Natural history and epidemiology of the spinocerebellar ataxias: Insights from the first description to nowadays

Age-dependent somatic expansion of the ATXN3 CAG repeat in the blood and buccal swab DNA of individuals with spinocerebellar ataxia type 3/Machado-Joseph disease

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is caused by the expansion of a genetically unstable polyglutamine-encoding CAG repeat in ATXN3. Longer alleles are generally associated with earlier onset and frequent intergenerational expansions mediate the anticipation observed in this disorder. Somatic expansion of the repeat has also been implicated in disease onset and slowing the rate of somatic expansion has been proposed as a therapeutic strategy. Here, we utilised high-throughput ultra-deep MiSeq amplicon sequencing to precisely define the number and sequence of the ATXN3 repeat, the genotype of an adjacent single nucleotide variant and quantify somatic expansion in blood and buccal swab DNA of a cohort of individuals with SCA3 from the Azores islands (Portugal). We revealed systematic mis-sizing of the ATXN3 repeat and high levels of inaccuracy of the traditional fragment length analysis that have important implications for attempts to identify modifiers of clinical and molecular phenotypes. Quantification of somatic expansion in blood DNA and multivariate regression revealed the expected effects of age at sampling and CAG repeat length, although the effect of repeat length was surprisingly modest with much stronger associations with age. We also observed an association of the downstream rs12895357 single nucleotide variant with the rate of somatic expansion, and a higher level of somatic expansion in buccal swab DNA compared to blood. These data suggest that the ATXN3 locus in SCA3 patients in blood or buccal swab DNA might serve as a good biomarker for clinical trials testing suppressors of somatic expansion with peripheral exposure.

Spinocerebellar Ataxia in Brazil: A Comprehensive Genotype - Phenotype Analysis

Spinocerebellar ataxias (SCAs) are a diverse group of hereditary neurodegenerative disorders characterized by progressive degeneration of the cerebellum and other parts of the nervous system. In this study, we examined the genotype‒phenotype correlations in SCAs within the Brazilian population by leveraging a comprehensive dataset of 763 individuals from SARAH Network of Rehabilitation Hospitals. Using a retrospective, cross-sectional, observational, multicentric approach, we analysed medical records and conducted standardized molecular testing to explore epidemiological characteristics, clinical manifestations, and genetic profiles of SCAs in Brazil. Our findings revealed the predominance of SCA3, followed by SCA7 and SCA2, which aligns with global trends and reflects the specific genetic landscape of Brazil. A significant inverse relationship between the age of symptom onset and CAG repeat length in the mutated allele was observed across SCAs 2, 3, and 7. This study also highlights a trend towards paternal inheritance in SCA2 and details the distribution of CAG repeat expansions, which correlates larger expansions with earlier onset and specific symptomatology. This extensive analysis underscores the critical importance of genetic testing in the diagnosis and management of SCAs and enlightens the intricate genotype‒phenotype interplay within a genetically diverse population. Despite certain limitations, such as potential selection bias and the retrospective nature of the study, our research provides invaluable insights into the prevalence, genetic underpinnings, and clinical variability of SCAs in Brazil. We suggest a broader demographic scope and investigations into nonmotor symptoms in future studies to obtain a more comprehensive understanding of SCAs.

A cost analysis of Machado-Joseph's disease (MJD)

A rare disease is that with a low prevalence in the population. However, it is estimated that there are between 6,000 and 8,000 different types of rare diseases in the world and, generally, they are incurable and deadly. Machado-Joseph's disease (MJD) is one of these cases; of genetic origin, autosomal dominant, with a high chance of transmission between generations and without curative treatment. Given the specificities of MJD and the lack of economic studies associated with it, this article aims to estimate the direct and indirect health-related costs of lost productivity attributable to Machado-Joseph's Disease. The data used were primarily collected at the Hospital de Clínicas de Porto Alegre (HCPA), during the period between October 2019 and March 2020. The bottom-up cost methodology was used, that is to say, to estimate costs across a sample of patients to produce an annual cost per patient. Among the main results, it was found that 90.8% of the sample does not work and of these, 72.73% reported that the reason they had stopped working was due to Machado-Joseph's disease. The average age of men when they stopped working was 39.05 years of age and for women it was 39.64 years of age. In relation to direct non-medical costs, with rehabilitation and transport, it was found that these items affect about 32% of men's income and 36% of women's income, as well as medication and diapers costs affect about 15% of women's income and 14% of the income of men who are no longer able to work. The study also showed that 50% of caregivers, who are generally close relatives of the patient, do not work. Of these, 33.3% reported having left the labor market to provide assistance to the patient, which means that the cost for families is even higher than that estimated for the patient.

Comparison of specialist ataxia centres with non-specialist services in terms of treatment, care, health services resource utilisation and costs in the UK using patient-reported data

OBJECTIVES

This study aims to assess the patient-reported benefits and the costs of coordinated care and multidisciplinary care at specialist ataxia centres (SACs) in the UK compared with care delivered in standard neurological clinics.

DESIGN

A patient survey was distributed between March and May 2019 to patients with ataxia or carers of patients with ataxia through the Charity Ataxia UK's mailing list, website, magazine and social media to gather information about the diagnosis, management of the ataxias in SAC and non-specialist settings, utilisation of various healthcare services and patients' satisfaction. We compared mean resource use for each contact type and health service costs per patient, stratifying patients by whether they were currently attending a SAC or never attended one.

SETTING

Secondary care including SACs and general neurology clinics.

PARTICIPANTS

We had 277 participants in the survey, aged 16 years old and over, diagnosed with ataxia and living in the UK.

PRIMARY OUTCOME MEASURES

Patient experience and perception of the two healthcare services settings, patient level of satisfaction, difference in healthcare services use and costs.

RESULTS

Patients gave positive feedback about the role of SAC in understanding their condition (96.8% of SAC group), in coordinating referrals to other healthcare specialists (86.6%), and in offering opportunities to take part in research studies (85.2%). Participants who attended a SAC reported a better management of their symptoms and a more personalised care received compared with participants who never attended a SAC (p<0.001). Costs were not significantly different in between those attending a SAC and those who did not. We identified some barriers for patients in accessing the SACs, and some gaps in the care provided, for which we made some recommendations.

CONCLUSIONS

This study provides useful information about ataxia patient care pathways in the UK. Overall, the results showed significantly higher patient satisfaction in SAC compared with non-SAC, at similar costs. The findings can be used to inform policy recommendations on how to improve treatment and care for people with these very rare and complex neurological diseases. Improving access to SAC for patients across the UK is one key policy recommendation of this study.

The Spectrum of Disease-Associated Alleles in Countries with a Predominantly Slavic Population

There are more than 260 million people of Slavic descent worldwide, who reside mainly in Eastern Europe but also represent a noticeable share of the population in the USA and Canada. Slavic populations, particularly Eastern Slavs and some Western Slavs, demonstrate a surprisingly high degree of genetic homogeneity, and, consequently, remarkable contribution of recurrent alleles associated with hereditary diseases. Along with pan-European pathogenic variants with clearly elevated occurrence in Slavic people (e.g., ATP7B c.3207C>A and PAH c.1222C>T), there are at least 52 pan-Slavic germ-line mutations (e.g., NBN c.657_661del and BRCA1 c.5266dupC) as well as several disease-predisposing alleles characteristic of the particular Slavic communities (e.g., Polish SDHD c.33C>A and Russian ARSB c.1562G>A variants). From a clinical standpoint, Slavs have some features of a huge founder population, thus providing a unique opportunity for efficient genetic studies.

Investigation of Spinocerebellar Ataxia (SCA) Disease in Iranian Patients and Accurate Trinucleotide Repeat Detection in the SCA3 by TP-PCR Method

SCA (spinocerebellar ataxia) which is autosomal dominantly transferred is a subset of inherited cerebellar ataxia. These progressive neurological diseases have clinical features of ataxia and are derived from the destruction of the cerebellum. These diseases can also affect other areas, including the brainstem. Frequent proliferation of CAG nucleotides can encode polyglutamine and, as a result, produce the toxic polyglutamine (poly Q) protein that leads to many types of SCAs. They are categorized based on specific genetic mutations. The main symptoms of SCA, gait ataxia and incoordination, nystagmus, vision problems, and dysarthria, can be mentioned. In this study, 31 Iranians who were suspected of SCA disease were clinically diagnosed from November 2019 to September 2021. For these 31 patients suspected of spinocerebellar ataxia, PCR was performed, and the analysis was based on vertical electrophoresis. For SCA3 patients, the TP-PCR technique was carried out and evaluated by capillary electrophoresis. For all 31 patients, PCR function was successful according to the results attained by conventional PCR. The number of three nucleotide replications was within the normal range for 22 people, and nine patients were reported. Studies showed that three people suspected of SCA were infected with SCA3 according to the TP-PCR technique, and this was while seven people were diagnosed with SCA3 using the PCR method. As the purpose of this test is to provide a more accurate diagnostic method and prenatal diagnosis of this disease, the TP-PCR method proved to be more suitable when applied for the diagnosis of abnormal trinucleotides CAG in spinocerebellar ataxia type 3.

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.

Increased intrinsic membrane excitability is associated with hypertrophic olivary degeneration in spinocerebellar ataxia type 1

One of the characteristic areas of brainstem degeneration across multiple spinocerebellar ataxias (SCAs) is the inferior olive (IO), a medullary nucleus that plays a key role in motor learning. In addition to its vulnerability in SCAs, the IO is also susceptible to a distinct pathology known as hypertrophic olivary degeneration (HOD). Clinically, HOD has been exclusively observed after lesions in the brainstem disrupt inhibitory afferents to the IO. Here, for the first time, we describe HOD in another context: spinocerebellar ataxia type 1 (SCA1). Using the genetically-precise SCA1 knock-in mouse model (SCA1-KI; both sexes used), we assessed SCA1-associated changes in IO neuron structure and function. Concurrent with degeneration, we found that SCA1-KI IO neurons are hypertrophic, exhibiting early dendrite lengthening and later somatic expansion. Unlike in previous descriptions of HOD, we observed no clear loss of IO inhibitory innervation; nevertheless, patch-clamp recordings from brainstem slices reveal that SCA1-KI IO neurons are hyperexcitable. Rather than synaptic disinhibition, we identify increases in intrinsic membrane excitability as the more likely mechanism underlying this novel SCA1 phenotype. Specifically, transcriptome analysis indicates that SCA1-KI IO hyperexcitability is associated with a reduced medullary expression of ion channels responsible for spike afterhyperpolarization (AHP) in IO neurons - a result that has a functional consequence, as SCA1-KI IO neuron spikes exhibit a diminished AHP. These results reveal membrane excitability as a potential link between disparate causes of IO degeneration, suggesting that HOD can result from any cause, intrinsic or extrinsic, that increases excitability of the IO neuron membrane.

Demographics and Clinical Characteristics of Autosomal Dominant Spinocerebellar Ataxia in Canada

Background

Autosomal dominant (AD) spinocerebellar ataxias (SCAs) encompass a large group of rare disorders, which occurs in individuals of different ethnic backgrounds. To date, demographics, and clinical descriptions of AD SCA in Canada are lacking.

Methods

A retrospective chart review of patients with a genetically confirmed diagnosis of AD SCAs was performed at five tertiary centers across Canada in the provinces of Quebec, Alberta, and Ontario. Demographic, genetic, and clinical information were collected and analyzed.

Results

A total of 203 patients with AD SCA were identified. Weighted estimated prevalence of AD SCA in three large Canadian provinces was calculated (2.25 cases per 100.000) which is in keeping with the figures documented worldwide. We found that the distribution of the most common SCA differed when comparing provinces. The most prevalent SCA diagnosis in Ontario was SCA3 (49%), while the most prevalent SCA diagnosis in Alberta and Quebec was SCA2 in 26% and 47%, respectively. SCA6 was the third most prevalent SCA subtype in Quebec (14%), which was not seen as commonly in other provinces. SCA1 was uncommonly seen in both Alberta and Quebec, despite being common in Ontario.

Conclusions

In this largest Canadian study, we describe the prevalence, distribution, and clinical characteristics of AD SCA. We found that the distribution of the most common SCA differed in the three provinces studied. This finding reflects the heterogenous nature of the Canadian population.

Dystonia, Chorea, and Ataxia: Three Challenging Cases

Movement disorders comprise a heterogeneous and complex group of neurological disorders that increase (hyperkinetic) or decrease (hypokinetic) the speed or amplitude of movements, or disrupt their coordinated sequencing. In this article, we describe three instructive cases, exemplifying classic movement disorders, namely dystonia, chorea, and ataxia. We highlight the diagnostic approach based on clinical clues, syndromic reasoning, evaluation, and management recommendations. Each case ends with key messages for the clinicians.

Pharmacotherapy for the management of the symptoms of Machado-Joseph Disease

INTRODUCTION

Machado-Joseph disease or spinocerebellar ataxia type 3 (SCA3/MJD) is the leading cause of autosomal dominant ataxia worldwide. This is a slowly progressive, but very disabling disorder. Ataxia is the main clinical feature, but additional motor and non-motor manifestations may be found. Many of these manifestations are amenable to pharmacological treatments, which may impact the quality of life of affected subjects.

AREAS COVERED

Authors review available literature on both disease-modifying and symptomatic pharmacological therapies for SCA3/MJD. Discussion is stratified into motor (ataxic and non-ataxic syndromes) and non-motor manifestations. Ongoing clinical trials and future perspectives are also discussed in the manuscript.

EXPERT OPINION

Symptomatic treatment is the mainstay of clinical care and should be tailored for each patient with SCA3/MJD. Management of ataxia is still a challenging task, but relief (at least partial) of dystonia, pain/cramps, fatigue, and sleep disorders is an achievable goal for many patients. Even though there are no disease-modifying treatments so far, recent advances in understanding the biology of disease and international collaborations of clinical researchers are now paving the way for a new era where more clinical trials will be available for this devastating disorder.

Expanding the Landscape of Spinocerebellar Ataxia Type 5

Spinocerebellar ataxia type 5 (SCA5) is a rare subtype of SCA that usually affects adults. It has been recently reported in children in Europe, North America, and China. This study aims to describe clinical, radiological, and genetic data of a child presenting with SCA5, caused by a heterozygous likely pathogenic missense variant in SPTBN2 (NM_006946.3: c.1052G > C, p.Arg351Pro). According to databases and a review of the literature, this is one of few cases of SCA5 from Latin America. Expanding the landscape of SCA5 is relevant to the differential diagnosis of ataxic cerebral palsy and the autosomal recessive cerebellar ataxias.

Nutritional status and eating habits of patients with hereditary ataxias: a case-control study

INTRODUCTION

Hereditary Ataxias (HAs) comprise a wide spectrum of genetically determined neurodegenerative diseases with progressive ataxia as the main symptom. Few studies have evaluated nutritional profile in HA patients and most of these focused on specific ataxia subtypes. The objectives of this study were: (1) to investigate whether hereditary ataxias were associated with changes in energy expenditure, body composition and dietary intake; (2) to verify differences in these variables according to ataxia subtype, sex, age, and disease severity.

METHODS

Thirty-eight hereditary ataxia patients from two neurology centers in Northeastern Brazil and 38 controls were evaluated. Body composition was assessed with bio-impedance analysis and dietary intake was estimated with a validated questionnaire (24-hour dietary recall).

RESULTS

Mean body mass index (BMI) was lower in HA compared to controls (p = 0.032). Hereditary ataxia patients showed lower protein intake, higher frequency of dysphagia and higher incidence of nausea and diarrhea. The difference in average estimated caloric intake did not reach statistical significance (2359kcal ± 622 in patients × 2713kcal ± 804 in controls, p = 0.08). Disease severity measured by the SARA scale was not associated with BMI, nor was ataxia subtype (autosomal dominant × non-autosomal dominant ataxias).

CONCLUSION

Hereditary ataxia patients have lower BMI compared to healthy controls. There was no difference in this cohort between dominant or non-dominant ataxia regarding BMI. Weight loss may be a common finding among hereditary ataxias and may affect the quality of life in these patients.

Genetic Distribution of Five Spinocerebellar Ataxia Microsatellite Loci in Mexican Native American Populations and Its Impact on Contemporary Mestizo Populations

Spinocerebellar ataxias (SCAs) conform a heterogeneous group of neurodegenerative disorders with autosomal dominant inheritance. Five of the most frequent SCAs are caused by a CAG repeat expansion in the exons of specific genes. The SCAs incidence and the distribution of polymorphic CAG alleles vary among populations and ethnicities. Thus, characterization of the genetic architecture of ethnically diverse populations, which have undergone recent admixture and demographic events, could facilitate the identification of genetic risk factors. Owing to the great ethnic diversity of the Mexican population, this study aimed to analyze the allele frequencies of five SCA microsatellite loci (SCA1, SCA2, SCA3, SCA6, and SCA7) in eleven Mexican Native American (MNA) populations. Data from the literature were used to compare the allelic distribution of SCA loci with worldwide populations. The SCA loci allelic frequencies evidenced a certain genetic homogeneity in the MNA populations, except for Mayans, who exhibited distinctive genetic profiles. Neither pathological nor large normal alleles were found in MNA populations, except for the SCA2 pre-mutated allele in the Zapotec population. Collectively, our findings demonstrated the contribution of the MNA ancestry in shaping the genetic structure of contemporary Mexican Mestizo populations. Our results also suggest that Native American ancestry has no impact on the origin of SCAs in the Mexican population. Instead, the acquisition of pathological SCA alleles could be associated with European migration.

Deletion of the SELENOP gene leads to CNS atrophy with cerebellar ataxia in dogs

We investigated a hereditary cerebellar ataxia in Belgian Shepherd dogs. Affected dogs developed uncoordinated movements and intention tremor at two weeks of age. The severity of clinical signs was highly variable. Histopathology demonstrated atrophy of the CNS, particularly in the cerebellum. Combined linkage and homozygosity mapping in a family with four affected puppies delineated a 52 Mb critical interval. The comparison of whole genome sequence data of one affected dog to 735 control genomes revealed a private homozygous structural variant in the critical interval, Chr4:66,946,539_66,963,863del17,325. This deletion includes the entire protein coding sequence of SELENOP and is predicted to result in complete absence of the encoded selenoprotein P required for selenium transport into the CNS. Genotypes at the deletion showed the expected co-segregation with the phenotype in the investigated family. Total selenium levels in the blood of homozygous mutant puppies of the investigated litter were reduced to about 30% of the value of a homozygous wildtype littermate. Genotyping >600 Belgian Shepherd dogs revealed an additional homozygous mutant dog. This dog also suffered from pronounced ataxia, but reached an age of 10 years. Selenop^-/- knock-out mice were reported to develop ataxia, but their histopathological changes were less severe than in the investigated dogs. Our results demonstrate that deletion of the SELENOP gene in dogs cause a defect in selenium transport associated with CNS atrophy and cerebellar ataxia (CACA). The affected dogs represent a valuable spontaneous animal model to gain further insights into the pathophysiological consequences of CNS selenium deficiency.

We studied a form of inherited ataxia in a family of Belgian Shepherd dogs that we termed CNS atrophy and cerebellar ataxia (CACA). Clinical signs were evident at 2 weeks of age and the affected puppies had to be euthanized at 4 weeks of age. The pedigree of the index family with 4 affected and 4 unaffected puppies suggested autosomal recessive inheritance. Using a purely positional cloning approach, we identified a complete deletion of the SELENOP gene as the most likely causative variant. SELENOP encodes selenoprotein P, a protein with multiple selenocysteine residues, which is required for the transport of selenium into the CNS. Selenium measurements in affected dogs demonstrated blood selenium levels of about 30% compared to normal control dogs. Genotyping a cohort of additional Belgian Shepherd dogs with unexplained ataxia identified another CACA case that had a relatively stable clinical condition and reached an age of 10 years. Selenop^-/- knock-out mice show a related but not identical ataxia phenotype. Our finding of a SELENOP gene deletion in CACA affected dogs identifies a spontaneous animal model to gain further insights into the pathophysiological consequences of CNS selenium deficiency.

Mutant Ataxin-3-Containing Aggregates (MATAGGs) in Spinocerebellar Ataxia Type 3: Dynamics of the Disorder

Spinocerebellar ataxia type 3 (SCA3) is the most common type of SCA worldwide caused by abnormal polyglutamine expansion in the coding region of the ataxin-3 gene. Ataxin-3 is a multi-faceted protein involved in various cellular processes such as deubiquitination, cytoskeletal organisation, and transcriptional regulation. The presence of an expanded poly(Q) stretch leads to altered processing and misfolding of the protein culminating in the production of insoluble protein aggregates in the cell. Various post-translational modifications affect ataxin-3 fibrillation and aggregation. This review provides an exhaustive assessment of the various pathogenic mechanisms undertaken by the mutant ataxin-3-containing aggregates (MATAGGs) for disease induction and neurodegeneration. This includes in-depth discussion on MATAGG dynamics including their formation, role in neuronal pathogenesis, and the debate over the toxic v/s protective nature of the MATAGGs in disease progression. Additionally, the currently available therapeutic strategies against SCA3 have been reviewed. The shift in the focus of such strategies, from targeting the steps that lead to or reduce aggregate formation to targeting the expression of mutant ataxin-3 itself via RNA-based therapeutics, has also been presented. We also discuss the intriguing promise that various growth and neurotrophic factors, especially the insulin pathway, hold in the modulation of SCA3 progression. These emerging areas show the newer directions through which SCA3 can be targeted including various preclinical and clinical trials. All these advances made in the last three decades since the discovery of the ataxin-3 gene have been critically reviewed here.