, parkinsonism, and cerebellar ataxia, with a median survival of 8-10 years from symptom onset."

Characterises MSA and gives the two features that separate it from SCA48 - prominent autonomic failure and a rapid course. Graded OTHER because this is a narrative review rather than a primary clinical study.

PMID:32342324 SUPPORT Other

"SCA48 is an adult-onset syndrome characterized by ataxia and cognitive-psychiatric features, variably associated with chorea, parkinsonism, dystonia, and urinary symptoms."

Documents the SCA48 side of the overlap - adult-onset ataxia with parkinsonism and urinary symptoms - which is what makes MSA-C a live alternative before genetic testing.

Frontotemporal dementia and Huntington disease phenocopies

Overlapping Features Because the cognitive-affective syndrome can dominate and precede ataxia, and because chorea occurs, SCA48 can present as an apparent frontotemporal dementia or Huntington disease phenocopy.

Distinguishing Features

Cerebellar atrophy with dentate T2 hyperintensity on MRI, and cerebellar signs on examination, redirect the diagnosis. Screening in the reverse direction has a low yield: no STUB1 variant was found in 115 patients with frontotemporal dementia, so STUB1 should be pursued when the phenotype has a cerebellar component rather than in unselected FTD.

Show evidence (1 reference)

PMID:32713943 SUPPORT Human Clinical

"including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia"

Supports both the phenocopy presentation and the negative yield of unselected FTD screening.

📊

Related Datasets

1

Transcriptomic analysis of STUB1 knockdown in HEK293 cells under normal and heat-shock conditions geo:GSE310700

human BULK RNA SEQ

PMID:42567515

RNA-seq of STUB1 knockdown under normal and heat-shock conditions, the CHIP-insufficiency model reported in the SCA48 domain-uncoupling study (PMID:42567515). It is a HEK293 cell system, not a neuronal or patient one, so it speaks to the transcriptional consequences of reduced CHIP dosage rather than to Purkinje cell biology. No patient-derived SCA48 transcriptomic, proteomic or single-cell dataset was found.

🐁

Animal Models

2

stub1 mutant with truncated Chip U-box domain Danio rerio

A zebrafish stub1 mutant truncating the functional U-box domain shows impaired ubiquitination of Hsc70 and of Chip itself, decreased total brain 26S proteasome activity, reduced Purkinje cell number and soma size, abnormal Purkinje dendrite organisation, and behavioural changes. It recapitulates the cellular Purkinje phenotype but not the gross cerebellar atrophy of human disease, which is its main limitation. stub1 mRNA is predominantly expressed in the cerebellum including the Purkinje cell layer, consistent with the cell-type selectivity of the human disorder.

Species

Danio rerio

Genotype

stub1 mutant with truncated Chip U-box domain

Publication

PMID:34630034

Pathograph links

Impaired Chaperone-Assisted Protein Quality Control recapitulates fidelity: high Truncating the Chip U-box abolishes ubiquitination of Hsc70 and of Chip itself and lowers whole-brain 26S proteasome activity, reproducing the molecular lesion of U-box SCA48 variants.

Show evidence (1 reference)

PMID:34630034 SUPPORT Model Organism

"Recombinant wild-type zebrafish Chip showed ubiquitin ligase activity highly comparable to human CHIP, while the mutant Chip protein showed impaired ubiquitination of the Hsc70 substrate and Chip itself."

Establishes that the zebrafish enzyme is functionally equivalent to human CHIP and that the mutant loses the same activity, which is what makes this model informative for the human quality-control node.

Cerebellar Purkinje Cell Degeneration recapitulates fidelity: moderate

Limitations: Purkinje cell number, soma size and dendritic organisation are abnormal, but the fish show no gross cerebellar atrophy, so the model captures the cellular phenotype without the tissue-level one.

Show evidence (1 reference)

PMID:34630034 SUPPORT Model Organism

"these fish displayed reduced numbers and sizes of Purkinje cell bodies and abnormal organization of Purkinje cell dendrites"

The measured Purkinje cell phenotype is what licenses treating this model as informative for the human Purkinje degeneration node.

Show evidence (2 references)

PMID:34630034 SUPPORT Model Organism

"In the brain, stub1 mRNA was predominantly detected in the cerebellum, including the Purkinje cell layer and granular layer."

Expression pattern supports cerebellar and Purkinje cell selectivity in the model organism.

PMID:34630034 SUPPORT Model Organism

"In conclusion, truncation of the Chip U-box domain leads to impaired ubiquitin ligase activity and behavioral and anatomical changes in zebrafish, illustrating the potential of zebrafish to study STUB1-mediated diseases."

Summarises the model's recapitulation of the molecular lesion and its behavioural and anatomical consequences.

transgenic expression of human CHIP p.Ala52Gly Caenorhabditis elegans

A transgenic C. elegans line expressing the de novo SCA48 CHIP A52G variant develops neurodegeneration, providing a variant-specific in vivo readout. The organism has no cerebellum, so the model addresses proteostatic neurotoxicity rather than the human cerebellar syndrome.

Species

Caenorhabditis elegans

Genotype

transgenic expression of human CHIP p.Ala52Gly

Publication

PMID:35398354

Pathograph links

CHIP Loss of Function from Heterozygous STUB1 Variants recapitulates fidelity: low Expression of the human CHIP A52G SCA48 variant causes neurodegeneration in an intact organism.

Limitations: C. elegans has no cerebellum and no Purkinje cells, so the model speaks to proteostatic neurotoxicity rather than to the cerebellar syndrome.

Show evidence (1 reference)

PMID:35398354 SUPPORT INDIRECT Model Organism

"induces neurodegeneration in a transgenic Caenorhabditis elegans model of SCA48"

The patient-derived variant causes neurodegeneration in the transgenic worm, which is the basis for treating the model as informative for the CHIP dysfunction node. Recorded as INDIRECT because the organism has no cerebellum, so relevance to the human node requires an inference step.

Show evidence (1 reference)

PMID:35398354 SUPPORT Model Organism

"We further show that this mutant decreases cellular fitness in response to certain cellular stressors and induces neurodegeneration in a transgenic Caenorhabditis elegans model of SCA48."

Documents neurodegeneration caused by an SCA48 variant in an intact organism.

{ }

Source YAML

click to show

name: Spinocerebellar Ataxia 48
creation_date: "2026-08-31T00:00:00Z"
category: Mendelian
description: >-
  Spinocerebellar ataxia 48 (SCA48; ATX-STUB1) is an adult-onset autosomal
  dominant cerebellar ataxia caused by heterozygous pathogenic variants in
  STUB1, which encodes CHIP (C-terminus of HSC70-interacting protein), a
  co-chaperone and U-box E3 ubiquitin ligase that couples the HSP70/HSC70
  chaperone machinery to the ubiquitin-proteasome system. Its distinguishing
  feature is the pairing of progressive cerebellar ataxia and dysarthria with a
  prominent cerebellar cognitive-affective syndrome (dysexecutive and
  psychiatric/behavioural disturbance) that frequently precedes the motor
  syndrome by years; chorea, dystonia, parkinsonism, tremor and urinary
  symptoms broaden the phenotype. Brain MRI shows cerebellar atrophy with a
  postero-lateral hemispheric predominance together with T2 hyperintensity of
  both dentate nuclei (the "crab sign"), and neuropathology shows marked
  Purkinje cell loss with ubiquitin/p62-positive neuronal inclusions.
  Biallelic STUB1 variants cause the allelic autosomal recessive disorder
  SCAR16 / Gordon Holmes syndrome (MONDO:0008935), curated separately in this
  knowledge base as Cerebellar Ataxia-Hypogonadism Syndrome; the two
  presentations form a continuous clinical spectrum; hypogonadism, early
  onset and prominent spastic/pyramidal involvement predominate at the
  recessive end, but pyramidal signs and hypertonia are also reported in SCA48
  and their absence in one cohort should not be read as a rule.
  Intermediate-length CAG/CAA repeat expansions in TBP co-occur with STUB1
  variants often enough that digenic inheritance was proposed, but patients
  with the full SCA48 phenotype and normal TBP alleles establish that SCA48
  also occurs as a monogenic disorder.
disease_term:
  preferred_term: Spinocerebellar ataxia 48
  term:
    id: MONDO:0032526
    label: spinocerebellar ataxia 48
synonyms:
- SCA48
- ATX-STUB1
- SCA-STUB1
- STUB1-related autosomal dominant cerebellar ataxia
- autosomal dominant cerebellar ataxia with cerebellar cognitive-affective syndrome

parents:
- autosomal dominant cerebellar ataxia
- spinocerebellar ataxia

references:
- reference: PMID:20301317
  title: "Hereditary Ataxia Overview."
  tags:
  - GeneReviews

notes: >-
  GeneReviews baseline: no STUB1-, SCA48- or SCAR16-specific GeneReviews
  chapter exists (PubMed searches for "STUB1 GeneReviews", "spinocerebellar
  ataxia 48 GeneReviews" returned no disease-specific chapter). The closest
  authoritative GeneReviews resource is the Hereditary Ataxia Overview
  (PMID:20301317), tagged above; its PubMed record is a scope statement with
  no per-phenotype clinical content, so it could not be used as a phenotype
  baseline and no evidence item quotes it. Phenotype coverage was therefore
  built from the primary cohort literature (Genis 2018, De Michele 2019, Lieto
  2020, Chen 2020, Roux 2020, Mol 2020, Zochowski 2024).

  Deep research: research/Spinocerebellar_Ataxia_48-deep-research-falcon.md
  (Edison/falcon, 33 citations). The report contained no PMIDs at all - 13 of
  its 33 citations carried a DOI and 20 were bare author-year keys. Every DOI
  was converted to a PMID before use and every snippet below was taken from
  the PubMed abstract cached by `just fetch-reference`, not from the report.
  The report's claims sourced only to author-year keys were either
  independently re-sourced or dropped.

classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:32342324
      reference_title: "Spinocerebellar ataxia type 48: last but not least."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "SCA48 is an adult-onset syndrome characterized by ataxia and cognitive-psychiatric features, variably associated with chorea, parkinsonism, dystonia, and urinary symptoms."
      explanation: >-
        A review of the entity characterises SCA48 as an adult-onset
        neurodegenerative ataxia syndrome with cognitive, psychiatric and
        movement-disorder features, placing it in Harrison's neurologic Part.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:30381368
      reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report a heterozygous STUB1 pathogenic genetic variant causing dominant cerebellar ataxia."
      explanation: >-
        The discovery study establishes SCA48 as a Mendelian, dominantly
        inherited single-gene disorder, supporting the hereditary-disease Part
        alongside the neurologic one.
  mechanistic_category:
  - classification_value: proteotoxic disease
    evidence:
    - reference: PMID:35398354
      reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "These interactions allow CHIP to mediate the ubiquitination of chaperone-bound, misfolded proteins to promote their degradation via the proteasome."
      explanation: >-
        SCA48 arises from loss of the chaperone-coupled degradation of
        misfolded proteins, i.e. a failure of proteostasis, which is what the
        proteotoxic-disease category names.

inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    SCA48 segregates as an autosomal dominant trait: heterozygous STUB1
    variants cosegregate with disease across multiple generations in
    independent pedigrees. Penetrance is incomplete and age-dependent, and de
    novo variants occur, so a negative family history does not exclude the
    diagnosis. This is the dominant counterpart of the recessive STUB1
    disorder SCAR16 / Gordon Holmes syndrome, and dominant and recessive
    variants produce indistinguishable in vitro defects.
  evidence:
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since recessive mutations in STUB1 gene have been previously associated with SCAR16, these findings suggest a previously undescribed SCA locus (SCA48; MIM# 618093)."
    explanation: >-
      The discovery study reports a heterozygous, cosegregating STUB1 variant
      and explicitly distinguishes the new dominant locus from the previously
      known recessive SCAR16 disorder.
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study confirms a dominant inheritance pattern in STUB1-ataxia in addition to a recessive one and documents its association with cognitive and behavioral disability, including autism."
    explanation: >-
      Independent replication in two further families confirms that dominant
      inheritance coexists with the recessive pattern for the same gene.

- name: De novo variant occurrence
  inheritance_term:
    preferred_term: Sporadic
    term:
      id: HP:0003745
      label: Sporadic
  description: >-
    SCA48 can arise from a de novo heterozygous STUB1 variant in a patient
    with no family history, so the absence of an affected parent does not
    exclude the diagnosis.
  evidence:
  - reference: PMID:35398354
    reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we have identified a novel, de novo mutation in STUB1 in a patient with SCA48 encoding for an A52G point mutation in the tetratricopeptide repeat domain of CHIP."
    explanation: >-
      A de novo TPR-domain STUB1 variant in an SCA48 patient establishes that
      the disorder occurs sporadically as well as by transmission. Graded
      HUMAN_CLINICAL because the quoted claim is a patient genetic observation,
      even though the rest of this paper is biochemistry.

pathophysiology:
- name: CHIP Loss of Function from Heterozygous STUB1 Variants
  description: >-
    The initiating lesion is a heterozygous germline pathogenic STUB1 variant.
    STUB1 encodes CHIP, a 35 kDa cytosolic protein whose N-terminal
    tetratricopeptide-repeat (TPR) domain binds the HSC70/HSP70 chaperones and
    whose C-terminal U-box recruits E2 ubiquitin-conjugating enzymes.
    Missense, nonsense, frameshift, splice and in-frame deletion variants are
    distributed across the coding sequence with no hotspot. The functional
    consequence is domain-dependent rather than uniform: TPR-domain variants
    retain intrinsic ligase activity but lose HSP70 binding and protein
    stability, while U-box variants abolish ligase activity, oligomerise
    abnormally and only partly impair co-chaperone function. Dominant SCA48
    variants and recessive SCAR16 variants produce biochemically
    indistinguishable defects in vitro, which is why the two disorders form a
    continuous clinical spectrum rather than two mechanisms.
  biological_scale: MOLECULAR
  genes:
  - preferred_term: STUB1
    term:
      id: hgnc:11427
      label: STUB1
  molecular_functions:
  - preferred_term: ubiquitin protein ligase activity
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  - preferred_term: Hsp70 protein binding
    term:
      id: GO:0030544
      label: Hsp70 protein binding
    modifier: DECREASED
  evidence:
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the candidate variants, only the frameshift heterozygous c.823_824delCT STUB1 (p.L275Dfs*16) pathogenic variant cosegregated with the disease."
    explanation: >-
      Identifies the initiating molecular lesion: a single heterozygous STUB1
      frameshift variant cosegregating with SCA48 in the discovery pedigree.
  - reference: PMID:42567515
    reference_title: "Domain-dependent uncoupling of the co-chaperone and E3 ubiquitin ligase CHIP underlies heterogeneity in spinocerebellar ataxia 48."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "TPR variants retained intrinsic ligase activity but showed significantly reduced HSP70 binding, impaired substrate ubiquitination, and decreased stability. Conversely, U-box variants abolished ligase function, promoted the formation of high-molecular-weight oligomers, and often increased CHIP levels while only partially impairing co-chaperone activity."
    explanation: >-
      Systematic biochemical analysis of 13 SCA48 variants shows that the
      molecular consequence is domain-dependent, splitting the initiating
      lesion into a chaperone-binding arm and a ligase arm.
  - reference: PMID:42567515
    reference_title: "Domain-dependent uncoupling of the co-chaperone and E3 ubiquitin ligase CHIP underlies heterogeneity in spinocerebellar ataxia 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Meta-analysis of 87 SCA48 patients linked TPR-like biochemical signatures to upper motor neuron involvement and U-box-like profiles to prominent dysarthria."
    explanation: >-
      The first reported genotype-phenotype signal in SCA48: which CHIP domain
      the variant hits tracks with which clinical features dominate. This
      supersedes the earlier position that no genotype-phenotype correlation
      exists, and is the source of the upper-motor-neuron phenotype curated
      below. Graded HUMAN_CLINICAL because the quoted claim is a meta-analysis
      of patient phenotypes, not the paper's biochemistry.
  - reference: PMID:34070858
    reference_title: "Genetic Dominant Variants in STUB1, Segregating in Families with SCA48, Display In Vitro Functional Impairments Indistinctive from Recessive Variants Associated with SCAR16."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "These studies revealed that dominantly and recessively inherited STUB1 variants showed similar biochemical defects, including impaired ubiquitin ligase activity and altered oligomerization properties of the CHIP."
    explanation: >-
      Dominant SCA48 variants and recessive SCAR16 variants are biochemically
      indistinguishable in vitro, supporting one shared molecular lesion
      underlying the allelic pair rather than two mechanisms.
  - reference: PMID:34565360
    reference_title: "Clinical and functional characterization of a novel STUB1 frameshift mutation in autosomal dominant spinocerebellar ataxia type 48 (SCA48)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Further in vitro experiments demonstrated that this novel heterozygous STUB1 frameshift variant impairs the CHIP protein's activity and its interaction with the E2 ubiquitin ligase, UbE2D1, leading to neuronal accumulation of tau and α-synuclein, caspase-3 activation, and promoting cellular apoptosis through a dominant-negative pathogenic effect."
    explanation: >-
      A U-box frameshift variant acts by a dominant-negative mechanism on E2
      recruitment, one of the non-exclusive routes by which a heterozygous
      variant produces CHIP dysfunction.
  downstream:
  - target: Impaired Chaperone-Assisted Protein Quality Control
    description: >-
      Loss of TPR-mediated chaperone engagement and/or U-box-mediated E2
      recruitment removes CHIP from the chaperone-to-proteasome hand-off.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:35398354
      reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Utilizing an array of biophysical, biochemical, and cellular assays, we demonstrate that the CHIPA52G point mutant retains E3-ligase activity but has decreased affinity for chaperones."
      explanation: >-
        Shows directly that an SCA48 variant degrades the chaperone-binding
        arm of CHIP function, the step that links the genetic lesion to
        failure of chaperone-assisted quality control.
  - target: Dysregulated PINK1/Parkin-Mediated Mitophagy
    description: >-
      CHIP normally restrains PINK1/Parkin-mediated mitophagy; disease
      variants dysregulate this branch independently of the aggregation arm.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39117117
      reference_title: "Disease-associated mutations in C-terminus of HSP70 interacting protein (CHIP) impair its ability to negatively regulate mitophagy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "we find that multiple disease-associated mutations in CHIP dysregulate mitophagy both in vitro and in vivo in C. elegans neurons"
      explanation: >-
        Establishes the edge from disease-associated CHIP variants to mitophagy
        dysregulation. Graded MODEL_ORGANISM for the in vivo C. elegans neuronal
        result the sentence rests on; the cell-culture arm of the same paper is
        cited as IN_VITRO on the mitophagy node itself.

- name: Impaired Chaperone-Assisted Protein Quality Control
  description: >-
    CHIP is the physical link between the cytosolic chaperone machinery and
    the ubiquitin-proteasome system. Through its TPR domain it binds HSC70 and
    HSP70 and attenuates their folding cycle; through its U-box it acts as a
    bona fide E3 ubiquitin ligase, recruiting UBCH5-family E2 enzymes and
    ubiquitinating chaperone-bound clients so that terminally misfolded
    proteins are routed to the proteasome instead of being refolded
    indefinitely. Loss of CHIP function therefore removes the triage step of
    cytosolic protein quality control. Loss of Chip ubiquitin ligase activity
    in zebrafish reduces total brain 26S proteasome activity, showing that the
    proteasomal arm is degraded in vivo and not only in reconstituted assays.
  biological_scale: MOLECULAR
  conforms_to: "loss_of_proteostasis#Loss of Proteostasis"
  molecular_functions:
  - preferred_term: ubiquitin protein ligase activity
    term:
      id: GO:0061630
      label: ubiquitin protein ligase activity
    modifier: DECREASED
  - preferred_term: protein-folding chaperone binding
    term:
      id: GO:0051087
      label: protein-folding chaperone binding
    modifier: DECREASED
  biological_processes:
  - preferred_term: protein ubiquitination
    term:
      id: GO:0016567
      label: protein ubiquitination
    modifier: DECREASED
  - preferred_term: proteasome-mediated ubiquitin-dependent protein catabolic process
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
    modifier: DECREASED
  - preferred_term: protein quality control for misfolded or incompletely synthesized proteins
    term:
      id: GO:0006515
      label: protein quality control for misfolded or incompletely synthesized proteins
    modifier: DECREASED
  evidence:
  - reference: PMID:10330192
    reference_title: "Identification of CHIP, a novel tetratricopeptide repeat-containing protein that interacts with heat shock proteins and negatively regulates chaperone functions."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro binding assays demonstrated direct interactions between CHIP and both Hsc70 and Hsp70, and complexes containing CHIP and Hsc70 were identified in immunoprecipitates of human skeletal muscle cells in vivo."
    explanation: >-
      Establishes the baseline biology this node depends on: CHIP is a direct
      HSC70/HSP70-binding co-chaperone.
  - reference: PMID:11557750
    reference_title: "CHIP is a U-box-dependent E3 ubiquitin ligase: identification of Hsc70 as a target for ubiquitylation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we demonstrate that CHIP possesses intrinsic E3 ubiquitin ligase activity and promotes ubiquitylation. This activity is dependent on the carboxyl-terminal U-box."
    explanation: >-
      Establishes the second half of the baseline biology: the U-box confers
      genuine E3 ubiquitin ligase activity, the function lost in U-box SCA48
      variants.
  - reference: PMID:35398354
    reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "CHIP is known to regulate proteostasis by recruiting chaperones via a N-terminal tetratricopeptide repeat domain and recruiting E2 ubiquitin-conjugating enzymes via a C-terminal U-box domain. These interactions allow CHIP to mediate the ubiquitination of chaperone-bound, misfolded proteins to promote their degradation via the proteasome."
    explanation: >-
      States the coupling of the chaperone machinery to the proteasome that
      this node describes, in the specific context of SCA48.
  - reference: PMID:34630034
    reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mutant fish also had decreased total 26S proteasome activity in the brain and showed behavioral changes."
    explanation: >-
      Shows in a whole vertebrate brain that loss of Chip ligase activity
      lowers proteasome throughput, extending the in vitro claim to an in vivo
      nervous system.
  downstream:
  - target: Accumulation of Misfolded Client Proteins and Neuronal Inclusions
    description: >-
      Undegraded chaperone clients accumulate and aggregate; in cellular
      models of SCA48 variants this includes tau and alpha-synuclein.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39707479
      reference_title: "Clinical and functional characterization of a novel STUB1 mutation in a Chinese spinocerebellar ataxia 48 pedigree."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We found that the variant STUB1 c.755A>C caused a significant reduction of CHIP level and the loss function of ubiquitin ligase activity as the pathogenic STUB1 mutations reported before. Besides, we also found that the CHIP p. Y252S could cause tau aggregation, which is considered to contribute to the progression of neurodegenerative disorders."
      explanation: >-
        Ties loss of ligase activity in an SCA48 variant directly to
        aggregation of a client protein in the same experiment, which is the
        causal step this edge asserts.

- name: Dysregulated PINK1/Parkin-Mediated Mitophagy
  description: >-
    CHIP acts as a negative regulator of PINK1/Parkin-mediated mitophagy,
    promoting PINK1 degradation and limiting Parkin recruitment to stressed
    mitochondria. Disease-associated CHIP variants dysregulate this pathway in
    cell culture and in C. elegans neurons, giving a parallel branch of
    mitochondrial quality control alongside the aggregation branch. This arm
    is mechanistically plausible for SCA48 but has not been demonstrated in
    human SCA48 tissue, so it is recorded as a provisional mechanism.
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  biological_processes:
  - preferred_term: mitophagy
    term:
      id: GO:0000423
      label: mitophagy
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:39117117
    reference_title: "Disease-associated mutations in C-terminus of HSP70 interacting protein (CHIP) impair its ability to negatively regulate mitophagy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we demonstrate that CHIP acts as a negative regulator of the PTEN-induced kinase 1 (PINK1)/Parkin-mediated mitophagy pathway, promoting the degradation of PINK1, impairing Parkin translocation to the mitochondria, and suppressing mitophagy in response to mitochondrial stress."
    explanation: >-
      Defines the normal regulatory relationship whose loss constitutes this
      node.
  downstream:
  - target: Cerebellar Purkinje Cell Degeneration
    description: >-
      Loss of mitochondrial quality control is proposed to contribute to
      neuronal vulnerability in CHIP-associated disease. The link to Purkinje
      cell loss in SCA48 specifically is inferred, not demonstrated.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES

- name: Accumulation of Misfolded Client Proteins and Neuronal Inclusions
  description: >-
    Failure of CHIP-mediated triage leaves misfolded chaperone clients
    undegraded. In cellular models of SCA48 variants this produces
    accumulation of tau and alpha-synuclein with caspase-3 activation and
    apoptosis. In patients, the corresponding pathology is ubiquitin- and
    p62-positive neuronal inclusions, which are found in the cerebellum,
    neocortex and brainstem and are regarded as a pathological hallmark of the
    disease. Cortical neurons derived from patient iPSCs show dysfunctional
    protein (re)folding and elevated basal oxidative stress, while the same
    study found that impaired heat-shock response - an earlier candidate
    mechanism - was not specific to mutant cells. Those patient lines came from
    the recessive (SCAR16) end of the STUB1 spectrum, so the finding is carried
    here on the strength of the shared molecular lesion rather than observed in
    SCA48 patients directly.
  biological_scale: CELLULAR
  conforms_to: "loss_of_proteostasis#Misfolded-Protein Aggregation"
  cellular_components:
  - preferred_term: inclusion body
    term:
      id: GO:0016234
      label: inclusion body
    modifier: INCREASED
  biological_processes:
  - preferred_term: protein refolding
    term:
      id: GO:0042026
      label: protein refolding
    modifier: DECREASED
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  evidence:
  - reference: PMID:32337344
    reference_title: "Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem."
    explanation: >-
      Human neuropathology in three heterozygous STUB1 cases documents the
      protein-inclusion pathology this node asserts, and its anatomical
      distribution.
  - reference: PMID:32337344
    reference_title: "Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of intranuclear inclusions is a pathologic hallmark of the disease."
    explanation: >-
      States that inclusion pathology is a defining feature of SCA48 rather
      than an incidental finding.
  - reference: PMID:34565360
    reference_title: "Clinical and functional characterization of a novel STUB1 frameshift mutation in autosomal dominant spinocerebellar ataxia type 48 (SCA48)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "leading to neuronal accumulation of tau and α-synuclein, caspase-3 activation, and promoting cellular apoptosis through a dominant-negative pathogenic effect"
    explanation: >-
      Identifies the specific accumulating clients and the downstream
      apoptotic response in a neuronal model of an SCA48 variant.
  - reference: PMID:33097556
    reference_title: "CHIP mutations affect the heat shock response differently in human fibroblasts and iPSC-derived neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Proteomic analysis of CNs showed dysfunctional protein (re)folding and higher basal oxidative stress levels in patients."
    explanation: >-
      Patient iPSC-derived cortical neurons show the folding defect and
      oxidative-stress phenotype expected of failed proteostasis. Note this
      study used STUB1 patient lines from the recessive end of the spectrum.
  - reference: PMID:33097556
    reference_title: "CHIP mutations affect the heat shock response differently in human fibroblasts and iPSC-derived neurons."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: "Our results question the role of impaired HSR in SCAR16 neuropathology and highlight the need for careful selection of proper cell types for modeling human diseases."
    explanation: >-
      Recorded as a refutation of the specific candidate mechanism that a
      defective heat-shock response drives STUB1-related neurodegeneration -
      patient and CRISPR STUB1-null neurons behaved like controls. Retained so
      the entry does not silently carry a mechanism the primary data question.
  downstream:
  - target: Peripheral neuropathy
    description: >-
      Where peripheral involvement is reported, failed proteostasis in
      peripheral neurons is the presumed route. No study establishes the
      intermediate steps, and two cohorts report no peripheral involvement at
      all, so this edge is speculative and deliberately uncited.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Cerebellar Purkinje Cell Degeneration
    description: >-
      Accumulated misfolded protein and inclusion pathology in a cell type
      with high proteostatic demand drives Purkinje cell dysfunction and loss.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:32211513
      reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Unique neuropathologic examination of the 4 brains showed the marked loss of Purkinje cells (PCs) without microscopic evidence of significant pathology outside the cerebellum."
      explanation: >-
        Human neuropathology in dominant STUB1 disease shows that the
        proteostatic lesion is cashed out as selective Purkinje cell loss,
        which is the downstream node.

- name: Cerebellar Purkinje Cell Degeneration
  description: >-
    The Purkinje cell is the selectively vulnerable cell type in SCA48. Human
    neuropathology in heterozygous STUB1 patients shows marked to massive
    Purkinje cell loss, most severe in the vermis and substantial in the
    hemispheres, with strikingly little pathology elsewhere in one series and
    no atrophy of pons, hippocampus or cerebral cortex in another. A second
    cell-autonomous abnormality is loss of the normal polarised somatodendritic
    distribution of CHIP within surviving Purkinje cells, with aberrant
    protein in the distal dendritic arbor. A zebrafish chip U-box truncation
    reproduces the cellular phenotype - reduced Purkinje cell number and soma
    size and disorganised dendrites - without gross cerebellar atrophy.
  biological_scale: CELLULAR
  conforms_to: "cerebellar_purkinje_degeneration#Purkinje Neuron Degeneration"
  cell_types:
  - preferred_term: cerebellar Purkinje cell
    term:
      id: CL:0000121
      label: Purkinje cell
  biological_processes:
  - preferred_term: neuron apoptotic process
    term:
      id: GO:0051402
      label: neuron apoptotic process
    modifier: INCREASED
  locations:
  - preferred_term: cerebellar cortex
    term:
      id: UBERON:0002129
      label: cerebellar cortex
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report neuropathological findings of a STUB1 heterozygous patient, showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex."
    explanation: >-
      Human autopsy in a heterozygous (i.e. SCA48, not SCAR16) patient
      localises the degeneration to Purkinje cells with a vermian gradient.
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The normal pattern of polarized somatodendritic STUB1 protein expression in PCs was lost, resulting in aberrant STUB1 localization in the distal PC dendritic arbors."
    explanation: >-
      Adds a cell-autonomous subcellular abnormality in surviving Purkinje
      cells, indicating the degeneration is not only a loss of cell number.
  - reference: PMID:34630034
    reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "In contrast to SCAR16/SCA48 patients, no gross cerebellar atrophy was evident in mutant fish, however, these fish displayed reduced numbers and sizes of Purkinje cell bodies and abnormal organization of Purkinje cell dendrites."
    explanation: >-
      A vertebrate model reproduces the Purkinje cell phenotype but not the
      gross atrophy. Recorded as INDIRECT because it corroborates the cellular
      claim through a non-human system while marking the limit of the model.
  downstream:
  - target: Cerebellar Atrophy and Dentate Nucleus Involvement
    description: >-
      Progressive Purkinje cell loss is the cellular substrate of the
      macroscopic cerebellar atrophy seen on MRI.
    causal_link_type: DIRECT

- name: Cerebellar Atrophy and Dentate Nucleus Involvement
  description: >-
    At tissue level, SCA48 produces cerebellar atrophy involving both vermis
    and hemispheres with a postero-lateral hemispheric predominance,
    accompanied in around 90% of patients by T2-weighted hyperintensity of
    both dentate nuclei; the combination is described as the "crab sign". The
    topography is not uniform over time. In the discovery pedigree,
    presymptomatic carriers already had focal atrophy restricted to the
    vermis, paravermis and the medial parts of lobules VI and VII - cerebellar
    territories serving cognition and emotion - before any ataxia, with later
    spread to the whole cerebellum. This staged topography is what makes the
    cognitive-affective syndrome precede the motor syndrome.
  biological_scale: TISSUE
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  - preferred_term: dentate nucleus
    term:
      id: UBERON:0002132
      label: dentate nucleus
  - preferred_term: cerebellar vermis
    term:
      id: UBERON:0004720
      label: cerebellar vermis
  evidence:
  - reference: PMID:32285148
    reference_title: "The \"crab sign\": an imaging feature of spinocerebellar ataxia type 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrophy of the cerebellum was present in all cases, involving both the vermis and the hemispheres, but particularly affecting the postero-lateral portions of the cerebellar hemispheres."
    explanation: >-
      Defines the tissue-level topography of atrophy in a dedicated SCA48
      imaging series.
  - reference: PMID:32285148
    reference_title: "The \"crab sign\": an imaging feature of spinocerebellar ataxia type 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In all patients, with the exception of only one subject (90.0% of the cases), a T2WI hyperintensity of both dentate nuclei was found."
    explanation: >-
      Documents dentate nucleus involvement and quantifies it, supporting the
      inclusion of the dentate nucleus as an affected structure.
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three presymptomatic patients showed focal cerebellar atrophy in the vermian, paravermian, and the medial part of cerebellar lobes VI and VII, suggesting that cerebellar atrophy preceded the ataxia, and that the neurodegeneration begins in cerebellar areas related to cognition and emotion, spreading later to the whole cerebellum."
    explanation: >-
      Establishes the staged topography - cognitive/affective cerebellar
      territories first, whole cerebellum later - that this node asserts.
  downstream:
  - target: Disruption of Cerebello-Cerebral Motor and Cognitive Circuits
    description: >-
      Loss of cerebellar cortical output and dentate/efferent pathway
      involvement corrupts the cerebellar contribution to both motor and
      cognitive-affective circuits.
    causal_link_type: DIRECT
  - target: Cerebellar atrophy
    description: >-
      The tissue-level volume loss is what is observed clinically as cerebellar
      atrophy on MRI.
    causal_link_type: DIRECT

- name: Disruption of Cerebello-Cerebral Motor and Cognitive Circuits
  description: >-
    The clinical syndrome follows from the loss of cerebellar output to both
    motor and associative/limbic cerebro-cerebellar loops. The motor loop
    failure produces gait and limb ataxia, dysarthria, dysmetria and tremor;
    the cognitive-affective loop failure produces the cerebellar
    cognitive-affective syndrome - a predominantly frontal/dysexecutive
    picture with behavioural and psychiatric change that can present years
    before ataxia. FDG-PET in SCA48 families shows glucose hypometabolism not
    only in cerebellum but also in striatum and cerebral cortex, consistent
    with remote (diaschisis-like) effects on connected forebrain territories
    and matching the extrapyramidal features seen clinically.
  biological_scale: ORGANISM
  conforms_to: "cerebellar_purkinje_degeneration#Loss of Cerebellar Cortical Output"
  locations:
  - preferred_term: cerebellum
    term:
      id: UBERON:0002037
      label: cerebellum
  evidence:
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MRI showed a significant cerebellar atrophy, coupled to a T2-weighted hyperintensity affecting the dentate nuclei and extending to the middle cerebellar peduncles, whereas FDG-PET studies revealed glucose hypometabolism in cerebellum, striatum, and cerebral cortex."
    explanation: >-
      Functional imaging shows the cerebellar lesion is accompanied by
      hypometabolism in connected striatal and cortical territories, which is
      the circuit-level disruption this node describes.
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Six patients fully developed cognitive-affective and complete motor cerebellar syndrome associated with vermian and hemispheric cerebellar atrophy, suggesting a continuum from a dysexecutive syndrome slowly evolving to a complete and severe CCAS with late truncal ataxia."
    explanation: >-
      Describes the dual motor and cognitive-affective output failure, and its
      temporal ordering, that this node is asserting.
  downstream:
  - target: Ataxia
    causal_link_type: DIRECT
  - target: Dysarthria
    causal_link_type: DIRECT
  - target: Cerebellar cognitive-affective syndrome
    causal_link_type: DIRECT
  - target: Dysmetria
    causal_link_type: DIRECT
  - target: Dysphagia
    causal_link_type: DIRECT
  - target: Abnormal conjugate eye movement
    causal_link_type: DIRECT
  - target: Cognitive impairment
    causal_link_type: DIRECT
  - target: Depression
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Anxiety
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Behavioural and personality change
    causal_link_type: DIRECT
  - target: Psychiatric symptoms
    causal_link_type: DIRECT
  - target: Upper motor neuron involvement
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Urinary symptoms
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Seizure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Tremor
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Parkinsonism
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Chorea
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Dystonia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES

- name: TBP Intermediate Repeat Expansion as a Genetic Modifier
  description: >-
    Intermediate-length CAG/CAA repeat expansions in TBP (roughly 40-49
    repeats), which are themselves incompletely penetrant for SCA17, co-occur
    with heterozygous STUB1 variants far more often than chance. The original
    interpretation was digenic inheritance - TBP41-46 alleles and STUB1
    variants cosegregating, with neither genotype alone associated with
    disease - and this reading questioned whether SCA48 exists as a monogenic
    entity at all. Subsequent work resolved the question in favour of a
    modifier model rather than obligate digenic inheritance: probands with the
    full SCA48 phenotype and normal TBP alleles exclude digenic inheritance as
    the sole mode, while longer TBP repeats predict more cognitive impairment
    and faster progression. Patients carrying both genotypes have a more
    severe, fully penetrant multidomain ataxia-dementia phenotype with reduced
    cerebellar and brainstem volumes. This node therefore modifies the
    severity and penetrance of the main chain rather than initiating it.
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  genes:
  - preferred_term: TBP
    term:
      id: hgnc:11588
      label: TBP
  evidence:
  - reference: PMID:34906452
    reference_title: "Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All except 1 (30/31) of the index cases with TBP41-46 alleles carried a heterozygous pathogenic variant in the STUB1 gene associated with spinocerebellar ataxias SCAR16 (autosomal recessive) and SCA48 (autosomal dominant)."
    explanation: >-
      Documents the strong non-random co-occurrence of intermediate TBP
      alleles with STUB1 variants that motivated the digenic hypothesis.
  - reference: PMID:34906452
    reference_title: "Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "raise questions on the existence of SCA48 as a monogenic disease with crucial implications for diagnosis and counseling"
    explanation: >-
      Recorded as REFUTE because this sentence argues against the modifier
      framing this node asserts - the authors read the same STUB1/TBP
      interaction as obligate digenic inheritance rather than as modification
      of a monogenic disorder. It is kept on the node so the position the later
      literature had to answer is visible here; the digenic reading itself is
      curated under the sca48_tbp_digenic hypothesis.
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We show that intermediate TBP40-49 alleles act as disease modifiers of SCA48 rather than a STUB1/TBP digenic model."
    explanation: >-
      The direct answer to the digenic hypothesis from the same kind of
      cohort: the interaction is modifier, not obligate digenic.
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The longer the TBP repeat length, the more likely the occurrence of cognitive impairment (P = .0129) and the faster the disease progression until death (P = .0003)."
    explanation: >-
      Quantifies the dose-dependent modifier effect on the cognitive phenotype
      and on progression rate.
  - reference: PMID:36799493
    reference_title: "Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cerebellar volume and thickness of cerebellar cortex were reduced in SCATBP/STUB1 compared with SCA17 patients (P = 0.03; P = 0.008). Basal ganglia volumes were reduced in both patient groups, as compared with controls, whereas brainstem volumes were significantly reduced in SCATBP/STUB1 , but not in SCA17 patients."
    explanation: >-
      Characterises the more severe structural phenotype of the combined
      genotype, supporting a modifier effect that is visible on imaging.
  - reference: PMID:39950762
    reference_title: "TBP Repeat Expansion Analysis in Patients Carrying Heterozygous STUB1 Variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous STUB1 variants are associated with a milder phenotype and reduced penetrance compared with the cosegregation with intermediate TBP alleles, which causes a fully penetrant complicated form of cerebellar ataxia."
    explanation: >-
      States the penetrance consequence of the modifier: STUB1 alone is milder
      and incompletely penetrant, STUB1 plus intermediate TBP is fully
      penetrant.
  downstream:
  - target: Disruption of Cerebello-Cerebral Motor and Cognitive Circuits
    description: >-
      Co-inherited intermediate TBP expansions increase the penetrance and
      severity of the SCA48 phenotype, particularly its cognitive component,
      rather than causing a separate disease process.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:38973070
      reference_title: "A New Case Series Suggests That SCA48 (ATX/STUB1) Is Primarily a Monogenic Disorder."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Still, co-occurrence of TBP 41-42 or high-normal TBP40 alleles was relatively frequent and associated with marked cognitive defects (28.5%), suggesting a modifying effect on clinical expression in some cases."
      explanation: >-
        Supports the modifier edge specifically - TBP allele length modifying
        the clinical expression of the STUB1 phenotype - in a cohort whose
        main conclusion is that SCA48 is monogenic.

mechanistic_hypotheses:
- hypothesis_group_id: sca48_monogenic
  hypothesis_label: SCA48 as a monogenic STUB1 disorder
  status: CANONICAL
  description: >-
    A heterozygous pathogenic STUB1 variant is by itself sufficient to cause
    the SCA48 phenotype. Multiple independent series report probands with the
    complete clinical picture - ataxia, dysarthria, cerebellar atrophy and
    cognitive impairment - and TBP repeat lengths within the normal range.
  evidence:
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Importantly, 13 STUB1 probands presenting with the full SCA48 clinical phenotype had normal TBP37-39 alleles, excluding digenic inheritance as the sole mode."
    explanation: >-
      Thirteen probands with normal TBP alleles and the full phenotype
      directly establish that STUB1 alone suffices.
  - reference: PMID:38973070
    reference_title: "A New Case Series Suggests That SCA48 (ATX/STUB1) Is Primarily a Monogenic Disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SCA48 is predominantly a monogenic disorder, because most patients carried an isolated, heterozygous STUB1 variant and presented with the typical combined phenotype of ataxia and cognitive dysfunction."
    explanation: >-
      An independent 21-patient cohort reaches the same conclusion.
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our cases lacked pathological TBP expansions and provide additional evidence that STUB1 (SCA48) can manifest as a monogenic disease."
    explanation: >-
      Three further unrelated probands with normal TBP repeats support the
      monogenic model.
  - reference: PMID:38625442
    reference_title: "Two more families supporting the existence of monogenic spinocerebellar ataxia 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This report provides supportive evidence that this specific ataxia can also occur as a monogenic disease, considering classical TBP allelic ranges."
    explanation: >-
      Two additional families with the same STUB1 variant and normal TBP
      alleles.

- hypothesis_group_id: sca48_tbp_digenic
  hypothesis_label: Obligate digenic TBP/STUB1 inheritance
  status: DEPRECATED
  description: >-
    The competing model held that SCA48 is not a monogenic entity but the
    digenic product of a heterozygous STUB1 variant plus an intermediate-length
    TBP expansion, with neither genotype pathogenic alone. This was a serious
    proposal supported by near-complete co-occurrence in one cohort. It is
    recorded as rejected in its strong form: probands with the full phenotype
    and normal TBP alleles exclude obligate digenic inheritance. The weaker
    modifier claim survives and is curated in the "TBP Intermediate Repeat
    Expansion as a Genetic Modifier" pathophysiology node.
  evidence:
  - reference: PMID:34906452
    reference_title: "Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TBP41-46 expansions and STUB1 variants cosegregate in all affected family members, whereas the presence of either TBP41-46 expansions or STUB1 variants individually was never associated with the disease."
    explanation: >-
      The observation on which the digenic hypothesis rested, quoted from the
      paper that proposed it.
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Importantly, 13 STUB1 probands presenting with the full SCA48 clinical phenotype had normal TBP37-39 alleles, excluding digenic inheritance as the sole mode."
    explanation: >-
      Direct refutation of obligate digenic inheritance in a cohort assembled
      to test it.

phenotypes:
- category: Neurologic
  name: Ataxia
  description: >-
    Progressive cerebellar ataxia is the core motor phenotype: truncal and
    gait instability with limb incoordination, typically of adult onset and
    slowly progressive. In the discovery pedigree truncal ataxia was a late
    development, appearing after years of cognitive-affective symptoms; in
    other families ataxia is the presenting complaint.
  phenotype_term:
    preferred_term: Cerebellar ataxia
    term:
      id: HP:0001251
      label: Ataxia
    clinical_course: PROGRESSIVE
    onset:
      onset_category: ADULT
      min_age_years: 17
      max_age_years: 74
      notes: >-
        Onset is characteristically adult but the range is wide. An independent
        three-proband series reported onset at 34-65 years; the largest cohort
        (n=50 STUB1 carriers) reported a 17-74 year range and emphasised that
        both age at onset and severity are remarkably variable.
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All our SCA48 patients had cerebellar ataxia and dysarthria associated with cerebellar atrophy on brain magnetic resonance imaging; of note, many cases were also associated with parkinsonism, chorea and dystonia."
    explanation: >-
      Cerebellar ataxia was present in all 11 patients across eight independent
      SCA48 index families (11/11 = 100%), which is the derived count
      supporting the VERY_FREQUENT band (80-100%).
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms. Age of onset varied from 34 to 65 years of age."
    explanation: >-
      Confirms the slowly progressive course and adult onset in an
      independent, TBP-negative case series, and is the source of the 34-65
      year onset range recorded in the onset notes.
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "STUB1 variants were detected in 50 patients. Age at onset and severity were remarkably variable."
    explanation: >-
      The largest cohort documents the variability of age at onset and
      severity that qualifies the adult-onset label.

- category: Neurologic
  name: Dysarthria
  description: >-
    Cerebellar dysarthria accompanies the ataxia and can be a presenting
    symptom. It was present in all patients across the eight-family Italian
    series.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All our SCA48 patients had cerebellar ataxia and dysarthria associated with cerebellar atrophy on brain magnetic resonance imaging"
    explanation: >-
      Dysarthria co-occurred with ataxia in all 11 SCA48 patients across eight
      index families (11/11 = 100%), which is the derived count supporting the
      VERY_FREQUENT band (80-100%).

- category: Cognitive
  name: Cerebellar cognitive-affective syndrome
  description: >-
    The cerebellar cognitive-affective syndrome (CCAS) is the phenotype that
    distinguishes SCA48 from most other dominant ataxias. It combines
    executive dysfunction, behavioural and personality change, and affective
    or frankly psychiatric disturbance, and it frequently precedes the ataxia
    by years - in the discovery family a slowly evolving dysexecutive syndrome
    ran ahead of truncal ataxia, and presymptomatic carriers already had focal
    atrophy of cognition- and emotion-related cerebellar territories.
  phenotype_term:
    preferred_term: Impaired executive functioning
    term:
      id: HP:0033051
      label: Impaired executive functioning
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To describe a new spinocerebellar ataxia (SCA48) characterized by early cerebellar cognitive-affective syndrome (CCAS) and late-onset SCA."
    explanation: >-
      The defining study frames early CCAS with late ataxia as the
      characteristic pairing of the disorder.
  - reference: PMID:31741143
    reference_title: "Cerebellar cognitive-affective syndrome preceding ataxia associated with complex extrapyramidal features in a Turkish SCA48 family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CCAS is a prominent and often early feature of SCA48 which may be followed years after the onset of the disease by other complex neurological signs and symptoms."
    explanation: >-
      Independent replication of the temporal ordering in an unrelated
      (Turkish) family.

- category: Cognitive
  name: Cognitive impairment
  description: >-
    Cognitive impairment in SCA48 is predominantly a frontal/dysexecutive
    syndrome and is common enough to be a leading reason for referral. In the
    largest cohort it was present in 54% of STUB1 variant carriers, and five
    families presented with phenotypes mimicking Huntington disease or
    frontotemporal dementia.
  phenotype_term:
    preferred_term: Cognitive impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
    clinical_course: PROGRESSIVE
  frequency: FREQUENT
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cognitive impairment, predominantly frontal syndrome, was observed in 54% of STUB1 variant carriers, including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia."
    explanation: >-
      Direct quantitative support for both the phenotype and the FREQUENT
      band: 54% falls in the 30-79% range.
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cerebellar atrophy on imaging and cognitive deficits often preceded ataxia."
    explanation: >-
      Confirms cognitive impairment as a core, often pre-ataxic feature in an
      independent dominant STUB1 cohort.

- category: Psychiatric
  name: Behavioural and personality change
  description: >-
    Behavioural change and personality alteration are prominent
    neuropsychiatric features, and in the large Dutch pedigree accompanied
    cognitive decline as a cardinal presenting feature alongside the gait
    disturbance.
  phenotype_term:
    preferred_term: Personality changes
    term:
      id: HP:0000751
      label: Personality changes
  evidence:
  - reference: PMID:32337344
    reference_title: "Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with adult-onset gait disturbance (ataxia or parkinsonism), combined with prominent cognitive decline and behavioral changes."
    explanation: >-
      Behavioural change is documented as a presenting feature in a large
      heterozygous STUB1 pedigree.

- category: Psychiatric
  name: Psychiatric symptoms
  description: >-
    Psychiatric disturbance accompanies the cognitive syndrome and is a routine
    part of the clinical picture in SCA48 case series. This entry is the
    residual category: the two named psychiatric features that sources report
    specifically, depression and anxiety, are curated as their own phenotypes,
    and this term covers the behavioural disturbance that the sources describe
    without further resolution.
  phenotype_term:
    preferred_term: Psychiatric symptoms
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms."
    explanation: >-
      Psychiatric symptoms were present in all three probands of this series
      alongside the motor and cognitive features.
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe a complex syndrome characterized by ataxia and cognitive-psychiatric disorder in all cases, variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy."
    explanation: >-
      Cognitive-psychiatric disorder was present in all eight patients from
      two independent families.

- category: Neurologic
  name: Tremor
  description: >-
    Tremor is an increasingly recognised feature, including upper-limb rest
    tremor as well as action tremor, and can be the presenting symptom. Its
    presence together with parkinsonian signs can misdirect the differential
    towards a primary movement disorder.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We highlight the importance of tremor as part of the clinical phenotype including upper limb rest tremor and Parkinsonian signs."
    explanation: >-
      A case series dedicated to this feature establishes tremor, including
      rest tremor, as part of the SCA48 phenotype.

- category: Neurologic
  name: Parkinsonism
  description: >-
    Parkinsonism occurs in a substantial minority and may even be the mode of
    presentation of the gait disturbance rather than ataxia.
  phenotype_term:
    preferred_term: Parkinsonism
    term:
      id: HP:0001300
      label: Parkinsonism
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "of note, many cases were also associated with parkinsonism, chorea and dystonia"
    explanation: >-
      Parkinsonism was a recurring associated feature across eight SCA48
      families.
  - reference: PMID:32337344
    reference_title: "Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients presented with adult-onset gait disturbance (ataxia or parkinsonism)"
    explanation: >-
      Shows parkinsonism can be the presenting form of the gait disorder, not
      merely an add-on sign.

- category: Neurologic
  name: Chorea
  description: >-
    Chorea is a recurrent hyperkinetic feature and contributes to the
    Huntington-disease-like presentations that bring some SCA48 patients to
    attention.
  phenotype_term:
    preferred_term: Chorea
    term:
      id: HP:0002072
      label: Chorea
  evidence:
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"
    explanation: >-
      Chorea is listed among the extrapyramidal features variably present in
      SCA48 patients from two families.

- category: Neurologic
  name: Dystonia
  description: >-
    Dystonia is part of the extrapyramidal spectrum of SCA48 and has been
    reported both within multi-feature series and as a comparatively isolated
    presenting sign.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "many cases were also associated with parkinsonism, chorea and dystonia"
    explanation: >-
      Dystonia recurs across the eight-family SCA48 cohort.

- category: Neurologic
  name: Upper motor neuron involvement
  description: >-
    Pyramidal features - hypertonia, brisk or pathological reflexes - occur in
    SCA48 and were reported in all three probands of one Australian series
    alongside the cerebellar syndrome. A domain-stratified meta-analysis of 87
    patients associated TPR-domain biochemical signatures with upper motor
    neuron involvement. This qualifies, and partly contradicts, the observation
    from one Italian cohort that pyramidal signs were absent; it is a
    variable feature, not an exclusion criterion. No frequency is asserted
    because the two supporting cohorts disagree.
  phenotype_term:
    preferred_term: Hypertonia and pyramidal signs
    term:
      id: HP:0001276
      label: Hypertonia
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All presented with slowly progressive cerebellar ataxia with tremor and additional findings of dysarthria, parkinsonism, hypertonia, cognitive and psychiatric symptoms."
    explanation: >-
      Hypertonia is reported in all three probands of this TBP-negative SCA48
      series, establishing pyramidal involvement as part of the phenotype.
  - reference: PMID:42567515
    reference_title: "Domain-dependent uncoupling of the co-chaperone and E3 ubiquitin ligase CHIP underlies heterogeneity in spinocerebellar ataxia 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Meta-analysis of 87 SCA48 patients linked TPR-like biochemical signatures to upper motor neuron involvement"
    explanation: >-
      An 87-patient meta-analysis reports upper motor neuron involvement in
      SCA48 and ties it to TPR-domain variants.
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pyramidal signs were reported in 43% of patients."
    explanation: >-
      The largest STUB1 cohort reports pyramidal signs in 43% of patients, which
      is the strongest single argument that pyramidal involvement belongs in the
      SCA48 phenotype. No frequency band is asserted on the phenotype because a
      second cohort reports the sign as absent.
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "definite signs of pyramidal tract dysfunction and peripheral nervous system involvement were absent"
    explanation: >-
      Recorded as REFUTE because this cohort found no definite pyramidal signs.
      Kept alongside the supporting evidence so the disagreement between
      cohorts is visible rather than resolved by curator preference.

- category: Neurologic
  name: Dysmetria
  description: >-
    Limb dysmetria is part of the complete motor cerebellar syndrome and sits
    alongside gait ataxia and cerebellar dysarthria on examination. It is
    documented on serial neurological examination of index cases in the largest
    STUB1 cohort.
  phenotype_term:
    preferred_term: Dysmetria
    term:
      id: HP:0001310
      label: Dysmetria
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological examination revealed an ataxic gait, dysmetria of the upper limbs, and cerebellar dysarthria."
    explanation: >-
      Examination findings in the index case of family AAD-541, a heterozygous
      STUB1 p.Y49C carrier with dominant transmission, so this is an SCA48 and
      not a SCAR16 observation. That family also carries a candidate AFG3L2
      second hit, which the entry records as an open question about modifier
      loci; it does not affect the presence of the cerebellar sign.

- category: Neurologic
  name: Dysphagia
  description: >-
    Swallowing impairment is among the reported clinical features of SCA48 and
    matters clinically because it drives aspiration and nutrition risk as the
    disease advances. It is the phenotype targeted by the swallowing half of
    speech and swallowing therapy.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Reported clinical syndromes include gait ataxia, dysarthria, dysphagia, and oculomotor abnormalities, as well as cognitive affective symptoms, such as language impairment, depression, anxiety."
    explanation: >-
      Lists dysphagia among the reported clinical features of SCA48. Recorded as
      INDIRECT because this sentence is the paper's introductory synthesis of
      prior SCA48 case reports rather than an observation in its own three
      probands.

- category: Neurologic
  name: Abnormal conjugate eye movement
  description: >-
    Oculomotor abnormalities occur in SCA48 and take several forms - nystagmus,
    saccadic pursuit, slow saccades, diplopia and ptosis are all reported. The
    largest cohort describes them as sometimes present, with ophthalmoplegia
    rare, so this is a variable rather than a defining feature.
  phenotype_term:
    preferred_term: Oculomotor abnormality
    term:
      id: HP:0000549
      label: Abnormal conjugate eye movement
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diplopia, ptosis, nystagmus, or saccadic pursuit was sometimes present but ophthalmoplegia was rare."
    explanation: >-
      Cohort-level examination findings across 50 STUB1 variant carriers give
      both the range of oculomotor signs and the qualifier that they are
      intermittent, which is why no frequency is asserted.
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Reported clinical syndromes include gait ataxia, dysarthria, dysphagia, and oculomotor abnormalities"
    explanation: >-
      Independent confirmation that oculomotor abnormalities are part of the
      reported SCA48 spectrum. INDIRECT because the sentence summarises prior
      reports rather than this series' own probands.

- category: Neurologic
  name: Peripheral neuropathy
  description: >-
    Peripheral neuropathy is listed among the rarer features of SCA48, but the
    two largest phenotyping cohorts explicitly did not find it: one reported no
    wasting or sensory loss across 50 variant carriers and the other reported
    that peripheral nervous system involvement was absent. Both the positive and
    the negative reports are kept here because peripheral involvement is one of
    the features used to steer a case towards the recessive SCAR16 end of the
    spectrum, so whether it occurs in SCA48 is diagnostically load-bearing.
  phenotype_term:
    preferred_term: Peripheral neuropathy
    term:
      id: HP:0009830
      label: Peripheral neuropathy
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Rarer clinical features including chorea, Parkinsonism, dystonia, peripheral neuropathies, and epilepsy have been reported."
    explanation: >-
      Places peripheral neuropathy among the rarer reported SCA48 features.
      INDIRECT because it summarises prior reports rather than this series' own
      probands.
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "There was no wasting or sensory loss."
    explanation: >-
      The 50-carrier cohort found no wasting or sensory loss, which contradicts
      peripheral involvement as a general SCA48 feature. Kept so the
      disagreement between cohorts is visible on the phenotype rather than
      resolved by curator preference.
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "definite signs of pyramidal tract dysfunction and peripheral nervous system involvement were absent"
    explanation: >-
      A second cohort independently reports absent peripheral nervous system
      involvement.

- category: Psychiatric
  name: Depression
  description: >-
    Depression is among the affective features of the cerebellar
    cognitive-affective syndrome in SCA48 and can bring patients to psychiatric
    rather than neurological attention.
  phenotype_term:
    preferred_term: Depression
    term:
      id: HP:0000716
      label: Depression
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "cognitive affective symptoms, such as language impairment, depression, anxiety"
    explanation: >-
      Names depression among the cognitive-affective symptoms reported in
      SCA48. INDIRECT because the sentence summarises prior case reports rather
      than this series' own probands.

- category: Psychiatric
  name: Anxiety
  description: >-
    Anxiety is reported alongside depression among the affective features of
    SCA48 and is part of what makes a psychiatric-first presentation possible.
  phenotype_term:
    preferred_term: Anxiety
    term:
      id: HP:0000739
      label: Anxiety
  evidence:
  - reference: PMID:39680235
    reference_title: "Case Series of Cerebellar Ataxia with Tremor Due to Heterozygous STUB1 Variants (SCA48) without TBP Expansions: Further Evidence for SCA48 as a Monogenic Disease."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "cognitive affective symptoms, such as language impairment, depression, anxiety"
    explanation: >-
      Names anxiety among the cognitive-affective symptoms reported in SCA48.
      INDIRECT because the sentence summarises prior case reports rather than
      this series' own probands.

- category: Neurologic
  name: Cerebellar atrophy
  description: >-
    Cerebellar atrophy on MRI is a near-constant finding, involving vermis and
    hemispheres. It can be detected in presymptomatic carriers, initially
    confined to the vermis, paravermis and medial lobules VI-VII, before any
    motor sign.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:32285148
    reference_title: "The \"crab sign\": an imaging feature of spinocerebellar ataxia type 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrophy of the cerebellum was present in all cases, involving both the vermis and the hemispheres"
    explanation: >-
      Cerebellar atrophy was present in all ten patients of a dedicated SCA48
      imaging series.
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cerebellar atrophy on imaging and cognitive deficits often preceded ataxia."
    explanation: >-
      Documents that the atrophy is detectable before the motor phenotype
      declares itself.

- category: Neurologic
  name: Urinary symptoms
  description: >-
    Urinary symptoms (urgency, incontinence) are a recognised non-motor
    feature of the SCA48 syndrome.
  phenotype_term:
    preferred_term: Urinary urgency
    term:
      id: HP:0000012
      label: Urinary urgency
  evidence:
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"
    explanation: >-
      Urinary symptoms are listed among the variable features of the SCA48
      syndrome in two independent families.

- category: Neurologic
  name: Seizure
  description: >-
    Epilepsy is an uncommon but reported feature of SCA48, occurring within
    the broader complex phenotype.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variably associated with chorea, parkinsonism, dystonia, urinary symptoms, and epilepsy"
    explanation: >-
      Epilepsy is reported as a variable feature in these SCA48 families.

- category: Neurologic
  name: Autism
  description: >-
    Autism was documented among the behavioural phenotypes in one of the two
    families in which dominant STUB1 missense variants were characterised
    neuropathologically. It is reported in individual patients rather than as
    a general feature, so no frequency is asserted.
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "documents its association with cognitive and behavioral disability, including autism"
    explanation: >-
      Autism is explicitly reported among the behavioural manifestations of
      dominant STUB1-ataxia in this study.

imaging_findings:
- name: Dentate nucleus T2 hyperintensity with postero-lateral cerebellar atrophy (crab sign)
  modality: MRI
  imaging_finding_term:
    preferred_term: Abnormal dentate nucleus morphology
    term:
      id: HP:0100321
      label: Abnormal dentate nucleus morphology
  located_in:
    preferred_term: dentate nucleus
    term:
      id: UBERON:0002132
      label: dentate nucleus
  laterality: BILATERAL
  description: >-
    The most specific imaging feature of SCA48 is bilateral T2-weighted
    hyperintensity of the dentate nuclei combined with atrophy predominantly
    of the postero-lateral cerebellar hemispheres; the two together were
    likened to a crab and named the "crab sign". Supratentorial volume loss
    and signal change are typically absent. In a separate series the dentate
    signal change extended into the middle cerebellar peduncles. Term-binding
    caveat: HPO has no dentate-nucleus signal-intensity term (it has thalamic,
    brainstem and basal-ganglia siblings), so this finding is bound to the
    morphology term HP:0100321, which is a different kind of claim from a T2
    signal abnormality; preferred_term carries the intended meaning.
  evidence:
  - reference: PMID:32285148
    reference_title: "The \"crab sign\": an imaging feature of spinocerebellar ataxia type 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We propose that the association of such signal change, along with the atrophy of the lateral portion of the cerebellar hemispheres, resembled the appearance of a crab, and therefore, we propose the \"crab sign\" as a neuroradiological sign present in SCA48 patients."
    explanation: >-
      Names and defines the composite imaging sign in the series that
      described it.
  - reference: PMID:32285148
    reference_title: "The \"crab sign\": an imaging feature of spinocerebellar ataxia type 48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In SCA48 patients, no meaningful supratentorial changes were found, both in terms of volume loss or MRI signal changes."
    explanation: >-
      Supports the negative half of the imaging pattern, which is part of what
      makes the sign discriminating.
  - reference: PMID:31126790
    reference_title: "Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: A report of two Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MRI showed a significant cerebellar atrophy, coupled to a T2-weighted hyperintensity affecting the dentate nuclei and extending to the middle cerebellar peduncles"
    explanation: >-
      Independent replication of the dentate signal abnormality with extension
      into the middle cerebellar peduncles.

- name: Cerebellar atrophy in presymptomatic carriers
  modality: MRI
  imaging_finding_term:
    preferred_term: Cerebellar vermis atrophy
    term:
      id: HP:0006855
      label: Cerebellar vermis atrophy
  located_in:
    preferred_term: cerebellar vermis
    term:
      id: UBERON:0004720
      label: cerebellar vermis
  spatial_extent: FOCAL
  description: >-
    Focal atrophy of the vermis, paravermis and medial lobules VI-VII is
    detectable in presymptomatic STUB1 variant carriers, before motor ataxia.
    These are the cerebellar territories serving cognition and emotion, which
    is why the cognitive-affective syndrome precedes the motor syndrome. This
    has practical consequences: it defines an imaging-detectable prodromal
    window that any future disease-modifying therapy would likely need to
    target.
  evidence:
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Three presymptomatic patients showed focal cerebellar atrophy in the vermian, paravermian, and the medial part of cerebellar lobes VI and VII, suggesting that cerebellar atrophy preceded the ataxia"
    explanation: >-
      Directly documents presymptomatic focal cerebellar atrophy and its
      topography in variant carriers.

histopathology:
- name: Purkinje cell loss with vermian predominance
  finding_term:
    preferred_term: Purkinje cell loss
    term:
      id: NCIT:C120874
      label: Degeneration and Atrophy
  description: >-
    Post-mortem examination in heterozygous STUB1 patients shows marked to
    massive Purkinje cell loss, most severe in the vermis and substantial in
    the hemispheres, with little or no involvement of pons, hippocampus or
    cerebral cortex on gross and microscopic assessment. Term-binding note:
    NCIT:C120874 (Degeneration and Atrophy) is generic, but it is the most
    specific term available under the Histopathology Result branch that the
    schema draws on - NCIT's only cell-loss-specific terms are for sensory hair
    cells and corneal endothelium. preferred_term carries the cell type.
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showing massive loss of Purkinje cells in the vermis and major loss in the cerebellar hemispheres without atrophy of the pons, hippocampus, or cerebral cortex"
    explanation: >-
      Autopsy findings in a heterozygous STUB1 patient define the
      histopathological signature and its anatomical selectivity.
  - reference: PMID:32211513
    reference_title: "Heterozygous STUB1 missense variants cause ataxia, cognitive decline, and STUB1 mislocalization."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Unique neuropathologic examination of the 4 brains showed the marked loss of Purkinje cells (PCs) without microscopic evidence of significant pathology outside the cerebellum."
    explanation: >-
      Four independent brains confirm selective Purkinje cell loss as the
      histopathological substrate.

- name: Ubiquitin/p62-positive neuronal inclusions
  finding_term:
    preferred_term: Ubiquitin/p62-positive neuronal inclusion body
    term:
      id: NCIT:C120945
      label: Inclusion Body
  description: >-
    Ubiquitin- and p62-immunoreactive neuronal inclusions, including
    intranuclear inclusions, are found in cerebellum, neocortex and brainstem
    and are regarded as a pathological hallmark of SCA48. Tau pathology was
    additionally present in one of three examined cases.
  evidence:
  - reference: PMID:32337344
    reference_title: "Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem. In addition, tau pathology was present in 1 case."
    explanation: >-
      Documents the inclusion pathology, its distribution and the variable tau
      co-pathology in a heterozygous STUB1 pedigree.

genetic:
- name: STUB1 heterozygous pathogenic variants
  gene_term:
    preferred_term: STUB1
    term:
      id: hgnc:11427
      label: STUB1
  association: Causative heterozygous pathogenic variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal dominant inheritance
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
    evidence:
    - reference: PMID:32713943
      reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Pathogenic variants in STUB1 were initially described in autosomal recessive spinocerebellar ataxia type 16 and dominant cerebellar ataxia with cerebellar cognitive dysfunction (SCA48)."
      explanation: >-
        States the dominant inheritance of SCA48 and simultaneously names the
        allelic recessive disorder, keeping the pair explicit.
  notes: >-
    Variants are germline, distributed across the coding sequence with no
    hotspot, and include missense, nonsense, frameshift, splice-site and
    in-frame deletion changes. Reported examples include the discovery
    frameshift c.823_824delCT (p.Leu275Aspfs*16), the de novo TPR-domain
    missense c.155C>G (p.Ala52Gly), the U-box frameshift c.832del
    (p.Glu278fs), and the missense c.755A>C (p.Tyr252Ser). Because dominant
    and recessive STUB1 variants are biochemically indistinguishable in vitro,
    zygosity and phenotype - not variant class - separate SCA48 from SCAR16.
  evidence:
  - reference: PMID:30381368
    reference_title: "Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the candidate variants, only the frameshift heterozygous c.823_824delCT STUB1 (p.L275Dfs*16) pathogenic variant cosegregated with the disease."
    explanation: >-
      The founding genetic observation: a single heterozygous STUB1 variant
      cosegregating with SCA48.
  - reference: PMID:34565360
    reference_title: "Clinical and functional characterization of a novel STUB1 frameshift mutation in autosomal dominant spinocerebellar ataxia type 48 (SCA48)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified a novel heterozygous frameshift variant, c.832del (p.Glu278fs), in STUB1 in two patients from the same family."
    explanation: >-
      Independent identification of a novel heterozygous U-box frameshift
      variant in an SCA48 family, illustrating allelic heterogeneity.
  - reference: PMID:39707479
    reference_title: "Clinical and functional characterization of a novel STUB1 mutation in a Chinese spinocerebellar ataxia 48 pedigree."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we reported a Chinese SCA48 family exhibited typical features and defined a novel missense mutation STUB1 c.755A>C (CHIP p. Y252S) through whole-exome sequencing."
    explanation: >-
      Extends the reported allelic and geographic spectrum with a functionally
      characterised missense variant.

- name: TBP intermediate CAG/CAA repeat expansion (modifier)
  gene_term:
    preferred_term: TBP
    term:
      id: hgnc:11588
      label: TBP
  association: Modifier of penetrance and severity, not an independent cause of SCA48
  relationship_type: MODIFIER
  variant_origin: GERMLINE
  notes: >-
    Intermediate TBP alleles (approximately 40-49 CAG/CAA repeats) are
    themselves incompletely penetrant for SCA17 and co-occur with STUB1
    variants far more often than expected. Current evidence favours a modifier
    role: repeat length predicts cognitive impairment and speed of
    progression, and the combined genotype is fully penetrant, but SCA48 also
    occurs with normal TBP alleles. TBP repeat sizing is therefore
    recommended alongside STUB1 sequencing for prognosis and counselling, not
    as a diagnostic requirement.
  evidence:
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We show that intermediate TBP40-49 alleles act as disease modifiers of SCA48 rather than a STUB1/TBP digenic model. This distinction from what has been proposed before has crucial consequences for genetic counseling in SCA48."
    explanation: >-
      Establishes the modifier relationship_type used here and states its
      counselling consequence.
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "STUB1 variants were found in half of the TBP40-49 cohort. Mirroring this finding, TBP40-49 alleles were detected in 40% of STUB1 probands."
    explanation: >-
      Quantifies the reciprocal co-occurrence that makes TBP sizing clinically
      worth doing in STUB1 probands.

prevalence:
- population: Index cerebellar ataxia cases, mostly with dominant inheritance (SPATAX network, 440 index cases)
  measure_type: UNKNOWN
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    STUB1 variants were detected in 50 patients across the 440 index cases, an
    implication of 7% among dominantly inherited cerebellar ataxias. This is a
    diagnostic yield in a selected cohort, not a population prevalence. No population prevalence, incidence or carrier frequency for
    SCA48 has been established; the figure is recorded because it is the best
    available measure of how often SCA48 is encountered among dominant
    ataxias. measure_type is UNKNOWN because diagnostic yield is not one of
    the enumerated epidemiological measures.
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results reveal an unexpectedly frequent (7%) implication of STUB1 among dominantly inherited cerebellar ataxias, and suggest that the penetrance of STUB1 variants could be modulated by other factors, including sex and variants in other ataxia-related genes."
    explanation: >-
      Source of the 7% figure and of the accompanying caution that penetrance
      is modulated by other factors.

- population: Unrelated patients with adult-onset dominant or sporadic cerebellar ataxia negative for common repeat expansions (Italy, 235 patients)
  measure_type: UNKNOWN
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    SCA48 accounted for 3.4% (8/235) of the cohort. Diagnostic yield, not
    population prevalence. The yield rises to 23.5%
    (4/17) when only familial cases are considered, illustrating how strongly
    the figure depends on cohort ascertainment.
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "giving an estimated overall frequency of 3.4% (8/235) for SCA48 in our study cohort, rising to 23.5% (4/17) when considering only familial cases"
    explanation: >-
      Provides both the overall and familial-only diagnostic yields quoted in
      the notes.

diagnosis:
- name: STUB1 sequencing with parallel TBP repeat sizing
  description: >-
    Diagnosis rests on identifying a heterozygous pathogenic STUB1 variant in
    a patient with a compatible progressive ataxia-plus-cognitive phenotype
    and cerebellar atrophy on MRI. Because STUB1 is a conventional
    (non-repeat) gene it is missed by the repeat-expansion panels used
    first-line in dominant ataxia, so it must be covered by a sequencing panel
    or exome/genome test. TBP CAG/CAA repeat length should be sized in
    parallel: it alters expected penetrance, severity and recurrence-risk
    counselling even though it is not required for the diagnosis.
  evidence:
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Molecular screening was performed in a cohort of 235 unrelated patients with adult-onset, autosomal dominant (17) or sporadic (218) cerebellar ataxia, negative for pathological trinucleotide expansions in the common SCAs, FRDA and FXTAS loci, by using targeted multigene panels or whole-exome sequencing."
    explanation: >-
      Describes the diagnostic route by which SCA48 is actually found -
      sequencing after negative repeat-expansion testing.
  - reference: PMID:36799493
    reference_title: "Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests."
    explanation: >-
      Supports sizing TBP alongside STUB1 for counselling purposes.

differential_diagnoses:
- name: SCAR16 / Gordon Holmes syndrome (biallelic STUB1)
  disease_term:
    preferred_term: cerebellar ataxia-hypogonadism syndrome
    term:
      id: MONDO:0008935
      label: cerebellar ataxia-hypogonadism syndrome
  description: >-
    The allelic autosomal recessive STUB1 disorder, curated in this knowledge
    base as Cerebellar Ataxia-Hypogonadism Syndrome. It shares the ataxia,
    cognitive dysfunction, hyperkinetic movement disorder and epilepsy of
    SCA48, so the two form a continuous clinical spectrum rather than
    separable syndromes.
  distinguishing_features:
  - >-
    SCAR16 is biallelic and typically earlier in onset, with spastic ataxia,
    peripheral neuropathy and hypogonadotropic hypogonadism; SCA48 is
    heterozygous, adult-onset, and defined by the cerebellar
    cognitive-affective syndrome, with pyramidal and peripheral nervous system
    signs conspicuously absent in some cohorts. Hypogonadism is rare in SCA48
    - the eight-family Italian series reported it in one patient, in whom it
    was accompanied by other autoimmune endocrine dysfunction.
  evidence:
  - reference: PMID:32342324
    reference_title: "Spinocerebellar ataxia type 48: last but not least."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SCAR16 is characterized by early onset spastic ataxia and a wide disease spectrum, including cognitive dysfunction, hyperkinetic disorders, epilepsy, peripheral neuropathy, and hypogonadism."
    explanation: >-
      Characterises the recessive counterpart and the features that pull a
      case towards it.
  - reference: PMID:32342324
    reference_title: "Spinocerebellar ataxia type 48: last but not least."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The overlap of several clinical signs between SCAR16 and SCA48 indicates the presence of a continuous clinical spectrum among recessively and dominantly inherited mutations of STUB1."
    explanation: >-
      States the continuity of the two entities, which is why zygosity rather
      than phenotype alone settles the distinction.
  - reference: PMID:31571321
    reference_title: "The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CCAS also occurred frequently, whereas definite signs of pyramidal tract dysfunction and peripheral nervous system involvement were absent. One SCA48 patient presented with hypogonadism, associated with other autoimmune endocrine dysfunctions."
    explanation: >-
      Supports both distinguishing points: absent pyramidal/peripheral signs
      in this SCA48 cohort, and hypogonadism as a single-patient exception.

- name: Spinocerebellar ataxia 17 (TBP)
  description: >-
    SCA17 is caused by fully penetrant TBP CAG/CAA expansions above 49
    repeats and is the principal Huntington-disease-like SCA. It is the
    critical differential because intermediate TBP alleles sit at the
    interface between the two disorders.
  distinguishing_features:
  - >-
    SCA17 with TBP>=47 alleles is a monogenic dominant disorder; intermediate
    TBP40-49 alleles are incompletely penetrant and their carriers usually
    also carry a STUB1 variant. Patients with both genotypes have more severe
    multidomain dementia and greater cerebellar and brainstem volume loss than
    those with fully expanded TBP alleles alone.
  evidence:
  - reference: PMID:34906452
    reference_title: "Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "demonstrate a dual inheritance pattern for SCA17, which is a monogenic dominant disorder for TBP≥47 alleles and a digenic TBP/STUB1 disease (SCA17-DI) for intermediate expansions"
    explanation: >-
      Defines the repeat-length boundary that separates monogenic SCA17 from
      the STUB1-associated intermediate-allele form.
  - reference: PMID:36799493
    reference_title: "Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SCATBP/STUB1 patients had multi-domain dementia with a more severe impairment in respect to patient carrying only fully expanded SCA17 alleles."
    explanation: >-
      Supports the severity distinction between the combined genotype and
      monogenic SCA17.

- name: Multiple system atrophy, cerebellar type (MSA-C)
  disease_term:
    preferred_term: multiple system atrophy, cerebellar type
    term:
      id: MONDO:0016418
      label: multiple system atrophy, cerebellar type
  description: >-
    Sporadic adult-onset cerebellar ataxia with parkinsonism and urinary
    symptoms is the MSA-C presentation, and it overlaps closely with the SCA48
    phenotype set. Most SCA48 patients reach genetic testing only after
    repeat-expansion panels come back negative, so MSA-C is a realistic
    competing label at that point.
  distinguishing_features:
  - >-
    MSA-C is a sporadic synucleinopathy with prominent autonomic failure and a
    median survival of 8-10 years; SCA48 is dominantly inherited, slowly
    progressive over decades, and is defined by the cerebellar
    cognitive-affective syndrome rather than by dysautonomia. Dentate T2
    hyperintensity with postero-lateral hemispheric atrophy (the crab sign) and
    a family history point to SCA48; a STUB1 variant settles it.
  evidence:
  - reference: PMID:42501123
    reference_title: "Multiple system atrophy: cure and care."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Multiple system atrophy (MSA) is a rare and rapidly progressive neurodegenerative disorder characterized by a variable combination of autonomic failure, parkinsonism, and cerebellar ataxia, with a median survival of 8-10 years from symptom onset."
    explanation: >-
      Characterises MSA and gives the two features that separate it from SCA48
      - prominent autonomic failure and a rapid course. Graded OTHER because
      this is a narrative review rather than a primary clinical study.
  - reference: PMID:32342324
    reference_title: "Spinocerebellar ataxia type 48: last but not least."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SCA48 is an adult-onset syndrome characterized by ataxia and cognitive-psychiatric features, variably associated with chorea, parkinsonism, dystonia, and urinary symptoms."
    explanation: >-
      Documents the SCA48 side of the overlap - adult-onset ataxia with
      parkinsonism and urinary symptoms - which is what makes MSA-C a live
      alternative before genetic testing.

- name: Frontotemporal dementia and Huntington disease phenocopies
  description: >-
    Because the cognitive-affective syndrome can dominate and precede ataxia,
    and because chorea occurs, SCA48 can present as an apparent
    frontotemporal dementia or Huntington disease phenocopy.
  distinguishing_features:
  - >-
    Cerebellar atrophy with dentate T2 hyperintensity on MRI, and cerebellar
    signs on examination, redirect the diagnosis. Screening in the reverse
    direction has a low yield: no STUB1 variant was found in 115 patients with
    frontotemporal dementia, so STUB1 should be pursued when the phenotype has
    a cerebellar component rather than in unselected FTD.
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "including five families with Huntington or frontotemporal dementia disease-like phenotypes associated with ataxia, while no STUB1 variant was found in 115 patients with frontotemporal dementia"
    explanation: >-
      Supports both the phenocopy presentation and the negative yield of
      unselected FTD screening.

treatments:
- name: Multidisciplinary Supportive Care
  description: >-
    No disease-modifying therapy exists for SCA48, and no SCA48-specific
    interventional trial has been reported. Management is symptomatic and
    coordinated across neurology, clinical genetics, rehabilitation,
    neuropsychology/psychiatry, speech-language pathology and dietetics.
    Expert consensus for degenerative cerebellar disorders is that no
    medication has been shown to be effective outside episodic ataxia type 2,
    so pharmacological trials should be framed as symptomatic and
    individualised rather than disease-modifying.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:24222635
    reference_title: "Consensus paper: management of degenerative cerebellar disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "There is consensus that up to date, no medication has been proven effective."
    explanation: >-
      Expert consensus across degenerative cerebellar ataxias establishes the
      absence of proven pharmacotherapy, which is the premise of a supportive
      management strategy.

- name: Physiotherapy and Coordinative Training
  description: >-
    Physiotherapy is the mainstay of treatment for degenerative cerebellar
    ataxia, together with occupational therapy and speech therapy. A
    meta-analysis of 18 randomised trials in degenerative cerebellar ataxia
    found a significant reduction in SARA score with physiotherapy, with
    multi-aspect, balance and aerobic training each showing effects; the
    certainty of evidence was low and no trial was SCA48-specific, so this is
    generalised from the degenerative-ataxia population.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - preferred_term: Cerebellar ataxia
    term:
      id: HP:0001251
      label: Ataxia
  evidence:
  - reference: PMID:24222635
    reference_title: "Consensus paper: management of degenerative cerebellar disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "As such, all authors agreed that the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy."
    explanation: >-
      Expert consensus identifies physiotherapy as the mainstay of management
      for this class of disorder.
  - reference: PMID:39866519
    reference_title: "Effects of physiotherapy on degenerative cerebellar ataxia: a systematic review and meta-analysis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Overall, physiotherapy significantly reduced SARA scores (MD = -1.41, [95% CI: -2.16, -0.66])"
    explanation: >-
      Quantifies the effect in the degenerative-ataxia population. Recorded as
      INDIRECT because the pooled trials were not SCA48-specific, and the
      review itself reports a serious risk of bias and low certainty of
      evidence.

- name: Speech and Swallowing Therapy
  description: >-
    Speech therapy addresses the cerebellar dysarthria that is present in
    essentially all SCA48 patients, and swallowing assessment becomes relevant
    as the disease advances.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech and swallowing therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  target_phenotypes:
  - preferred_term: Dysarthria
    term:
      id: HP:0001260
      label: Dysarthria
  - preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:24222635
    reference_title: "Consensus paper: management of degenerative cerebellar disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy"
    explanation: >-
      Speech therapy is named among the consensus mainstays of management for
      degenerative cerebellar ataxia.

- name: Occupational Therapy
  description: >-
    Occupational therapy supports activities of daily living, home safety and
    fall prevention as gait ataxia, tremor and dysmetria progress.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: occupational therapy
    term:
      id: NCIT:C121351
      label: Occupational Therapy
  evidence:
  - reference: PMID:24222635
    reference_title: "Consensus paper: management of degenerative cerebellar disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy"
    explanation: >-
      Occupational therapy is named among the consensus mainstays of
      management.

- name: Genetic Counselling and Cascade Testing
  description: >-
    Counselling must cover the 50% transmission risk, the incomplete and
    age-dependent penetrance of heterozygous STUB1 variants, the possibility
    of de novo occurrence, and the effect of TBP repeat length on expected
    penetrance and severity. Because TBP and STUB1 alleles segregate
    independently, recurrence-risk calculation and predictive testing in
    families carrying both must account for that independence.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:36799493
    reference_title: "Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The identification of the complex SCATBP/STUB1 phenotype may impact on diagnosis and genetic counseling in the families with both hereditary and sporadic ataxia. The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests."
    explanation: >-
      States the specific counselling complication that this treatment entry
      exists to capture.
  - reference: PMID:36422518
    reference_title: "Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This distinction from what has been proposed before has crucial consequences for genetic counseling in SCA48."
    explanation: >-
      Confirms that the modifier-versus-digenic resolution changes what
      families are told.

animal_models:
- species: Danio rerio
  genotype: stub1 mutant with truncated Chip U-box domain
  description: >-
    A zebrafish stub1 mutant truncating the functional U-box domain shows
    impaired ubiquitination of Hsc70 and of Chip itself, decreased total brain
    26S proteasome activity, reduced Purkinje cell number and soma size,
    abnormal Purkinje dendrite organisation, and behavioural changes. It
    recapitulates the cellular Purkinje phenotype but not the gross cerebellar
    atrophy of human disease, which is its main limitation. stub1 mRNA is
    predominantly expressed in the cerebellum including the Purkinje cell
    layer, consistent with the cell-type selectivity of the human disorder.
  publication: PMID:34630034
  modeled_mechanisms:
  - target: Impaired Chaperone-Assisted Protein Quality Control
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Truncating the Chip U-box abolishes ubiquitination of Hsc70 and of Chip
      itself and lowers whole-brain 26S proteasome activity, reproducing the
      molecular lesion of U-box SCA48 variants.
    evidence:
    - reference: PMID:34630034
      reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Recombinant wild-type zebrafish Chip showed ubiquitin ligase activity highly comparable to human CHIP, while the mutant Chip protein showed impaired ubiquitination of the Hsc70 substrate and Chip itself."
      explanation: >-
        Establishes that the zebrafish enzyme is functionally equivalent to
        human CHIP and that the mutant loses the same activity, which is what
        makes this model informative for the human quality-control node.
  - target: Cerebellar Purkinje Cell Degeneration
    relationship: RECAPITULATES
    fidelity: MODERATE
    limitations: >-
      Purkinje cell number, soma size and dendritic organisation are abnormal,
      but the fish show no gross cerebellar atrophy, so the model captures the
      cellular phenotype without the tissue-level one.
    evidence:
    - reference: PMID:34630034
      reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "these fish displayed reduced numbers and sizes of Purkinje cell bodies and abnormal organization of Purkinje cell dendrites"
      explanation: >-
        The measured Purkinje cell phenotype is what licenses treating this
        model as informative for the human Purkinje degeneration node.
  evidence:
  - reference: PMID:34630034
    reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In the brain, stub1 mRNA was predominantly detected in the cerebellum, including the Purkinje cell layer and granular layer."
    explanation: >-
      Expression pattern supports cerebellar and Purkinje cell selectivity in
      the model organism.
  - reference: PMID:34630034
    reference_title: "Chip Protein U-Box Domain Truncation Affects Purkinje Neuron Morphology and Leads to Behavioral Changes in Zebrafish."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In conclusion, truncation of the Chip U-box domain leads to impaired ubiquitin ligase activity and behavioral and anatomical changes in zebrafish, illustrating the potential of zebrafish to study STUB1-mediated diseases."
    explanation: >-
      Summarises the model's recapitulation of the molecular lesion and its
      behavioural and anatomical consequences.

- species: Caenorhabditis elegans
  genotype: transgenic expression of human CHIP p.Ala52Gly
  description: >-
    A transgenic C. elegans line expressing the de novo SCA48 CHIP A52G
    variant develops neurodegeneration, providing a variant-specific in vivo
    readout. The organism has no cerebellum, so the model addresses
    proteostatic neurotoxicity rather than the human cerebellar syndrome.
  publication: PMID:35398354
  modeled_mechanisms:
  - target: CHIP Loss of Function from Heterozygous STUB1 Variants
    relationship: RECAPITULATES
    fidelity: LOW
    description: >-
      Expression of the human CHIP A52G SCA48 variant causes neurodegeneration
      in an intact organism.
    limitations: >-
      C. elegans has no cerebellum and no Purkinje cells, so the model speaks
      to proteostatic neurotoxicity rather than to the cerebellar syndrome.
    evidence:
    - reference: PMID:35398354
      reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: MODEL_ORGANISM
      snippet: "induces neurodegeneration in a transgenic Caenorhabditis elegans model of SCA48"
      explanation: >-
        The patient-derived variant causes neurodegeneration in the transgenic
        worm, which is the basis for treating the model as informative for the
        CHIP dysfunction node. Recorded as INDIRECT because the organism has no
        cerebellum, so relevance to the human node requires an inference step.
  evidence:
  - reference: PMID:35398354
    reference_title: "The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase CHIP."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We further show that this mutant decreases cellular fitness in response to certain cellular stressors and induces neurodegeneration in a transgenic Caenorhabditis elegans model of SCA48."
    explanation: >-
      Documents neurodegeneration caused by an SCA48 variant in an intact
      organism.

discussions:
- discussion_id: sca48-tbp-modifier-magnitude
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    How large is the TBP modifier effect on SCA48 penetrance, and does it
    extend to other repeat loci?
  attaches_to:
  - pathophysiology#TBP Intermediate Repeat Expansion as a Genetic Modifier
  rationale: >-
    The modifier reading of the STUB1/TBP interaction is well supported, but
    its magnitude is not quantified: there is no penetrance estimate stratified
    by TBP repeat length, variant domain, age and sex. The same cohort that
    reported the 7% yield also reported second hits in AFG3L2 and PRKCG in
    three families and a 70% female excess, neither of which has been
    replicated. Until these are quantified, prognostic counselling for a
    STUB1-positive individual rests on cohort-level associations rather than
    an individual risk estimate.
  proposed_experiments:
  - experiment_id: exp_sca48_penetrance_registry
    name: Genotype-curated SCA48 penetrance registry with TBP sizing
    description: >-
      Prospective, genotype-curated multicentre registry with TBP repeat sizing
      on all STUB1 variant carriers, including asymptomatic relatives, powered
      to estimate age-specific penetrance stratified by TBP repeat length, CHIP
      domain and sex, with independent replication of the reported female
      excess and of the AFG3L2/PRKCG second hits.
    decision_criterion: >-
      An age-specific penetrance curve that separates by TBP repeat length with
      non-overlapping confidence intervals would establish the magnitude of the
      modifier effect; overlapping curves would place an upper bound on it.
  evidence:
  - reference: PMID:32713943
    reference_title: "Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This screening of STUB1 variants revealed new features: (1) the majority of patients were women (70%) and (2) \"second hits\" in AFG3L2, PRKCG, and TBP were detected in three families suggesting synergic effects."
    explanation: >-
      Source of the unreplicated sex ratio and additional candidate modifier
      loci that this gap asks to be quantified or refuted.

- discussion_id: sca48-mitophagy-human-relevance
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does CHIP-dependent mitophagy dysregulation contribute to Purkinje cell
    loss in human SCA48?
  attaches_to:
  - pathophysiology#Dysregulated PINK1/Parkin-Mediated Mitophagy
  rationale: >-
    CHIP negatively regulates PINK1/Parkin mitophagy and disease-associated
    CHIP variants dysregulate it in cell culture and in C. elegans neurons,
    but no human SCA48 tissue has been examined for mitophagy or mitochondrial
    pathology. The node is therefore recorded with PROVISIONAL confidence and
    an indirect downstream edge. A comparable candidate mechanism - impaired
    heat-shock response - was tested in SCAR16 (biallelic) patient iPSC-derived
    neurons against isogenic STUB1-null controls and did not survive, which is
    the cautionary precedent here.
  proposed_experiments:
  - experiment_id: exp_sca48_mitophagy_human_neurons
    name: Mitophagy flux in SCA48 patient iPSC-derived Purkinje-like neurons
    description: >-
      Measure mitophagy flux, PINK1/Parkin recruitment and mitochondrial
      morphology in iPSC-derived Purkinje-like neurons from patients carrying
      dominant SCA48 STUB1 variants against isogenic corrected controls, and
      stain the existing SCA48 autopsy cerebellum series for mitochondrial and
      PINK1/Parkin pathology.
    decision_criterion: >-
      A mitophagy defect present in patient neurons but absent from isogenic
      controls, and corroborated in autopsy tissue, would move this node from
      PROVISIONAL to ESTABLISHED; a null result matching the heat-shock-response
      precedent would justify removing the node.
  evidence:
  - reference: PMID:33097556
    reference_title: "CHIP mutations affect the heat shock response differently in human fibroblasts and iPSC-derived neurons."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, STUB1(-/-) neurons generated by CRISPR/Cas9-mediated genome editing from an isogenic healthy control line showed a similar HSR to patients."
    explanation: >-
      The precedent for the caution: a plausible CHIP-linked mechanism failed
      when tested in the right cell type with isogenic controls. The patient
      lines were SCAR16 (biallelic), so the precedent bears on CHIP biology
      generally rather than on SCA48 zygosity specifically.

datasets:
- accession: geo:GSE310700
  title: Transcriptomic analysis of STUB1 knockdown in HEK293 cells under normal and heat-shock conditions
  data_type: BULK_RNA_SEQ
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:42567515
  notes: >-
    RNA-seq of STUB1 knockdown under normal and heat-shock conditions, the
    CHIP-insufficiency model reported in the SCA48 domain-uncoupling study
    (PMID:42567515). It is a HEK293 cell system, not a neuronal or patient one,
    so it speaks to the transcriptional consequences of reduced CHIP dosage
    rather than to Purkinje cell biology. No patient-derived SCA48
    transcriptomic, proteomic or single-cell dataset was found.

📚

References & Deep Research

References

1

PMID:20301317

Hereditary Ataxia Overview.

No top-level findings curated for this source.

Deep Research

1

Falcon ▸

Spinocerebellar Ataxia Type 48 (SCA48): Disease-Characteristics Report

Edison Scientific Literature 33 citations 2026-08-31T20:56:02.230068

Spinocerebellar Ataxia Type 48 (SCA48): Disease-Characteristics Report

Executive summary

Spinocerebellar ataxia type 48 (SCA48; ATX-STUB1/SCA-STUB1) is a rare, usually adult-onset, progressive neurodegenerative disorder caused primarily by heterozygous germline variants in STUB1, which encodes the co-chaperone and E3 ubiquitin ligase CHIP. Its characteristic combination is cerebellar ataxia, cerebellar atrophy, and a frequently early cognitive-affective or psychiatric syndrome; tremor, parkinsonism, pyramidal signs, dystonia, chorea, neuropathy, epilepsy, and autonomic symptoms broaden the phenotype. The largest retrieved cohort found candidate STUB1 variants in 30/440 ataxia families (approximately 7%), with cognitive impairment in 54% of carriers, but this is a diagnostic-cohort proportion—not population prevalence. Mean onset was 40.0 ± 13.8 years, with a 17–74-year range and marked age-dependent penetrance. (roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 1-2)

The strongest current model is that many SCA48 cases are monogenic STUB1 disorders, while intermediate TBP CAG/CAA expansions and possibly variants in other ataxia genes can modify penetrance or severity. Three unrelated 2024 cases had pathogenic/likely pathogenic STUB1 variants, normal TBP alleles, and SCA48, directly supporting monogenic causation. (zochowski2024caseseriesof pages 3-5)

No SCA48-specific disease-modifying treatment, validated prognostic biomarker, population incidence estimate, or interventional clinical trial was identified. Current implementation consists of molecular diagnosis, counseling and cascade testing, rehabilitation, assistive care, and symptom-directed management.

1. Disease information

Definition

SCA48 is a Mendelian, autosomal-dominant spinocerebellar degeneration in which cognitive-affective dysfunction may precede conventional motor ataxia by years. The original family showed a continuum from dysexecutive symptoms to severe cerebellar cognitive-affective syndrome (CCAS) and finally truncal ataxia, with neurodegeneration initially concentrated in cerebellar regions supporting cognition and emotion. (genis2018heterozygousstub1mutation pages 1-2)

Identifiers and nomenclature

Preferred name: Spinocerebellar ataxia type 48.
Synonyms: SCA48; ATX-STUB1; SCA-STUB1; autosomal-dominant STUB1-related ataxia; dominant cerebellar ataxia with cognitive-affective syndrome.
OMIM phenotype: 618093.
Causal gene: STUB1, OMIM 607207; chromosome 16p13.3. (genis2018heterozygousstub1mutation pages 1-2)
MONDO: A dedicated, confidently verified MONDO identifier was not recovered; it should not be inferred from identifiers for other SCA subtypes. Open Targets did not return a specific SCA48–STUB1 record in the retrieved search, illustrating incomplete database indexing rather than evidence against the association. (OpenTargets Search: spinocerebellar ataxia type 48)
Orphanet: No dedicated identifier was verified from the retrieved material.
ICD-10: Usually represented under a nonspecific hereditary ataxia category, commonly G11.8/G11.9, depending on jurisdiction; there is no verified SCA48-specific code.
ICD-11/MeSH: No SCA48-specific term was verified; broader hereditary/cerebellar ataxia concepts are used.
Suggested MONDO mapping: map to a dedicated SCA48 concept if present in the target terminology release, with parent concepts autosomal dominant cerebellar ataxia and spinocerebellar ataxia; do not substitute SCA1 or another numbered subtype.

Evidence granularity

The evidence is principally aggregated disease-level evidence derived from pedigrees, multicenter research cohorts, case series, imaging studies, and postmortem pathology—not population EHR surveillance. Individual-patient observations contribute materially because the disorder was only delineated in 2018 and remains exceptionally rare. The discovery study followed one family for more than a decade using serial neurological/neuropsychological assessments, MRI, SPECT, and genetics. (genis2018heterozygousstub1mutation pages 1-2)

2. Etiology, risk, and protective factors

Primary cause

The initiating lesion is generally a heterozygous germline pathogenic or likely pathogenic STUB1 sequence variant. Frameshift, nonsense, splice, in-frame deletion, and missense variants are reported throughout the coding sequence, including the N-terminal tetratricopeptide-repeat (TPR) chaperone-binding region and C-terminal U-box E3-ligase region. The original pathogenic variant was c.823_824delCT (p.Leu275Aspfs*16). (genis2018heterozygousstub1mutation pages 1-2, roux2020clinicalneuropathologicaland pages 2-3)

Genetic risk and modifiers

Family history: An affected first-degree relative raises prior probability, but negative family history does not exclude SCA48 because de novo variants, late onset, and incomplete penetrance occur. A de novo c.155C>G (p.Ala52Gly) TPR-domain variant caused progressive ataxia with pan-cerebellar atrophy. (umano2022themolecularbasis pages 1-2)
TBP: Intermediate-length TBP alleles—typically discussed around 40–46 or 40–49 CAG/CAA repeats—can coexist with STUB1 variants. A 2023 digenic cohort described a severe multidomain ataxia-dementia phenotype, reduced cerebellar cortex and brainstem volumes, and implications for recurrence-risk calculations. (nanetti2023complexataxia‐dementiaphenotype pages 1-2)
Countervailing evidence: Three 2024 Australian probands had normal TBP alleles (34/35, 35/35, and 34/35 repeats) yet unequivocal SCA48 phenotypes, supporting STUB1 monogenic disease. (zochowski2024caseseriesof pages 3-5)
Penetrance example: One p.Pro243Leu carrier without a TBP expansion remained asymptomatic at age 77, whereas STUB1 plus TBP45 segregated with severe, fully penetrant disease in another family. This supports—but does not prove—a modifier role. (winter2025tbprepeatexpansion pages 6-10)
Other proposed modifiers: second hits in AFG3L2, PRKCG, and TBP were found in three families; their causal magnitude remains uncertain. (roux2020clinicalneuropathologicaland pages 1-2)
Sex: A multicenter cohort was 72% female (36/50), and maternal transmission was frequent, prompting a hypothesis of sex-dependent penetrance. This was not consistently replicated and should not be treated as established biology. (roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 3-4)

Environmental, lifestyle, infectious, and protective factors

No reproducible environmental toxin, occupational exposure, infection, diet, smoking pattern, exercise exposure, or protective allele has been established as causing or preventing SCA48. Cellular stress can expose functional defects in mutant CHIP experimentally, but this is not evidence that ordinary heat or environmental stress causes human disease. (umano2022themolecularbasis pages 1-2)

No validated gene–environment interaction is known. Avoiding alcohol intoxication, sedating medication, and other factors that acutely worsen balance is sensible clinical risk reduction, not primary prevention of the molecular disease.

3. Phenotypes

The principal ontology-ready phenotypes, frequencies, temporal characteristics, and functional consequences are summarized below.

Domain / phenotype	Evidence / frequency and temporal characteristics	Suggested HPO term	Functional / QoL consequence
Cerebellar ataxia / gait ataxia	Core phenotype. Discovery family: late truncal ataxia emerging after years of cognitive-affective symptoms; adult-onset, slowly progressive (genis2018heterozygousstub1mutation pages 1-2). Multicenter cohort: mean age at onset 40.0 ± 13.8 years, range 17–74; age at onset highly variable (roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 1-2). Australian 2024 series: ataxia in 3/3, onset ages 32, 57, 61; summary of all reported patients in that series: gait ataxia 8/9 (zochowski2024caseseriesof pages 3-5, zochowski2024caseseriesof pages 6-8).	HP:0001251	Progressive imbalance, falls, loss of independent mobility; disease-specific QoL metrics not reported in collected SCA48 sources.
Dysarthria	Common motor cerebellar sign. Australian 2024 series: dysarthria 3/3; presenting symptom in 2/3 (zochowski2024caseseriesof pages 3-5, zochowski2024caseseriesof pages 5-6). Qualitative reports across families describe adult-onset progressive speech impairment (li2024clinicalandfunctional pages 1-2).	HP:0001260	Reduced speech intelligibility and communication; no SCA48-specific QoL scale reported.
Cerebellar cognitive-affective syndrome / cognitive impairment	Hallmark non-motor feature. Discovery family: 6 fully affected patients showed cognitive-affective syndrome; 3 presymptomatic carriers already had focal cerebellar atrophy before ataxia (genis2018heterozygousstub1mutation pages 1-2). Multicenter cohort: cognitive impairment in 54% of STUB1 variant carriers, predominantly frontal syndrome (roux2020clinicalneuropathologicaland pages 1-2). Australian 2024 series: cognitive impairment 2/3 (zochowski2024caseseriesof pages 3-5).	HP:0100543	Executive dysfunction, memory/language deficits, impaired daily planning and judgment; no standardized SCA48 QoL outcome reported.
Psychiatric / behavioral symptoms	Frequently reported qualitatively: depression, anxiety, behavioral changes, psychiatric dysfunction (zochowski2024caseseriesof pages 3-5, li2024clinicalandfunctional pages 1-2). Large Dutch family had prominent behavioral changes with cognitive decline (mol2020clinicalandpathologic pages 1-2). In the 9-patient summary from the Australian report, psychiatric symptoms were 6/9 (zochowski2024caseseriesof pages 6-8).	HP:0000708	Major impact on social/occupational functioning and caregiver burden; no disease-specific QoL metrics available.
Tremor	Increasingly recognized feature. Australian 2024 series: tremor 3/3, with rest tremor in 2 and action tremor in 1; summary frequency 3/9 in prior aggregate comparison cited in the same report (zochowski2024caseseriesof pages 5-6, zochowski2024caseseriesof pages 6-8). Can precede or accompany ataxia (rest tremor was presenting symptom in 1/3) (zochowski2024caseseriesof pages 3-5).	HP:0001337	Impairs handwriting, feeding, and fine motor tasks; no SCA48-specific QoL metric reported.
Dysmetria / limb incoordination	Discovery and later case reports describe complete motor cerebellar syndrome with dysmetria (genis2018heterozygousstub1mutation pages 1-2). Australian 2024 series: dysmetria 2/3 (zochowski2024caseseriesof pages 3-5).	HP:0001310	Fine motor inaccuracy affecting reaching, dressing, and utensil use; no formal QoL data reported.
Oculomotor abnormalities	Qualitative recurrent feature: oculomotor abnormalities and dysmetric saccades reported in SCA48 literature summarized in 2024 series (zochowski2024caseseriesof pages 3-5). In that series, ocular abnormalities occurred in 1/3 and impaired upward gaze in 1 patient (zochowski2024caseseriesof pages 3-5).	HP:0000508	Visual tracking difficulties may worsen gait/balance and reading; QoL metrics unavailable.
Pyramidal signs / hypertonia / pathologic reflexes	Positive pyramidal tract signs described as part of phenotypic spectrum (li2024clinicalandfunctional pages 1-2). Australian 2024 series: pathologic reflexes 2/3, hypertonia 2/3, extensor plantar responses reported in individual cases (zochowski2024caseseriesof pages 3-5).	HP:0002495	Adds stiffness and gait disability to cerebellar syndrome; no formal SCA48 QoL data reported.
Parkinsonism / bradykinesia / rigidity	Recognized less-common but recurrent feature. Dutch pedigree: gait disturbance could present as ataxia or parkinsonism (mol2020clinicalandpathologic pages 1-2). Australian 2024 series: bradykinesia 1/3, cogwheel rigidity 1/3, parkinsonian rest tremor in 2/3 (zochowski2024caseseriesof pages 3-5, zochowski2024caseseriesof pages 6-8).	HP:0001300	Slowness and rigidity worsen mobility and upper-limb function; QoL metrics unavailable.
Chorea / dystonia / hyperkinetic features	Reported as rarer clinical features in qualitative summaries (zochowski2024caseseriesof pages 3-5, li2024clinicalandfunctional pages 1-2). Dystonic head posturing documented in one 2024 Australian case (zochowski2024caseseriesof pages 3-5).	HP:0002072 / HP:0001332	May complicate diagnosis and interfere with speech/posture; no SCA48-specific QoL data.
Peripheral neuropathy / sensory loss / areflexia	Rarer but documented. Australian 2024 series: one patient had length-dependent sensorimotor axonal peripheral neuropathy on nerve conduction study with sensory loss, absent ankle jerks, pes cavus/hammer toes, and Romberg sign (1/3) (zochowski2024caseseriesof pages 3-5). Qualitative summaries mention peripheral neuropathies (zochowski2024caseseriesof pages 3-5).	HP:0009830	Sensory loss and neuropathy worsen gait instability and distal weakness; QoL metrics unavailable.
Dysphagia	Qualitative feature in disease summaries; explicitly present in 1/3 Australian patients and among presenting symptoms in 1/3 (zochowski2024caseseriesof pages 3-5).	HP:0002015	Risk for choking, nutrition problems, and aspiration burden; no SCA48-specific swallowing QoL measure reported.
Bladder dysfunction	Reported in one Australian patient as urinary urgency/incontinence during progression (1/3) (zochowski2024caseseriesof pages 3-5).	HP:0000020	Can reduce independence and increase caregiver burden; QoL metrics unavailable.
Cerebellar atrophy on MRI	Highly consistent biomarker-level phenotype. Discovery pedigree: vermian and hemispheric atrophy; presymptomatic focal vermian/paravermian and lobules VI–VII atrophy before ataxia (genis2018heterozygousstub1mutation pages 1-2). Australian 2024 series: cerebellar atrophy 3/3, often diffuse (zochowski2024caseseriesof pages 3-5). Umano 2022 de novo case: prominent pan-cerebellar atrophy (umano2022themolecularbasis pages 1-2).	HP:0001272	Correlates with progressive motor/cognitive disability; no direct MRI-QoL linkage quantified in collected SCA48 studies.
Purkinje cell loss / cerebellar degeneration (pathology)	Neuropathology: massive Purkinje cell loss in vermis and major loss in hemispheres reported in heterozygous STUB1 patient(s) (roux2020clinicalneuropathologicaland pages 1-2). Additional reports found subtotal Purkinje cell loss, molecular layer atrophy, p62-positive inclusions, and thalamic/brainstem degeneration (gorcenco2024clinicalandgenetic pages 9-9). Temporal pattern inferred as downstream pathology of progressive disease.	HP:0007366	Likely substrate of worsening coordination and cognition; patient-reported QoL metrics not available.

Table: This table summarizes ontology-ready clinical phenotypes for spinocerebellar ataxia 48 using only collected evidence. It distinguishes exact frequencies from qualitative reports and notes where disease-specific quality-of-life data are unavailable.

Additional observations include dysphagia, urinary urgency/incontinence, epilepsy in rare reports, distal wasting, pes cavus, hammer toes, myoclonus, and abnormal saccades. In the 2024 three-patient series, ataxia, dysarthria, tremor, and cerebellar atrophy each occurred in 3/3; cognitive impairment and dysmetria in 2/3; ocular abnormality, muscle wasting, sensory loss, neuropathy, dysphagia, bladder dysfunction, and bradykinesia occurred in individual patients. These small denominators must not be interpreted as population frequencies. (zochowski2024caseseriesof pages 3-5, zochowski2024caseseriesof pages 5-6)

Abstract quotation—discovery phenotype: “Six patients fully developed cognitive-affective and complete motor cerebellar syndrome associated with vermian and hemispheric cerebellar atrophy.” The same abstract reports focal vermian/paravermian and lobules VI–VII atrophy in three presymptomatic carriers. (genis2018heterozygousstub1mutation pages 1-2)

No SCA48-specific EQ-5D, SF-36, PROMIS, or validated patient-reported outcome data were recovered. Nevertheless, gait instability and falls impair mobility; dysarthria and dysphagia impair communication and nutrition; executive/behavioral disease compromises employment, decision-making, relationships, and independent living.

4. Genetic and molecular information

Gene and protein

Gene: STUB1 (STIP1 homology and U-box containing protein 1).
Protein: CHIP, the C-terminus of HSC70-interacting protein.
Core functions: molecular co-chaperone and E3 ubiquitin ligase at the interface of protein folding and degradation.
Domains: N-terminal TPR repeats recruit HSP70/HSP90-family chaperones; the central helical region supports dimerization; the C-terminal U-box recruits E2 conjugating enzymes and mediates ubiquitination. (umano2022themolecularbasis pages 1-2, pakdaman2021chipproteinubox pages 1-2)
Suggested GO molecular functions: ubiquitin-protein transferase activity; ubiquitin-protein ligase activity; heat-shock protein binding; chaperone binding.
Suggested GO biological processes: protein ubiquitination; proteasome-mediated ubiquitin-dependent protein catabolic process; cellular protein quality control; response to unfolded protein; regulation of autophagy/mitophagy; neuron apoptotic process.

Variant spectrum and interpretation

In 440 ataxia families, 26 different STUB1 variants were detected in 30 families. They included missense, nonsense/stop-gain, splice, frameshift, and in-frame deletion variants distributed across the coding sequence; no simple variant hot spot or robust genotype–phenotype correlation was established. Filtering used gnomAD minor allele frequency <0.001 and CADD >20. Most variants were absent or ultrarare; reported nonzero frequencies were generally approximately 1.5–3.3 × 10⁻⁵. (roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 3-4)

Representative variants include:

p.Leu275Aspfs*16: pathogenic discovery-family frameshift. (genis2018heterozygousstub1mutation pages 1-2)
c.689_692del, p.Tyr230Cysfs*9: pathogenic frameshift. (zochowski2024caseseriesof pages 3-5)
c.669+1G>A: likely pathogenic canonical splice variant. (zochowski2024caseseriesof pages 3-5)
c.327_328insCT, p.Tyr110Leufs*21: likely pathogenic loss-of-function variant. (zochowski2024caseseriesof pages 3-5)
c.832del, p.Glu278fs: U-box frameshift with dominant-negative functional evidence. (chen2021clinicalandfunctional pages 1-2)
c.155C>G, p.Ala52Gly: initially VUS, subsequently supported by de novo status and functional/animal evidence. (umano2022themolecularbasis pages 1-2)
c.755A>C, p.Tyr252Ser: reported as VUS but supported experimentally by reduced CHIP level/ligase function and increased tau aggregation; clinical classification should be periodically reassessed rather than automatically upgraded. (li2024clinicalandfunctional pages 1-2)

Variants are constitutional/germline, not somatic tumor mutations. Large chromosomal abnormalities are not the established usual cause. CMA, karyotyping, and FISH therefore have low first-line yield unless another syndromic or copy-number disorder is suspected.

Mode of action

Evidence supports several nonexclusive mechanisms: haploinsufficiency/loss of function, dominant-negative interference, reduced protein stability, defective chaperone binding, altered oligomerization, and impaired E3-ligase activity. The p.Glu278fs protein impaired interaction with UBE2D1 and produced a dominant-negative effect; p.Ala52Gly retained intrinsic E3 activity but had reduced chaperone affinity and cellular stability. Thus, “loss of CHIP-mediated proteostasis” is more accurate than a single universal molecular mechanism. (chen2021clinicalandfunctional pages 1-2, umano2022themolecularbasis pages 1-2)

No validated SCA48-specific epigenetic signature, DNA-methylation disorder, modifier locus from GWAS, or recurrent structural rearrangement was identified.

5. Environmental information

SCA48 is not infectious, toxic, nutritional, occupational, or radiation-induced. Environmental exposures have not been shown to alter penetrance. Lifestyle measures are supportive: safe aerobic/strength activity as tolerated, fall prevention, nutritional monitoring when dysphagia occurs, and avoidance of substances that worsen coordination. These measures may reduce complications but do not prevent inheritance or molecular onset.

6. Mechanism and pathophysiology

Ordered causal chain

A heterozygous STUB1 variant leads to reduced, unstable, mislocalized, or functionally abnormal CHIP protein. (chen2021clinicalandfunctional pages 1-2, umano2022themolecularbasis pages 1-2, li2024clinicalandfunctional pages 1-2)
Abnormal CHIP leads to defective chaperone engagement through the TPR domain and/or defective E2 recruitment and ubiquitin-ligase activity through the U-box. (umano2022themolecularbasis pages 1-2, pakdaman2021chipproteinubox pages 1-2)
These defects lead to impaired ubiquitination and proteasomal/autophagic disposal of damaged or chaperone-bound proteins, resulting in loss of neuronal proteostasis. (umano2022themolecularbasis pages 1-2, pakdaman2021chipproteinubox pages 1-2)
Branch A—demonstrated in vitro: impaired clearance leads to accumulation/aggregation of tau and α-synuclein, caspase-3 activation, and apoptosis. (chen2021clinicalandfunctional pages 1-2, li2024clinicalandfunctional pages 1-2)
Branch B—modifier model, partly inferred: reduced CHIP/CASA-mediated clearance leads to persistence of intermediate polyglutamine-expanded TBP; this can amplify cognitive, extrapyramidal, and ataxic disease in digenic TBP/STUB1 families. (winter2025tbprepeatexpansion pages 6-10, nanetti2023complexataxia‐dementiaphenotype pages 1-2)
Proteostasis failure and stress vulnerability lead to Purkinje-cell dysfunction, dendritic disorganization, and neuronal inclusions; human postmortem tissue demonstrates marked Purkinje-cell loss and ubiquitin/p62-positive inclusions. (mol2020clinicalandpathologic pages 1-2, roux2020clinicalneuropathologicaland pages 1-2, pakdaman2021chipproteinubox pages 1-2)
Purkinje-cell and cerebellar network degeneration leads first in some patients to dysfunction of vermian/paravermian and lobules VI–VII cognitive-affective circuits, followed by more diffuse cerebellar degeneration. (genis2018heterozygousstub1mutation pages 1-2)
Diffuse cerebellar and variable brainstem, basal-ganglia, cortical, peripheral-nerve, and long-tract involvement results in progressive ataxia, dysarthria, cognitive-affective disease, tremor/parkinsonism, pyramidal signs, and occasional neuropathy or epilepsy. (mol2020clinicalandpathologic pages 1-2, gorcenco2024clinicalandgenetic pages 9-9, zochowski2024caseseriesof pages 3-5)

Cellular and tissue mechanisms

The best-supported vulnerable cell is the cerebellar Purkinje neuron. Human pathology shows massive or subtotal Purkinje-cell loss, molecular-layer atrophy, and p62/ubiquitin inclusions. One family showed inclusions in cerebellum, neocortex, and brainstem; another case had broader thalamic/brainstem degeneration, demonstrating pathological heterogeneity. (mol2020clinicalandpathologic pages 1-2, gorcenco2024clinicalandgenetic pages 9-9, roux2020clinicalneuropathologicaland pages 1-2)

Suggested Cell Ontology mappings include Purkinje cell (CL:0000121), cerebellar granule cell, neuron, astrocyte, and peripheral sensory/motor neuron where clinically implicated. Suggested GO cellular components include cytosol, nucleus, proteasome complex, autophagosome, mitochondrion, neuronal soma, and Purkinje-cell dendritic arbor. CHIP normally has polarized somatodendritic expression; pathogenic missense variants can cause distal dendritic mislocalization.

Molecular profiling and advanced technologies

No replicated patient-derived SCA48 transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, or multi-omic diagnostic signature was identified through 2024. Functional evidence instead comes from recombinant biochemistry, transfected neuronal/cell systems, neuropathology, and animal models. Claims about immune activation, systemic metabolism, mTOR, Wnt, MAPK, or PI3K-AKT as core SCA48 pathways would presently be speculative.

7. Anatomical structures affected

Primary organ/system: central nervous system, especially cerebellum.
Primary sites: cerebellar cortex, vermis, paravermis, hemispheres, lobules VI–VII, Purkinje-cell layer, molecular layer, and dentate nuclei. Suggested UBERON terms: cerebellum (UBERON:0002037), cerebellar cortex, cerebellar vermis, cerebellar hemisphere, dentate nucleus.
Secondary/variable sites: brainstem, basal ganglia, neocortex, thalamus, hippocampus, spinal/long motor tracts, and peripheral nerves. The 2023 TBP/STUB1 cohort showed significantly reduced brainstem volume; one pathology series found p62-positive inclusions in cerebellum, neocortex, and brainstem. (mol2020clinicalandpathologic pages 1-2, nanetti2023complexataxia‐dementiaphenotype pages 1-2)
Peripheral tissue: length-dependent sensorimotor axonal neuropathy has been objectively demonstrated in an individual case. (zochowski2024caseseriesof pages 3-5)
Subcellular compartments: cytosol and neuronal soma/dendrites; ubiquitin-proteasome and autophagy machinery; nucleus in cases with intranuclear inclusions; mitochondria are biologically plausible through CHIP-regulated mitophagy but not yet a validated human diagnostic compartment.
Lateralization: degeneration is generally bilateral/diffuse, although motor manifestations such as rest tremor, rigidity, or plantar responses may be asymmetric. (zochowski2024caseseriesof pages 3-5)

8. Temporal development

SCA48 usually has insidious, chronic, progressive adult onset, but onset from adolescence to old age is documented. The multicenter mean was 40.0 ± 13.8 years (range 17–74). (roux2020clinicalneuropathologicaland pages 2-3)

A practical, nonvalidated staging framework is:

Preclinical: pathogenic-variant carrier, potentially with focal cerebellar atrophy but no motor ataxia.
Early: cognitive/affective change, subtle gait imbalance, dysarthria, tremor, or psychiatric presentation.
Intermediate: overt gait/limb ataxia, falls, dysarthria, movement disorder, pyramidal signs, and declining executive function.
Advanced: diffuse cerebellar atrophy, severe CCAS/dementia, dysphagia, incontinence, and dependence for daily activities.

The sequence varies: cognitive-affective disease can precede ataxia, whereas other patients first develop gait ataxia or tremor. One STUB1/TBP45 patient progressed from onset at 29 years to full daily dependency by 41, but this severe digenic example should not be generalized to monogenic SCA48. (winter2025tbprepeatexpansion pages 6-10)

No spontaneous remission is expected. No validated annual SARA progression rate, median disease duration, or critical therapeutic window has been established. Presymptomatic cerebellar atrophy suggests that a future disease-modifying intervention may need to begin before overt motor conversion. (genis2018heterozygousstub1mutation pages 1-2)

9. Inheritance and population

Inheritance

Pattern: autosomal dominant; a heterozygous affected individual theoretically transmits the variant to 50% of offspring.
Penetrance: incomplete, age-dependent, and potentially modifier-dependent. An unaffected heterozygous parent at 65 and another carrier at 77 have been described. (winter2025tbprepeatexpansion pages 6-10, roux2020clinicalneuropathologicaland pages 3-4)
Expressivity: highly variable, including cognitive-first, ataxia-first, tremor/parkinsonism-first, and multisystem phenotypes.
De novo disease: established. (umano2022themolecularbasis pages 1-2)
Anticipation: not established for monogenic STUB1 disease. Apparent anticipation can be confounded by ascertainment and TBP repeat inheritance.
Mosaicism: no established germline-mosaicism rate.
Consanguinity: not relevant to typical dominant SCA48, but important when distinguishing biallelic STUB1-related SCAR16.

Epidemiology

No reliable population prevalence, annual incidence, carrier frequency, birth prevalence, or mortality rate exists. The general SCA incidence figure of approximately 1.5/100,000 quoted in the discovery paper applies to the broader SCA group, not SCA48. (genis2018heterozygousstub1mutation pages 1-2)

In a selected multicenter ataxia series, STUB1 variants were found in 30/440 families (approximately 7%); this indicates diagnostic importance among unsolved/dominant ataxias but cannot be converted into general-population prevalence. Patients have been reported across Spain, Italy, France, the Netherlands, Turkey, Belgium, Germany, Britain, Taiwan, China, Korea, Sweden, and Australia, without a confirmed founder population. (zochowski2024caseseriesof pages 3-5, roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 1-2)

The apparent female enrichment (approximately 70–72%) in one cohort is hypothesis-generating; a true sex ratio remains unresolved. (roux2020clinicalneuropathologicaland pages 2-3, roux2020clinicalneuropathologicaland pages 1-2)

10. Diagnostics

Clinical and imaging assessment

Suspect SCA48 in progressive ataxia—especially when accompanied or preceded by executive/behavioral/psychiatric dysfunction, tremor, parkinsonism, chorea, dystonia, or pyramidal signs. Recommended assessment includes:

neurological examination and standardized ataxia rating, preferably SARA;
formal neuropsychological testing emphasizing executive function, verbal fluency, affect, memory, and social cognition;
brain MRI with careful assessment of vermian and hemispheric cerebellar atrophy, lobules VI–VII, dentate nuclei, brainstem, basal ganglia, and white matter;
speech/swallow evaluation, falls and occupational assessment;
EMG/nerve-conduction studies when sensory loss, wasting, areflexia, or pes cavus is present;
EEG only when seizures are suspected.

The diagnostic triad is a compatible progressive phenotype, selective/diffuse cerebellar atrophy, and a causative heterozygous STUB1 variant. (zochowski2024caseseriesof pages 3-5)

Genetic testing algorithm

Exclude acquired/treatable causes of progressive ataxia according to presentation—medication/toxin exposure, alcohol, vitamin E/B12/thiamine deficiency, thyroid disease, autoimmune/paraneoplastic ataxia, infection, neoplasm, and structural disease.
Test common repeat-expansion ataxias appropriate to ancestry and phenotype. In the retrieved cases these included SCA1, 2, 3, 6, 7, 12, 17, Friedreich ataxia, and related loci. (zochowski2024caseseriesof pages 3-5, roux2020clinicalneuropathologicaland pages 1-2)
Use a comprehensive ataxia panel containing STUB1, with single-nucleotide, indel, splice, and copy-number analysis.
If negative or the phenotype is atypical, use WES or preferably WGS, while recognizing that routine exome sequencing can miss repeat expansions, deep intronic variants, and some structural variants.
Confirm candidate variants by Sanger sequencing and perform segregation/de novo testing.
Independently size TBP CAG/CAA repeats, because an intermediate expansion can alter interpretation, penetrance, phenotype, and counseling. (winter2025tbprepeatexpansion pages 6-10, nanetti2023complexataxia‐dementiaphenotype pages 1-2)
Apply ACMG/AMP criteria cautiously. Functional studies can support a VUS but should be integrated with rarity, phenotype, segregation, and de novo evidence.

CMA, karyotype, FISH, and mitochondrial-genome testing are not routine SCA48 confirmation tests, although a broad panel/WGS may assess copy-number and mitochondrial alternatives. RNA sequencing may help resolve splice variants but is not a validated standalone diagnostic.

Differential diagnosis

Important alternatives include SCA17/TBP disease, digenic TBP/STUB1 disease, SCAR16/biallelic STUB1 disease, Huntington disease and phenocopies, frontotemporal dementia, multiple-system atrophy-cerebellar type, RFC1/CANVAS, SCA27B/FGF14 expansion, common polyglutamine SCAs, SPG7, AFG3L2/SCA28, PRKCG/SCA14, mitochondrial ataxias, and acquired immune/toxic/nutritional causes. Biallelic STUB1 disease more often has earlier-onset multisystem ataxia and may include hypogonadism, but phenotypic overlap is substantial.

Screening

There is no newborn or population screening. Once a familial pathogenic variant is established, offer genetics-led cascade testing to adult relatives, with pretest counseling about age-dependent penetrance and uncertain prognosis. Predictive testing in minors is generally inappropriate for a predominantly adult-onset disorder unless a clear childhood medical benefit exists.

11. Outcome and prognosis

SCA48 is chronic and usually progressive. Major morbidity arises from falls, impaired mobility and hand coordination, dysarthria/dysphagia, cognitive-behavioral decline, psychiatric disease, and eventual dependence. Some patients remain mildly affected for years, while severe STUB1/TBP presentations can reach daily dependency within approximately a decade. (winter2025tbprepeatexpansion pages 6-10, zochowski2024caseseriesof pages 3-5)

No SCA48-specific 5- or 10-year survival, life expectancy, standardized disability trajectory, aspiration rate, institutionalization rate, or disease-specific mortality estimate is available. Recovery of lost neurodegenerative function is not expected, although rehabilitation and assistive technology can improve safety and functional compensation.

Potential adverse prognostic features—still unvalidated—include early cognitive/psychiatric disease, extensive cerebellar/brainstem atrophy, intermediate TBP expansion, and multisystem neurological involvement. No fluid biomarker such as neurofilament light has been validated specifically for SCA48.

12. Treatment and current applications

Disease-modifying therapy and trials

There is no approved SCA48-specific disease-modifying drug, gene therapy, ASO, siRNA, cell therapy, or surgical treatment. Searches retrieved no SCA48-specific interventional ClinicalTrials.gov study. Trials of riluzole, varenicline, or N-acetyl-L-leucine in other ataxia genotypes cannot be extrapolated as evidence of SCA48 efficacy.

Current real-world management

Care should be coordinated by neurology, clinical genetics, rehabilitation medicine, neuropsychology/psychiatry, physiotherapy, occupational therapy, speech-language pathology, dietetics, and social services.

Ataxia/falls: balance and coordination training, strength/conditioning, gait aids, home-safety modifications, orthotics, wheelchair assessment, and driving/work review. Suggested NCIT concepts: Physical Therapy; Occupational Therapy; Rehabilitation Therapy.
Dysarthria/dysphagia: speech therapy, communication devices, instrumental swallow assessment, texture modification, nutrition monitoring, and enteral feeding when clinically necessary. Suggested NCIT: Speech Therapy; Swallowing Therapy; Enteral Nutrition.
Tremor/dystonia/parkinsonism: individualized symptomatic trials by a movement-disorder specialist; evidence is anecdotal and no SCA48 response rate is established. Botulinum toxin may be considered for focal dystonia. Suggested NCIT: Pharmacologic Therapy; Botulinum Toxin Therapy.
Spasticity: stretching, physiotherapy, and standard antispasticity agents when functionally useful.
Psychiatric/cognitive disease: neuropsychological evaluation, structured routines, caregiver education, psychotherapy, and conventional treatment of depression, anxiety, psychosis, or behavioral disturbance.
Neuropathy and bladder symptoms: standard neuropathic-pain, foot-care, orthotic, continence, and urological management.
Complication prevention: vaccination and pulmonary care are routine health maintenance, not SCA48-specific therapy; monitor aspiration, malnutrition, fractures, and caregiver strain.

Experimental directions

Mechanistically attractive strategies include restoring CHIP expression or function, enhancing chaperone/proteasome/autophagy capacity, preventing toxic protein accumulation, and targeting modifier pathways. However, CHIP has many substrates and systemic functions, making nonspecific activation or replacement potentially hazardous. The p.Ala52Gly animal work showed that raising normal CHIP can be neuroprotective in experimental systems, but no human efficacy or safety evidence exists. (umano2022themolecularbasis pages 1-2)

No SCA48 pharmacogenomic guidance, combination regimen, treatment response rate, or disease-specific adverse-event dataset is available.

13. Prevention

Primary prevention: the germline mutation cannot be prevented by lifestyle or vaccination. Reproductive options after identification of a familial pathogenic variant include preimplantation genetic testing, prenatal diagnosis, donor gametes, and adoption, following nondirective counseling.
Secondary prevention/early detection: cascade testing of adult relatives; baseline neurological, cognitive, and MRI assessment where appropriate; periodic follow-up of confirmed carriers. There is no evidence-based surveillance interval.
Tertiary prevention: fall prevention, exercise and rehabilitation, aspiration/nutrition surveillance, psychiatric treatment, bone-health measures, assistive devices, and caregiver support.
Public health: no population, newborn, infectious, or environmental-control program is indicated.

Counseling must address the nominal 50% transmission risk, incomplete and age-dependent penetrance, variable severity, possible de novo disease, and the potential influence of TBP alleles. (winter2025tbprepeatexpansion pages 6-10, nanetti2023complexataxia‐dementiaphenotype pages 1-2, roux2020clinicalneuropathologicaland pages 3-4)

14. Other species and natural disease

No well-established naturally occurring SCA48-equivalent disease in companion animals, livestock, or wildlife was identified. Accordingly, no breed-specific VBO annotation, veterinary prevalence, zoonotic potential, or cross-species transmission applies.

The STUB1/CHIP proteostasis function is strongly conserved, supporting comparative experimental work. Relevant taxa include Homo sapiens (NCBI Taxon 9606), Mus musculus (10090), Danio rerio (7955), Caenorhabditis elegans (6239), and common cultured human-cell systems. This is inherited molecular disease, not transmissible disease.

15. Model organisms

Zebrafish

A Danio rerio stub1 mutant truncating the CHIP U-box showed impaired ubiquitination of HSC70 and CHIP, decreased brain 26S-proteasome activity, reduced Purkinje-cell number and soma size, abnormal Purkinje dendrites, and behavioral changes. It did not show gross cerebellar atrophy, an important limitation relative to human disease. (pakdaman2021chipproteinubox pages 1-2)

Abstract quotation: “no gross cerebellar atrophy was evident in mutant fish,” but the fish displayed reduced Purkinje-cell number/size and abnormal dendritic organization. (pakdaman2021chipproteinubox pages 1-2)

C. elegans

Transgenic expression of human CHIP p.Ala52Gly produced neurodegeneration and constituted an initial variant-specific SCA48 animal model. The model is useful for stress sensitivity and modifier screening but lacks a vertebrate cerebellum and cannot reproduce CCAS or human MRI anatomy. (umano2022themolecularbasis pages 1-2)

Mouse and developmental systems

Manipulation of CHIP expression affected differentiation and migration of cerebellar granule-neuron progenitors. This supports a role in cerebellar development and neuronal homeostasis but does not by itself reproduce the full adult-onset dominant human syndrome. (chen2021clinicalandfunctional pages 1-2)

Cellular and biochemical models

Recombinant-protein assays, HEK293 and neuronal systems, minigene assays, ubiquitination assays, protein-stability studies, and apoptosis assays have been used to classify variants and dissect TPR-versus-U-box dysfunction. These models demonstrate defective chaperone affinity, E2 interaction, ubiquitination, protein stability, tau/α-synuclein accumulation, and caspase activation. Their limitation is that overexpression and acute stress may not reflect decades-long human Purkinje-cell disease. (chen2021clinicalandfunctional pages 1-2, umano2022themolecularbasis pages 1-2, li2024clinicalandfunctional pages 1-2)

Evidence appraisal and major knowledge gaps

The human genetic association is strong: cosegregation in multiple pedigrees, independent pathogenic variants, de novo occurrences, consistent cerebellar phenotypes, and convergent functional evidence. The principal unresolved issue is not whether monoallelic STUB1 can cause SCA48, but why penetrance and phenotype vary so markedly and how often TBP or other alleles materially modify disease.

Highest-priority research needs are an international genotype-curated registry; prospective SARA, cognitive, speech/swallow, digital-gait, and MRI natural history; penetrance estimates stratified by variant domain, age, sex, and TBP repeat size; validated fluid/imaging biomarkers; patient-reported quality-of-life studies; and faithful mammalian knock-in models. The 2024 monogenic case series and Chinese functional study strengthened variant interpretation, but neither supplies population epidemiology or treatment evidence. (zochowski2024caseseriesof pages 3-5, li2024clinicalandfunctional pages 1-2)

Key publication details

Genis et al., published online October 31, 2018, Neurology, DOI/URL: https://doi.org/10.1212/WNL.0000000000006550 — discovery pedigree and OMIM 618093. (genis2018heterozygousstub1mutation pages 1-2)
Roux et al., accepted June 26, 2020, Genetics in Medicine, DOI/URL: https://doi.org/10.1038/s41436-020-0899-x — 440-family cohort and neuropathology. (roux2020clinicalneuropathologicaland pages 1-2)
Mol et al., June 2020, Neurology Genetics, DOI/URL: https://doi.org/10.1212/NXG.0000000000000417 — large pedigree and ubiquitin/p62 inclusions. (mol2020clinicalandpathologic pages 1-2)
Chen et al., September 2021, Journal of Biomedical Science, DOI/URL: https://doi.org/10.1186/s12929-021-00763-1 — dominant-negative U-box mechanism. (chen2021clinicalandfunctional pages 1-2)
Pakdaman et al., September 24, 2021, Frontiers in Molecular Neuroscience, DOI/URL: https://doi.org/10.3389/fnmol.2021.723912 — zebrafish model. (pakdaman2021chipproteinubox pages 1-2)
Umano et al., published online April 7, 2022, Journal of Biological Chemistry, DOI/URL: https://doi.org/10.1016/j.jbc.2022.101899 — p.Ala52Gly biochemical and C. elegans model. (umano2022themolecularbasis pages 1-2)
Nanetti et al., published online February 17, 2023, Movement Disorders, DOI/URL: https://doi.org/10.1002/mds.29352 — digenic TBP/STUB1 phenotype. (nanetti2023complexataxia‐dementiaphenotype pages 1-2)
Li et al., 2024, Orphanet Journal of Rare Diseases 19:471, DOI/URL: https://doi.org/10.1186/s13023-024-03456-8 — Chinese pedigree and p.Tyr252Ser functional study. (li2024clinicalandfunctional pages 1-2)
Zochowski et al., December 2024, Cerebellum, DOI/URL: https://doi.org/10.1007/s12311-024-01762-2 — three cases without TBP expansions. (zochowski2024caseseriesof pages 3-5)

PMIDs were not present in the retrieved full-text metadata and are therefore not supplied speculatively; the DOI URLs above provide stable primary-source resolution.

References

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(zochowski2024caseseriesof pages 3-5): Yan Zochowski, Kishore R. Kumar, Matthew Katz, Paul Darveniza, Michel Tchan, Renee Smyth, Susan Tomlinson, Kathy H. C. Wu, and Stephen Tisch. Case series of cerebellar ataxia with tremor due to heterozygous stub1 variants (sca48) without tbp expansions: further evidence for sca48 as a monogenic disease. Cerebellum (London, England), Dec 2024. URL: https://doi.org/10.1007/s12311-024-01762-2, doi:10.1007/s12311-024-01762-2. This article has 4 citations.
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(umano2022themolecularbasis pages 1-2): A. Umano, K. Fang, Z. Qu, J.B. Scaglione, S. Altinok, C.J. Treadway, E.T. Wick, E. Paulakonis, C. Karunanayake, S. Chou, T.M. Bardakjian, P. Gonzalez-Alegre, R.C. Page, J.C. Schisler, N.G. Brown, D. Yan, and K.M. Scaglione. The molecular basis of spinocerebellar ataxia type 48 caused by a de novo mutation in the ubiquitin ligase chip. May 2022. URL: https://doi.org/10.1016/j.jbc.2022.101899, doi:10.1016/j.jbc.2022.101899. This article has 18 citations and is from a domain leading peer-reviewed journal.
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(roux2020clinicalneuropathologicaland pages 3-4): Thomas Roux, Mathieu Barbier, Mélanie Papin, Claire-Sophie Davoine, Sabrina Sayah, Giulia Coarelli, Perrine Charles, Cecilia Marelli, Livia Parodi, Christine Tranchant, Cyril Goizet, Stephan Klebe, Ebba Lohmann, Lionel Van Maldergem, Christine van Broeckhoven, Marie Coutelier, Christelle Tesson, Giovanni Stevanin, Charles Duyckaerts, Alexis Brice, Alexandra Durr, Alexandra Durr, Giovanni Stevanin, Alexis Brice, Frédéric Darios, Sylvie Forlani, Pitié-Salpêtrière Site, Guillaume Banneau, Cécile Cazeneuve, Perrine Charles, Charles Duyckaerts, Bertrand Fontaine, Jean-Philippe Azulay, Odile Boesfplug-Tanguy, Cyril Goizet, Didier Hannequin, Jamilé Hazan, Andrea Burgo, Christophe Verny, Michel Koenig, Pierre Labauge, Cecilia Marelli, Karine N’guyen, Diana Rodriguez, Soraya Belarbi, Abdelmadjid Hamri, Meriem Tazir, Sylvia Boesch, Massimo Pandolfo, Jardim Laura, Velina Guergueltcheva, Ivalo Tournev, Olga Lucia Pedraza Linarès, Jørgen E. Nielsen, Kirsten Svenstrup, Maha Zaki, Peter Bauer, Lüdger Schöls, Rebecca Schüle, Alexander Lossos, Maria-Teresa Bassi, Manuela Basso, Enrico Bertini, Alfredo Brusco, Carlo Casali, Giorgio Casari, Chiara Criscuolo, Alessandro Filla, Laura Orsi, Filippo M. Santorelli, Enza Maria Valente, Marinela Vavla, Giovanni Vazza, André Megarbane, Ali Benomar, Berry Kremer, Willeke Van Roon-Mom, Richard Roxburgh, Anne Kjersti Erichsen, Chantal Tallaksen, Isabel Alonso, Paula Coutinho, José Léal Loureiro, Jorge Sequeiros, Mustapha Salih, Vladimir S. Kostic, Idoia Rouco Axpe, Liena Elsayed, Martin Arce Paucar, Samir Roumani, Soong Bing-Wen, Evan Reid, Nethisinghe Suran, Thomas Warner, and Nicholas Wood. Clinical, neuropathological, and genetic characterization of stub1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment. Nov 2020. URL: https://doi.org/10.1038/s41436-020-0899-x, doi:10.1038/s41436-020-0899-x. This article has 54 citations and is from a highest quality peer-reviewed journal.
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Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

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Genetic Associations

Medical Actions

Diagnosis

Imaging Findings

Prevalence

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Spinocerebellar Ataxia Type 48 (SCA48): Disease-Characteristics Report

Executive summary

1. Disease information

Definition

Identifiers and nomenclature

Evidence granularity

2. Etiology, risk, and protective factors

Primary cause

Genetic risk and modifiers

Environmental, lifestyle, infectious, and protective factors

3. Phenotypes

4. Genetic and molecular information

Gene and protein

Variant spectrum and interpretation

Mode of action

5. Environmental information

6. Mechanism and pathophysiology

Ordered causal chain

Cellular and tissue mechanisms

Molecular profiling and advanced technologies

7. Anatomical structures affected

8. Temporal development

9. Inheritance and population

Inheritance

Epidemiology

10. Diagnostics

Clinical and imaging assessment

Genetic testing algorithm

Differential diagnosis

Screening

11. Outcome and prognosis

12. Treatment and current applications

Disease-modifying therapy and trials

Current real-world management

Experimental directions

13. Prevention

14. Other species and natural disease

15. Model organisms

Zebrafish

C. elegans

Mouse and developmental systems

Cellular and biochemical models

Evidence appraisal and major knowledge gaps

Key publication details

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