The role of the SCA2 trinucleotide repeat expansion in 89 autosomal dominant cerebellar ataxia families. Frequency, clinical and genetic correlates

Movement Disorders in Hereditary Cerebellar Ataxia

BACKGROUND

Hereditary cerebellar ataxia (HCA) represents a complex group of disorders, with a wide spectrum of neurological symptoms. Among these, non-ataxia movement disorders (MD) have been increasingly acknowledged, with variable frequency across different forms.

OBJECTIVES

To characterize the type and frequency of MD in patients with HCA. To identify factors associated with MD and analyze their impact on disability.

METHODS

We conducted a prospective study starting in 2017, with annual visits according to a structured protocol. Patients were selected from the study database and their clinical and genetic features analyzed.

RESULTS

The cohort comprised 193 symptomatic patients. Machado-Joseph disease (MJD, also SCA3 or ATX-ATXN3) and cerebellar ataxia, neuropathy and vestibular areflexia syndrome (ATX-RFC1) were the most common autosomal dominant (AD) or recessive forms, with a frequency of 14.0% and 15.0%, respectively. MD were present in 95 (54.4%), with dystonia being the most common (49.2%). Tremor was identified in 10.9%, Parkinsonism in 4.1% and chorea in 3.6% patients. Myoclonus and tics were rare (2.6% and 0.5%). The presence of MD was associated with AD inheritance and ATXN3. MD, regardless of type, correlated with higher SARA score at baseline, increased fall frequency, confinement to wheelchair, and earlier occurrence of falls and of permanent use of walking aid.

CONCLUSIONS

Movement disorders, particularly dystonia, were common in our cohort. This highlights the possible role of the cerebellum in MD, but also extra-cerebellar involvement in some HCA. Presence of MD significantly worsened motor disability, highlighting the need for strategies of early identification and tailored management.

CAG repeat mosaicism is gene specific in spinocerebellar ataxias

Expanded CAG repeats in coding regions of different genes are the most common cause of dominantly inherited spinocerebellar ataxias (SCAs). These repeats are unstable through the germline, and larger repeats lead to earlier onset. We measured somatic expansion in blood samples collected from 30 SCA1, 50 SCA2, 74 SCA3, and 30 SCA7 individuals over a mean interval of 8.5 years, along with postmortem tissues and fetal tissues from SCA1, SCA3, and SCA7 individuals to examine somatic expansion at different stages of life. We showed that somatic mosaicism in the blood increases over time. Expansion levels are significantly different among SCAs and correlate with CAG repeat lengths. The level of expansion is greater in individuals with SCA7 who manifest disease compared to that of those who do not yet display symptoms. Brain tissues from SCA individuals have larger expansions compared to the blood. The cerebellum has the lowest mosaicism among the studied brain regions, along with a high expression of ATXNs and DNA repair genes. This was the opposite in cortices, with the highest mosaicism and lower expression of ATXNs and DNA repair genes. Fetal cortices did not show repeat instability. This study shows that CAG repeats are increasingly unstable during life in the blood and the brain of SCA individuals, with gene- and tissue-specific patterns.

Epidemiology of ataxia and hereditary spastic paraplegia in Spain: a cross-sectional study

INTRODUCTION

Ataxia and hereditary spastic paraplegia are rare neurodegenerative syndromes. We aimed to determine the prevalence of these disorders in Spain in 2019.

PATIENTS AND METHODS

We conducted a cross-sectional, multicentre, retrospective, descriptive study of patients with ataxia and hereditary spastic paraplegia in Spain between March 2018 and December 2019.

RESULTS

We gathered data from a total of 1933 patients from 11 autonomous communities, provided by 47 neurologists or geneticists. Mean (SD) age in our sample was 53.64 (20.51) years; 982 patients were men (50.8%) and 951 were women (49.2%). The genetic defect was unidentified in 920 patients (47.6%). A total of 1371 patients (70.9%) had ataxia and 562 (29.1%) had hereditary spastic paraplegia. Prevalence rates for ataxia and hereditary spastic paraplegia were estimated at 5.48 and 2.24 cases per 100 000 population, respectively. The most frequent type of dominant ataxia in our sample was SCA3, and the most frequent recessive ataxia was Friedreich ataxia. The most frequent type of dominant hereditary spastic paraplegia in our sample was SPG4, and the most frequent recessive type was SPG7.

CONCLUSIONS

In our sample, the estimated prevalence of ataxia and hereditary spastic paraplegia was 7.73 cases per 100 000 population. This rate is similar to those reported for other countries. Genetic diagnosis was not available in 47.6% of cases. Despite these limitations, our study provides useful data for estimating the necessary healthcare resources for these patients, raising awareness of these diseases, determining the most frequent causal mutations for local screening programmes, and promoting the development of clinical trials.

TR-FRET-Based Immunoassay to Measure Ataxin-2 as a Target Engagement Marker in Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited neurodegenerative disease, which belongs to the trinucleotide repeat disease group with a CAG repeat expansion in exon 1 of the ATXN2 gene resulting in an ataxin-2 protein with an expanded polyglutamine (polyQ)-stretch. The disease is late manifesting leading to early death. Today, therapeutic interventions to cure the disease or even to decelerate disease progression are not available yet. Furthermore, primary readout parameter for disease progression and therapeutic intervention studies are limited. Thus, there is an urgent need for quantifiable molecular biomarkers such as ataxin-2 becoming even more important due to numerous potential protein-lowering therapeutic intervention strategies. The aim of this study was to establish a sensitive technique to measure the amount of soluble polyQ-expanded ataxin-2 in human biofluids to evaluate ataxin-2 protein levels as prognostic and/or therapeutic biomarker in SCA2. Time-resolved fluorescence energy transfer (TR-FRET) was used to establish a polyQ-expanded ataxin-2-specific immunoassay. Two different ataxin-2 antibodies and two different polyQ-binding antibodies were validated in three different concentrations and tested in cellular and animal tissue as well as in human cell lines, comparing different buffer conditions to evaluate the best assay conditions. We established a TR-FRET-based immunoassay for soluble polyQ-expanded ataxin-2 and validated measurements in human cell lines including iPSC-derived cortical neurons. Additionally, our immunoassay was sensitive enough to monitor small ataxin-2 expression changes by siRNA or starvation treatment. We successfully established the first sensitive ataxin-2 immunoassay to measure specifically soluble polyQ-expanded ataxin-2 in human biomaterials.

Adult-onset Niemann-Pick disease type C masquerading as spinocerebellar ataxia

Background

Adult‐onset Nieman–Pick disease type C (NPC) is a rare progressive ataxia caused by lysosomal accumulation of unesterified cholesterol resulting in severe disability and death. The diagnosis of NPC can be challenging as clinical features overlap with other more common hereditary ataxias. This study pursued the molecular genetic basis of adult‐onset cerebellar ataxia manifesting in two siblings. A prior diagnosis of spinocerebellar ataxia type 2 (SCA2) based on an ataxia gene panel was questioned when the younger sibling developed similar symptoms but had discordant genetic results.

Methods

Neurologic examination, whole exome sequence (WES), targeted sequence to establish genome phasing, and cytochemical and biochemical studies of fibroblast cultures were employed.

Results

The pedigree and neurological examinations suggested a recessive or possibly dominant cerebellar ataxia. WES showed the siblings were both compound heterozygous for two rare variants in the NPC1 gene—one pathogenic, stop gain at p.Arg934Ter (NM_000271.4), and a missense change, p.Pro471Leu (NM_000271.4), of uncertain significance. Filipin staining of fibroblast cultures showed lysosomal cholesterol accumulation and biochemical assay demonstrated impaired cholesterol esterification.

Conclusions

The study established the correct molecular diagnosis of biallelic, adult‐onset NPC in a patient initially diagnosed with SCA. Additionally, the p.Pro471Leu variant was identified as likely pathogenic. Inaccurate molecular diagnosis will deprive NPC patients of treatment options. Investigation using WES is justified when a detected expansion size is in the borderline range for pathogenicity.

RNA Toxicity and Perturbation of rRNA Processing in Spinocerebellar Ataxia Type 2

BACKGROUND

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease caused by expansion of a CAG repeat in Ataxin-2 (ATXN2) gene. The mutant ATXN2 protein with a polyglutamine tract is known to be toxic and contributes to the SCA2 pathogenesis.

OBJECTIVE

Here, we tested the hypothesis that the mutant ATXN2 transcript with an expanded CAG repeat (expATXN2) is also toxic and contributes to SCA2 pathogenesis.

METHODS

The toxic effect of expATXN2 transcripts on SK-N-MC neuroblastoma cells and primary mouse cortical neurons was evaluated by caspase 3/7 activity and nuclear condensation assay, respectively. RNA immunoprecipitation assay was performed to identify RNA binding proteins (RBPs) that bind to expATXN2 RNA. Quantitative PCR was used to examine if ribosomal RNA (rRNA) processing is disrupted in SCA2 and Huntington's disease (HD) human brain tissue.

RESULTS

expATXN2 RNA induces neuronal cell death, and aberrantly interacts with RBPs involved in RNA metabolism. One of the RBPs, transducin β-like protein 3 (TBL3), involved in rRNA processing, binds to both expATXN2 and expanded huntingtin (expHTT) RNA in vitro. rRNA processing is disrupted in both SCA2 and HD human brain tissue.

CONCLUSION

These findings provide the first evidence of a contributory role of expATXN2 transcripts in SCA2 pathogenesis, and further support the role of expHTT transcripts in HD pathogenesis. The disruption of rRNA processing, mediated by aberrant interaction of RBPs with expATXN2 and expHTT transcripts, suggest a point of convergence in the pathogeneses of repeat expansion diseases with potential therapeutic implications. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

SCA2 in the Indian population: Unified haplotype and variable phenotypic patterns in a large case series

BACKGROUND

Spinocerebellar ataxia-2 is one of the most prevalent SCA type across the world and one of the commonest in India. We aimed to characterize SCA2 patients both clinically and genetically (ATXN2-CAG repeats and its haplotypic background).

METHODS

A total of 436 SCA2 patients were recruited consecutively comprising individuals of multiple ethnicities and two large multigenerational families. A detailed clinical evaluation and genetic analysis for CAG repeat length estimation and two marker based haplotype analysis [rs695871 and rs695872 located 177 bp and 106 bp upstream of CAG sequence in Exon 1 of ATXN2] was performed.

RESULTS

Generalized limb ataxia and slow saccades were prevalent features in majority of our patients, while hyporeflexia and extrapyramidal features were less commonly observed manifestations. Slow ocular saccades, upper limb ataxia and tremor showed significant associations with age of onset, CAG repeat length and disease duration. We observed a 100% association of C-C haplotype with the expanded ATXN2 repeats.

CONCLUSION

This study represents the largest study of SCA2 Indian patients that highlights the clinico-genetic manifestations and haplotype analysis. A significant proportion of patients have not shown the characteristic slow saccades and hyporeflexia thus indicating the influences of other factors in modulation of the disease which warrants further investigations. The observation of CC haplotype in all our SCA2 patients indicates a common origin across all Indian sub populations and that also indicate a common global founder event in the past.

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.

Epidemiology of ataxia and hereditary spastic paraplegia in Spain: a cross-sectional study

INTRODUCTION

Ataxia and hereditary spastic paraplegia are rare neurodegenerative syndromes. We aimed to determine the prevalence of these disorders in Spain in 2019.

PATIENTS AND METHODS

We conducted a cross-sectional, multicentre, retrospective, descriptive study of patients with ataxia and hereditary spastic paraplegia in Spain between March 2018 and December 2019.

RESULTS

We gathered data from a total of 1.809 patients from 11 autonomous communities, provided by 47 neurologists or geneticists. Mean (SD) age in our sample was 53.64 (20.51) years; 920 patients were men (50.8%) and 889 were women (49.2%). The genetic defect was unidentified in 920 patients (47.6%). A total of 1371 patients (70.9%) had ataxia and 562 (29.1%) had hereditary spastic paraplegia. Prevalence rates for ataxia and hereditary spastic paraplegia were estimated at 5.48 and 2.24 cases per 100 000 population, respectively. The most frequent type of dominant ataxia in our sample was SCA3, and the most frequent recessive ataxia was Friedreich ataxia. The most frequent type of dominant hereditary spastic paraplegia in our sample was SPG4, and the most frequent recessive type was SPG7.

CONCLUSIONS

In our sample, the estimated prevalence of ataxia and hereditary spastic paraplegia was 7.73 cases per 100 000 population. This rate is similar to those reported for other countries. Genetic diagnosis was not available in 47.6% of cases. Despite these limitations, our study provides useful data for estimating the necessary healthcare resources for these patients, raising awareness of these diseases, determining the most frequent causal mutations for local screening programmes, and promoting the development of clinical trials.

Huntington's disease: lessons from prion disorders

Decades of research on the prion protein and its associated diseases have caused a paradigm shift in our understanding of infectious agents. More recent years have been marked by a surge of studies supporting the application of these findings to a broad array of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here, we present evidence to suggest that Huntington's disease, a monogenic disorder of the central nervous system, shares features with prion disorders and that, it too, may be governed by similar mechanisms. We further posit that these similarities could suggest that, like other common neurodegenerative disorders, sporadic forms of Huntington's disease may exist.

EMG Rectification Is Detrimental for Identifying Abnormalities in Corticomuscular and Intermuscular Coherence in Spinocerebellar Ataxia Type 2

Corticomuscular and intermuscular coherence (CMC, IMC) reflect connectivity between neuronal activity in the motor cortex measured by electroencephalography (EEG) and muscular activity measured by electromyography (EMG), or between activity in different muscles, respectively. There is an ongoing debate on the appropriateness of EMG rectification prior to coherence estimation. This work examines the effects of EMG rectification in CMC and IMC estimation in 20 spinocerebellar ataxia type 2 (SCA2) patients, 16 prodromal SCA2 gene mutation carriers, and 26 healthy controls during a repetitive upper or lower limb motor task. Coherence estimations were performed using the non-rectified raw EMG signal vs. the rectified EMG signal. EMG rectification decreases the level of significance of lower beta-frequency band CMC and IMC values in SCA2 patients and prodromal SCA2 mutation carriers vs. healthy controls, and also results in overall lower coherence values. EMG rectification is detrimental for beta-frequency band CMC and IMC estimation. One likely reason for this effect is distortion of coherence estimation in high-frequency signals, where the level of amplitude cancelation is high.

Non-ataxic manifestations of Spinocerebellar ataxia-2, their determinants and predictors

INTRODUCTION

To evaluate the non-ataxic clinical manifestations in genetically proven Spinocerebellar ataxia 2 (SCA2) and identify their determinants and predictors.

METHODS

Seventy-three subjects with genetically proven SCA2 were evaluated clinically for the common non-ataxic manifestations. Based on the presence or absence of non-ataxic manifestations, patients were classified into groups and then compared for significant differences in the CAG repeat length, age at onset (AAO), duration of disease, and ataxia rating score. Predictors of non-ataxic symptoms were identified using multivariable binary logistic regression.

RESULTS

The most common non-ataxic clinical manifestations were peripheral neuropathy, extrapyramidal features, pyramidal signs, cognitive impairment and lower motor neuron signs. The CAG repeat length was inversely related to the AAO of symptoms (r = -0.46, p < .001). Patients with peripheral neuropathy and psychiatric symptoms had earlier AAO. Patients with cognitive impairment and extrapyramidal symptoms had higher CAG repeat length whereas presence of lower motor neuron signs was more common in patients with lower CAG repeat length.

CONCLUSION

The lower strength of association between CAG repeat length and AAO in our cohort suggests the presence of additional factors underlying the variability in AAO. Both CAG repeat length and AAO were identified as significant determinants and predictors of non-ataxic symptoms.

Optokinetic nystagmus in patients with SCA: A bedside test for oculomotor dysfunction grading

OBJECTIVE

To characterize the clinical features in patients with spinocerebellar ataxia (SCA) type 1, SCA2, and SCA3 and to evaluate the oculomotor dysfunction by using optokinetic nystagmus (OKN) testing, which may be a sensitive marker.

METHODS

In this prospective observational study, all patients underwent detailed neurologic examination with special emphasis on eye movements. OKN was evaluated with a tape. Disease severity was measured with the International Co-Operative Ataxia Rating Scale (ICARS).

RESULTS

A total of 73 genetically confirmed patients were included, of whom 28, 30, and 15 patients were positive for SCA1, SCA2, and SCA3, respectively. Dystonia was more common in patients with SCA3 (46%), and absent ankle jerk was more common in those with SCA2 (21.4%). Brisk deep tendon reflexes were common in patients with SCA1 (46.6%), followed by patients with SCA3 (26.6%) and SCA2 (7.1%). Vertical OKN was impaired in all patients and absent in 86.6% of patients with SCA1, 96% of those with SCA2, and 80% of those with SCA3. Horizontal OKN was absent in 30% of patients with SCA1, 57% of patients with SCA2, and 33% of those with SCA3. Higher motor disability (posture and gait, kinetic functions [Motor Disability] subscore on the ICARS) was associated with higher oculomotor dysfunction measured by OKN-saccades impairment grading but not with the Ocular Disorder subscore of ICARS (ICARS-OD).

CONCLUSION

OKN-saccades are a better and sensitive bedside clinical tool to quantify oculomotor dysfunction in neurodegenerative ataxias. Its role needs to be tested further in presymptomatic carriers. The current ICARS-OD scale to grade oculomotor dysfunction in degenerative ataxias need to be modified.

Challenges in sleep stage R scoring in patients with autosomal dominant spinocerebellar ataxias (SCA1, SCA2 and SCA3) and oculomotor abnormalities: a whole night polysomnographic evaluation

OBJECTIVES

Spinocerebellar ataxias are progressive neurodegenerative disorders characterized by progressive cerebellar features with additional neuro-axis involvement. Oculomotor abnormality is one of the most frequent manifestations. This study was done to assess the polysomnographic abnormalities in patients with Spinocerebellar ataxia (SCA1, SCA2 and SCA3) and also to evaluate whether oculomotor abnormalities interfere with sleep stage R scoring.

METHODS

The study was carried out using 36 genetically positive SCA patients. All patients underwent neurological examination with special focus on oculomotor function (optokinetic nystagmus-OKN and extraocular movement restriction-EOM). The sleep quality was measured with Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS). Disease severity was assessed with International Cooperative Ataxia Rating Scale (ICARS). All the patients underwent over-night video-polysomnography (VPSG).

RESULTS

Out of 36 patients studied, the data of 34 patients [SCA1 (n = 12), SCA2 (n = 13), SCA3 (n = 9)] were used for final analysis. Patients from SCA1, SCA2, and SCA3 category did not show significant differences in age and diseases severity (ICARS). All patients had vertical OKN impairment. Oculomotor impairment was higher in SCA2 patients. Sleep macro-architecture analysis showed absent stage R sleep, predominantly in SCA2 (69%) followed by SCA3 (44%) and SCA1 (8%). Patients showed a strong negative correlation of stage R sleep percentage with disease severity and oculomotor dysfunction.

CONCLUSION

Voluntary saccadic eye movement velocity and rapid eye movements (REMs) in sleep are strongly correlated. The more severe the saccadic velocity impairment, the less likely was it to generate REMs (rapid eye movements) during stage R. Accordingly 69% of SCA2 patients with severe occulomotor impairments showed absent stage R as per the AASM sleep scoring. We presume that the impaired REMs generation in sleep could be due to oculomotor abnormality and has resulted in spuriously low or absent stage R sleep percentage in SCA patients with conventional VPSG scoring rules. The present study recommends the modification of AASM scoring rules for stage R in patients with oculomotor abnormalities.

Epidemiological, clinical, and genotype characterization of spinocerebellar ataxia type in families in Buriram province, northeast Thailand

Background

In Thais, the most prevalent type of spinocerebellar ataxia (SCA) is type 3, most commonly known as Machado–Joseph disease (MJD), followed by SCA type 1 (SCA1), SCA2, and SCA6.

Objectives

To describe the epidemiological, clinical, and genotypic features of SCA in northeastern Thailand and to study 2 associations: between syndromic features and the genotype of SCA, and between health determinants and scores on the scale for the assessment and rating of ataxia (SARA).

Methods

We conducted a cross-sectional study of 24 patients with autosomal dominant SCA from 13 families recruited from Buriram province in northeast Thailand between December 2009 and January 2014. Patients provided a clinical history and were examined by a neurologist. DNA was extracted from the peripheral blood of each patient. We analyzed associations between the type of SCA and sex, age, family history, clinical features, any underlying disease, age at onset, body weight, smoking status, family history, alcohol consumption, head injury history, and SARA.

Results

Seven of the families were positive for SCA1 and 6 for MJD. There were 24 index patients from these autosomal dominant SCA families, including 13 with SCA1 and 11 with MJD. Their average age was 43.7 years (range 20–72 years), whereas their average age at disease onset was 36.9 years (range 18–59 years). Pyramidal signs between MJD and SCA1 were not significantly different. Extrapyramidal features appeared uncommon. Horizontal nystagmus and upward gaze paresis were significantly associated with MJD. There were no significant differences in demographic data between the groups with SARA scores ≥15 or <15.

Conclusions

MJD and SCA1 were the 2 adult-onset cerebellar degenerative diseases found in Buriram province. Clinical clues for differentiating between them were upward gaze paresis and horizontal nystagmus, which were significantly more common in MJD.

Presentation and care of a family with Huntington disease in a resource-limited community

BACKGROUND

In high-income countries patients with Huntington disease (HD) typically present to healthcare providers after developing involuntary movements, or for pre-symptomatic genetic testing if at familial risk. A positive family history is a major guide when considering the decision to perform genetic testing for HD, both in affected and unaffected patients. Management of HD is focused upon control of symptoms, whether motor, cognitive, or psychiatric. There is no clear evidence to date of any disease-modifying agents. Referral of families and caregivers for psychological and social support, whether to HD-focused centers, or through virtual communities, is viewed as an important consequence of diagnosis. The experience of healthcare for such progressive neurodegenerative diseases in low- and middle-income nations is in stark contrast with the standard of care in high-income countries.

METHODS

An extended family with many members affected with an autosomal dominantly inherited movement disorder came to medical attention when one family member presented following a fall. Apart from one family member who was taking a benzodiazepine for involuntary movements, no other affected family members had sought medical attention. Members of this family live on several resource-limited Caribbean islands. Care of the chronically ill is often the responsibility of the family, and access to specialty care is difficult to obtain, or is unavailable. Computed tomography scan of one patient's brain revealed severe caudate atrophy and moderate generalized cortical atrophy. Genetic diagnosis of HD was obtained.

RESULTS

Through family recollection and by direct observation we identified four generations of individuals affected with HD. Outreach programs and collaborations helped to provide medical imaging and genetic diagnosis. Additionally these efforts helped with patient and family support, education, and genetic counseling to many members of this family.

CONCLUSIONS

Affected members of this family have limited healthcare access, and rely heavily on family support for care. Genetic and clinical diagnosis of these patients was impeded by lack of resources and lack of access to specialty care. Importantly, obtaining a definitive diagnosis has had a positive impact for this family by facilitating genetic counseling, education, community outreach, and dispelling myths regarding this hereditary disease and its progression.

Motor Dysfunctions and Neuropathology in Mouse Models of Spinocerebellar Ataxia Type 2: A Comprehensive Review

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant ataxia caused by an expansion of CAG repeats in the exon 1 of the gene ATXN2, conferring a gain of toxic function that triggers the appearance of the disease phenotype. SCA2 is characterized by several symptoms including progressive gait ataxia and dysarthria, slow saccadic eye movements, sleep disturbances, cognitive impairments, and psychological dysfunctions such as insomnia and depression, among others. The available treatments rely on palliative care, which mitigate some of the major symptoms but ultimately fail to block the disease progression. This persistent lack of effective therapies led to the development of several models in yeast, C. elegans, D. melanogaster, and mice to serve as platforms for testing new therapeutic strategies and to accelerate the research on the complex disease mechanisms. In this work, we review 4 transgenic and 1 knock-in mouse that exhibit a SCA2-related phenotype and discuss their usefulness in addressing different scientific problems. The knock-in mice are extremely faithful to the human disease, with late onset of symptoms and physiological levels of mutant ataxin-2, while the other transgenic possess robust and well-characterized motor impairments and neuropathological features. Furthermore, a new BAC model of SCA2 shows promise to study the recently explored role of non-coding RNAs as a major pathogenic mechanism in this devastating disorder. Focusing on specific aspects of the behavior and neuropathology, as well as technical aspects, we provide a highly practical description and comparison of all the models with the purpose of creating a useful resource for SCA2 researchers worldwide.

A longitudinal investigation into cognition and disease progression in spinocerebellar ataxia types 1, 2, 3, 6, and 7

Background

The natural history of clinical symptoms in the spinocerebellar ataxias (SCA)s has been well characterised. However there is little longitudinal data comparing cognitive changes in the most common SCA subtypes over time. The present study provides a preliminary longitudinal characterisation of the clinical and cognitive profiles in patients with SCA1, SCA2, SCA3, SCA6 and SCA7, with the aim of elucidating the role of the cerebellum in cognition.

Methods

13 patients with different SCAs all caused by CAG repeat expansion (SCA1, n = 2; SCA2, n = 2; SCA3, n = 2; SCA6, n = 4; and SCA7, n = 3) completed a comprehensive battery of cognitive and mood assessments at two time points, a mean of 7.35 years apart. All patients were evaluated clinically using the Scale for the Rating and Assessment of Ataxia (SARA) and the Inventory of Non-Ataxia Signs (INAS). Patients underwent structural MRI imaging at follow-up.

Results

Clinical scale scores increased in all patients over time, most prominently in the SCA1 (SARA) and SCA3 (INAS) groups. New impairments on neuropsychological tests were most commonly observed with executive functions, speed, attention, visual memory and Theory of Mind. Results suggest possible differences in cognitive decline in SCA subtypes, with the most rapid cognitive decline observed in the SCA1 patients, and the least in the SCA6 patients, congruent with observed patterns of motor deterioration. Minimal changes in mood were observed, and MRI measures of atrophy did not correlate with cognitive decline.

Conclusion

As well as increasing physical impairment, cognitive decline over time appears to be a distinct aspect of the SCA phenotype, in keeping with the cerebellar cognitive-affective syndrome. Our data suggest a trend of cognitive decline that is different for each SCA subtype, and for the majority is related to the severity of cerebellar motor impairment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0447-6) contains supplementary material, which is available to authorized users.

In Vitro Expansion of CAG, CAA, and Mixed CAG/CAA Repeats

Polyglutamine diseases, including Huntington’s disease and a number of spinocerebellar ataxias, are caused by expanded CAG repeats that are located in translated sequences of individual, functionally-unrelated genes. Only mutant proteins containing polyglutamine expansions have long been thought to be pathogenic, but recent evidence has implicated mutant transcripts containing long CAG repeats in pathogenic processes. The presence of two pathogenic factors prompted us to attempt to distinguish the effects triggered by mutant protein from those caused by mutant RNA in cellular models of polyglutamine diseases. We used the SLIP (Synthesis of Long Iterative Polynucleotide) method to generate plasmids expressing long CAG repeats (forming a hairpin structure), CAA-interrupted CAG repeats (forming multiple unstable hairpins) or pure CAA repeats (not forming any secondary structure). We successfully modified the original SLIP protocol to generate repeats of desired length starting from constructs containing short repeat tracts. We demonstrated that the SLIP method is a time- and cost-effective approach to manipulate the lengths of expanded repeat sequences.

Hereditary Cerebellar Ataxias: A Korean Perspective

Hereditary ataxia is a heterogeneous disorder characterized by progressive ataxia combined with/without peripheral neuropathy, extrapyramidal symptoms, pyramidal symptoms, seizure, and multiple systematic involvements. More than 35 autosomal dominant cerebellar ataxias have been designated as spinocerebellar ataxia, and there are 55 recessive ataxias that have not been named systematically. Conducting genetic sequencing to confirm a diagnosis is difficult due to the large amount of subtypes with phenotypic overlap. The prevalence of hereditary ataxia can vary among countries, and estimations of prevalence and subtype frequencies are necessary for planning a diagnostic strategy in a specific population. This review covers the various hereditary ataxias reported in the Korean population with a focus on the prevalence and subtype frequencies as the clinical characteristics of the various subtypes.

Magnetic Resonance Imaging of Asians with Multiple Sclerosis was Similar to that of the West

Magnetic resonance imaging (MRI) of the brain is the most important paraclinical diagnostic test in multiple sclerosis (MS). The appearance of MRI in Asians with MS is not well defined. We retrospectively surveyed the first brain and spinal cord MRI in patients diagnosed to have MS, according to Poser's criteria in seven regions throughout Asia to define the MRI changes among Asians with MS. There were 101 patients with first brain, and 86 with first spinal cord MRI, 66 of whom had both. The brain MRI showed a mean of 17 lesions per patient in T2 weighted images, mostly asymptomatic. Almost all the lesions were in the white matter, particularly in the juxtacortical, deep and periventricular white matter. A third of the lesions were greater than 5 mm, 14% enhanced with gadolinium. There were more supratentorial than infratentorial lesions at a ratio of 7.5: 1. Ninety five percent of the spinal cord lesions were in cervical and thoracic regions, 34% enhanced with gadolinium. The lesions extended over a mean of 3.6 +/- 3.3 vertebral bodies in length. Fifty (50%) of the brain and 54 (63%) of the spinal MRI patients had the optic-spinal form of MS. The MRI of the optic-spinal and classical groups of patients were similar in appearance and distribution, except that the optic-spinal MS patients have fewer brain but longer and more severe spinal cord lesions. In conclusion, the brain and spinal cord MRI of Asian patients with MS was similar to that of the West, although, in this study, Asian MS patients had larger spinal cord lesions.

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.

Clinical analysis of adult-onset spinocerebellar ataxias in Thailand

Background

Non-ataxic symptoms of spinocerebellar ataxias (SCAs) vary widely and often overlap with various types of SCAs. Duration and severity of the disease and genetic background may play a role in such phenotypic diversity. We conducted the study in order to study clinical characteristics of common SCAs in Thailand and the factors that may influence their phenotypes.

Methods

131 (49.43%) out of 265 Thai ataxia families with cerebellar degeneration had positive tests for SCA1, SCA2, Machado-Joseph disease (MJD) or SCA6. The study evaluated 83 available families including SCA1 (21 patients), SCA2 (15), MJD (39) and SCA6 (8). Comparisons of frequency of each non-ataxic sign among different SCA subtypes were analysed. Multivariate logistic regression analyses were undertaken to analyze parameters in association with disease severity and size of CAG repeat.

Results

Mean ages at onset were not different among patients with different SCAs (40.31 ± 11.33 years, mean ± SD). Surprisingly, SCA6 patients often had age at onset and phenotypes indistinguishable from SCA1, SCA2 and MJD. Frequencies of ophthalmoparesis, nystagmus, hyperreflexia and areflexia were significantly different among the common SCAs, whilst frequency of slow saccade was not. In contrast to Caucasian patients, parkinsonism, dystonia, dementia, and facial fasciculation were uncommon in Thai patients. Multivariate logistic regression analysis demonstrated that ophthalmoparesis (p < 0.001) and sensory impairment (p = 0.025) were associated with the severity of the disease.

Conclusions

We described clinical characteristics of the 4 most common SCAs in Thailand accounting for almost 90% of familial spinocerebellar ataxias. There were some different observations compared to Caucasian patients including earlier age at onset of SCA6 and the paucity of extrapyramidal features, cognitive impairment and facial fasciculation. Severity of the disease, size of the pathological CAG repeat allele, genetic background and somatic heterogeneity of pathological alleles may influence clinical expressions of these common SCAs.

The global epidemiology of hereditary ataxia and spastic paraplegia: a systematic review of prevalence studies

BACKGROUND

Hereditary cerebellar ataxias (HCA) and hereditary spastic paraplegias (HSP) are two groups of neurodegenerative disorders that usually present with progressive gait impairment, often leading to permanent disability. Advances in genetic research in the last decades have improved their diagnosis and brought new possibilities for prevention and future treatments. Still, there is great uncertainty regarding their global epidemiology.

SUMMARY

Our objective was to assess the global distribution and prevalence of HCA and HSP by a systematic review and meta-analysis of prevalence studies. The MEDLINE, ISI Web of Science and Scopus databases were searched (1983-2013) for studies performed in well-defined populations and geographical regions. Two independent reviewers assessed the studies and extracted data and predefined methodological parameters. Overall, 22 studies were included, reporting on 14,539 patients from 16 countries. Multisource population-based studies yielded higher prevalence values than studies based primarily on hospitals or genetic centres. The prevalence range of dominant HCA was 0.0-5.6/10(5), with an average of 2.7/10(5) (1.5-4.0/10(5)). Spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease was the most common dominant ataxia, followed by SCA2 and SCA6. The autosomal recessive (AR) HCA (AR-HCA) prevalence range was 0.0-7.2/10(5), the average being 3.3/10(5) (1.8-4.9/10(5)). Friedreich ataxia was the most frequent AR-HCA, followed by ataxia with oculomotor apraxia or ataxia-telangiectasia. The prevalence of autosomal dominant (AD) HSP (AD-HSP) ranged from 0.5 to 5.5/10(5) and that of AR-HSP from 0.0 to 5.3/10(5), with pooled averages of 1.8/10(5) (95% CI: 1.0-2.7/10(5)) and 1.8/10(5) (95% CI: 1.0-2.6/10(5)), respectively. The most common AD-HSP form in every population was spastic paraplegia, autosomal dominant, type 4 (SPG4), followed by SPG3A, while SPG11 was the most frequent AR-HSP, followed by SPG15. In population-based studies, the number of families without genetic diagnosis after systematic testing ranged from 33 to 92% in the AD-HCA group, and was 40-46% in the AR-HCA, 45-67% in the AD-HSP and 71-82% in the AR-HSP groups.

KEY MESSAGES

Highly variable prevalence values for HCA and HSP are reported across the world. This variation reflects the different genetic make-up of the populations, but also methodological heterogeneity. Large areas of the world remain without prevalence studies. From the available data, we estimated that around 1:10,000 people are affected by HCA or HSP. In spite of advances in genetic research, most families in population-based series remain without identified genetic mutation after extensive testing. © 2014 S. Karger AG, Basel.

The role of interruptions in polyQ in the pathology of SCA1

At least nine dominant neurodegenerative diseases are caused by expansion of CAG repeats in coding regions of specific genes that result in abnormal elongation of polyglutamine (polyQ) tracts in the corresponding gene products. When above a threshold that is specific for each disease the expanded polyQ repeats promote protein aggregation, misfolding and neuronal cell death. The length of the polyQ tract inversely correlates with the age at disease onset. It has been observed that interruption of the CAG tract by silent (CAA) or missense (CAT) mutations may strongly modulate the effect of the expansion and delay the onset age. We have carried out an extensive study in which we have complemented DNA sequence determination with cellular and biophysical models. By sequencing cloned normal and expanded SCA1 alleles taken from our cohort of ataxia patients we have determined sequence variations not detected by allele sizing and observed for the first time that repeat instability can occur even in the presence of CAG interruptions. We show that histidine interrupted pathogenic alleles occur with relatively high frequency (11%) and that the age at onset inversely correlates linearly with the longer uninterrupted CAG stretch. This could be reproduced in a cellular model to support the hypothesis of a linear behaviour of polyQ. We clarified by in vitro studies the mechanism by which polyQ interruption slows down aggregation. Our study contributes to the understanding of the role of polyQ interruption in the SCA1 phenotype with regards to age at disease onset, prognosis and transmission.

Spinocerebellar ataxia type 1 (SCA1) is a progressive neurodegenerative disorder resulting in loss of coordination and balance. It is caused by an expanded repeated DNA sequence (CAG) in the gene ATXN1. The CAG repeat region is normally interrupted by the DNA sequence CAT. Loss of this interruption is believed to cause instability whereby the CAG repeat expands beyond a key threshold resulting, ultimately, in polyglutamine protein aggregation and cell death. Here we examine how interruptions influence pathology in patients and establish a cellular model to support our findings. We distinguish our patients into two sub-groups based on whether or not their expanded CAG repeat stretches contained an interruption. This is not possible with conventional diagnostic techniques. Differentiating the sub-group with no interruptions led to improved accuracy in predicting their age at onset. The other sub-group, with interruptions, reveals a delay in age at onset that shows greater alignment with the longest stretch of CAG repeats. These findings are significant for genetic counselling and prognosis. Our cellular model and in vitro studies confirmed the relationship between disease severity and uninterrupted repeat length and showed that interruptions do not significantly affect the polyglutamine protein aggregation, but do slow down the aggregation rate.

Pattern of peripheral nerve involvement in Machado-Joseph disease: neuronopathy or distal axonopathy? A clinical and neurophysiological evaluation

OBJECTIVE

Neuropathy is a well-recognized feature in spinocerebellar ataxia type 3 (SCA3) or Machado-Joseph disease (MJD), but the pattern of neuropathy is still a matter of debate. This study aimed to evaluate peripheral nerve involvement in MJD patients. Neurophysiological and clinical data were analyzed to distinguish neuronopathy from length-dependent distal axonopathy.

METHODS

In the present study we evaluated 26 patients with clinical and molecular-proven MJD and investigated their peripheral nerve involvement. Neurophysiological and clinical data were compared and correlated aiming to distinguish neuronopathy from distal axonopathy.

RESULTS

The neurophysiological evaluation showed that 42.3% of the patients had polyneuropathy. Among these patients, 81.8% presented neuronopathy.

CONCLUSION

We concluded that neuronopathy is the most common form of peripheral nerve involvement in MJD patients.

A review of the inherited ataxias: recent advances in genetic, clinical and neuropathologic aspects

Inherited ataxias are a heterogeneous group of disorders characterized by autosomal dominant and recessive inheritance. Recent advances in genetic research have resulted in an improved comprehension of their clinical presentation. Autosomal dominant cerebellar ataxias (ADCAs) include spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA); six of these have been found to be trinucleotide repeat disorders. Episodic ataxia, types 1 and 2, are at present recognized to be channelopathies, caused by point mutations. Friedreich's ataxia (FA) which is an autosomal recessive disorder, resulting from a a unique trinucleotide repeat, is now recognized to have a wide age of onset and clinical spectrum. Ataxia-telangiectasia (AT), also an autosomal recessive cerebellar ataxia, is characterized by immunodeficiency. In this article, the genetic and clinical characteristics of these diseases are reviewed in detail.

Spinocerebellar ataxia type 2: clinical presentation, molecular mechanisms, and therapeutic perspectives

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant genetic disease characterized by cerebellar dysfunction associated with slow saccades, early hyporeflexia, severe tremor of postural or action type, peripheral neuropathy, cognitive disorders, and other multisystemic features. SCA2, one of the most common ataxias worldwide, is caused by the expansion of a CAG triplet repeat located in the N-terminal coding region of the ATXN2 gene, which results in the incorporation of a segment of polyglutamines in the mutant protein, being longer expansions associated with earlier onset and more sever disease in subsequent generations. In this review, we offer a detailed description of the clinical manifestations of SCA2 and compile the experimental evidence showing the participation of ataxin-2 in crucial cellular processes, including messenger RNA maturation and translation, and endocytosis. In addition, we discuss in the light of present data the potential molecular mechanisms underlying SCA2 pathogenesis. The mutant protein exhibits a toxic gain of function that is mainly attributed to the generation of neuronal inclusions of phosphorylated and/or proteolytic cleaved mutant ataxin-2, which might alter normal ataxin-2 function, leading to cell dysfunction and death of target cells. In the final part of this review, we discuss the perspectives of development of therapeutic strategies for SCA2. Based on previous experience with other polyglutamine disorders and considering the molecular basis of SCA2 pathogenesis, a nuclei-acid-based strategy focused on the specific silencing of the dominant disease allele that preserves the expression of the wild-type allele is highly desirable and might prevent toxic neurodegenerative sequelae.

ATXN2-CAG42 sequesters PABPC1 into insolubility and induces FBXW8 in cerebellum of old ataxic knock-in mice

Spinocerebellar Ataxia Type 2 (SCA2) is caused by expansion of a polyglutamine encoding triplet repeat in the human ATXN2 gene beyond (CAG)₃₁. This is thought to mediate toxic gain-of-function by protein aggregation and to affect RNA processing, resulting in degenerative processes affecting preferentially cerebellar neurons. As a faithful animal model, we generated a knock-in mouse replacing the single CAG of murine Atxn2 with CAG42, a frequent patient genotype. This expansion size was inherited stably. The mice showed phenotypes with reduced weight and later motor incoordination. Although brain Atxn2 mRNA became elevated, soluble ATXN2 protein levels diminished over time, which might explain partial loss-of-function effects. Deficits in soluble ATXN2 protein correlated with the appearance of insoluble ATXN2, a progressive feature in cerebellum possibly reflecting toxic gains-of-function. Since in vitro ATXN2 overexpression was known to reduce levels of its protein interactor PABPC1, we studied expansion effects on PABPC1. In cortex, PABPC1 transcript and soluble and insoluble protein levels were increased. In the more vulnerable cerebellum, the progressive insolubility of PABPC1 was accompanied by decreased soluble protein levels, with PABPC1 mRNA showing no compensatory increase. The sequestration of PABPC1 into insolubility by ATXN2 function gains was validated in human cell culture. To understand consequences on mRNA processing, transcriptome profiles at medium and old age in three different tissues were studied and demonstrated a selective induction of Fbxw8 in the old cerebellum. Fbxw8 is encoded next to the Atxn2 locus and was shown in vitro to decrease the level of expanded insoluble ATXN2 protein. In conclusion, our data support the concept that expanded ATXN2 undergoes progressive insolubility and affects PABPC1 by a toxic gain-of-function mechanism with tissue-specific effects, which may be partially alleviated by the induction of FBXW8.

Frequent age-associated neurodegenerative disorders like Alzheimer's, Parkinson's, and Lou Gehrig's disease are being elucidated molecularly by studying rare heritable variants. Various hereditary neurodegenerative disorders are caused by polyglutamine expansions in different proteins. In spite of this common pathogenesis and the pathological aggregation of most affected proteins, investigators were puzzled that the pattern of affected neuron population varies and that molecular mechanisms seem different between such disorders. The polyglutamine expansions in the Ataxin-2 (ATXN2) protein are exceptional in view of the lack of aggregate clumps in nuclei of affected Purkinje neurons and well documented alterations of RNA processing in the resulting disorders SCA2 and ALS. Here, as a faithful disease model and to overcome the unavailability of autopsied patient brain tissues, we generated and characterized an ATXN2-CAG42-knock-in mouse mutant. Our data show that the unspecific, chronically present mutation leads to progressive insolubility and to reduced soluble levels of the disease protein and of an interactor protein, which modulates RNA processing. Compensatory efforts are particularly weak in vulnerable tissue. They appear to include the increased degradation of the toxic disease protein by FBXW8. Thus the link between protein and RNA pathology becomes clear, and crucial molecular targets for preventive therapy are identified.

A comprehensive review of spinocerebellar ataxia type 2 in Cuba

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant cerebellar ataxia characterized by a progressive cerebellar syndrome associated to saccadic slowing, peripheral neuropathy, cognitive disorders, and other multisystem features. SCA2 is caused by the abnormal expansion of cytosine-adenine-guanine triplet repeats in the encoding region of the ATXN2 gene and therefore the expression of toxic polyglutamine expansions in the ataxin 2 protein, which cause progressive neuronal death of Purkinje cells in the cerebellum and several pontine, mesencephalic, and thalamic neurons among other cells. Worldwide, SCA2 is the second most frequent type of spinocerebellar ataxia, only surpassed by SCA3. Nevertheless, in Holguin, Cuba, the disease reaches the highest prevalence, resulting from a putative foundational effect. This review discusses the most important advances in the genotypical and phenotypical studies of SCA2, highlighting the comprehensive characterization reached in Cuba through clinical, neuroepidemiological, neurochemical, and neurophysiological evaluation of SCA2 patients and pre-symptomatic subjects, which has allowed the identification of new disease biomarkers and therapeutical opportunities. These findings provide guidelines, from a Cuban viewpoint, for the clinical management of the disease, its diagnosis, genetic counseling, and therapeutical options through rehabilitative therapy and/or pharmacological options.

Brain stem and cerebellum volumetric analysis of Machado Joseph disease patients

Machado-Joseph disease, or spinocerebellar ataxia type 3(MJD/SCA3), is the most frequent late onset spinocerebellar ataxia and results from a CAG repeat expansion in the ataxin-3 gene. Previous studies have found correlation between atrophy of cerebellum and brainstem with age and CAG repeats, although no such correlation has been found with disease duration and clinical manifestations. In this study we test the hypothesis that atrophy of cerebellum and brainstem in MJD/SCA3 is related to clinical severity, disease duration and CAG repeat length as well as to other variables such as age and ICARS (International Cooperative Ataxia Rating Scale). Whole brain high resolution MRI and volumetric measurement with cranial volume normalization were obtained from 15 MJD/SCA3 patients and 15 normal, age and sex-matchedcontrols. We applied ICARS and compared the score with volumes and CAG number, disease duration and age. We found significant correlation of both brain stem and cerebellar atrophy with CAG repeat length, age, disease duration and degree of disability. The Spearman rank correlation was stronger with volumetric reduction of the cerebellum than with brain stem. Our data allow us to conclude that volumetric analysis might reveal progressive degeneration after disease onset, which in turn is linked to both age and number of CAG repeat expansions in SCA 3.

Model organisms reveal insight into human neurodegenerative disease: ataxin-2 intermediate-length polyglutamine expansions are a risk factor for ALS

Model organisms include yeast Saccromyces cerevisae and fly Drosophila melanogaster. These systems have powerful genetic approaches, as well as highly conserved pathways, both for normal function and disease. Here, we review and highlight how we applied these systems to provide mechanistic insight into the toxicity of TDP-43. TDP-43 accumulates in pathological aggregates in ALS and about half of FTD. Yeast and fly studies revealed an interaction with the counterparts of human Ataxin-2, a gene whose polyglutamine repeat expansion is associated with spinocerebellar ataxia type 2. This finding raised the hypothesis that repeat expansions in ataxin-2 may associate with diseases characterized by TDP-43 pathology such as ALS. DNA analysis of patients revealed that intermediate-length polyglutamine expansions in ataxin-2 are a risk factor for ALS, such that repeat lengths are greater than normal, but lower than that associated with spinocerebellar ataxia type 2 (SCA2), and are more frequent in ALS patients than in matched controls. Moreover, repeat expansions associated with ALS are interrupted CAA-CAG sequences as opposed to the pure CAG repeat expansions typically associated with SCA2. These studies provide an example of how model systems, when extended to human cells and human patient tissue, can reveal new mechanistic insight into disease.

PolyQ repeat expansions in ATXN2 associated with ALS are CAA interrupted repeats

Amyotrophic lateral sclerosis (ALS) is a devastating, rapidly progressive disease leading to paralysis and death. Recently, intermediate length polyglutamine (polyQ) repeats of 27-33 in ATAXIN-2 (ATXN2), encoding the ATXN2 protein, were found to increase risk for ALS. In ATXN2, polyQ expansions of ≥ 34, which are pure CAG repeat expansions, cause spinocerebellar ataxia type 2. However, similar length expansions that are interrupted with other codons, can present atypically with parkinsonism, suggesting that configuration of the repeat sequence plays an important role in disease manifestation in ATXN2 polyQ expansion diseases. Here we determined whether the expansions in ATXN2 associated with ALS were pure or interrupted CAG repeats, and defined single nucleotide polymorphisms (SNPs) rs695871 and rs695872 in exon 1 of the gene, to assess haplotype association. We found that the expanded repeat alleles of 40 ALS patients and 9 long-repeat length controls were all interrupted, bearing 1-3 CAA codons within the CAG repeat. 21/21 expanded ALS chromosomes with 3CAA interruptions arose from one haplotype (GT), while 18/19 expanded ALS chromosomes with <3CAA interruptions arose from a different haplotype (CC). Moreover, age of disease onset was significantly earlier in patients bearing 3 interruptions vs fewer, and was distinct between haplotypes. These results indicate that CAG repeat expansions in ATXN2 associated with ALS are uniformly interrupted repeats and that the nature of the repeat sequence and haplotype, as well as length of polyQ repeat, may play a role in the neurological effect conferred by expansions in ATXN2.

Movement disorders in spinocerebellar ataxias

Autosomal dominant spinocerebellar ataxias (SCAs) can present with a large variety of noncerebellar symptoms, including movement disorders. In fact, movement disorders are frequent in many of the various SCA subtypes, and they can be the presenting, dominant, or even isolated disease feature. When combined with cerebellar ataxia, the occurrence of a specific movement disorder can provide a clue toward the underlying genotype. There are reasons to believe that for some coexisting movement disorders, the cerebellar pathology itself is the culprit, for example, in the case of cortical myoclonus and perhaps dystonia. However, movement disorders in SCAs are more likely related to extracerebellar pathology, and imaging and neuropathological data indeed show involvement of other parts of the motor system (substantia nigra, striatum, pallidum, motor cortex) in some SCA subtypes. When confronted with a patient with an isolated movement disorder, that is, without ataxia, there is currently no reason to routinely screen for SCA gene mutations, the only exceptions being SCA2 in autosomal dominant parkinsonism (particularly in Asian patients) and SCA17 in the case of a Huntington's disease-like presentation without an HTT mutation.

Genetic and clinical analysis in a Chinese parkinsonism-predominant spinocerebellar ataxia type 2 family

Parkinson's disease is a degenerative central nervous system disorder that often impairs motor skills, speech and other functions. We discovered a large Chinese family showing primarily parkinsonism symptoms with autosomal dominant inheritance. Six affected individuals in the family showed typical parkinsonism symptoms, including pill-rolling tremor. Two other affected individuals showed cerebellar ataxia symptoms. A whole-genome scan using the 50K single nucleotide polymorphism array with three different linkage methods detected two positive regions on chromosome 12q24.1 and 5q13.3. The ATXN2 gene, responsible for spinocerebellar ataxia type 2 (SCA2) was located precisely in the center of the positive region on chromosome 12. Further analysis of SCA2 revealed heterozygous pathological CAG expansions in the family. The affected individuals' symptoms were typical of parkinsonism, but complex. Inverse correlation between CAG repeat size and age of onset is not obvious in this pedigree. This parkinsonism-predominant SCA2 family shared the same disease gene locus with other 'standard' SCA2 families, but it is possible that variations in one or more modifier genes might account for the parkinsonism-predominant SCA2 predisposition observed in this pedigree.

[A case of spinocerebellar ataxia type 2 presenting with a clinical course similar to spastic paraparesis]

We report a 50-year-old woman with an unremarkable birth and developmental history, and with no family history of neurological disorders. The patient had a 6-year history of progressive cervical dystonia, oral dyskinesia, and hyperreflexia. She was initially considered to have spastic paraparesis of unknown cause. Because brain MRI showed mild atrophy of the cerebellar vermis, genetic analysis for spinocerebellar ataxia types 1, 2, 3, 6, 7, 8, 12, and 17, and dentatorubral-pallidoluysian atrophy was performed. The results revealed an abnormal expansion of CAG repeats (38 repeats) in one allele of ATXN2, and the patient was diagnosed with spinocerebellar ataxia type 2 (SCA2). She had no major clinical features of SCA2 such as cerebellar ataxia, slow saccade, or hyporeflexia. Recent reports have shown the CAG repeat expansion in ATXN2 to be detected in patients with familial L-dopa-responsive parkinsonism. The present case suggests that CAG repeat expansion in ATXN2 may be detected in some patients with spastic paraparesis, and that wide variations of clinical manifestations exist in SCA2.

[Autopsy case of SCA2 with Parkinsonian phenotype]

This is the first autopsy case of SCA2 with parkinsonian phenotype. At the age of 46, the patient got symptoms of parkinsonism to which anti-parkinsonian drugs were effective. He had mosaic 38, 40 CAG repeat expansions on chromosome 12q23-24, being diagnosed as SCA2, and his mother and his son also had CAG expansions on the same locus. In addition to parkinsonism, he also exhibited autonomic disturbance, dementia, and mild cerebellar ataxia Brain images revealed severe atrophy of pons and medulla oblongata, resembling MSA-C. HVA and 5-HIAA were reduced in the cerebrospinal fluid, and the heart-mediastinum (H/M) ratio in myocardial 123I-MIBG cintigram was decreased, which suggested Lewy body pathology. He died at the age of 75 and the autopsy revealed atrophy of the olivo-ponto-cerebellar (OPC) system and substantia nigra which was compatible to SCA2, although the OPC system atrophy was less severe than formerly reported SCA2 cases. The degrees of atrophy of the OPC system and substantia nigra might explain the predominancy of clinical symptoms. Anti-1C2 positive inclusions in the pontine nuclei, inferior olive nuclei, cerebellum and substantia nigra confirmed a polyglutamine disease. In addition, there were the anti-phosphorylated alpha-synuclein positive, Lewy body related pathological changes in the substantia nigra, the locus ceruleus, the dorsal motor nuclei of vagus, and the sympathetic nerve in the myocardium. Major genetic abnormalities related to Parkinson disease were not detected. As another case of SCA2 with Lewy body pathology was reported in Japan, the coexistence of SCA2 and Lewy body pathology may not be accidental. Since myocardial MIBG scincigram can predict Lewy body pathology, we should seek more clinical cases of SCA2 with Lewy body pathology.

Nucleation of protein aggregation kinetics as a basis for genotype-phenotype correlations in polyglutamine diseases

Recent studies of inherited neurodegenerative disorders have suggested a linkage between the propensity toward aggregation of mutant protein and disease onset. This is particularly apparent for polyglutamine (polyQ) diseases caused by expansion of CAG-trinucleotide repeats. However, a quantitative framework for relating aggregation kinetics with molecular mechanisms of neurodegeneration initiation is lacking. Here, using the repeat-length-dependent age-of-onset in polyQ diseases, we derived a mathematical model based on nucleation of aggregation kinetics to describe genotype-phenotype correlations, and validated the model using both in vitro data and clinical data. Instead of describing polyQ aggregation kinetics with a derivative equation, our model divided age-of-onset (equivalent to the time required for aggregation) into two processes: nucleation lag time (a first-order exponential function of CAG-repeat length) and elongation time. With the exception of spinocerebellar ataxia (SCA) 3, the relation between CAG-repeat length and age-of-onset in all examined polyQ diseases, including Huntington's disease, dentatorubral-pallidoluysian atrophy and SCA1, -2, -6 and -7, could be well explained by three parameters derived from linear regression analysis based on the nucleated growth polymerization model. These parameters composed of probability of nucleation at an individual repeat, a protein concentration associated factor, and elongation time predict the overall features of neurodegeneration initiation, including constant risk for cell death, toxic polyQ species, main pathological subcellular site and the contribution of cellular factors. Our model also presents an alternative therapeutic strategy according to the distinct subcellular loci by the finding that nuclear localization of soluble mutant protein monomers itself has great impact on disease onset.

Spinocerebellar ataxia type 2 (SCA2): clinical features and genetic analysis

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease that results from the expansion of an unstable trinucleotide CAG repeat encoding for a polyglutamine tract. In normal individuals, alleles contain between 14 and 31 CAG repeats, whereas the pathological alleles have more than 35 CAG repeats. The clinical phenotype of SCA2 includes a progressive cerebellar ataxia with additional features such as ophthalmoplegia, extra-pyramidal or pyramidal signs and peripheral neuropathy. We report a SCA2 large African family with several affected individuals. A major pathological allele carrying 43 CAG repeats was identified in the proband. To our knowledge, this is a first report of a SCA disorder described in Central African patients, thus indicating the need to consider this diagnosis in young African ataxic patients.

Cervical dystonia in spinocerebellar ataxia type 2: clinical and polymyographic findings

Eighteen patients from three large multigenerational families with genetically established spinocerebellar ataxia type 2 (SCA2) were examined, with special attention to the presence of dystonic features. Cervical dystonia (CD) was diagnosed according to standardised clinical criteria. CD was scored using the Tsui score. Polymyography was performed in six cases using bilateral surface electrode recordings of the sternocleidomastoid and trapezius muscles together with needle electrode recordings of the splenius capitis muscles bilaterally. CD was found in 11 of 18 patients (61%), and was the presenting symptom in one case. Severity of CD was mild to moderate, with Tsui scores ranging from 5 to 12 points. Polymyography in 6 of 11 SCA2 patients with CD showed the typical pattern of dystonia with spontaneous, involuntary muscle activation at rest in at least one neck muscle with disturbed reciprocal inhibition of antagonistic neck muscles. CD appears to be a common clinical feature in SCA2 and may precede ataxia and gait disturbance. By contrast, none of the 18 patients had dystonic features in other body regions. CD has probably been underreported in patients with the ataxic SCA2 phenotype and should be considered as an additional clinical manifestation in patients with hereditary ataxia.

Prism adaptation in spinocerebellar ataxia type 2

Patients with spinocerebellar ataxia type 2 (SCA2), develop severe pontine nuclei, inferior olives, and Purkinje cell degeneration. This form of autosomal dominant cerebellar ataxia is accompanied by progressive ataxia and dysarthria. Although the motor dysfunction is well characterized in these patients, nothing is known about their motor learning capabilities. Here we tested 43 SCA2 patients and their matched controls in prism adaptation, a kind of visuomotor learning task. Our results show that their pattern of brain damage does not entirely disrupt motor learning. Rather, patients had impaired adaptation decrement, but surprisingly a normal aftereffect. Moreover, the mutation degree could discriminate the degree of adaptation. This pattern could reflect the net contribution of two adaptive mechanisms: strategic control and spatial realignment. Accordingly, SCA2 patients show an impaired strategic control that affects the adaptation rate, but a normal spatial realignment measured through the aftereffect. Our results suggest that the neural areas subserving spatial realignment are spared in this form of spinocerebellar ataxia.

Varied electrophysiologic patterns in spinocerebellar ataxia type 2

The autosomal dominant ataxias are a heterogenous group of disorders. Almost 30 different genetic loci have been identified. Spinocerebellar ataxia type 2 (SCA2) is one of many autosomal dominant cerebellar ataxias. Electrophysiologic studies in SCA2 have shown mainly a sensory neuropathy or neuronopathy. To determine if electrophysiologic testing reveals concomitant or isolated involvement of motor nerves in SCA2 we reviewed historic and electrophysiologic data on all cases of genetically confirmed SCA2 who underwent nerve conduction studies and needle electromyographic during initial evaluation at our institution. We performed electrophysiologic studies in six genetically confirmed, unrelated, cases of SCA2 and discovered that in three patients, there were findings consistent with motor neuronopathy or neuropathy without sensory involvement. One patient had normal results and only one had a pure sensory neuropathy or neuronopathy. The sixth patients had mixed sensorimotor neuropathy. This is the first study that demonstrates isolated involvement of motor neurons and/or axons occur in SCA2. Therefore, electrophysiologic findings in SCA2 are not limited to mainly a sensory neuropathy but are varied and can even mimic slowly progressive motor neuron disease.

Spinocerebellar ataxia types 2 and 3 segregating simultaneously in a single family

Spinocerebellar ataxia (SCA) types 2 and 3 are autosomal-dominant neurodegenerative disorders caused by mutations in two different genes. We identified mutations for SCA2 and SCA3 segregating simultaneously in a single Brazilian family. The index patient had SCA2, whereas her two second-degree cousins had SCA3. Disease was more rapidly progressive in the SCA2 patient, who presented severe brainstem and pancerebellar atrophy, as opposed to the two SCA3 patients, who had only mild cerebellar vermian atrophy. In such situations, molecular confirmation of all patients may avoid misdiagnosis of SCA subtypes and eventual errors in predictive testing of unaffected family members.

Ataxin-2 and huntingtin interact with endophilin-A complexes to function in plastin-associated pathways

Spinocerebellar ataxia type 2 is an inherited neurodegenerative disorder that is caused by an expanded trinucleotide repeat in the SCA2 gene, encoding a polyglutamine stretch in the gene product ataxin-2. Although evidence has been provided that ataxin-2 is involved in RNA metabolism, the physiological function of ataxin-2 remains unclear. Here, we demonstrate that ataxin-2 interacts with two members of the endophilin family, endophilin-A1 and endophilin-A3. To elucidate the physiological implications of these interactions, we exploited yeast as a model system and discovered that expression of ataxin-2 as well as both endophilin proteins is toxic for yeast lacking the SAC6 gene product fimbrin, a protein involved in actin filament organization and endocytotic processes. Intriguingly, expression of huntingtin, another polyglutamine protein interacting with endophilin-A3, was also toxic in Deltasac6 yeast. These effects can be suppressed by simultaneous expression of one of the two human fimbrin orthologs, L- or T-plastin. Moreover, we have discovered that ataxin-2 associates with L- and T-plastin and that overexpression of ataxin-2 leads to accumulation of T-plastin in mammalian cells. Thus, our findings suggest an interplay between ataxin-2, endophilin proteins and huntingtin in plastin-associated cellular pathways.