CAG repeat length and clinical features in three Italian families with spinocerebellar ataxia type 2 (SCA2): early impairment of Wisconsin Card Sorting Test and saccade velocity

Cognitive Impairments in Spinocerebellar Ataxia Type 10 and Their Relation to Cortical Thickness

BACKGROUND

Spinocerebellar ataxia type 10 is a neurodegenerative disorder caused by the expansion of an ATTCT pentanucleotide repeat. Its clinical features include ataxia and, in some cases, epileptic seizures. There is, however, a dearth of information about its cognitive deficits and the neural bases underpinning them.

OBJECTIVES

The objectives of this study were to characterize the performance of spinocerebellar ataxia type 10 patients in 2 cognitive domains typically affected in spinocerebellar ataxias, memory and executive function, and to correlate the identified cognitive impairments with ataxia severity and cerebral/cerebellar cortical thickness, as quantified by MRI.

METHODS

Memory and executive function tests were administered to 17 genetically confirmed Mexican spinocerebellar ataxia type 10 patients, and their results were compared with 17 healthy matched volunteers. MRI was performed in 16 patients.

RESULTS

Patients showed deficits in visual and visuospatial short-term memory, reduced storage capacity for verbal memory, and impaired monitoring, planning, and cognitive flexibility, which were ataxia independent. Patients with seizures (n = 9) and without seizures (n = 8) did not differ significantly in cognitive performance. There were significant correlations between short-term visuospatial memory impairment and posterior cerebellar lobe cortical thickness (bilateral lobule VI, IX, and right X). Cognitive flexibility deficiencies correlated with cerebral cortical thickness in the left middle frontal, cingulate, opercular, and temporal gyri. Cerebellar cortical thickness in several bilateral regions was correlated with motor impairment.

CONCLUSIONS

Patients with spinocerebellar ataxia type 10 show significant memory and executive dysfunction that can be correlated with deterioration in the posterior lobe of the cerebellum and prefrontal, cingulate, and middle temporal cortices.

Spinocerebellar ataxia type 2 from an evolutionary perspective: Systematic review and meta-analysis

Dominant diseases due to expanded CAG repeat tracts, such as spinocerebellar ataxia type 2 (SCA2), are prone to anticipation and worsening of clinical picture in subsequent generations. There is insufficient data about selective forces acting on the maintenance of these diseases in populations. We made a systematic review and meta-analysis on the effect of the CAG length over age at onset, instability of transmissions, anticipation, de novo or sporadic cases, fitness, segregation of alleles, and ancestral haplotypes. The correlation between CAG expanded and age at onset was r²  = 0.577, and transmission of the mutant allele was associated with an increase of 2.42 CAG repeats in the next generation and an anticipation of 14.62 years per generation, on average. One de novo and 18 sporadic cases were detected. Affected SCA2 individuals seem to have more children than controls. The expanded allele was less segregated than the 22-repeat allele in children of SCA2 subjects. Several ancestral SCA2 haplotypes were published. Data suggest that SCA2 lineages may tend to disappear eventually, due to strong anticipation phenomena. Whether or not the novel cases come from common haplotypes associated with a predisposition to further expansions is a question that needs to be addressed by future studies.

Cerebello-Cortical Alterations Linked to Cognitive and Social Problems in Patients With Spastic Paraplegia Type 7: A Preliminary Study

Spastic paraplegia type 7 (SPG7), which represents one of the most common forms of autosomal recessive spastic paraplegia (MIM#607259), often manifests with a complicated phenotype, characterized by progressive spastic ataxia with evidence of cerebellar atrophy on brain MRI. Recent studies have documented the presence of peculiar dentate nucleus hyperintensities on T2-weighted images and frontal executive dysfunction in neuropsychological tests in SPG7 patients. Therefore, we decided to assess whether any particular MRI pattern might be specifically associated with SPG7 mutations and possibly correlated with patients' cognitive profiles. For this purpose, we evaluated six SPG7 patients, studying the cerebello-cortical network by MRI voxel-based morphometry and functional connectivity techniques, compared to 30 healthy control subjects. In parallel, we investigated the cognitive and social functioning of the SPG7 patients. Our results document specific cognitive alterations in language, verbal memory, and executive function in addition to an impairment of social task and emotional functions. The MRI scans showed a diffuse symmetric reduction in the cerebellar gray matter of the right lobule V, right Crus I, and bilateral lobule VI, together with a cerebral gray matter reduction in the lingual gyrus, precuneus, thalamus, and superior frontal gyrus. The evidence of an over-connectivity pattern between both the right and left cerebellar dentate nuclei and specific cerebral regions (the lateral occipital cortex, precuneus, left supramarginal gyrus, and left superior parietal lobule) confirms the presence of cerebello-cortical dysregulation in different networks involved in cognition and social functioning in SPG7 patients.

Nonmotor symptoms in spinocerebellar ataxias (SCAs)

Nonmotor symptoms (NMS) have been increasingly recognized in a number of neurodegenerative diseases with a burden of disability that parallels or even surpasses that induced by motor symptoms. As NMS have often been poorly recognized and inadequately treated, much of the most recent developments in the investigation of these disorders has focused on the recognition and quantification of NMS, which will form the basis of improved clinical care for these complex cases. NMS have been only sparsely investigated in a limited number of spinocerebellar ataxias (SCAs), particularly SCA3, and have not been systematically reviewed for other forms of SCAs. The aim of the present study was to review the available literature on the presence of NMS among different types of SCAs.

The cerebellar topography of attention sub-components in spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease characterized by a progressive cerebellar syndrome and multiple-domain cognitive impairments. The cerebellum is known to contribute to distinct functional networks related to higher-level functions. The aims of the present study were to investigate the different sub-components of attention and to analyse possible correlations between attention deficits and specific cerebellar regions in SCA2 patients. To this purpose, 11 SCA2 patients underwent an exhaustive attention battery that evaluated several attention sub-components. The SCA2 group performed below the normal range in tasks assessing selective attention, divided attention, and sustained attention, obtaining negative Z-scores. These results were confirmed by non-parametric Mann-Whitney U tests that showed significant differences between SCA2 and control subjects in the same sub-components of the attention battery, allowing us to speculate on cerebellar involvement when a high cognitive demand is required (i.e., multisensory integration, sequencing, prediction of events, and inhibition of inappropriate response behaviours). The voxel-based morphometry analysis showed a pattern of significantly reduced grey matter volume in specific cerebellar lobules. In particular, the SCA2 patients showed significant grey matter loss in bilateral regions of the anterior cerebellar hemisphere (IV) and in the posterior lobe (VI-IX) and posterior vermis (VI-IX). Statistical analysis found significant correlations between grey matter reductions in the VIIb/VIIIa cerebellar lobules and impairments in Sustained and Divided Attention tasks and between grey matter reduction in the vermal VI lobule and impairment in the Go/NoGo task. For the first time, the study demonstrated the involvement of specific cerebellar lobules in different sub-components of the attention domain, giving further support to the inclusion of the cerebellum within the attention network.

The Multiple Faces of Spinocerebellar Ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is among the most common forms of autosomal dominant ataxias, accounting for 15% of the total families. Occurrence is higher in specific populations such as the Cuban and Southern Italian. The disease is caused by a CAG expansion in ATXN2 gene, leading to abnormal accumulation of the mutant protein, ataxin‐2, in intracellular inclusions. The clinical picture is mainly dominated by cerebellar ataxia, although a number of other neurological signs have been described, ranging from parkinsonism to motor neuron involvement, making the diagnosis frequently challenging for neurologists, particularly when information about the family history is not available. Although the functions of ataxin‐2 have not been completely elucidated, the protein is involved in mRNA processing and control of translation. Recently, it has also been shown that the size of the CAG repeat in normal alleles represents a risk factor for ALS, suggesting that ataxin‐2 plays a fundamental role in maintenance of neuronal homeostasis.

Cognitive Changes in the Spinocerebellar Ataxias Due to Expanded Polyglutamine Tracts: A Survey of the Literature

The dominantly-inherited ataxias characterised by expanded polyglutamine tracts—spinocere bellar ataxias (SCAs) 1, 2, 3, 6, 7, 17, dentatorubral pallidoluysian atrophy (DRPLA) and, in part, SCA 8—have all been shown to result in various degrees of cognitive impairment. We survey the literature on the cognitive consequences of each disorder, attempting correlation with their published neuropathological, magnetic resonance imaging (MRI) and clinical features. We suggest several psychometric instruments for assessment of executive function, whose results are unlikely to be confounded by visual, articulatory or upper limb motor difficulties. Finally, and with acknowledgement of the inadequacies of the literature to date, we advance a tentative classification of these disorders into three groups, based on the reported severity of their cognitive impairments, and correlated with their neuropathological topography and MRI findings: group 1—SCAs 6 and 8—mild dysexecutive syndrome based on disruption of cerebello-cortical circuitry; group 2—SCAs 1, 2, 3, and 7—more extensive deficits based largely on disruption of striatocortical in addition to cerebello-cerebral circuitry; and group 3—SCA 17 and DRPLA—in which cognitive impairment severe enough to cause a dementia syndrome is a frequent feature.

FTLD-ALS of TDP-43 type and SCA2 in a family with a full ataxin-2 polyglutamine expansion

Polyglutamine expansions in the ataxin-2 gene (ATXN2) cause autosomal dominant spinocerebellar ataxia type 2 (SCA2), but have recently also been associated with amyotrophic lateral sclerosis (ALS). We present clinical and pathological features of a family in which a pathological ATXN2 expansion led to frontotemporal lobar degeneration with ALS (FTLD-ALS) in the index case, but typical SCA2 in a son, and compare the neuropathology with a case of typical SCA2. The index case shares the molecular signature of SCA2 with prominent polyglutamine and p62-positive intranuclear neuronal inclusions mainly in the pontine nuclei, while harbouring more pronounced neocortical and spinal TDP-43 pathology. We conclude that ATXN2 mutations can cause not only ALS, but also a neuropathological overlap syndrome of SCA2 and FTLD presenting clinically as pure FTLD-ALS without ataxia. The cause of the phenotypic heterogeneity remains unexplained, but the presence of a CAA-interrupted CAG repeat in the FTLD case in this family suggests that one potential mechanism may be variation in repeat tract composition between members of the same family.

Longitudinal study of cognitive and psychiatric functions in spinocerebellar ataxia types 1 and 2

The role of the cerebellum in cognition, both in healthy subjects and in patients with cerebellar diseases, is debated. Neuropsychological studies in spinocerebellar ataxia type 1 (SCA1) and type 2 (SCA2) demonstrated impairments in executive functions, verbal memory, and visuospatial performances, but prospective evaluations are not available. Our aims were to assess progression of cognitive and psychiatric functions in patients with SCA1 and SCA2 in a longitudinal study. We evaluated at baseline 20 patients with SCA1, 22 patients with SCA2 and 17 matched controls. Two subgroups of patients (9 SCA1, 11 SCA2) were re-evaluated after 2 years. We tested cognitive functions (Mini Mental State Examination, digit span, Corsi span, verbal memory, attentional matrices, modified Wisconsin Card Sorting Test, Raven Progressive Matrices, Benton test, phonemic and semantic fluency), psychiatric status (Scales for Assessment of Negative and Positive Symptoms, Hamilton Depression and Anxiety Scales), neurological conditions (Scale for Assessment and Rating of Ataxia), and functional abilities (Unified Huntington Disease Rating Scale–part IV). At baseline, SCA1 and SCA2 patients had significant deficits compared to controls, mainly in executive functions (phonemic and semantic fluencies, attentional matrices); SCA2 showed further impairment in visuospatial and visuoperceptive tests (Raven matrices, Benton test, Corsi span). Both SCA groups had higher depression and negative symptoms, particularly apathy, compared to controls. After 2 years, motor and functional disability worsened, while only attentive performances deteriorated in SCA2. This longitudinal study showed dissociation in progression of motor disability and cognitive impairment, suggesting that in SCA1 and SCA2 motor and cognitive functions might be involved with different progression rates.

Saccadic latency is prolonged in Spinocerebellar Ataxia type 2 and correlates with the frontal-executive dysfunctions

Data on saccadic latency in patients with Spinocerebellar Ataxia 2 (SCA2) are sparse and contradictory. In order to determine whether saccadic latency is definitely prolonged, identify its possible determinants and evaluate it as disease biomarker we assessed the saccadic latency by electronystagmography in 110 SCA2 patients and their paired controls. Mean saccadic latencies were significantly longer in patients when compared to controls for all tested target displacements. Forty-six percent of SCA2 patients had saccadic latencies above the normal range. Reciprobit plots of saccadic latency demonstrated a skewed distribution in the direction of longer latencies for the patients compared to controls. As saccadic latency increased, the velocity and amplitude of saccades significantly decreased in SCA2 subjects but not in controls. Saccadic latency was not influenced by any demographical, clinical or molecular SCA2 variables, but it showed a significant correlation with the performance of the Stroop test, the verbal fluency test and the Wisconsin Card Sorting Test in SCA2 patients. This paper demonstrated that saccadic latency is prolonged in SCA2 patients and it significantly correlates with the performance of frontal-executive functions, thus this parameter could be a useful biomarker to evaluate the efficiency of future therapeutical options on these dysfunctions.

No observable relationship between the 12 genes of nervous system and reasoning skill in a young Chinese Han population

Reasoning skill is an advanced cognitive ability which is needed for drawing inferences from given information. It is well known that the ability depends on the neural network of the frontal and parietal brain regions. In this study, we hypothesized that some genes involved in neurotransmitter systems were related to reasoning skill. To confirm this hypothesis, we examined the effects of 13 genes (BDNF, NRSF, COMT, DBH, DRD(2), DRD(3), DAT(1), MAOA, GRM(1), GRIN2B, TPH(2), 5-HT(2A), and 5-HT(6)) in neurotransmitter systems on the non-verbal reasoning and verbal reasoning skills. The results indicated there were on significant effects of the 17 functional variants of these genes on the performance of non-verbal reasoning and verbal analogical reasoning skills (χ(2) > 3.84, df = 1, P > 0.05). This study suggests that some of the functional variations in BDNF, COMT, DBH, DRD(2), DRD(3), MAOA, 5-HT(2A), 5-HT(6), GRM(1), and GRIN2B have no observable effects on the certain reasoning skills in a young healthy Chinese Han population.

Cognition in hereditary ataxia

Apart from motor control the cerebellum has been implicated in higher cortical functions such as memory, fronto-executive functions, visuoconstructive skills and emotion. Clinical descriptions of hereditary ataxias mention cognitive impairment to a variable extent. Systematic neuropsychological studies are limited. Regarding the neuropathological pattern in different SCA types, cognitive deficits in hereditary ataxias are not likely to be contingent upon cerebellar degeneration but to result from disruption of cerebrocerebellar circuitries at various levels in the CNS.

Cognitive impairment in spinocerebellar ataxia type 8

OBJECTIVES

Only a limited number of studies have investigated the cognitive performances of spinocerebellar ataxia (SCA) patients. In none of the SCA8 studies have the neuropsychological test performances been the primary measures. The objective of the current study was to investigate the characteristics of cognitive deficits in SCA8.

METHODS

Ten SCA8 patients and ten case-by-case matched control subjects underwent a comprehensive neuropsychological examination evaluating attention and information processing, concept formation, reasoning and executive functions, verbal production, memory and learning and visuoperceptual and -constructive functions.

RESULTS

SCA8 patients demonstrated deficits primarily in attention and information processing, as well as in concept formation, reasoning, executive functions and verbal production. Visuoperceptual and -constructive functions, as well as most of the performances of memory were unaffected.

CONCLUSIONS

Cognitive impairments, especially those related to attention, information processing and executive functions, seem to be a clinical feature of SCA8 disease.

Cognitive findings in spinocerebellar ataxia type 2: relationship to genetic and clinical variables

Several authors have recently reported a broad cognitive impairment in autosomal dominant cerebellar ataxias (ADCAs) patients. However, only a few studies on neuropsychological features in spinocerebellar ataxia type 2 (SCA2) patients are present in the current literature. The aim of this study is to evaluate the cognitive impairment in a wide sample of SCA2 patients and to verify the role of different disease-related factors (age of onset, disease duration, and clinical severity) on intellectual abilities. We administered a battery of neuropsychological tests assessing handedness, attention, short- and long-term verbal and visuo-spatial memory, executive functions, constructive abilities, general intellectual abilities and depression to 18 SCA2 patients belonging to eight families who came to our observation. Evidence of impaired verbal memory, executive functions and attention was found. The cognitive status was partially related to clinical severity rather than to disease duration or age at onset of symptoms. We partially confirmed data on cognitive defects already reported by others but we also found defective attention skills as well as significant lower performances in a nonverbal intelligence task.