Spinocerebellar ataxia type 6: Systematic patho-anatomical study reveals different phylogenetically defined regions of the cerebellum and neural pathways undergo different evolutions of the degenerative process

Simple and clear differentiation of spinocerebellar degenerations: Overview of macroscopic and low-power view findings

Spinocerebellar degenerations (SCDs) are a diverse group of rare and slowly progressive neurological diseases that include spinocerebellar ataxia type 1 (SCA1), SCA2, SCA3, SCA6, SCA7, dentatorubral-pallidoluysian atrophy (DRPLA) and multiple system atrophy (MSA). They are often inherited, and affect the cerebellum and related pathways. The combination of clinical findings and lesion distribution has been the gold-standard for classifying SCDs. This conventional approach has not been very successful in providing a solid framework shared among researchers because their points of views have been quite variable. After identification of genetic abnormalities, classification was overwhelmed by genotyping, replacing the conventional approach far behind. In this review, we describe a stepwise operational approach that we constructed based only on macroscopic findings without microscopy to classify SCDs into three major groups: pure cerebellar type for SCA6 and SCA31; olivopontocerebellar (OPC) type for SCA1, SCA2, SCA7 and MSA; and dentatorubral-pallidoluysian (DRPL) type for SCA1, SCA3, DRPLA and progressive supranuclear palsy (PSP). Spinocerebellar tract involvement distinguishes SCA1 and SCA3 from DRPLA. Degeneration of the internal segment of the pallidum is accentuated in SCA3 and PSP, while degeneration of the external segment is accentuated in SCA1 and DRPLA. These contrasts are helpful in subdividing OPC and DRPL types to predict their genotypes. Lesion distribution represents disease-specific selective vulnerability, which is readily differentiated macroscopically using our stepwise operational approach. Precise prediction of the major genotypes will provide a basis to understand how genetic abnormalities lead to corresponding phenotypes through disease-specific selective vulnerabilities.

White Matter Integrity Underlies the Physical-Cognitive Correlations in Subjective Cognitive Decline

Objective: Although previous studies postulated that physical and cognitive decline codeveloped in preclinical dementia, the interconnected relationship among subjective cognitive complaints (SCCs), objective cognitive performance, and physical activity remained hazy. We investigated the mediating roles of physical activity between subjective and objective cognition. Diffusion tensor imaging (DTI) was utilized to test our hypothesis that brain white matter microstructural changes underlie the physical-cognitive decline in subjective cognitive decline (SCD).

Methods: We enrolled cognitively normal older adults aged > 50 years in the Community Medicine Research Center of Keelung Chang Gung Memorial Hospital during 2017–2020. Regression models analyzed mediation effects of physical activity between subjective and objective cognition. The self-reported AD8 questionnaire assessed SCCs. The SCD group, defined by AD8 score ≥ 2, further underwent diffusion MRI scans. Those who agreed to record actigraphy also wore the SOMNOwatch™ for 72 h. Spearman's correlation coefficients evaluated the associations of diffusion indices with physical activity and cognitive performance.

Results: In 95 cognitively normal older adults, the AD8 score and the Montreal Cognitive Assessment (MoCA) score were mediated partially by the metabolic equivalent of the International Physical Activity Questionnaire-Short Form (IPAQ-SF MET) and fully by the sarcopenia score SARC-F. That is, the relation between SCCs and poorer cognitive performance was mediated by physical inactivity. The DTI analysis of 31 SCD participants found that the MoCA score correlated with mean diffusivity at bilateral inferior cerebellar peduncles and the pyramids segment of right corticospinal tract [p < 0.05, false discovery rate (FDR) corrected]. The IPAQ-SF MET was associated with fractional anisotropy (FA) at the right posterior corona radiata (PCR) (p < 0.05, FDR corrected). In 15 SCD participants who completed actigraphy recording, the patterns of physical activity in terms of intradaily variability and interdaily stability highly correlated with FA of bilateral PCR and left superior corona radiata (p < 0.05, FDR corrected).

Conclusions: This study addressed the role of physical activity in preclinical dementia. Physical inactivity mediated the relation between higher SCCs and poorer cognitive performance. The degeneration of specific white matter tracts underlay the co-development process of physical-cognitive decline in SCD.

Modulation of error-sensitivity during a prism adaptation task in people with cerebellar degeneration

Cerebellar damage can profoundly impair human motor adaptation. For example, if reaching movements are perturbed abruptly, cerebellar damage impairs the ability to learn from the perturbation-induced errors. Interestingly, if the perturbation is imposed gradually over many trials, people with cerebellar damage may exhibit improved adaptation. However, this result is controversial, since the differential effects of gradual vs. abrupt protocols have not been observed in all studies. To examine this question, we recruited patients with pure cerebellar ataxia due to cerebellar cortical atrophy (n = 13) and asked them to reach to a target while viewing the scene through wedge prisms. The prisms were computer controlled, making it possible to impose the full perturbation abruptly in one trial, or build up the perturbation gradually over many trials. To control visual feedback, we employed shutter glasses that removed visual feedback during the reach, allowing us to measure trial-by-trial learning from error (termed error-sensitivity), and trial-by-trial decay of motor memory (termed forgetting). We found that the patients benefited significantly from the gradual protocol, improving their performance with respect to the abrupt protocol by exhibiting smaller errors during the exposure block, and producing larger aftereffects during the postexposure block. Trial-by-trial analysis suggested that this improvement was due to increased error-sensitivity in the gradual protocol. Therefore, cerebellar patients exhibited an improved ability to learn from error if they experienced those errors gradually. This improvement coincided with increased error-sensitivity and was present in both groups of subjects, suggesting that control of error-sensitivity may be spared despite cerebellar damage.

Macro- and microstructural changes in patients with spinocerebellar ataxia type 6: assessment of phylogenetic subdivisions of the cerebellum and the brain stem

BACKGROUND AND PURPOSE

Site-specific degeneration patterns of the infratentorial brain in relation to phylogenetic origins may relate to symptoms in patients with spinocerebellar degeneration, but the patterns are still unclear. We investigated macro- and microstructural changes of the infratentorial brain based on phylogenetic origins and their correlation with symptoms in patients with spinocerebellar ataxia type 6.

MATERIALS AND METHODS

MR images of 9 patients with spinocerebellar ataxia type 6 and 9 age- and sex-matched controls were obtained. We divided the infratentorial brain on the basis of phylogenetic origins and performed an atlas-based analysis. Comparisons of the 2 groups and a correlation analysis assessed with the International Cooperative Ataxia Rating Scale excluding age effects were performed.

RESULTS

A significant decrease of fractional volume and an increase of mean diffusivity were seen in all subdivisions of the cerebellum and in all the cerebellar peduncles except mean diffusivity in the inferior cerebellar peduncle in patients compared with controls (P < .0001 to <.05). The bilateral anterior lobes showed the strongest atrophy. Fractional volume decreased mainly in old regions, whereas mean diffusivity increased mainly in new regions of the cerebellum. Reflecting this tendency, the International Cooperative Ataxia Rating Scale total score showed strong correlations in fractional volume in the right flocculonodular lobe and the bilateral deep structures and in mean diffusivity in the bilateral posterior lobes (r = 0.73 to ±0.87).

CONCLUSIONS

We found characteristic macro- and microstructural changes, depending on phylogenetic regions of the infratentorial brain, that strongly correlated with clinical symptoms in patients with spinocerebellar ataxia type 6.

A review of quality of life after predictive testing for and earlier identification of neurodegenerative diseases

The past decade has witnessed an explosion of evidence suggesting that many neurodegenerative diseases can be detected years, if not decades, earlier than previously thought. To date, these scientific advances have not provoked any parallel translational or clinical improvements. There is an urgency to capitalize on this momentum so earlier detection of disease can be more readily translated into improved health-related quality of life for families at risk for, or suffering with, neurodegenerative diseases. In this review, we discuss health-related quality of life (HRQOL) measurement in neurodegenerative diseases and the importance of these "patient reported outcomes" for all clinical research. Next, we address HRQOL following early identification or predictive genetic testing in some neurodegenerative diseases: Huntington disease, Alzheimer's disease, Parkinson's disease, Dementia with Lewy bodies, frontotemporal dementia, amyotrophic lateral sclerosis, prion diseases, hereditary ataxias, Dentatorubral-pallidoluysian atrophy and Wilson's disease. After a brief report of available direct-to-consumer genetic tests, we address the juxtaposition of earlier disease identification with assumed reluctance toward predictive genetic testing. Forty-one studies examining health-related outcomes following predictive genetic testing for neurodegenerative disease suggested that (a) extreme or catastrophic outcomes are rare; (b) consequences commonly include transiently increased anxiety and/or depression; (c) most participants report no regret; (d) many persons report extensive benefits to receiving genetic information; and (e) stigmatization and discrimination for genetic diseases are poorly understood and policy and laws are needed. Caution is appropriate for earlier identification of neurodegenerative diseases but findings suggest further progress is safe, feasible and likely to advance clinical care.

Spinocerebellar ataxia types 1, 2, 3 and 6: the clinical spectrum of ataxia and morphometric brainstem and cerebellar findings

To assess the clinical spectrum of ataxia and cerebellar oculomotor deficits in the most common spinocerebellar ataxias (SCAs), we analysed the baseline data of the EUROSCA natural history study, a multicentric cohort study of 526 patients with either spinocerebellar ataxia type 1, 2, 3 or 6. To quantify ataxia symptoms, we used the Scale for the Assessment and Rating of Ataxia (SARA). The presence of cerebellar oculomotor signs was assessed using the Inventory of Non-Ataxia Symptoms (INAS). In a subgroup of patients, in which magnetic resonance images (MRIs) were available, we correlated MRI morphometric measures with clinical signs on an exploratory basis. The SARA subscores posture and gait (items 1-3), speech (item 4) and the limb kinetic subscore (items 5-8) did not differ between the genotypes. The scores of SARA item 3 (sitting), 5 (finger chase) and 6 (nose-finger test) differed between the subtypes whereas the scores of the remaining items were not different. In SCA1, ataxia symptoms were correlated with brainstem atrophy and in SCA3 with both brainstem and cerebellar atrophy. Cerebellar oculomotor deficits were most frequent in SCA6 followed by SCA3, whereas these abnormalities were less frequent in SCA1 and SCA2. Our data suggest that vestibulocerebellar, spinocerebellar and pontocerebellar circuits in SCA1, SCA2, SCA3 and SCA6 are functionally impaired to almost the same degree, but at different anatomical levels. The seemingly low prevalence of cerebellar oculomotor deficits in SCA1 and SCA2 is most probably related to the defective saccadic system in these disorders.