Early Cerebellar Network Shifting in Spinocerebellar Ataxia Type 6

[Recent clinical advances in hereditary spinocerebellar degeneration]

Spinocerebellar degeneration (SCD) is a neurodegenerative disorder characterized by cerebellar ataxia and other multisystem manifestations, such as Parkinsonism and pyramidal tract symptoms. No effective treatment is available for SCD. Approximately one-third of the cases of SCD are inherited, and the remaining two-third are sporadic, including multiple system atrophy. This article provides an overview of hereditary SCD, its clinical features, recent treatment advances, biomarkers, role of genomic medicine, and future treatment prospects.

Compressed cerebellar functional connectome hierarchy in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is an inherited movement disorder characterized by a progressive decline in motor coordination. Despite the extensive functional connectivity (FC) alterations reported in previous SCA3 studies in the cerebellum and cerebellar-cerebral pathways, the influence of these FC disturbances on the hierarchical organization of cerebellar functional regions remains unclear. Here, we compared 35 SCA3 patients with 48 age- and sex-matched healthy controls using a combination of voxel-based morphometry and resting-state functional magnetic resonance imaging to investigate whether cerebellar hierarchical organization is altered in SCA3. Utilizing connectome gradients, we identified the gradient axis of cerebellar hierarchical organization, spanning sensorimotor to transmodal (task-unfocused) regions. Compared to healthy controls, SCA3 patients showed a compressed hierarchical organization in the cerebellum at both voxel-level (p < .05, TFCE corrected) and network-level (p < .05, FDR corrected). This pattern was observed in both intra-cerebellar and cerebellar-cerebral gradients. We observed that decreased intra-cerebellar gradient scores in bilateral Crus I/II both negatively correlated with SARA scores (left/right Crus I/II: r = -.48/-.50, p = .04/.04, FDR corrected), while increased cerebellar-cerebral gradients scores in the vermis showed a positive correlation with disease duration (r = .48, p = .04, FDR corrected). Control analyses of cerebellar gray matter atrophy revealed that gradient alterations were associated with cerebellar volume loss. Further FC analysis showed increased functional connectivity in both unimodal and transmodal areas, potentially supporting the disrupted cerebellar functional hierarchy uncovered by the gradients. Our findings provide novel evidence regarding alterations in the cerebellar functional hierarchy in SCA3.

Abnormal saccade profiles in hereditary spinocerebellar degeneration reveal cerebellar contribution to visually guided saccades

OBJECTIVE

To study how the pathophysiology underlying hereditary spinocerebellar degeneration (spinocerebellar ataxia; SCA) with pure cerebellar manifestation evolves with disease progression using saccade recordings.

METHODS

We recorded visually- (VGS) and memory-guided saccade (MGS) task performance in a homogeneous population of 20 genetically proven SCA patients (12 SCA6 and eight SCA31 patients) and 19 normal controls.

RESULTS

For VGS but not MGS, saccade latency and amplitude were increased and more variable than those in normal subjects, which correlated with cerebellar symptom severity assessed using the International Cooperative Ataxia Rating Scale (ICARS). Parameters with significant correlations with cerebellar symptoms showed an aggravation after disease stage progression (ICARS > 50). The saccade velocity profile exhibited shortened acceleration and prolonged deceleration, which also correlated with disease progression. The main sequence relationship between saccade amplitude and peak velocity as well as saccade inhibitory control were preserved.

CONCLUSIONS

The cerebellum may be involved in initiating VGS, which was aggravated acutely during disease stage progression. Dysfunction associated with disease progression occurs mainly in the cerebellum and brainstem interaction but may also eventually involve cortical saccade processing.

SIGNIFICANCE

Saccade recording can reveal cerebellar pathophysiology underlying SCA with disease progression.

Age-related differences of cerebellar cortex and nuclei: MRI findings in healthy controls and its application to spinocerebellar ataxia (SCA6) patients

Understanding cerebellar alterations due to healthy aging provides a reference point against which pathological findings in late-onset disease, for example spinocerebellar ataxia type 6 (SCA6), can be contrasted. In the present study, we investigated the impact of aging on the cerebellar nuclei and cerebellar cortex in 109 healthy controls (age range: 16 - 78 years) using 3 Tesla magnetic resonance imaging (MRI). Findings were compared with 25 SCA6 patients (age range: 38 - 78 years). A subset of 16 SCA6 (included: 14) patients and 50 controls (included: 45) received an additional MRI scan at 7 Tesla and were re-scanned after one year. MRI included T1-weighted, T2-weighted FLAIR, and multi-echo T2*-weighted imaging. The T2*-weighted phase images were converted to quantitative susceptibility maps (QSM). Since the cerebellar nuclei are characterized by elevated iron content with respect to their surroundings, two independent raters manually outlined them on the susceptibility maps. T1-weighted images acquired at 3T were utilized to automatically identify the cerebellar gray matter (GM) volume. Linear correlations revealed significant atrophy of the cerebellum due to tissue loss of cerebellar cortical GM in healthy controls with increasing age. Reduction of the cerebellar GM was substantially stronger in SCA6 patients. The volume of the dentate nuclei did not exhibit a significant relationship with age, at least in the age range between 18 and 78 years, whereas mean susceptibilities of the dentate nuclei increased with age. As previously shown, the dentate nuclei volumes were smaller and magnetic susceptibilities were lower in SCA6 patients compared to age- and sex-matched controls. The significant dentate volume loss in SCA6 patients could also be confirmed with 7T MRI. Linear mixed effects models and individual paired t-tests accounting for multiple comparisons revealed no statistical significant change in volume and susceptibility of the dentate nuclei after one year in neither patients nor controls. Importantly, dentate volumes were more sensitive to differentiate between SCA6 (Cohen's d = 3.02) and matched controls than the cerebellar cortex volume (d = 2.04). In addition to age-related decline of the cerebellar cortex and atrophy in SCA6 patients, age-related increase of susceptibility of the dentate nuclei was found in controls, whereas dentate volume and susceptibility was significantly decreased in SCA6 patients. Because no significant changes of any of these parameters was found at follow-up, these measures do not allow to monitor disease progression at short intervals.

Myelinating Glia: Potential Therapeutic Targets in Polyglutamine Spinocerebellar Ataxias

Human studies, in combination with animal and cellular models, support glial cells as both major contributors to neurodegenerative diseases and promising therapeutic targets. Among glial cells, oligodendrocytes and Schwann cells are the myelinating glial cells of the central and peripheral nervous system, respectively. In this review, we discuss the contributions of these central and peripheral myelinating glia to the pathomechanisms of polyglutamine (polyQ) spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, and 17. First, we highlight the function of oligodendrocytes in healthy conditions and how they are disrupted in polyQ SCA patients and diseased model systems. We then cover the role of Schwann cells in peripheral nerve function and repair as well as their possible role in peripheral neuropathy in polyQ SCAs. Finally, we discuss potential polyQ SCA therapeutic interventions in myelinating glial.

Social concepts and the cerebellum: behavioural and functional connectivity signatures in cerebellar ataxic patients

Neurocognitive research on social concepts underscores their reliance on fronto-temporo-limbic regions mediating broad socio-cognitive skills. Yet, the field has neglected another structure increasingly implicated in social cognition: the cerebellum. The present exploratory study examines this link combining a novel naturalistic text paradigm, a relevant atrophy model and functional magnetic resonance imaging. Fifteen cerebellar ataxia (CA) patients with focal cerebellar atrophy and 29 matched controls listened to a social text (highlighting interpersonal events) as well as a non-social text (focused on a single person's actions), and answered comprehension questionnaires. We compared behavioural outcomes between groups and examined their association with cerebellar connectivity. CA patients showed deficits in social text comprehension and normal scores in the non-social text. Also, social text outcomes in controls selectively correlated with connectivity between the cerebellum and key regions subserving multi-modal semantics and social cognition, including the superior and medial temporal gyri, the temporal pole and the insula. Conversely, brain-behaviour associations involving the cerebellum were abolished in the patients. Thus, cerebellar structures and connections seem involved in processing social concepts evoked by naturalistic discourse. Such findings invite new theoretical and translational developments integrating social neuroscience with embodied semantics. This article is part of the theme issue 'Concepts in interaction: social engagement and inner experiences'.

Targeting Circuit Abnormalities in Neurodegenerative Disease

Despite significant improvement in our ability to diagnose both common and rare neurodegenerative diseases and understand their underlying biologic mechanisms, there remains a disproportionate lack of effective treatments, reflecting the complexity of these disorders. Successfully advancing novel treatments for neurodegenerative disorders will require reconsideration of traditional approaches, which to date have focused largely on specific disease proteins or cells of origin. This article proposes reframing these diseases as conditions of dysfunctional circuitry as a complement to ongoing efforts. Specifically reviewed is how aberrant spiking is a common downstream mechanism in numerous neurodegenerative diseases, often driven by dysfunction in specific ion channels. Surgical modification of this electrical activity via deep brain stimulation is already an approved modality for many of these disorders. Therefore, restoring proper electrical activity by targeting these channels pharmacologically represents a viable strategy for intervention, not only for symptomatic management but also as a potential disease-modifying therapy. Such an approach is likely to be a promising route to treating these devastating disorders, either as monotherapy or in conjunction with current drugs. SIGNIFICANCE STATEMENT: Despite extensive research and improved understanding of the biology driving neurodegenerative disease, there has not been a concomitant increase in approved therapies. Accordingly, it is time to shift our perspective and recognize these diseases also as disorders of circuitry to further yield novel drug targets and new interventions. An approach focused on treating dysfunctional circuitry has the potential to reduce or reverse patient symptoms and potentially modify disease course.

Cerebello-cerebral resting-state functional connectivity in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder characterized by progressive motor and nonmotor deficits concomitant with degenerative pathophysiological changes within the cerebellum. The cerebellum is topographically organized into cerebello-cerebral circuits that create distinct functional networks regulating movement, cognition, and affect. SCA3-associated motor and nonmotor symptoms are possibly related not only to intracerebellar changes but also to disruption of the connectivity within these cerebello-cerebral circuits. However, to date, no comprehensive investigation of cerebello-cerebral connectivity in SCA3 has been conducted. The present study aimed to identify cerebello-cerebral functional connectivity alterations and associations with downstream clinical phenotypes and upstream topographic markers of cerebellar neurodegeneration in patients with SCA3. This study included 45 patients with SCA3 and 49 healthy controls. Voxel-based morphometry and resting-state functional magnetic resonance imaging (MRI) were performed to characterize the cerebellar atrophy and to examine the cerebello-cerebral functional connectivity patterns. Structural MRI confirmed widespread gray matter atrophy in the motor and cognitive cerebellum of patients with SCA3. We found reduced functional connectivity between the cerebellum and the cerebral cortical networks, including the somatomotor, frontoparietal, and default networks; however, increased connectivity was observed between the cerebellum and the dorsal attention network. These abnormal patterns correlated with the CAG repeat expansion and deficits in global cognition. Our results indicate the contribution of cerebello-cerebral networks to the motor and cognitive impairments in patients with SCA3 and reveal that such alterations occur in association with cerebellar atrophy. These findings add important insights into our understanding of the role of the cerebellum in SCA3.

Non-Invasive Electrical Stimulation in Patients with Neurodegenerative Ataxia and Spasticity: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

BACKGROUND

There are limited treatment options for patients with neurodegenerative ataxia and spasticity. Non-invasive electrostimulation (NES) is receiving increasing interest because of its ease of implementation, cost-effectiveness, and safety. We conducted a meta-analysis to evaluate the efficacy of NES.

METHODS

We screened Medline and Embase for studies using NES in ataxias and spasticity. Key outcome measurements of effectiveness included changes in: (1) Modified Ashworth Scale (MAS) scores, (2) cerebellar brain inhibition (CBI), (3) 9-hole peg test (9HPT), (4) 8-meter walking time (8MWT), (5) International Cooperative Ataxia Rating Scale (ICARS) scores, (6) Scale for Assessment and Rating of Ataxia (SARA) scores.

RESULTS

Seven randomised controlled trials (RCTs) involving 203 patients were included. There were significant improvements in MAS (MD -0.42, 95% CI -0.76 to -0.08, P=0.015), CBI (MD -0.35%, 95% CI -0.42 to -0.28, P<0.001), 8MWT (MD -1.88 seconds, 95% CI -3.26 to -0.49, P=0.008), ICARS (MD -7.84, 95% CI -11.90 to -3.78, P<0.001), and SARA (MD -3.01, 95% CI -4.74 to -1.28, P<0.001). There was almost no heterogeneity across all outcomes except for CBI (I² =79%). No significant changes in 9HPT were observed when comparing NES to a sham procedure (MD -3.52 seconds, 95% CI -9.15 to 2.10, P=0.220). Most included studies were at low risk of bias, and no severe adverse effects were reported.

CONCLUSION

We demonstrated that NES is an effective treatment for improving coordination and balance, and increased exercise capacity in patients with ataxia and spasticity. There was also a significant modulation of CBI in ataxic patients.

Deficiency of TRIM32 Impairs Motor Function and Purkinje Cells in Mid-Aged Mice

Proper functioning of the cerebellum is crucial to motor balance and coordination in adult mammals. Purkinje cells (PCs), the sole output neurons of the cerebellar cortex, play essential roles in cerebellar motor function. Tripartite motif-containing protein 32 (TRIM32) is an E3 ubiquitin ligase that is involved in balance activities of neurogenesis in the subventricular zone of the mammalian brain and in the development of many nervous system diseases, such as Alzheimer's disease, autism spectrum disorder, attention deficit hyperactivity disorder. However, the role of TRIM32 in cerebellar motor function has never been examined. In this study we found that motor balance and coordination of mid-aged TRIM32 deficient mice were poorer than those of wild-type littermates. Immunohistochemical staining was performed to assess cerebella morphology and TRIM32 expression in PCs. Golgi staining showed that the extent of dendritic arborization and dendritic spine density of PCs were decreased in the absence of TRIM32. The loss of TRIM32 was also associated with a decrease in the number of synapses between parallel fibers and PCs, and in synapses between climbing fibers and PCs. In addition, deficiency of TRIM32 decreased Type I inositol 1,4,5-trisphosphate 5-phosphatase (INPP5A) levels in cerebellum. Overall, this study is the first to elucidate a role of TRIM32 in cerebellar motor function and a possible mechanism, thereby highlighting the importance of TRIM32 in the cerebellum.

Spinocerebellar ataxia clinical trials: opportunities and challenges

The spinocerebellar ataxias (SCAs) are a group of dominantly inherited diseases that share the defining feature of progressive cerebellar ataxia. The disease process, however, is not confined to the cerebellum; other areas of the brain, in particular, the brainstem, are also affected, resulting in a high burden of morbidity and mortality. Currently, there are no disease‐modifying treatments for the SCAs, but preclinical research has led to the development of therapeutic agents ripe for testing in patients. Unfortunately, due to the rarity of these diseases and their slow and variable progression, there are substantial hurdles to overcome in conducting clinical trials. While the epidemiological features of the SCAs are immutable, the feasibility of conducting clinical trials is being addressed through a combination of strategies. These include improvements in clinical outcome measures, the identification of imaging and fluid biomarkers, and innovations in clinical trial design. In this review, we highlight current challenges in initiating clinical trials for the SCAs and also discuss pathways for researchers and clinicians to mitigate these challenges and harness opportunities for clinical trial development.

MR imaging and spectroscopy in degenerative ataxias: toward multimodal, multisite, multistage monitoring of neurodegeneration

PURPOSE OF REVIEW

Degenerative ataxias are rare and currently untreatable movement disorders, primarily characterized by neurodegeneration in the cerebellum and brainstem. We highlight MRI studies with the most potential for utility in pending ataxia trials and underscore advances in disease characterization and diagnostics in the field.

RECENT FINDINGS

With availability of advanced MRI acquisition methods and specialized software dedicated to the analysis of MRI of the cerebellum, patterns of cerebellar atrophy in different degenerative ataxias are increasingly well defined. The field further embraced rigorous multimodal investigations to study network-level microstructural and functional brain changes and their neurochemical correlates. MRI and magnetic resonance spectroscopy were shown to be more sensitive to disease progression than clinical scales and to detect abnormalities in premanifest mutation carriers.

SUMMARY

Magnetic resonance techniques are increasingly well placed for characterizing the expression and progression of degenerative ataxias. The most impactful work has arguably come through multi-institutional studies that monitor relatively large cohorts, multimodal investigations that assess the sensitivity of different measures and their interrelationships, and novel imaging approaches that are targeted to known pathophysiology (e.g., iron and spinal imaging in Friedreich ataxia). These multimodal, multi-institutional studies are paving the way to clinical trial readiness and enhanced understanding of disease in degenerative ataxias.

Clinical, Imaging, and Laboratory Markers of Premanifest Spinocerebellar Ataxia 1, 2, 3, and 6: A Systematic Review

Background and Purpose

Premanifest mutation carriers with spinocerebellar ataxia (SCA) can exhibit subtle abnormalities before developing ataxia. We summarized the preataxic manifestations of SCA1, -2, -3, and -6, and their associations with ataxia onset.

Methods

We included studies of the premanifest carriers of SCA published between January 1998 and December 2019 identified in Scopus and PubMed by searching for terms including ‘spinocerebellar ataxia’ and several synonyms of ‘preataxic manifestation’. We systematically reviewed the results obtained in studies categorized based on clinical, imaging, and laboratory markers.

Results

We finally performed a qualitative analysis of 48 papers. Common preataxic manifestations appearing in multiple SCA subtypes were muscle cramps, abnormal muscle reflexes, instability in gait and posture, lower Composite Cerebellar Functional Severity scores, abnormalities in video-oculography and transcranial magnetic stimulation, and gray-matter loss and volume reduction in the brainstem and cerebellar structures. Also, decreased sensory amplitudes in nerve conduction studies were observed in SCA2. Eotaxin and neurofilament light-chain levels were revealed as sensitive blood biomarkers in SCA3. Concerning potential predictive markers, hyporeflexia and abnormalities of somatosensory evoked potentials showed correlations with the time to ataxia onset in SCA2 carriers. However, no longitudinal data were found for the other SCA gene carriers.

Conclusions

Our results suggest that preataxic manifestations vary among SCA1, -2, -3, and -6, with some subtypes sharing specific features. Combining various markers into a standardized index for premanifest carriers may be useful for early screening and assessing the risk of disease progression in SCA carriers.

MR Imaging of SCA3/MJD

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a progressive autosomal dominantly inherited cerebellar ataxia characterized by the aggregation of polyglutamine-expanded protein within neuronal nuclei in the brain, which can lead to brain damage that precedes the onset of clinical manifestations. Magnetic resonance imaging (MRI) techniques such as morphometric MRI, diffusion tensor imaging (DTI), functional magnetic resonance imaging (fMRI), and magnetic resonance spectroscopy (MRS) have gained increasing attention as non-invasive and quantitative methods for the assessment of structural and functional alterations in clinical SCA3/MJD patients as well as preclinical carriers. Morphometric MRI has demonstrated typical patterns of atrophy or volume loss in the cerebellum and brainstem with extensive lesions in some supratentorial areas. DTI has detected widespread microstructural alterations in brain white matter, which indicate disrupted brain anatomical connectivity. Task-related fMRI has presented unusual brain activation patterns within the cerebellum and some extracerebellar tissue, reflecting the decreased functional connectivity of these brain regions in SCA3/MJD subjects. MRS has revealed abnormal neurochemical profiles, such as the levels or ratios of N-acetyl aspartate, choline, and creatine, in both clinical cases and preclinical cases before the alterations in brain anatomical structure. Moreover, a number of studies have reported correlations of MR imaging alterations with clinical and genetic features. The utility of these MR imaging techniques can help to identify preclinical SCA3/MJD carriers, monitor disease progression, evaluate response to therapeutic interventions, and illustrate the pathophysiological mechanisms underlying the occurrence, development, and prognosis of SCA3/MJD.

Non-invasive Transcranial Electrical Stimulation in Movement Disorders

Dysfunction within large-scale brain networks as the basis for movement disorders is an accepted hypothesis. The treatment options for restoring network function are limited. Non-invasive brain stimulation techniques such as repetitive transcranial magnetic stimulation are now being studied to modify the network. Transcranial electrical stimulation (tES) is also a portable, cost-effective, and non-invasive way of network modulation. Transcranial direct current stimulation and transcranial alternating current stimulation have been studied in Parkinson’s disease, dystonia, tremor, and ataxia. Transcranial pulsed current stimulation and transcranial random noise stimulation are not yet studied enough. The literature in the use of these techniques is intriguing, yet many unanswered questions remain. In this review, we highlight the studies using these four potential tES techniques and their electrophysiological basis and consider the therapeutic implication in the field of movement disorders. The objectives are to consolidate the current literature, demonstrate that these methods are feasible, and encourage the application of such techniques in the near future.

Assessment of Cerebral and Cerebellar White Matter Microstructure in Spinocerebellar Ataxias 1, 2, 3, and 6 Using Diffusion MRI

Development of imaging biomarkers for rare neurodegenerative diseases such as spinocerebellar ataxia (SCA) is important to non-invasively track progression of disease pathology and monitor response to interventions. Diffusion MRI (dMRI) has been shown to identify cross-sectional degeneration of white matter (WM) microstructure and connectivity between healthy controls and patients with SCAs, using various analysis methods. In this paper, we present dMRI data in SCAs type 1, 2, 3, and 6 and matched controls, including longitudinal acquisitions at 12-24-month intervals in a subset of the cohort, with up to 5 visits. The SCA1 cohort also contained 3 premanifest patients at baseline, with 2 showing ataxia symptoms at the time of the follow-up scans. We focused on two aspects: first, multimodal evaluation of the dMRI data in a cross-sectional approach, and second, longitudinal trends in dMRI data in SCAs. Three different pipelines were used to perform cross-sectional analyses in WM: region of interest (ROI), tract-based spatial statistics (TBSS), and fixel-based analysis (FBA). We further analyzed longitudinal changes in dMRI metrics throughout the brain using ROI-based analysis. Both ROI and TBSS analyses identified higher mean (MD), axial (AD), and radial (RD) diffusivity and lower fractional anisotropy (FA) in the cerebellum for all SCAs compared to controls, as well as some cerebral alterations in SCA1, 2, and 3. FBA showed lower fiber density (FD) and fiber crossing (FC) regions similar to those identified by ROI and TBSS analyses. FBA also highlighted corticospinal tract (CST) abnormalities, which was not detected by the other two pipelines. Longitudinal ROI-based analysis showed significant increase in AD in the middle cerebellar peduncle (MCP) for patients with SCA1, suggesting that the MCP may be a good candidate region to monitor disease progression. The patient who remained symptom-free throughout the study displayed no microstructural abnormalities. On the other hand, the two patients who were at the premanifest stage at baseline, and showed ataxia symptoms in their follow-up visits, displayed AD values in the MCP that were already in the range of symptomatic patients with SCA1 at their baseline visit, demonstrating that microstructural abnormalities are detectable prior to the onset of ataxia.

The Relationship Between Zebrin Expression and Cerebellar Functions: Insights From Neuroimaging Studies

The cerebellum has long been known to play an important role in motor and balance control, and accumulating evidence has revealed that it is also involved in multiple cognitive functions. However, the evidence from neuroimaging studies and clinical observations is not well-integrated at the anatomical or molecular level. The goal of this review is to summarize and link different aspects of the cerebellum, including molecular patterning, functional topography images, and clinical cerebellar disorders. More specifically, we explored the potential relationships between the cerebrocerebellar connections and the expression of particular molecules and, in particular, zebrin stripe (a Purkinje cell-specific antibody molecular marker, which is a glycolytic enzyme expressed in cerebellar Purkinje cells). We hypothesized that the zebrin patterns contribute to cerebellar functional maps—especially when cerebrocerebellar circuit changes exist in cerebellar-related diseases. The zebrin stripe receives input from climbing fibers and project to different parts of the cerebral cortex through its cerebrocerebellar connection. Since zebrin-positive cerebellar Purkinje cells are resistant to excitotoxicity and cell injury while zebrin-negative zones are more prone to damage, we suggest that motor control dysfunction symptoms such as ataxia and dysmetria present earlier and are easier to observe than non-ataxia symptoms due to zebrin-negative cell damage by cerebrocerebellar connections. In summary, we emphasize that the molecular zebrin patterns provide the basis for a new viewpoint from which to investigate cerebellar functions and clinico-neuroanatomic correlations.

Spinocerebellar ataxias: prospects and challenges for therapy development

The spinocerebellar ataxias (SCAs) comprise more than 40 autosomal dominant neurodegenerative disorders that present principally with progressive ataxia. Within the past few years, studies of pathogenic mechanisms in the SCAs have led to the development of promising therapeutic strategies, especially for SCAs caused by polyglutamine-coding CAG repeats. Nucleotide-based gene-silencing approaches that target the first steps in the pathogenic cascade are one promising approach not only for polyglutamine SCAs but also for the many other SCAs caused by toxic mutant proteins or RNA. For these and other emerging therapeutic strategies, well-coordinated preparation is needed for fruitful clinical trials. To accomplish this goal, investigators from the United States and Europe are now collaborating to share data from their respective SCA cohorts. Increased knowledge of the natural history of SCAs, including of the premanifest and early symptomatic stages of disease, will improve the prospects for success in clinical trials of disease-modifying drugs. In addition, investigators are seeking validated clinical outcome measures that demonstrate responsiveness to changes in SCA populations. Findings suggest that MRI and magnetic resonance spectroscopy biomarkers will provide objective biological readouts of disease activity and progression, but more work is needed to establish disease-specific biomarkers that track target engagement in therapeutic trials. Together, these efforts suggest that the development of successful therapies for one or more SCAs is not far away.

Transcranial magnetic stimulation for diplopia in a patient with spinocerebellar ataxia type 6: a case report

Background

In Patients with spinocerebellar ataxia type 6 (SCA6) are often treated by transcranial magnetic stimulation (TMS) over the motor cortex and cerebellum. However, few reports have examined effective therapeutic modalities for diplopia in SCA6 patients. In the current case, we applied single-pulse TMS over the motor cortex and cerebellum to improve ataxia, and observed an unexpected improvement of diplopia.

Case presentation

A 62-year-old Japanese male with spinocerebellar ataxia type 6 (SCA6) was admitted to our hospital for exacerbation of ataxia. We administered single-pulse transcranial magnetic stimulation (TMS) over the hand motor area and the cerebellum with a circular coil to reduce ataxia. After the initiation of TMS, since diplopia unexpectedly improved, we started a quantitative assessment of diplopia by counting the number of fixation spots that he observed in his visual field. This assessment suggested that TMS had an immediate and cumulative effect on diplopia. We also delivered more localized stimulation only over the motor cortex with a Figure-8 coil, and diplopia improved immediately. Additionally, we administered a sham stimulation before the real stimulation over the motor cortex and the cerebellum. The sham stimulation improved diplopia, and greater improvement was observed with subsequent real stimulation. We also used a Hess chart examination and video recordings of binocular gross appearance to elucidate the changes in ocular movement objectively. However, these examinations did not reveal any obvious oculomotor changes.

Conclusions

We applied single-pulse TMS to a SCA6 patient with diplopia, which improved without any adverse effects. TMS may have potential for the treatment of diplopia in SCA6 patients.

Abnormal eyeblink conditioning is an early marker of cerebellar dysfunction in preclinical SCA3 mutation carriers

Background

Spinocerebellar ataxias (SCAs) are a group of autosomal dominantly inherited degenerative diseases. As the pathological process probably commences years before the first appearance of clinical symptoms, preclinical carriers of a SCA mutation offer the opportunity to study the earliest stages of cerebellar dysfunction and degeneration. Eyeblink classical conditioning (EBCC) is a motor learning paradigm, crucially dependent on the integrity of the olivocerebellar circuit, and has been shown to be able to detect subtle alterations of cerebellar function, which might already be present in preclinical carriers.

Methods

In order to acquire conditioned responses, we performed EBCC, delay paradigm, in 18 preclinical carriers of a SCA3 mutation and 16 healthy, age-matched controls by presenting repeated pairings of an auditory tone with a supraorbital nerve stimulus with a delay interval of 400 ms.

Results

Preclinical carriers acquired significantly less conditioned eyeblink responses than controls and learning rates were significantly reduced. This motor learning defect was, however, not associated with the predicted time to onset.

Conclusions

EBCC is impaired in preclinical carriers of a SCA3 mutation, as a result of impaired motor learning capacities of the cerebellum and is thus suggestive of cerebellar dysfunction. EBCC can be used to detect but probably not monitor preclinical cerebellar dysfunction in genetic ataxias, such as SCA3.

Electronic supplementary material

The online version of this article (10.1007/s00221-018-5424-y) contains supplementary material, which is available to authorized users.

Neuroimaging Applications in Chronic Ataxias

Magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT) and positron emission tomography (PET) are the main instruments for neuroimaging investigation of patients with chronic ataxia. MRI has a predominant diagnostic role in the single patient, based on the visual detection of three patterns of atrophy, namely, spinal atrophy, cortical cerebellar atrophy and olivopontocerebellar atrophy, which correlate with the aetiologies of inherited or sporadic ataxia. In fact spinal atrophy is observed in Friedreich ataxia, cortical cerebellar atrophy in Ataxia Telangectasia, gluten ataxia and Sporadic Adult Onset Ataxia and olivopontocerebellar atrophy in Multiple System Atrophy cerebellar type. The 39 types of dominantly inherited spinocerebellar ataxias show either cortical cerebellar atrophy or olivopontocerebellar atrophy. T2 or T2* weighted MR images can contribute to the diagnosis by revealing abnormally increased or decreased signal with a characteristic distribution. These include symmetric T2 hyperintensity of the posterior and lateral columns of the cervical spinal cord in Friedreich ataxia, diffuse and symmetric hyperintensity of the cerebellar cortex in Infantile Neuro-Axonal Dystrophy, symmetric hyperintensity of the peridentate white matter in Cerebrotendineous Xanthomatosis, and symmetric hyperintensity of the middle cerebellar peduncles and peridentate white matter, cerebral white matter and corpus callosum in Fragile X Tremor Ataxia Syndrome. Abnormally decreased T2 or T2* signal can be observed with a multifocal distribution in Ataxia Telangectasia and with a symmetric distribution in the basal ganglia in Multiple System Atrophy. T2 signal hypointensity lining diffusely the outer surfaces of the brainstem, cerebellum and cerebrum enables diagnosis of superficial siderosis of the central nervous system. The diagnostic role of nuclear medicine techniques is smaller. SPECT and PET show decreased uptake of radiotracers investigating the nigrostriatal system in Multiple System Atrophy and in patients with Fragile X Tremor Ataxia Syndrome. Semiquantitative or quantitative MRI, SPECT and PET data describing structural, microstructural and functional changes of the cerebellum, brainstem, and spinal cord have been widely applied to investigate physiopathological changes in patients with chronic ataxias. Moreover they can track diseases progression with a greater sensitivity than clinical scales. So far, a few small-size and single center studies employed neuroimaging techniques as surrogate markers of treatment effects in chronic ataxias.

The cerebellum from the fetus to the elderly: history, advances, and future challenges

The cerebellum is now at the forefront of research in neuroscience. This is not just a coincidence, occurring about 250 years after the first description of the human cerebellum. The cerebellum contains the majority of neurons in the central nervous system and it is heavily connected with almost all cortical and subcortical areas of the supratentorial region as well as with the brainstem and the spinal cord. Cerebellar circuits are embedded in large-scale networks contributing to motor control and neurocognition. From a phenotypic standpoint, damage to cerebellar lobules interconnected with the sensorimotor cortices leads to a cerebellar motor syndrome, whereas lesions of the posterolateral cerebellum cause cognitive and neuropsychiatric impairments which may or may not be subtle. This topographic rule is valid in children and adults. Midline posterior vermal lesions cause behavioral/affective dysregulation, especially in kids. The extent of the spectrum of human cerebellar disorders is increasingly recognized from the fetus to the elderly, with recognition of consequences for the quality of life and socioeconomic costs due to lifelong morbidity of many cerebellar ataxias/pathologies. The prolonged duration of human cerebellar development makes the cerebellum especially susceptible to developmental disruption, both genetic and nongenetic. This explains the current emphasis on the clarification of the developmental course and impact of the cerebellum. The understanding of how germinal matrix zones and migration of neurons and glial cells end in a highly organized and foliated human cerebellum is essential. This is greatly accelerated by inputs from rodent developmental studies, in particular because cerebellar anatomy is conserved across species. Still, numerous questions on human fetal development remain unanswered. Although both advanced neuroimaging and genetic studies are currently leading to a better definition and understanding of the multitude of cerebellar symptoms, there is a gap, with a great need to develop therapies aiming at first, protection of the cerebellum during development, and second, restoration of cerebellar function in children and in adults. Dynamic profiles of the compensatory processes from newborns to elderly require specific studies.

Spinocerebellar [corrected] Ataxia Type 6: Molecular Mechanisms and Calcium Channel Genetics

Spinocerebellar ataxia (SCA) type 6 is an autosomal dominant disease affecting cerebellar degeneration. Clinically, it is characterized by pure cerebellar dysfunction, slowly progressive unsteadiness of gait and stance, slurred speech, and abnormal eye movements with late onset. Pathological findings of SCA6 include a diffuse loss of Purkinje cells, predominantly in the cerebellar vermis. Genetically, SCA6 is caused by expansion of a trinucleotide CAG repeat in the last exon of longest isoform CACNA1A gene on chromosome 19p13.1-p13.2. Normal alleles have 4-18 repeats, while alleles causing disease contain 19-33 repeats. Due to presence of a novel internal ribosomal entry site (IRES) with the mRNA, CACNA1A encodes two structurally unrelated proteins with distinct functions within an overlapping open reading frame (ORF) of the same mRNA: (1) α1A subunit of P/Q-type voltage gated calcium channel; (2) α1ACT, a newly recognized transcription factor, with polyglutamine repeat at C-terminal end. Understanding the function of α1ACT in physiological and pathological conditions may elucidate the pathogenesis of SCA6. More importantly, the IRES, as the translational control element of α1ACT, provides a potential therapeutic target for the treatment of SCA6.

Microstructural Alterations in Asymptomatic and Symptomatic Patients with Spinocerebellar Ataxia Type 3: A Tract-Based Spatial Statistics Study

Objective

Spinocerebellar ataxia type 3 (SCA3) is the most commonly occurring type of autosomal dominant spinocerebellar ataxia. The present study aims to investigate progressive changes in white matter (WM) fiber in asymptomatic and symptomatic patients with SCA3.

Methods

A total of 62 participants were included in this study. Among them, 16 were asymptomatic mutation carriers (pre-SCA3), 22 were SCA3 patients with clinical symptoms, and 24 were normal controls (NC). Group comparison of tract-based spatial statistics was performed to identify microstructural abnormalities at different SCA3 disease stages.

Results

Decreased fractional anisotropy (FA) and increased mean diffusivity (MD) were found in the left inferior cerebellar peduncle and superior cerebellar peduncle (SCP) in the pre-SCA3 group compared with NC. The symptomatic SCA3 group showed brain-wide WM tracts impairment in both supratentorial and infratentorial networks, and the mean FA value of the WM skeleton showed a significantly negative correlation with the International Cooperative Ataxia Rating Scale (ICARS) scores. Specifically, FA of the bilateral posterior limb of the internal capsule negatively correlated with SCA3 disease duration. We also found that FA values in the right medial lemniscus and SCP negatively correlated with ICARS scores, whereas FA in the right posterior thalamic radiation positively correlated with Montreal Cognitive Assessment scores. In addition, MD in the middle cerebellar peduncle, left anterior limb of internal capsule, external capsule, and superior corona radiate positively correlated with ICARS scores in SCA3 patients.

Conclusion

WM microstructural changes are present even in the asymptomatic stages of SCA3. In individuals in which the disease has progressed to the symptomatic stage, the integrity of WM fibers across the whole brain is affected. Furthermore, abnormalities in WM tracts are closely related to SCA3 disease severity, including movement disorder and cognitive dysfunction. These findings can deepen our understanding of the neural basis of SCA3 dysfunction.

Sensorimotor adaptation as a behavioural biomarker of early spinocerebellar ataxia type 6

Early detection of the behavioural deficits of neurodegenerative diseases may help to describe the pathogenesis of such diseases and establish important biomarkers of disease progression. The aim of this study was to identify how sensorimotor adaptation of the upper limb, a cerebellar-dependent process restoring movement accuracy after introduction of a perturbation, is affected at the pre-clinical and clinical stages of spinocerebellar ataxia type 6 (SCA6), an inherited neurodegenerative disease. We demonstrate that initial adaptation to the perturbation was significantly impaired in the eighteen individuals with clinical motor symptoms but mostly preserved in the five pre-clinical individuals. Moreover, the amount of error reduction correlated with the clinical symptoms, with the most symptomatic patients adapting the least. Finally both pre-clinical and clinical individuals showed significantly reduced de-adaptation performance after the perturbation was removed in comparison to the control participants. Thus, in this large study of motor features in SCA6, we provide novel evidence for the existence of subclinical motor dysfunction at a pre-clinical stage of SCA6. Our findings show that testing sensorimotor de-adaptation could provide a potential predictor of future motor deficits in SCA6.

Resting-state functional connectivity and cognitive dysfunction correlations in spinocerebelellar ataxia type 6 (SCA6)

OBJECTIVE

The aim of this study is to evaluate the correlation between resting state functional MRI (RS-fMRI) activity and motor and cognitive impairment in spinocerebellar ataxia type 6 (SCA6).

METHODS

Twelve patients with genetically confirmed SCA6 and 14 age matched healthy controls were imaged with RS-fMRI. Whole brain gray matter was automatically parcellated into 1000 regions of interest (ROIs). For each ROI, the first eigenvariate of voxel time courses was extracted. For each patient, Pearson correlation coefficients between each pair of ROI time courses were calculated across the 1000 ROIs. The set of average control correlation coefficients were fed as an undirected weighted adjacency matrix into the Rubinov and Sporns (2010) modularity algorithm. The intranetwork global efficiency of the thresholded adjacency sub-matrix was calculated and correlated with ataxia scores and cognitive performance.

RESULTS

SCA6 patients showed mild cognitive impairments in executive function and visual-motor processing compared to control subjects. These neuropsychological impairments were correlated with decreased RS functional connectivity (FC) in the attention network.

CONCLUSIONS

Mild cognitive executive functions and visual-motor coordination impairments seen in SCA6 patients correlate with decreased resting-state connectivity in the attention network, suggesting a possible metric for the study of cognitive dysfunction in cerebellar disease. Hum Brain Mapp 38:3001-3010, 2017. © 2017 Wiley Periodicals, Inc.

Sensory and motor cortex function contributes to symptom severity in spinocerebellar ataxia type 6

Spinocerebellar ataxia type 6 (SCA6) is a genetic disease that causes degeneration of Purkinje cells, and recent evidence points to degeneration of Betz cells in the motor cortex. The relation between functional activity of motor cortex and symptom severity during a hand-grip motor control in vivo has not yet been investigated. This study explored both functional changes in the sensorimotor cortex and cerebellar regions and structural alterations in the cerebellum for SCA6 patients as compared to age-matched healthy controls using a multimodal imaging approach (task-based fMRI, task-based functional connectivity, and free-water diffusion MRI). Further, we tested their relation with the severity of ataxia symptoms. SCA6 patients had reduced functional activity in the sensorimotor cortex, supplementary motor area (SMA), cerebellar vermis, and cerebellar lobules I-VI (corrected P < 0.05). Reduced task-based functional connectivity between cortical motor regions (i.e., primary motor cortex and SMA) and cerebellar regions (i.e., vermis and lobules I-VI) was found in SCA6 (corrected P < 0.05). SCA6 had elevated free-water values throughout the cerebellum as compared with controls (corrected P < 0.05). Importantly, reduced functional activity in the sensorimotor cortex and SMA and increased free-water in the superior cerebellar peduncle and cerebellar lobule V were related to more severe symptoms in SCA6 (all pairs: R 2 ≥ 0.4 and corrected P < 0.05). Current results demonstrate that impaired functional activity in sensorimotor cortex and SMA and elevated free-water of lobule V and superior cerebellar peduncle are both related to symptom severity, and may provide candidate biomarkers for SCA6.

CAG repeat length does not associate with the rate of cerebellar degeneration in spinocerebellar ataxia type 3

This cross-sectional study investigated the correlation between the CAG repeat length and the degeneration of cerebellum in spinocerebellar ataxia type 3 (SCA3) patients based on neuroimaging approaches. Forty SCA3 patients were recruited and classified into two subgroups according to their CAG repeat lengths (≥ 74 and < 74). We measured each patient's Scale for the Assessment and Rating of Ataxia (SARA) score, N-acetylaspartate (NAA)/creatine (Cr) ratios based on magnetic resonance spectroscopy (MRS), and 3-dimensional fractal dimension (3D-FD) values derived from magnetic resonance imaging (MRI) results. Furthermore, the 3D-FD values were used to construct structural covariance networks based on graph theoretical analysis. The results revealed that SCA3 patients with a longer CAG repeat length demonstrated earlier disease onset. However, the CAG repeat length did not significantly correlate with their SARA scores, cerebellar NAA/Cr ratios or cerebellar 3D-FD values. Network dissociation between cerebellar regions and parietal-occipital regions was found in SCA3 patients with CAG ≥ 74, but not in those with CAG < 74. In conclusion, the CAG repeat length is uncorrelated with the change of SARA score, cerebellar function and cerebellar structure in SCA3. Nevertheless, a longer CAG repeat length may indicate early structural covariance network dissociation.

Parametric fMRI of paced motor responses uncovers novel whole-brain imaging biomarkers in spinocerebellar ataxia type 3

Machado-Joseph Disease, inherited type 3 spinocerebellar ataxia (SCA3), is the most common form worldwide. Neuroimaging and neuropathology have consistently demonstrated cerebellar alterations. Here we aimed to discover whole-brain functional biomarkers, based on parametric performance-level-dependent signals. We assessed 13 patients with early SCA3 and 14 healthy participants. We used a combined parametric behavioral/functional neuroimaging design to investigate disease fingerprints, as a function of performance levels, coupled with structural MRI and voxel-based morphometry. Functional magnetic resonance imaging (fMRI) was designed to parametrically analyze behavior and neural responses to audio-paced bilateral thumb movements at temporal frequencies of 1, 3, and 5 Hz. Our performance-level-based design probing neuronal correlates of motor coordination enabled the discovery that neural activation and behavior show critical loss of parametric modulation specifically in SCA3, associated with frequency-dependent cortico/subcortical activation/deactivation patterns. Cerebellar/cortical rate-dependent dissociation patterns could clearly differentiate between groups irrespective of grey matter loss. Our findings suggest functional reorganization of the motor network and indicate a possible role of fMRI as a tool to monitor disease progression in SCA3. Accordingly, fMRI patterns proved to be potential biomarkers in early SCA3, as tested by receiver operating characteristic analysis of both behavior and neural activation at different frequencies. Discrimination analysis based on BOLD signal in response to the applied parametric finger-tapping task significantly often reached >80% sensitivity and specificity in single regions-of-interest.Functional fingerprints based on cerebellar and cortical BOLD performance dependent signal modulation can thus be combined as diagnostic and/or therapeutic targets in hereditary ataxia. Hum Brain Mapp 37:3656-3668, 2016. © 2016 Wiley Periodicals, Inc.