Spinocerebellar Ataxia Type Research Articles

Long-Term Follow-Up before and during Riluzole Treatment in Six Patients from Two Families with Spinocerebellar Ataxia Type 7.

Currently no curative treatment exists for spinocerebellar ataxias (SCAs). Riluzole repurposing was proposed as a symptomatic treatment in different types of cerebellar ataxia. We report a long-term-follow up under riluzole treatment in SCA type 7. Six patients received Riluzole 50mg twice daily on a compassionate use program for a mean of 4.8 years (range 3.5-9). We measured ataxia onset and progression through the Scale for the Assessment and Rating of Ataxia (SARA), and collected extensive ophthalmological data before and after Riluzole treatment. Electrocardiogram and laboratory profile for drug safety were performed every six months. Riluzole treatment showed no effect on visual function in two patients with an advanced retinal damage. Improvements of visual function occurred in four patients followed by ophthalmologic stability up to 5 years after starting treatment. Two patients had a less steep deterioration of ataxia after treatment compared to pre-treatment, during the first 2,5 years of therapy. One showed soon after therapy an improvement of the SARA score, and then overall stability lasting 3,5 years, followed by ataxia worsening. One visually impaired patient without neurological impairment did not worse until the last visit after 3,5 years of follow-up. The remaining 2 patients showed an improvement of SARA scores soon after therapy, and an overall stability lasting respectively 5 and 3 years. No adverse event was registered during the observation period. This study suggests a possible beneficial action of Riluzole in SCA7 and provides a detailed description of the ophthalmologic profile of these patients.

Spinocerebellar ataxia type 27B (SCA27B) in India: insights from a large cohort study suggest ancient origin.

The ethnic diversity of India provides a unique opportunity to study the history of the origin of mutations of genetic disorders. Spinocerebellar ataxia type 27B (SCA27B), a recently identified dominantly inherited cerebellar disorder is caused by GAA-repeat expansions in intron 1 of Fibroblast Growth Factor 14 (FGF14). Predominantly reported in the European population, we aimed to screen this mutation and study the founder haplotype of SCA27B in Indian ataxia patients. We have undertaken screening of GAA repeats in a large Indian cohort of ~ 1400 uncharacterised ataxia patients and kindreds and long-read sequencing-based GAA repeat length assessment. High throughput genotyping-based haplotype analysis was also performed. We utilized ~ 1000 Indian genomes to study the GAA at-risk expansion alleles. We report a high frequency of 1.83% (n = 23) of SCA27B in the uncharacterized Indian ataxia cohort. We observed several biallelic GAA expansion mutations (n = 5) with younger disease onset. We observed a risk haplotype (AATCCGTGG) flanking the FGF14-GAA locus over a 74kb region in linkage disequilibrium. We further studied the frequency of this risk haplotype across diverse geographical population groups. The highest prevalence of the risk haplotype was observed in the European population (29.9%) followed by Indians (21.5%). The observed risk haplotype has existed through ~ 1100 generations (~ 22,000 years), assuming a correlated genealogy. This study provides valuable insights into SCA27B and its Upper Paleolithic origin in the Indian subcontinent. The high occurrence of biallelic expansion is probably relevant to the endogamous nature of the Indian population.

Spinocerebellar ataxia type 4 is caused by a GGC expansion in the ZFHX3 gene and is associated with prominent dysautonomia and motor neuron signs.

Spinocerebellar ataxia 4 (SCA4), characterized in 1996, features adult-onset ataxia, polyneuropathy, and linkage to chromosome 16q22.1; its underlying mutation has remained elusive. To explore the radiological and neuropathological abnormalities in the entire neuroaxis in SCA4 and search for its mutation. Three Swedish families with undiagnosed ataxia went through clinical, neurophysiological, and neuroimaging tests, including PET studies and genetic investigations. In four cases, neuropathological assessments of the neuroaxis were performed. Genetic testing included short read whole genome sequencing, short tandem repeat analysis with ExpansionHunter de novo, and long read sequencing. Novel features for SCA4 include dysautonomia, motor neuron affection, and abnormal eye movements. We found evidence of anticipation; neuroimaging demonstrated atrophy in the cerebellum, brainstem, and spinal cord. [18F]FDG-PET demonstrated brain hypometabolism and [11C]Flumazenil-PET reduced binding in several brain lobes, insula, thalamus, hypothalamus, and cerebellum. Moderate to severe loss of Purkinje cells in the cerebellum and of motor neurons in the anterior horns of the spinal cord along with pronounced degeneration of posterior tracts was also found. Intranuclear, mainly neuronal, inclusions positive for p62 and ubiquitin were sparse but widespread in the CNS. This finding prompted assessment for nucleotide expansions. A polyglycine stretch encoding GGC expansions in the last exon of the zink finger homeobox 3 gene was identified segregating with disease and not found in 1000 controls. SCA4 is a neurodegenerative disease caused by a novel GGC expansion in the coding region of ZFHX3, and its spectrum is expanded to include dysautonomia and neuromuscular manifestations.

STUB1 Mutations as Possible Genetic Modifiers in Spinocerebellar Ataxia Type 8.

Spinocerebellar ataxia type 8 (SCA8) is a dominantly inherited expansion disorder with highly variable penetrance. ATXN8OS/ATXN8 expanded alleles have been identified in association with other types of hereditary ataxias, pointing to a possible genetic synergism. We aimed to further investigate the molecular background of patients with SCA8 diagnosis. Patients were selected from our cohort of 346 families. A total of 14 probands with SCA8 underwent additional investigation through exome sequencing. Pathogenic heterozygous STUB1 variants were found in 21.4% of SCA8 patients (3 of 14) compared to only 0.5% in the non-SCA8 group (1 of 222), indicating a statistically significant association (P < 0.05). The findings reported in this study might suggest a genetic synergism between STUB1 and ATXN8OS/ATXN8 expanded alleles. Further studies are needed to validate this observation and better define the clinical impact of this genetic interaction. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Ensemble of HMMs for Sequence Prediction on Multivariate Biomedical Data

Background: Biomedical data are usually collections of longitudinal data assessed at certain points in time. Clinical observations assess the presences and severity of symptoms, which are the basis for the description and modeling of disease progression. Deciphering potential underlying unknowns from the distinct observation would substantially improve the understanding of pathological cascades. Hidden Markov Models (HMMs) have been successfully applied to the processing of possibly noisy continuous signals. We apply ensembles of HMMs to categorically distributed multivariate time series data, leaving space for expert domain knowledge in the prediction process. Methods: We use an ensemble of HMMs to predict the loss of free walking ability as one major clinical deterioration in the most common autosomal dominantly inherited ataxia disorder worldwide. Results: We present a prediction pipeline that processes data paired with a configuration file, enabling us to train, validate and query an ensemble of HMMs. In particular, we provide a theoretical and practical framework for multivariate time-series inference based on HMMs that includes constructing multiple HMMs, each to predict a particular observable variable. Our analysis is conducted on pseudo-data, but also on biomedical data based on Spinocerebellar ataxia type 3 disease. Conclusions: We find that the model shows promising results for the data we tested. The strength of this approach is that HMMs are well understood, probabilistic and interpretable models, setting it apart from most Deep Learning approaches. We publish all code and evaluation pseudo-data in an open-source repository.

Trehalose prevents the formation of aggregates of mutant ataxin-3 and reduces soluble ataxin-3 protein levels in an SCA3 cell model

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder caused by mutant ataxin-3 with an abnormally expanded polyQ tract and is the most common dominantly inherited ataxia worldwide. There are no suitable therapeutic options for this disease. Autophagy, a defense mechanism against the toxic effects of aggregation-prone misfolded proteins, has been shown to have beneficial effects on neurodegenerative diseases. Thus, trehalose, which is an autophagy inducer, may have beneficial effects on SCA3. In the present study, we examined the effects of trehalose on an SCA3 cell model. After trehalose treatment, aggregate formation, soluble ataxin-3 protein levels and cell viability were evaluated in HEK293T cells overexpressing ataxin-3-15Q or ataxin-3-77Q. We also explored the mechanism by which trehalose affects autophagy and stress pathways. A filter trap assay showed that trehalose decreased the number of aggregates formed by mutant ataxin-3 containing an expanded polyQ tract. Western blot and Cell Counting Kit-8 (CCK-8) results demonstrated that trehalose also reduced the ataxin-3 protein levels and was safe for ataxin-3-expressing cells, respectively. Western blot and total antioxidant capacity assays suggested that trehalose had great therapeutic potential for treating SCA3, likely through its antioxidant activity. Our data indicate that trehalose plays a neuroprotective role in SCA3 by inhibiting the aggregation and reducing the protein level of ataxin-3, which is also known to protect against oxidative stress. These findings provide a new insight into the possibility of treating SCA3 with trehalose and highlight the importance of inducing autophagy in SCA3.

Exploring functional and structural connectivity disruptions in spinocerebellar ataxia type 3: Insights from gradient analysis.

Spinocerebellar Ataxia Type 3 (SCA3) is a rare genetic ataxia that impacts the entire brain and is characterized as a neurodegenerative disorder affecting the neural network. This study explores how alterations in the functional hierarchy, connectivity, and structural changes within specific brain regions significantly contribute to the heterogeneity of symptom manifestations in patients with SCA3. We prospectively recruited 51 patients with SCA3 and 59 age-and sex-matched healthy controls. All participants underwent comprehensive multimodal neuroimaging and clinical assessments. In SCA3 patients, an innovative approach utilizing gradients in resting-state functional connectivity (FC) was employed to examine atypical patterns of hierarchical processing topology from sensorimotor to supramodal regions in the cerebellum and cerebrum. Coupling analyses of abnormal FC and structural connectivity among regions of interest (ROIs) in the brain were also performed to characterize connectivity alterations. Additionally, relationships between quantitative ROI values and clinical variables were explored. Patients with SCA3 exhibited either compression or expansion within the primary sensorimotor-to-supramodal gradient through four distinct calculation methods, along with disruptions in FC and structural connectivity coupling. A comprehensive correlation was identified between the altered gradients and the clinical manifestations observed in patients. Notably, altered fractional anisotropy values were not significantly correlated with clinical variables. Abnormal gradients and connectivity in the cerebellar and cerebral cortices in SCA3 patients may contribute to disrupted motor-to-supramodal functions. Moreover, these findings support the potential utility of FCG analysis as a biomarker for diagnosing SCA3 and assessing treatment efficacy.

Antibody-assisted selective isolation of Purkinje cell nuclei from mouse cerebellar tissue

We developed a method that utilizes fluorescent labeling of nuclear envelopes alongside cytometry sorting for the selective isolation of Purkinje cell (PC) nuclei. Beginning with SUN1 reporter mice, we GFP-tagged envelopes to confirm that PC nuclei could be accurately separated from other cell types. We then developed an antibody-based protocol to make PC nuclear isolation more robust and adaptable to cerebellar tissues of any genotypic background. Immunofluorescent labeling of the nuclear membrane protein RanBP2 enabled the isolation of PC nuclei from C57BL/6 cerebellum. By analyzing the expression of PC markers, nuclear size, and nucleoli number, we confirmed that our method delivers a pure fraction of PC nuclei. To demonstrate its applicability, we isolated PC nuclei from spinocerebellar ataxia type 7 (SCA7) mice and identified transcriptional changes in known and new disease-associated genes. Access to pure PC nuclei offers insights into PC biology and pathology, including the nature of selective neuronal vulnerability.

Production of Spinocerebellar Ataxia Type 3 Model Mice by Intravenous Injection of AAV-PHP.B Vectors.

We aimed to produce a mouse model of spinocerebellar ataxia type 3 (SCA3) using the mouse blood-brain barrier (BBB)-penetrating adeno-associated virus (AAV)-PHP.B. Four-to-five-week-old C57BL/6 mice received injections of high-dose (2.0 × 1011 vg/mouse) or low-dose (5.0 × 1010 vg/mouse) AAV-PHP.B encoding a SCA3 causative gene containing abnormally long 89 CAG repeats [ATXN3(Q89)] under the control of the ubiquitous chicken β-actin hybrid (CBh) promoter. Control mice received high doses of AAV-PHP.B encoding ATXN3 with non-pathogenic 15 CAG repeats [ATXN3(Q15)] or phosphate-buffered saline (PBS) alone. More than half of the mice injected with high doses of AAV-PHP.B encoding ATXN3(Q89) died within 4 weeks after the injection. No mice in other groups died during the 12-week observation period. Mice injected with low doses of AAV-PHP.B encoding ATXN3(Q89) exhibited progressive motor uncoordination starting 4 weeks and a shorter stride in footprint analysis performed at 12 weeks post-AAV injection. Immunohistochemistry showed thinning of the molecular layer and the formation of nuclear inclusions in Purkinje cells from mice injected with low doses of AAV-PHP.B encoding ATXN3(Q89). Moreover, ATXN3(Q89) expression significantly reduced the number of large projection neurons in the cerebellar nuclei to one third of that observed in mice expressing ATXN3(Q15). This AAV-based approach is superior to conventional methods in that the required number of model mice can be created simply by injecting AAV, and the expression levels of the responsible gene can be adjusted by changing the amount of AAV injected. Moreover, this method may be applied to produce SCA3 models in non-human primates.

Whole Exome Sequencing Indicating GGCCTG Hexanucleotide Repeat in Patients with Spinocerebellar Ataxia Type 36

Introduction: Spinocerebellar ataxia type 36 (SCA36) is caused by large GGCCTG repeat expansion in the NOP56 gene. The genetic diagnosis based on Southern blot is expensive and time-consuming. This study aimed to evaluate the reliability and effectiveness of whole exome sequencing (WES) for routine genetic diagnosis of suspected SCA36 patients. Methods: Pathogenic repeat expansions for SCAs including SCA36 were first analyzed based on WES data using ExpansionHunter in five probands from SCA families, then the results were confirmed by triplet repeat primed polymerase chain reaction (TP-PCR) and Southern blot. Results: GGCCTG repeat expansion in NOP56 was indicated in all five probands by WES, then it was found in 11 SCA patients and three asymptomatic individuals by TP-PCR. The sizes of GGCCTG repeat expansions were confirmed to be 1,390–1,556 by Southern blot. The mean age at onset of the patients was 51.0 ± 9.3 (ranging from 41 to 71), and they presented slowly progressive cerebellar ataxia, atrophy and fasciculation in tongue or limb muscles. Conclusion: The patients were clinically and genetically diagnosed as SCA36. This study proposed that WES could be a rapid, reliable, and cost-effective routine test for the preliminarily detection of SCA36 and other ataxia diseases.

Imbalanced optimal feedback motor control system in spinocerebellar ataxia type 3.

Human motor planning and control depend highly on optimal feedback control systems, such as the neocortex-cerebellum circuit. Here, diffusion tensor imaging was used to verify the disruption of the neocortex-cerebellum circuit in spinocerebellar ataxia type 3 (SCA3), and the circuit's disruption correlation with SCA3 motor dysfunction was investigated. This study included 45 patients with familial SCA3, aged 17-67 years, and 49 age- and sex-matched healthy controls, aged 21-64 years. Tract-based spatial statistics and probabilistic tractography was conducted using magnetic resonance images of the patients and controls. The correlation between the local probability of probabilistic tractography traced from the cerebellum and clinical symptoms measured using specified symptom scales was also calculated. The cerebellum-originated probabilistic tractography analysis showed that structural connectivity, mainly in the subcortical cerebellar-thalamo-cortical tract, was significantly reduced and the cortico-ponto-cerebellar tract was significantly stronger in the SCA3 group than in the control group. The enhanced tract was extended to the right lateral parietal region and the right primary motor cortex. The enhanced neocortex-cerebellum connections were highly associated with disease progression, including duration and symptomatic deterioration. Tractography probabilities from the cerebellar to parietal and sensorimotor areas were significantly negatively correlated with motor abilities in patients with SCA3. To our knowledge, this study is the first to reveal that disrupting the neocortex-cerebellum loop can cause SCA3-induced motor dysfunctions. The specific interaction between the cerebellar-thalamo-cortical and cortico-ponto-cerebellar pathways in patients with SCA3 and its relationship with ataxia symptoms provides a new direction for future research.

Progressive degeneration in a new Drosophila model of spinocerebellar ataxia type 7

Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder resulting from abnormal expansion of an uninterrupted polyglutamine (polyQ) repeat in its disease protein, ataxin-7 (ATXN7). ATXN7 is part of Spt-Ada-Gcn5 acetyltransferase (SAGA), an evolutionarily conserved transcriptional coactivation complex with critical roles in chromatin remodeling, cell signaling, neurodifferentiation, mitochondrial health and autophagy. SCA7 is dominantly inherited and characterized by genetic anticipation and high repeat-length instability. Patients with SCA7 experience progressive ataxia, atrophy, spasticity, and blindness. There is currently no cure for SCA7, and therapies are aimed at alleviating symptoms to increase quality of life. Here, we report novel Drosophila lines of SCA7 with polyQ repeats in wild-type and human disease patient range. We find that ATXN7 expression has age- and polyQ repeat length-dependent reduction in fruit fly survival and retinal instability, concomitant with increased ATXN7 protein aggregation. These new lines will provide important insight on disease progression that can be used in the future to identify therapeutic targets for SCA7 patients.

Cerebral cortical functional hyperconnectivity in a mouse model of spinocerebellar ataxia type 8 (SCA8).

Spinocerebellar Ataxia Type 8 (SCA8) is an inherited neurodegenerative disease caused by a bidirectionally expressed CTG●CAG expansion mutation in the ATXN-8 and ATXN8-OS genes. While primarily a motor disorder, psychiatric and cognitive symptoms have been reported. It is difficult to elucidate how the disease alters brain function in areas with little or no degeneration producing both motor and cognitive symptoms. Using transparent polymer skulls and CNS-wide GCaMP6f expression, we studied neocortical networks throughout SCA8 progression using wide-field Ca2+ imaging in a transgenic mouse model of SCA8. We observed that neocortical networks in SCA8+ mice were hyperconnected globally which led to network configurations with increased global efficiency and centrality. At the regional level, significant network changes occurred in nearly all cortical regions, however mainly involved sensory and association cortices. Changes in functional connectivity in anterior motor regions worsened later in the disease. Near perfect decoding of animal genotype was obtained using a generalized linear model based on canonical correlation strengths between activity in cortical regions. The major contributors to decoding were concentrated in the somatosensory, higher visual and retrosplenial cortices and occasionally extended into the motor regions, demonstrating that the areas with the largest network changes are predictive of disease state.

Endosome mediated nucleocytoplasmic trafficking and endomembrane allocation is crucial to polyglutamine toxicity

Aggregation of aberrant proteins is a common pathological hallmark in neurodegeneration such as polyglutamine (polyQ) and other repeat-expansion diseases. Here through overexpression of ataxin3 C-terminal polyQ expansion in Drosophila gut enterocytes, we generated an intestinal obstruction model of spinocerebellar ataxia type3 (SCA3) and reported a new role of nuclear-associated endosomes (NAEs)–the delivery of polyQ to the nucleoplasm. In this model, accompanied by the prominently increased RAB5-positive NAEs are abundant nucleoplasmic reticulum enriched with polyQ, abnormal nuclear envelope invagination, significantly reduced endoplasmic reticulum, indicating dysfunctional nucleocytoplasmic trafficking and impaired endomembrane organization. Consistently, Rab5 but not Rab7 RNAi further decreased polyQ-related NAEs, inhibited endomembrane disorganization, and alleviated disease model. Interestingly, autophagic proteins were enriched in polyQ-related NAEs and played non-canonical autophagic roles as genetic manipulation of autophagic molecules exhibited differential impacts on NAEs and SCA3 toxicity. Namely, the down-regulation of Atg1 or Atg12 mitigated while Atg5 RNAi aggravated the disease phenotypes both in Drosophila intestines and compound eyes. Our findings, therefore, provide new mechanistic insights and underscore the fundamental roles of endosome-centered nucleocytoplasmic trafficking and homeostatic endomembrane allocation in the pathogenesis of polyQ diseases.Graphical

Lexical associations in patients with neurodegenerative disorders. Two case studies: A patient with spinocerebellar ataxia type 1 (SCA-1) and a patient with Parkinson’s disease (PD

This article presents case studies of the relative ability of two subjects (OB1 and OB2) to make lexical associations; they have spinocerebellar ataxia type 1 and Parkinson’s disease, respectively. Test method: subjects gave associations (orally, with no time limit) to 63 verbal stimuli presented on a computer screen. Verbal stimuli were selected from Gatkowska’s experimental study (Gatkowska 2017). Responses were recorded on an Olympus 650 digital voice recorder, then analysed linguistically and psychologically. Results: psychological analysis – subjects within intellectual norm (Raven’s Matrices test), dysarthric disorder, difficulty in implementing instructions. Linguistic analysis: OB1 – predominance of paradigmatic relations (hyponymy, meronymy, synonymy) over syntagmatic relations (diffi culty building context), lack of causality. OB2 – richer paradigmatic relations (hyponymy, meronymy, synonymy, antonymy, complementarity), syntagmatic relations diverse. Conclusions: possible complex background of language disorders (executive, emotional), higher level of language functioning of OB2 compared to OB1. The study illustrates the need for an interdisciplinary and holistic approach in diagnostic and therapeutic management.

Careful Phenotypic Characterization of Tremor Phenomenology in a Patient with Spinocerebellar Ataxia Type 12-Tremor Features Do Not Match Those of Essential Tremor

Careful Phenotypic Characterization of Tremor Phenomenology in a Patient with Spinocerebellar Ataxia Type 12-Tremor Features Do Not Match Those of Essential Tremor

SCAR32: Functional characterization and expansion of the clinical-genetic spectrum.

Biallelic mutations in PRDX3 have been linked to autosomal recessive spinocerebellar ataxia type 32. In this study, which aims to contribute to the growing body of knowledge on this rare disease, we identified two unrelated patients with mutations in PRDX3. We explored the impact of PRDX3 mutation in patient skin fibroblasts and the role of the gene in neurodevelopment. We performed trio exome sequencing that identified mutations in PRDX3 in two unrelated patients. We also performed functional studies in patient skin fibroblasts and generated a "crispant" zebrafish (Danio rerio) model to investigate the role of the gene during nervous system development. Our study reports two additional patients. Patient 1 is a 19-year-old male who showed a novel homozygous c.525_535delGTTAGAAGGTT (p. Leu176TrpfsTer11) mutation as the genetic cause of cerebellar ataxia. Patient 2 is a 20-year-old male who was found to present the known c.425C>G/p. Ala142Gly variant in compound heterozygosity with the p. Leu176TrpfsTer11 one. While the fibroblast model failed to recapitulate the pathological features associated with PRDX3 loss of function, our functional characterization of the prdx3 zebrafish model revealed motor defects, increased susceptibility to reactive oxygen species-triggered apoptosis, and an impaired oxygen consumption rate. We identified a new variant, thereby expanding the genetic spectrum of PRDX3-related disease. We developed a novel zebrafish model to investigate the consequences of prdx3 depletion on neurodevelopment and thus offered a potential new tool for identifying new treatment opportunities.

Extended haplotype with rs41524547-G defines the ancestral origin of SCA10.

Spinocerebellar ataxia type 10 (SCA10) is a rare autosomal dominant ataxia caused by a large expansion of the (ATTCT)n repeat in ATXN10. SCA10 was described in Native American and Asian individuals which prompted a search for an expanded haplotype to confirm a common ancestral origin for the expansion event. All patients with SCA10 expansions in our cohort share a single haplotype defined at the 5'-end by the minor allele of rs41524547, located ~35kb upstream of the SCA10 expansion. Intriguingly, rs41524547 is located within the miRNA gene, MIR4762, within its DROSHA cleavage site and just outside the seed sequence for mir4792-5p. The world-wide frequency of rs41524547-G is less than 5% and found almost exclusively in the Americas and East Asia-a geographic distribution that mirrors reported SCA10 cases. We identified rs41524547-G(+) DNA from the 1000 Genomes/International Genome Sample Resource and our own general population samples and identified SCA10 repeat expansions in up to 25% of these samples. The reduced penetrance of these SCA10 expansions may be explained by a young (pre-onset) age at sample collection, a small repeat size, purity of repeat units, or the disruption of miR4762-5p function. We conclude that rs41524547-G is the most robust at-risk SNP allele for SCA10, is useful for screening of SCA10 expansions in population genetics studies and provides the most compelling evidence to date for a single, prehistoric origin of SCA10 expansions sometime prior to or during the migration of individuals across the Bering Land Bridge into the Americas.

Disrupted cerebellar structural connectome in spinocerebellar ataxia type 3 and its association with transcriptional profiles

Abstract Spinocerebellar ataxia type 3 (SCA3) is primarily characterized by progressive cerebellar degeneration, including gray matter atrophy and disrupted anatomical and functional connectivity. The alterations of cerebellar white matter structural network in SCA3 and the underlying neurobiological mechanism remain unknown. Using a cohort of 20 patients with SCA3 and 20 healthy controls, we constructed cerebellar structural networks from diffusion MRI and investigated alterations of topological organization. Then, we mapped the alterations with transcriptome data from the Allen Human Brain Atlas to identify possible biological mechanisms for regional selective vulnerability to white matter damage. Compared with healthy controls, SCA3 patients exhibited reduced global and nodal efficiency, along with a widespread decrease in edge strength, particularly affecting edges connected to hub regions. The strength of inter-module connections was lower in SCA3 group and negatively correlated with the Scale for the Assessment and Rating of Ataxia score, International Cooperative Ataxia Rating Scale score, and cytosine–adenine–guanine repeat number. Moreover, the transcriptome–connectome association study identified the expression of genes involved in synapse-related and metabolic biological processes. These findings suggest a mechanism of white matter vulnerability and a potential image biomarker for the disease severity, providing insights into neurodegeneration and pathogenesis in this disease.

Disease Progression and Multiparametric Imaging Characteristics of Spinocerebellar Ataxia Type 3 With Spastic Paraplegia.

Spinocerebellar ataxia type 3 (SCA3) is a hereditary ataxia that occurs worldwide. Clinical patterns were observed, including the one characterized by marked spastic paraplegia. This study investigated the clinical features, disease progression, and multiparametric imaging aspects of patients with SCA3. We retrospectively analyzed 249 patients with SCA3 recruited from the Organization for Southeast China for cerebellar ataxia research between October 2014 and December 2020. Of the 249 patients, 145 were selected and assigned to 2 groups based on neurologic examination: SCA3 patients with spastic paraplegia (SCA3-SP) and SCA3 patients with nonspastic paraplegia (SCA3-NSP). Participants underwent 3.0-T brain MRI examinations, and voxel-wise and volume-of-interest-based approaches were used for the resulting images. A tract-based spatial statistical approach was used to investigate the white matter (WM) alterations using diffusion tensor imaging, neurite orientation dispersion, and density imaging metrics. Multiple linear regression analyses were performed to compare the clinical and imaging parameters between the 2 groups. The longitudinal data were evaluated using a linear mixed-effects model. Forty-three patients with SCA3-SP (mean age, 37.58years ± 11.72 [SD]; 18 women) and 102 patients with SCA3-NSP (mean age, 47.42years ± 12.50 [SD]; 39 women) were analyzed. Patients with SCA3-SP were younger and had a lower onset age but a larger cytosine-adenine-guanine repeat number, as well as higher clinical severity scores (all corrected p < 0.05). The estimated progression rates of the Scale for the Assessment and Rating of Ataxia (SARA) and International Cooperative Ataxia Rating Scale scores were higher in the SCA3-SP subgroup than in the SCA3-NSP subgroup (SARA, 2.136 vs 1.218 points; ICARS, 5.576 vs 3.480 points; both p < 0.001). In addition, patients with SCA3-SP showed gray matter volume loss in the precentral gyrus with a decreased neurite density index in the WM of the corticospinal tract and cerebellar peduncles compared with patients with SCA3-NSP. SCA3-SP differs from SCA3-NSP in clinical features, multiparametric brain imaging findings, and longitudinal follow-up progression.