Clinical phenotype of Brazilian families with spinocerebellar ataxia 10

Spinocerebellar Ataxia Type 10 (SCA 10) in Brazil

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant inherited ataxia caused by the expansion of ATTCT pentanucleotide repeats in intron 9 of the ATXN10 gene. This rare form of SCA has predominantly been observed in individuals of Indigenous American and East Asian descent. Notably, in Mexico and the southern Brazilian states of Paraná and Santa Catarina, SCA10 is identified as the second most prevalent type of spinocerebellar ataxia. Initially, the phenotype described in Mexico featured a combination of cerebellar ataxia and epilepsy-a presentation also observed in other Latin American and Asian countries, as well as some Brazilian states. However, in Paraná and Santa Catarina, the predominant manifestation of SCA10 is pure cerebellar ataxia, which is distinguished from the presentations seen in other regions.

The impact of interrupted ATXN10 expansions on clinical findings of spinocerebellar ataxia type 10

BACKGROUND

Spinocerebellar ataxia type 10 (SCA10), due to an ATTCT repeat expansion in ATXN10, has variable expressivity and the role of presence (ATTCTint +) and absence (ATTCTint-) of interruptions in the repeat is not clear. We aimed to describe the relations between ATTCTint + and age at onset, seizures, and neurologic severity in ataxic and non-ataxic carriers from Brazil.

METHODS

Family, age at onset (AO), and seizures data plus DNA were obtained from symptomatic carriers already diagnosed in Porto Alegre, Curitiba, and São Paulo, Brazil. Patients and their relatives were invited to be evaluated through Scale of Assessment and Rating of Ataxia (SARA) and other clinical scales; a SARA > 2.5 classified subjects as ataxic carriers. Repeat-primed PCR (RP-PCR) defined the expansions with (ATTCTint +) or without (ATTCTint-) interruptions. Comparisons were performed for a p level of 0.05.

RESULTS

Among 78 ataxic carriers, earlier AO (p = 0.039) and higher occurrences of epilepsy (p < 0.0001) were seen in subjects with ATTCTint + than in those with ATTCTint-. Clinical scales were worse in 34 ataxics than in 7 non-ataxics and 10 related controls (p = 0.006) and did not discriminate non-ataxics from controls. The 11 ataxic ATTCTint + carriers had higher SARA scores per year of disease duration than the 23 ATTCTint- carriers (r = 0.879, beta = 0.45, p = 0.0001).

DISCUSSION

ATTCTint + carriers had worse clinical findings than ATTCTint- carriers: earlier AO, more seizures, and worse ataxia scores. Interruptions in the expanded repeat have a real impact in SCA10 phenotype.

Spinocerebellar ataxia type 10 and Huntington disease-like 2 in Venezuela: Further evidence of two different ancestral founder effects

INTRODUCTION

The American continent populations have a wide genetic diversity, as a product of the admixture of three ethnic groups: Amerindian, European, and African Sub-Saharan. Spinocerebellar ataxia type 10 (SCA10) and Huntington disease-like 2 (HDL2) have very ancient ancestral origins but are restricted to two populations: Amerindian and African Sub-Saharan, respectively. This study aimed to investigate the genetic epidemiological features of these diseases in Venezuela.

METHODS

In-phase haplotypes with the expanded alleles were established in seven unrelated index cases diagnosed with SCA10 and in 11 unrelated index cases diagnosed with HDL2. The origins of remote ancestors were recorded.

RESULTS

The geographic origin of the ancestors showed grouping in clusters. SCA10 had a minimal general prevalence of 1:256,174 families in the country, but within the identified geographic clusters, the prevalence ranged from 5 per 100,000 to 43 per 100,000 families. HDL2 had a general prevalence of 1:163,016 families, however, within the clusters, the prevalence ranged from 31 per 100,000 to 60 per 100,000 families. The locus-specific haplotype shared by all families worldwide, including the Venezuelans, supports a single old ancestral origin in each case.

CONCLUSION

Knowing the genetic ancestry and geographic origins of patients in Ibero-American mixed populations could have significant diagnostic implications; thus, both diseases in Venezuela should always be first explored in patients with a suggestive phenotype and ancestors coming from the same known geographic clusters.

Ataxias in Brazil: 17 years of experience in an ataxia center

BACKGROUND

 Cerebellar ataxias comprise sporadic and genetic etiologies. Ataxia may also be a presenting feature in hereditary spastic paraplegias (HSPs).

OBJECTIVE

 To report a descriptive analysis of the frequency of different forms of cerebellar ataxia evaluated over 17 years in the Ataxia Unit of Universidade Federal de São Paulo, Brazil.

METHODS

 Charts of patients who were being followed from January 2007 to December 2023 were reviewed. We used descriptive statistics to present our results as frequencies and percentages of the overall analysis. Diagnosed patients were classified according to the following 9 groups: sporadic ataxia, spinocerebellar ataxias (SCAs), other autosomal dominant cerebellar ataxias, autosomal recessive cerebellar ataxias (ARCAs), mitochondrial ataxias, congenital ataxias, X-linked ataxias, HSPs, and others.

RESULTS

 There were 1,332 patients with ataxias or spastic paraplegias. Overall, 744 (55.85%) of all cases were successfully diagnosed: 101 sporadic ataxia, 326 SCAs, 20 of other autosomal dominant cerebellar ataxias, 186 ARCAs, 6 X-linked ataxias, 2 mitochondrial ataxias, 4 congenital ataxias, and 51 HSPs.

CONCLUSION

 This study describes the frequency of cerebellar ataxias in a large group of patients followed for the past 17 years, of whom 55% obtained a definitive clinical or molecular diagnosis. Future demographic surveys in Brazil or Latin American remain necessary.

Genetic Epidemiology and Clinical Characteristics of Patients with Spinocerebellar Ataxias in an Unexplored Brazilian State, Using Strategies for Resource-Limited Settings

Spinocerebellar ataxias (SCAs) have a worldwide average prevalence of 2.7 cases per 100,000 individuals, with significant geographic variability. This study aimed to develop resource-limited strategies to detect and characterize the frequency and genetic-clinical profile of SCAs in an unexplored population from Alagoas State, a low Human Development Index state in northeastern Brazil. Active search strategies were employed to identify individuals with a diagnosis or clinical suspicion of SCAs, and a protocol for clinical and molecular evaluation was applied in collaboration with a reference center in Neurogenetics. A total of 73 individuals with SCAs were identified, with a minimum estimated prevalence of 2.17 cases per 100,000 inhabitants. SCA3 was the most common type (75.3%), followed by SCA7 (15.1%), SCA1 (6.8%), and SCA2 (2.7%). Patients with SCA3 subphenotype 2 were the most predominant. Detailed analysis of patients with SCA3 and SCA7 revealed age at onset and clinical features congruent with other studies, with gait disturbance and reduced visual capacity in SCA7 as the main initial manifestations. The study also identified many asymptomatic individuals at risk of developing SCAs. These findings demonstrate that simple and collaborative strategies can enhance the detection capacity of rare diseases such as SCAs in resource-limited settings and that Alagoas State has a minimum estimated prevalence of SCAs similar to the world average.

The molecular mechanisms of spinocerebellar ataxias for DNA repeat expansion in disease

Spinocerebellar ataxias (SCAs) are a heterogenous group of neurodegenerative disorders which commonly inherited in an autosomal dominant manner. They cause muscle incoordination due to degeneration of the cerebellum and other parts of nervous system. Out of all the characterized (>50) SCAs, 14 SCAs are caused due to microsatellite repeat expansion mutations. Repeat expansions can result in toxic protein gain-of-function, protein loss-of-function, and/or RNA gain-of-function effects. The location and the nature of mutation modulate the underlying disease pathophysiology resulting in varying disease manifestations. Potential toxic effects of these mutations likely affect key major cellular processes such as transcriptional regulation, mitochondrial functioning, ion channel dysfunction and synaptic transmission. Involvement of several common pathways suggests interlinked function of genes implicated in the disease pathogenesis. A better understanding of the shared and distinct molecular pathogenic mechanisms in these diseases is required to develop targeted therapeutic tools and interventions for disease management. The prime focus of this review is to elaborate on how expanded 'CAG' repeats contribute to the common modes of neurotoxicity and their possible therapeutic targets in management of such devastating disorders.

The genetic and molecular features of the intronic pentanucleotide repeat expansion in spinocerebellar ataxia type 10

Spinocerebellar ataxia type 10 (SCA10) is characterized by progressive cerebellar neurodegeneration and, in many patients, epilepsy. This disease mainly occurs in individuals with Indigenous American or East Asian ancestry, with strong evidence supporting a founder effect. The mutation causing SCA10 is a large expansion in an ATTCT pentanucleotide repeat in intron 9 of the ATXN10 gene. The ATTCT repeat is highly unstable, expanding to 280-4,500 repeats in affected patients compared with the 9-32 repeats in normal individuals, one of the largest repeat expansions causing neurological disorders identified to date. However, the underlying molecular basis of how this huge repeat expansion evolves and contributes to the SCA10 phenotype remains largely unknown. Recent progress in next-generation DNA sequencing technologies has established that the SCA10 repeat sequence has a highly heterogeneous structure. Here we summarize what is known about the structure and origin of SCA10 repeats, discuss the potential contribution of variant repeats to the SCA10 disease phenotype, and explore how this information can be exploited for therapeutic benefit.

Mechanistic and Therapeutic Insights into Ataxic Disorders with Pentanucleotide Expansions

Pentanucleotide expansion diseases constitute a special class of neurodegeneration. The repeat expansions occur in non-coding regions, have likely arisen from Alu elements, and often result in autosomal dominant or recessive phenotypes with underlying cerebellar neuropathology. When transcribed (potentially bidirectionally), the expanded RNA forms complex secondary and tertiary structures that can give rise to RNA-mediated toxicity, including protein sequestration, pentapeptide synthesis, and mRNA dysregulation. Since several of these diseases have recently been discovered, our understanding of their pathological mechanisms is limited, and their therapeutic interventions underexplored. This review aims to highlight new in vitro and in vivo insights into these incurable diseases.

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Comparing loss of balance and functional capacity among patients with SCA2, SCA3 and SCA10

BACKGROUND

Spinocerebellar ataxia (SCA) presents different rates of functional decline depending on the type of ataxia.

OBJECTIVE

To compare the progression of disability, imbalance and severity of ataxia in patients with the three most common types of SCA in southern Brazil.

METHODS

126 patients (31-SCA2, 58-SCA3 and 37-SCA10) were stratified into four groups based on disease duration. Progression rates were calculated in each group for ataxia severity (SARA), functioning (FIM-ADL and Lawton-IADL), and balance (Berg Balance Scale).

RESULTS

Differences across groups in terms of disease severity revealed a linear pattern of decline in SCA3, with a faster rate over time (p = 0.039) compared to SCA2 and SCA10. The pattern was nonlinear for SCA2 and SCA10, with a twofold faster rate in patients with up to seven years of disease compared to all other periods in SCA10 (p < 0.001) and to the longer follow up period in SCA2 (p = 0.049). Differences across groups regarding worsening of balance scores was significantly faster in SCA3 compared to SCA10 (p = 0.028) and SCA2 (p = 0.028). The rate of loss of independence of ADLs tended to diminish over time in the three types of ataxia and was faster in SCA3. Similarly, the rate for loss of independence (IADLs) was faster in SCA3 compared to SCA2 (p = 0.057) and significantly faster compared to SCA10 (p = 0.028).

CONCLUSION

The present findings suggest that the progression of the disease (severity/functioning/balance) varies according to the SCA subtype and the period in disease course. Progression is more linear and aggressive in patients with SCA3.

Molecular Mechanisms in Pentanucleotide Repeat Diseases

The number of neurodegenerative diseases resulting from repeat expansion has increased extraordinarily in recent years. In several of these pathologies, the repeat can be transcribed in RNA from both DNA strands producing, at least, one toxic RNA repeat that causes neurodegeneration by a complex mechanism. Recently, seven diseases have been found caused by a novel intronic pentanucleotide repeat in distinct genes encoding proteins highly expressed in the cerebellum. These disorders are clinically heterogeneous being characterized by impaired motor function, resulting from ataxia or epilepsy. The role that apparently normal proteins from these mutant genes play in these pathologies is not known. However, recent advances in previously known spinocerebellar ataxias originated by abnormal non-coding pentanucleotide repeats point to a gain of a toxic function by the pathogenic repeat-containing RNA that abnormally forms nuclear foci with RNA-binding proteins. In cells, RNA foci have been shown to be formed by phase separation. Moreover, the field of repeat expansions has lately achieved an extraordinary progress with the discovery that RNA repeats, polyglutamine, and polyalanine proteins are crucial for the formation of nuclear membraneless organelles by phase separation, which is perturbed when they are expanded. This review will cover the amazing advances on repeat diseases.

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.

Volumetric MRI Changes in Spinocerebellar Ataxia (SCA3 and SCA10) Patients

Spinocerebellar ataxias type 3 (SCA3) and type 10 (SCA10) are the most prevalent in southern Brazil. To analyze the relationships between volumetric MRI changes and clinical and genetic findings in SCA3 and SCA10 patients. All patients in the study had a confirmed genetic diagnosis. Demographic data, ataxia severity (SARA score), and the size of the expanded alleles were evaluated. Nineteen SCA3 and 18 SCA10 patients were selected and compared with a similar number of healthy controls. Patient and control groups underwent the same MRI protocol. The standard FreeSurfer pipeline was used for the morphometric data. Our results show more affected brain structures (volume reductions) in SCA3 patients than in SCA10 patients (15 vs. 5 structures). Volume reductions in brain structures were also greater in the former. The main areas with significant volumetric reductions in the former were the cerebellum, basal ganglia, brain stem, and diencephalon, whereas in the latter, significant volume reductions were observed in the cerebellum and pallidum. While SARA scores and disease duration were more correlated with volume reduction in SCA10, in SCA3, the expansion length (CAGn) correlated positively with cerebellar WM, thalamus, brain stem, and total GM volumes. There was no correlation between expansion length (ATTCTn) and neuroimaging findings in SCA10. Neuroimaging results differed significantly between SCA3 and SCA10 patients and were compatible with the differences in clinical presentation, disease progression, and molecular findings.

Founder Effects of Spinocerebellar Ataxias in the American Continents and the Caribbean

Spinocerebellar ataxias (SCAs) comprise a heterogeneous group of autosomal dominant disorders. The relative frequency of the different SCA subtypes varies broadly among different geographical and ethnic groups as result of genetic drifts. This review aims to provide an update regarding SCA founders in the American continents and the Caribbean as well as to discuss characteristics of these populations. Clusters of SCAs were detected in Eastern regions of Cuba for SCA2, in South Brazil for SCA3/MJD, and in Southeast regions of Mexico for SCA7. Prevalence rates were obtained and reached 154 (municipality of Báguano, Cuba), 166 (General Câmara, Brazil), and 423 (Tlaltetela, Mexico) patients/100,000 for SCA2, SCA3/MJD, and SCA7, respectively. In contrast, the scattered families with spinocerebellar ataxia type 10 (SCA10) reported all over North and South Americas have been associated to a common Native American ancestry that may have risen in East Asia and migrated to Americas 10,000 to 20,000 years ago. The comprehensive review showed that for each of these SCAs corresponded at least the development of one study group with a large production of scientific evidence often generalizable to all carriers of these conditions. Clusters of SCA populations in the American continents and the Caribbean provide unusual opportunity to gain insights into clinical and genetic characteristics of these disorders. Furthermore, the presence of large populations of patients living close to study centers can favor the development of meaningful clinical trials, which will impact on therapies and on quality of life of SCA carriers worldwide.

Clinical and Genetic Evaluation of Spinocerebellar Ataxia Type 10 in 16 Brazilian Families

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant disorder in which patients have a slowly progressive cerebellar ataxia, with dysarthria, dysphagia, and epilepsy. The aims of this study were to characterize the phenotypic expression of SCA10 and to examine its genotype-phenotype relationships. Ninety-one Brazilian patients with SCA10 from 16 families were selected. Clinical and epidemiological data were assessed by a standardized protocol, and severity of disease was measured by the Scale for the Assessment and Rating of Ataxia (SARA). The mean age of onset of symptoms was 34.8 ± 9.4 years. Sixty-two (68.2%) patients presented exclusively with pure cerebellar ataxia. Only 6 (6.6%) of the patients presented with epilepsy. Patients with epilepsy had a mean age of onset of symptoms lower than that of patients without epilepsy (23.5 ± 15.5 years vs 35.4 ± 8.7 years, p = 0.021, respectively). All cases of intention tremor were in women from one family. This family also had the lowest mean age of onset of symptoms, and a higher percentage of SCA10 cases in women. There was a positive correlation between duration of disease and severity of ataxia (rho = 0.272, p = 0.016), as quantified by SARA. We did not find a statistically significant correlation between age of onset of symptoms and expansion size (r = - 0.163, p = 0.185). The most common clinical presentation of SCA10 was pure cerebellar ataxia. Our data suggest that patients with epilepsy may have a lower age of onset of symptoms than those who do not have epilepsy. These findings and the description of a family with intention tremor in women with earlier onset of symptoms draw further attention to the phenotypic variability of SCA10.

Motor Performances of Spontaneous and Genetically Modified Mutants with Cerebellar Atrophy

Chance discovery of spontaneous mutants with atrophy of the cerebellar cortex has unearthed genes involved in optimizing motor coordination. Rotorod, stationary beam, and suspended wire tests are useful in delineating behavioral phenotypes of spontaneous mutants with cerebellar atrophy such as Grid2^Lc, Grid2^ho, Rora^sg, Agtpbp1^pcd, Reln^rl, and Dab1^scm. Likewise, transgenic or null mutants serving as experimental models of spinocerebellar ataxia (SCA) are phenotyped with the same tests. Among experimental models of autosomal dominant SCA, rotorod deficits were reported in SCA1 to 3, SCA5 to 8, SCA14, SCA17, and SCA27 and stationary beam deficits in SCA1 to 3, SCA5, SCA6, SCA13, SCA17, and SCA27. Beam tests are sensitive to experimental therapies of various kinds including molecules affecting glutamate signaling, mesenchymal stem cells, anti-oligomer antibodies, lentiviral vectors carrying genes, interfering RNAs, or neurotrophic factors, and interbreeding with other mutants.

Spinocerebellar ataxia type 10 (SCA10): Mutation analysis and common haplotype based inference suggest its rarity in Indian population

Spinocerebellar ataxia type 10 (SCA10) is a rare autosomal dominant cerebellar ataxia caused by nucleotide ATTCT expansion in ATXN10 gene. SCA10 has been reported in patients of cerebellar ataxia from Amerindian/Latin America and in East Asian ancestry. A common founder has been ascribed to the origin of ATTCT repeat expansion mutation in both the population. Here we present our investigation of the SCA10 pentanucleotide repeat expansion in 461 SCA patients of the Indian population. The analysis of multi-ethnic at-risk haplotype C-(ATTCT)n-GGC was performed using genotype data of various ethnic population included in the 1000 Genomes Project (KGP) to infer the prevalence of at-risk haplotype in the Indian populations. Unsurprisingly, none of the patient's DNA samples with (ATTCT)n expansion was observed in pathological range, however, the observed normal range of (ATTCT)n was 8-22 repeats, suggesting very rare or absence of the occurrence of SCA10 in Indian SCA patients. The at-risk haplotype, CGGC was found to be the most prevalent haplotype across different populations and no segregation of CGGC haplotype with large normal or small normal ATTCT repeats length was observed. However, on extended haplotype analysis, some lineage of CGGC with a flanking divergence at 5' end was observed specifically in the American or East Asian population but not in other population in KGP dataset. Together, these evidence points towards the absence of SCA10 in Indian population and haplotype-based analysis also suggests its occurrence to be rare in South Asian, European and African population. Further investigations are required to establish the present finding.

SIGNIFICANCE

The implications of the findings of this study are 1.) For the diagnostic work-up of SCAs in the Indian population and to decide upon inclusion of SCA10 in panel based genetic investigations even for Indians living abroad. 2.) The haplotype based inference of its presumptive prevalence through the estimation of at-risk haplotype using population genetics approach (South-Asians as the background) allowed us to estimate the possible absence of SCA10 in Indian population. SCA10 is a rare autosomal dominant cerebellar ataxia mostly reported among SCA patients from Latin America and recently described in East Asia population. The genetic study of SCA10 performed in the unrelated Indian spinocerebellar ataxia patients with heterogeneous ethnicity confirmed its absence from the Indian population and that conforms to population genetic based inference of its rarity or absence. 3.) This approach may be adopted for the screening of other subtypes of SCAs, i.e. other rare SCAs e.g. SCA31, SCA36, and SCA37.

The Geographic Diversity of Spinocerebellar Ataxias (SCAs) in the Americas: A Systematic Review

Background

The frequency and presentation of each of the most common forms of spinocerebellar ataxias (SCAs) varies widely. In the case of the Americas, this diversity is particularly dynamic given additional social, demographic, and cultural characteristics.

Objective

To describe the regional prevalence and clinical phenotypes of SCAs throughout the continent.

Methods

A literature search was performed in both MEDLINE and LILACS databases. The research was broadened to include the screening of reference lists of systematic review articles for additional studies. Investigations dating from the earliest available through 2019. Only studies in English, Portuguese, and Spanish were included. We analyzed publications with genetically confirmed cases only, ranging from robust samples with epidemiological data to case reports and case series from each country or regions.

Results

Overall, SCA3 is the most common form in the continent. Region-specific prevalence and ranking of the common forms vary. On the other hand, region-specific phenotypic variations were not consistently found based on the available literature analyzed, with the exception of the absence of epilepsy in SCA10 consistently described in a particular cluster of cases in South Brazil.

Conclusion

Systematic, multinational studies analyzing in detail the true frequencies of SCAs across the Americas as well as distinct clinical signs and clues of each form would be ideal to look for these potential variations.

Repeat-associated RNA structure and aberrant splicing

Over 30 hereditary disorders attributed to the expansion of microsatellite repeats have been identified. Despite variant nucleotide content, number of consecutive repeats, and different locations in the genome, many of these diseases have pathogenic RNA gain-of-function mechanisms. The repeat-containing RNAs can form structures in vitro predicted to contribute to the disease through assembly of intracellular RNA aggregates termed foci. The expanded repeat RNAs within these foci sequester RNA binding proteins (RBPs) with important roles in the regulation of RNA metabolism, most notably alternative splicing (AS). These deleterious interactions lead to downstream alterations in transcriptome-wide AS directly linked with disease symptoms. This review summarizes existing knowledge about the association between the repeat RNA structures and RBPs as well as the resulting aberrant AS patterns, specifically in the context of myotonic dystrophy. The connection between toxic, structured RNAs and dysregulation of AS in other repeat expansion diseases is also discussed. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.

Olfactory Function in SCA10

Although the main clinical manifestations of spinocerebellar ataxias (SCAs) result from damage of the cerebellum, other systems may also be involved. Olfactory deficits have been reported in other types of ataxias, especially in SCA3; however, there are no studies on olfactory deficits in SCA type 10 (SCA10). To analyze olfactory function of SCA10 patients compared with that of SCA3, Parkinson's, and healthy controls. Olfactory identification was tested in three groups of 30 patients (SCA10, SCA3, and Parkinson's disease (PD)) and 44 healthy controls using the Sniffin' Sticks (SS16) test. Mean SS16 score was 11.9 ± 2.9 for the SCA10 group, 12.3 ± 1.9 for the SCA3 group, 6.6 ± 2.8 for the PD group, and 12.1 ± 2.0 for the control group. Mean SS16 score for the SCA10 group was not significantly different from the scores for the SCA3 and control groups but was significantly higher than the score for the PD group (p < 0.001) when adjusted for age, gender, and history of smoking. There was no association between SS16 scores and disease duration in the SCA10 or SCA3 groups or number of repeat expansions. SS16 and Mini Mental State Examination scores were correlated in the three groups: SCA10 group (r = 0.59, p = 0.001), SCA3 group (r = 0.50, p = 0.005), and control group (r = 0.40, p = 0.007). We found no significant olfactory deficits in SCA10 in this large series.

Estimation of skeletal muscle mass in patients with spinocerebellar ataxia type 3 and 10

BACKGROUND

Neurodegenerative diseases may progress to a level in which patients present spontaneous weight loss, resulting in increased falls and functional disabilities when the disease is associated with muscle mass depletion.

OBJECTIVE

Evaluate the muscle compartment in patients presenting spinocerebellar ataxia (SCA) type 3 and 10.

METHODS

Forty-six patients presenting SCA type 3 and 10 were assessed and 76 volunteers were selected to the control group. In order to evaluate the muscle compartment, muscle mass anthropometric measurements were assessed and total skeletal muscle mass calculated through a predictive equation.

RESULTS

Women with SCA3 presented greater weight loss and muscle mass reduction compared to those with SCA10 and the control group. Among the predictive measurements, calf muscle circumference showed a more significant correlation with total skeletal muscle mass (p = 0.718).

CONCLUSION

Patients presenting both types of ataxia did not show severe depletion in their nutritional status; however, those with SCA3 displayed greater weight loss and muscle mass reduction compared to the SCA10 group.

Sleep disorders in spinocerebellar ataxia type 10

As sleep disturbances have been reported in spinocerebellar ataxias (SCAs), including types SCA1, SCA2, SCA3, SCA6 and SCA13, identification and management of these disturbances can help minimise their impact on SCA patients' overall body functions and quality of life. To our knowledge, there are no studies that investigate sleep disturbances in SCA10. Therefore, the aim of this study was to assess sleep disturbances in patients with SCA10. Twenty-three SCA10 patients and 23 healthy controls were recruited. Patients were evaluated in terms of their demographic and clinical data, including disease severity (Scale for the Assessment and Rating of Ataxia, SARA) and excessive daytime sleepiness (Epworth Sleepiness Scale, ESS), and underwent polysomnography. SCA10 patients had longer rapid eye movement (REM) sleep (p = .04) and more REM arousals than controls (p< .0001). There was a correlation of REM sleep onset with the age of onset of symptoms (r = .459), and with disease duration (r = -.4305). There also was correlation between the respiratory disturbance index (RDI) and SARA (r = -.4013), and a strong indirect correlation between arousal index and age at onset of symptoms (r = -.5756). In conclusion, SCA10 patients had sleep abnormalities that included more REM arousals and higher RDI than controls. Our SCA10 patients had sleep disorders related to shorter disease duration and lower severity of ataxia, in a pattern similar to that of other neurodegenerative diseases.

Haplotype Study in SCA10 Families Provides Further Evidence for a Common Ancestral Origin of the Mutation

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disorder characterized by progressive cerebellar ataxia and epilepsy. The disease is caused by a pentanucleotide ATTCT expansion in intron 9 of the ATXN10 gene on chromosome 22q13.3. SCA10 has shown a geographical distribution throughout America with a likely degree of Amerindian ancestry from different countries so far. Currently available data suggest that SCA10 mutation might have spread out early during the peopling of the Americas. However, the ancestral origin of SCA10 mutation remains under speculation. Samples of SCA10 patients from two Latin American countries were analysed, being 16 families from Brazil (29 patients) and 21 families from Peru (27 patients) as well as 49 healthy individuals from Indigenous Quechua population and 51 healthy Brazilian individuals. Four polymorphic markers spanning a region of 5.2 cM harbouring the ATTCT expansion were used to define the haplotypes, which were genotyped by different approaches. Our data have shown that 19-CGGC-14 shared haplotype was found in 47% of Brazilian and in 63% of Peruvian families. Frequencies from both groups are not statistically different from Quechua controls (57%), but they are statistically different from Brazilian controls (12%) (p < 0.001). The most frequent expanded haplotype in Quechuas, 19-15-CGGC-14-10, is found in 50% of Brazilian and in 65% of Peruvian patients with SCA10. These findings bring valuable evidence that ATTCT expansion may have arisen in a Native American chromosome.

Parkinson's disease associated with pure ATXN10 repeat expansion

Large, non-coding pentanucleotide repeat expansions of ATTCT in intron 9 of the ATXN10 gene typically cause progressive spinocerebellar ataxia with or without seizures and present neuropathologically with Purkinje cell loss resulting in symmetrical cerebellar atrophy. These ATXN10 repeat expansions can be interrupted by sequence motifs which have been attributed to seizures and are likely to act as genetic modifiers. We identified a Mexican kindred with multiple affected family members with ATXN10 expansions. Four affected family members showed clinical features of spinocerebellar ataxia type 10 (SCA10). However, one affected individual presented with early-onset levodopa-responsive parkinsonism, and one family member carried a large repeat ATXN10 expansion, but was clinically unaffected. To characterize the ATXN10 repeat, we used a novel technology of single-molecule real-time (SMRT) sequencing and CRISPR/Cas9-based capture. We sequenced the entire span of ~5.3-7.0 kb repeat expansions. The Parkinson's patient carried an ATXN10 expansion with no repeat interruption motifs as well as an unaffected sister. In the siblings with typical SCA10, we found a repeat pattern of ATTCC repeat motifs that have not been associated with seizures previously. Our data suggest that the absence of repeat interruptions is likely a genetic modifier for the clinical presentation of l-Dopa responsive parkinsonism, whereas repeat interruption motifs contribute clinically to epilepsy. Repeat interruptions are important genetic modifiers of the clinical phenotype in SCA10. Advanced sequencing techniques now allow to better characterize the underlying genetic architecture for determining accurate phenotype-genotype correlations.

First report of a Japanese family with spinocerebellar ataxia type 10: The second report from Asia after a report from China

Spinocerebellar ataxia type 10 (SCA10) is an autosomal-dominant cerebellar ataxia that is variably accompanied by epilepsy and other neurological disorders. It is caused by an expansion of the ATTCT pentanucleotide repeat in intron 9 of the ATXN10 gene. Until now, SCA10 was almost exclusively found in the American continents, while no cases had been identified in Japan. Here, we report the first case of an SCA10 family from Japan. The clinical manifestations in our cases were cerebellar ataxia accompanied by epilepsy, hyperreflexia and cognitive impairment. Although the primary pathology in SCA10 in humans is reportedly the loss of Purkinje cells, brain MRI revealed frontal lobe atrophy with white matter lesions. This pathology might be associated with cognitive dysfunction, indicating that the pathological process is not limited to the cerebellum. Examination of the SNPs surrounding the SCA10 locus in the proband showed the “C-expansion-G-G-C” haplotype, which is consistent with previously reported SCA10-positive individuals. This result was consistent with the findings that the SCA10 mutation may have occurred before the migration of Amerindians from East Asia to North America and the subsequent spread of their descendants throughout North and South America.

Spinocerebellar ataxia type 10 in the South of Brazil: the Amerindian-Belgian connection

Spinocerebellar ataxia type 10 (SCA10) is a rare form of autosomal dominant ataxia found predominantly in patients from Latin America with Amerindian ancestry. The authors report the history of SCA10 families from the south of Brazil (the states of Paraná and Santa Catarina), emphasizing the Belgian-Amerindian connection.

Spinocerebellar ataxias in Brazil--frequencies and modulating effects of related genes

This study describes the frequency of spinocerebellar ataxias and of CAG repeats range in different geographical regions of Brazil, and explores the hypothetical role of normal CAG repeats at ATXN1, ATXN2, ATXN3, CACNA1A, and ATXN7 genes on age at onset and on neurological findings. Patients with symptoms and family history compatible with a SCA were recruited in 11 cities of the country; clinical data and DNA samples were collected. Capillary electrophoresis was performed to detect CAG lengths at SCA1, SCA2, SCA3/MJD, SCA6, SCA7, SCA12, SCA17, and DRPLA associated genes, and a repeat primed PCR was used to detect ATTCT expansions at SCA10 gene. Five hundred forty-four patients (359 families) were included. There were 214 SCA3/MJD families (59.6 %), 28 SCA2 (7.8 %), 20 SCA7 (5.6 %), 15 SCA1 (4.2 %), 12 SCA10 (3.3 %), 5 SCA6 (1.4 %), and 65 families without a molecular diagnosis (18.1 %). Divergent rates of SCA3/MJD, SCA2, and SCA7 were seen in regions with different ethnic backgrounds. 64.7 % of our SCA10 patients presented seizures. Among SCA2 patients, longer ATXN3 CAG alleles were associated with earlier ages at onset (p < 0.036, linear regression). A portrait of SCAs in Brazil was obtained, where variation in frequencies seemed to parallel ethnic differences. New potential interactions between some SCA-related genes were presented.

Spinocerebellar ataxia type 10 in Peru: the missing link in the Amerindian origin of the disease

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disorder manifested by ataxia with a variable presentation of epileptic seizures, which is caused by a large expansion of an intronic ATTCT pentanucleotide repeat in ATXN10 on 22q13.3. Herein, we report the first description of SCA10 in a Peruvian family, supporting the Amerindian origin of SCA10 and the Panamerican geographical distribution of the disease in North, Central and South America. Moreover, the presence of an interruption motif in the SCA10 expansion along with epileptic seizures in this family supports the correlation between the two, as seen in other families. Finally, this is the first SCA10 patient ever observed outside of America, specifically in Italy. Since this patient is a Peruvian immigrant of Amerindian ancestry, our case report highlights the growing need for awareness amongst clinicians of seemingly geographically restricted rare diseases.

Repeat interruptions in spinocerebellar ataxia type 10 expansions are strongly associated with epileptic seizures

Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant neurodegenerative disorder, is the result of a non-coding, pentanucleotide repeat expansion within intron 9 of the Ataxin 10 gene. SCA10 patients present with pure cerebellar ataxia; yet, some families also have a high incidence of epilepsy. SCA10 expansions containing penta- and heptanucleotide interruption motifs, termed "ATCCT interruptions," experience large contractions during germline transmission, particularly in paternal lineages. At the same time, these alleles confer an earlier age at onset which contradicts traditional rules of genetic anticipation in repeat expansions. Previously, ATCCT interruptions have been associated with a higher prevalence of epileptic seizures in one Mexican-American SCA10 family. In a large cohort of SCA10 families, we analyzed whether ATCCT interruptions confer a greater risk for developing seizures in these families. Notably, we find that the presence of repeat interruptions within the SCA10 expansion confers a 6.3-fold increase in the risk of an SCA10 patient developing epilepsy (6.2-fold when considering patients of Mexican ancestry only) and a 13.7-fold increase in having a positive family history of epilepsy (10.5-fold when considering patients of Mexican ancestry only). We conclude that the presence of repeat interruptions in SCA10 repeat expansion indicates a significant risk for the epilepsy phenotype and should be considered during genetic counseling.

Clinical and genetic analysis of the first known Asian family with myotonic dystrophy type 2

Myotonic dystrophy type 2 (DM2) is more common than DM1 in Europe and is considered a rare cause of myotonic dystrophies in Asia. Its clinical course is also milder with more phenotypic variability than DM1. We herein describe the first known Asian family (three affected siblings) with DM2 based on clinical and genetic analyses. Notably, two of the affected siblings were previously diagnosed with limb-girdle muscular dystrophy. Myotonia (the inability of the muscle to relax) was absent or only faintly present in these individuals. The third sibling had grip myotonia and is the first known Asian DM2 patient. The three DM2 siblings share several systemic characteristics, including late-onset, proximal-dominant muscle weakness, diabetes, cataracts and asthma. Repeat-primed PCR across the DM2 repeat revealed a characteristic ladder pattern of a CCTG expansion in all siblings. Southern blotting analysis identified the presence of 3400 repeats. Further DM2 studies in Asian populations are needed to define the clinical presentation of Asian DM2 and as yet unidentified phenotypic differences from Caucasian patients.

Expansion of the Spinocerebellar ataxia type 10 (SCA10) repeat in a patient with Sioux Native American ancestry

Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant cerebellar ataxia, is caused by the expansion of the non-coding ATTCT pentanucleotide repeat in the ATAXIN 10 gene. To date, all cases of SCA10 are restricted to patients with ancestral ties to Latin American countries. Here, we report on a SCA10 patient with Sioux Native American ancestry and no reported Hispanic or Latino heritage. Neurological exam findings revealed impaired gait with mild, age-consistent cerebellar atrophy and no evidence of epileptic seizures. The age at onset for this patient, at 83 years of age, is the latest documented for SCA10 patients and is suggestive of a reduced penetrance allele in his family. Southern blot analysis showed an SCA10 expanded allele of 1400 repeats. Established SNPs surrounding the SCA10 locus showed a disease haplotype consistent with the previously described “SCA10 haplotype”. This case suggests that the SCA10 expansion represents an early mutation event that possibly occurred during the initial peopling of the Americas.

Paradoxical effects of repeat interruptions on spinocerebellar ataxia type 10 expansions and repeat instability

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disorder caused by a noncoding ATTCT pentanucleotide expansion. An inverse correlation between SCA10 expansion size and age at onset has been reported, and genetic anticipation has been documented. Interruptions in the ATTCT expansion are known to occur within the expansion. In order to determine the effect of repeat interruptions in SCA10 expansions, we designed a PCR assay to easily identify ATCCT repeat interruptions in the 5'-end of the expansion. We screened a cohort of 31 SCA10 families of Mexican, Brazilian and Argentinean ancestry to identify those with ATCCT repeat interruptions within their SCA10 expansions. We then studied the effects of ATCCT interruptions on intergenerational repeat instability, anticipation and age at onset. We find that the SCA10 expansion size is larger in SCA10 patients with an interrupted allele, but there is no difference in the age at onset compared with those expansions without detectable interruptions. An inverse correlation between the expansion size and the age at onset was found only with SCA10 alleles without interruptions. Interrupted expansion alleles show anticipation but are accompanied by a paradoxical contraction in intergenerational repeat size. In conclusion, we find that SCA10 expansions with ATCCT interruptions dramatically differ from SCA10 expansions without detectable ATCCT interruptions in repeat-size-instability dynamics and pathogenicity.

The unique co-occurrence of spinocerebellar ataxia type 10 (SCA10) and Huntington disease

We present a unique thirty-nine year old woman with both Huntington's disease (HD) and spinocerebellar ataxia type 10 (SCA10). She has 48 CAG repeats in the HD gene and 2511 ATTCT repeats in the ATX10 gene. Although both conditions are repeat expansion diseases they are thought to have quite different pathogenic mechanisms. The symptomatic age of onset in this patient (mid30s) is within the expected range for her repeat expansion sizes for each condition, but we discuss the evidence that the two conditions may interact to produce a more severe cognitive phenotype than would be expected for either of the conditions independently. The subject has Amerindian background on the maternal side from Colombia, South America, thus adding a 5th country expressing SCA10, all with Amerindian ancestry.

Transgenic models of spinocerebellar ataxia type 10: modeling a repeat expansion disorder

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant neurodegenerative disease with a spectrum of phenotypes. SCA10 is caused by a pentanucleotide repeat expansion of the ATTCT motif within intron 9 of ATAXIN 10 (ATXN10). Patients present with cerebellar ataxia; however, a subset also develops epileptic seizures which significantly contribute to the morbidity and mortality of the disease. Past research from our lab has demonstrated that epileptic SCA10 patients predominantly originate from or have ancestral ties to Mexico. In addition, a large proportion of epileptic SCA10 patients carry repeat interruptions within their SCA10 expansion. This paper outlines the variability in SCA10 phenotypes and our attempts to model these phenotypes using transgenic mouse models and highlights the benefits of using a transgenic model organism to understand the pathological mechanisms of a human disease.

Spinocerebellar ataxias: genotype-phenotype correlations in 104 Brazilian families

OBJECTIVE

Spinocerebellar ataxias are neurodegenerative disorders involving the cerebellum and its connections. There are more than 30 distinct subtypes, 16 of which are associated with an identified gene. The aim of the current study was to evaluate a large group of patients from 104 Brazilian families with spinocerebellar ataxias.

METHODS

We studied 150 patients from 104 families with spinocerebellar ataxias who had received molecular genetic testing for spinocerebellar ataxia types 1, 2, 3, 6, 7, 8, 10, 12, 17, and dentatorubral-pallidoluysian atrophy. A statistical analysis of the results was performed using basic descriptive statistics and the correlation coefficient (r), Student's t-test, chi-square test, and Yates' correction. The statistical significance level was established for p-values <0.05.

RESULTS

The results show that the most common subtype was spinocerebellar ataxia 3, which was followed by spinocerebellar ataxia 10. Moreover, the comparison between patients with spinocerebellar ataxia 3, spinocerebellar ataxia 10, and other types of spinocerebellar ataxia revealed distinct clinical features for each type. In patients with spinocerebellar ataxia 3, the phenotype was highly pleomorphic, although the most common signs of disease included cerebellar ataxia (CA), ophthalmoplegia, diplopia, eyelid retraction, facial fasciculation, pyramidal signs, and peripheral neuropathy. In patients with spinocerebellar ataxia 10, the phenotype was also rather distinct and consisted of pure cerebellar ataxia and abnormal saccadic eye movement as well as ocular dysmetria. Patients with spinocerebellar ataxias 2 and 7 presented highly suggestive features of cerebellar ataxia, including slow saccadic ocular movements and areflexia in spinocerebellar ataxia 2 and visual loss in spinocerebellar ataxia 7.

CONCLUSIONS

Spinocerebellar ataxia 3 was the most common subtype examined, followed by spinocerebellar ataxia 10. Patients with spinocerebellar ataxia 2 and 7 demonstrated highly suggestive features, whereas the phenotype of spinocerebellar ataxia 3 patients was highly pleomorphic and spinocerebellar ataxia 10 patients exhibited pure cerebellar ataxia. Epilepsy was absent in all of the patients with spinocerebellar ataxia 10 in this series.

Electronystagmography findings in spinocerebellar ataxia type 3 (SCA3) and type 2 (SCA2)

OBJECTIVE: To describe the alterations observed in electronystagmography (ENG) of patients with spinocerebellar ataxia (SCA) types 2 and 3. METHOD: Sixteen patients were studied and the following procedures were carried out: anamnesis, otorhinolaryngological and vestibular evaluations. RESULTS: The clinical findings in the entire group of patients were: gait disturbances (93.75%), dysarthria (43.75%), headache (43.75%), dizziness (37.50%) and dysphagia (37.50%). In the vestibular exam, the rotatory (62.50%) and caloric (75%) tests were among those which presented the largest indexes of abnormalities; the presence of alterations in the exams was 87.50%, with a predominance of central vestibular disorders in 68.75% of the exams. CONCLUSION: Vestibular exams could be an auxiliary tool to investigate SCAs, besides a precise clinical approach and, particularly, molecular genetic tests.