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

Large-scale evidence for the validity of remote MoCA administration among people with cerebellar ataxia

Objective: For over half a century, studies of rare diseases using in-person cognitive tools have faced challenges, such as long study periods and small sample sizes (e.g. n = 10). The Montreal Cognitive Assessment (MoCA) was widely employed to assess mild cognitive impairment (MCI). We aimed to validate a modified online version of the MoCA in a large sample of a rare disease (population prevalence < .01%). Method: First, we analyzed 20 previous findings (n = 1,377), comparing the MoCA scores between large groups of neurotypically healthy (NH; n = 837) and cerebellar ataxia (CA; n = 540), where studies were conducted in-person. Second, we administered the MoCA in-person to a group of NH (n = 41) and a large group of CA (n = 103). Third, we administered a video conferencing version of the MoCA to NH (n = 38) and a large group of CA (n = 83). Results: We observed no performance differences between online and in-person MoCA administration in the NH and CA groups (p > .05, η2 = 0.001), supporting reliability. Additionally, our online CA group had lower MoCA scores than the NH group (p < .001, Hedges' g = 0.68). This result is consistent with previous studies, as demonstrated by our forest plot across 20 previous in-person findings, supporting construct validity. Conclusion: The results indicate that an online screening tool is valid in a large sample of individuals with CA. Online testing is not only time and cost-effective, but facilitates disease management and monitoring, ultimately enabling early detection of MCI.

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.

Temporal Invariance in SCA6 Is Related to Smaller Cerebellar Lobule VI and Greater Disease Severity

Regulating muscle force and timing are fundamental for accurate motor performance. In spinocerebellar ataxia type 6 (SCA6), there is evidence that individuals have greater force dysmetria but display better temporal accuracy during fast goal directed contractions. Here, we test whether greater temporal accuracy occurs in all individuals with SCA6, and can be explained by lesser temporal variability. Further we examine whether it is linked to disease severity and specific degenerative changes in the cerebellum. Nineteen human participants with SCA6 (13 woman) and 18 healthy controls performed fast goal-directed ankle dorsiflexion contractions aiming at a spatiotemporal target. We quantified the endpoint control of these contractions, gray matter (GM) integrity of the cerebellum, and disease severity using the International Cooperative Ataxia Rating Scale (ICARS). SCA6 individuals exhibited lower temporal endpoint error and variability than the healthy controls (p = 0.008). Statistically, SCA6 clustered into two distinct groups for temporal variability. A group with low temporal variability ranging from 10 to 19% (SCA6a) and a group with temporal variability similar to healthy controls (SCA6b; 19-40%).SCA6a exhibited greater disease severity than SCA6b, as assessed with ICARS (p < 0.001). Lower temporal variability, which was not associated with disease duration (R ² = 0.1, p > 0.2), did correlate with both greater ICARS (R ² = 0.3) and reduced GM volume in cerebellar lobule VI (R ² = 0.35). Other cerebellar lobules did not relate to temporal variability. We provide new evidence that a subset of SCA6 with greater loss of GM in cerebellum lobule VI exhibit temporal invariance and more severe ataxia than other SCA6 individuals.SIGNIFICANCE STATEMENT Variability is an inherent feature of voluntary movement, and traditionally more variability in the targeted output infers impaired performance. For example, cerebellar patients present exacerbated temporal variability during multijoint movements, which is thought to contribute to their motor deficits. In the current work, we show that in a subgroup of spinocerebellar ataxia type 6 individuals, temporal variability is lower than that of healthy controls when performing single-joint fast-goal directed movements. This invariance related to exacerbated atrophy of lobule VI of the cerebellum and exacerbated disease severity. The relation between invariance and disease severity suggests that pathological motor variability can manifest not only as an exacerbation but also as a reduction relative to healthy controls.

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.

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.