Spinocerebellar ataxias types 1, 2 and 3: Age adjusted clinical severity of disease at presentation correlates with size of CAG repeat lengths

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.

Stability of Mosaic Divergent Repeat Interruptions in X-Linked Dystonia-Parkinsonism

BACKGROUND

X-Linked dystonia-parkinsonism (XDP) is an adult-onset neurodegenerative disorder characterized by rapidly progressive dystonia and parkinsonism. Mosaic Divergent Repeat Interruptions affecting motif Length and Sequence (mDRILS) were recently found within the TAF1 SVA repeat tract and were shown to associate with repeat stability and age at onset in XDP, specifically the AGGG [5'-SINE-VNTR-Alu(AGAGGG)2AGGG(AGAGGG)n] mDRILS.

OBJECTIVE

This study aimed to investigate the stability of mDRILS frequencies and stability of (AGAGGG)n repeat length during transmission in parent-offspring pairs.

METHODS

Fifty-six families (n = 130) were investigated for generational transmission of repeat length and mDRILS. The mDRILS stability of 16 individuals was assessed at two sampling points 1 year apart. DNA was sequenced with long-read technologies after long-range polymerase chain reaction amplification of the TAF1 SVA. Repeat number and mDRILS were detected with Noise-Cancelling Repeat Finder (NCRF).

RESULTS

When comparing the repeat domain, 51 of 65 children had either contractions or expansions of the repeat length. The AGGG frequency remained stable across generations at 0.074 (IQR: 0.069-0.078) (z = -0.526; P = 0.599). However, the median AGGG frequency in children with an expansion (0.072 [IQR: 0.066-0.076]) was lower compared with children with retention or contraction (0.080 [IQR: 0.073-0.083]) (z = -0.007; P = 0.003). In a logistic regression model, the AGGG frequency predicted the outcome of either expansion or retention/contraction when including repeat number and sex as covariates (β = 80.7; z-score = 2.63; P = 0.0085). The AGGG frequency varied slightly over 1 year (0.070 [IQR: 0.063-0.080] to 0.073 [IQR: 0.069-0.078]).

CONCLUSIONS

Our results show that a higher AGGG frequency may stabilize repeats across generations. This highlights the importance of further investigating mDRILS as a disease-modifying factor with generational differences. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Age is an important independent modifier of SCA3 phenotype severity

OBJECTIVE

This study aimed to investigate factors modulating spinocerebellar ataxia type 3 (SCA3) phenotype severity besides the expanded CAG repeats (ExpCAG) of ATXN3.

METHODS

Data regarding CAG trinucleotide repeats, age at onset (AO), duration, age, sex, transmitting parent, and scale scores of SCA3 patients were collected. Multiple linear regression analysis was performed to identify influential independent variables. Age, AO, ExpCAG, and duration were considered control variables to analyze the correlation between independent variables and scale scores.

RESULTS

Duration, age, and ExpCAG were screened as influential independent variables (P = 0.000). Age had the greatest impact on multiple linear regression models (P<5E-8). ExpCAG and SARA/ICARS/INAS/Barthel index were not correlated (P > 0.05); considering only age as the control, ExpCAG was slightly-to-moderately correlated with all aforementioned scores except INAS (P < 0.05). Age and all scores, except INAS, were positively correlated (P < 0.05); considering duration, AO, or ExpCAG as controls, their correlations did not change significantly. On controlling age, AO was negatively correlated with all scores (P < 0.05), except for the Barthel index (P > 0.05). Furthermore, the interaction model revealed that the interaction between age, duration, and ExpCAG was significantly associated with SCA3 disease severity (P < 0.05).

CONCLUSION

Age is a potentially important modifier of SCA3 phenotype severity, through the interaction between ExpCAG and aging factors.

Clinical features and genetic characteristics of homozygous spinocerebellar ataxia type 3

Background

Homozygous spinocerebellar ataxia type 3 (SCA3) patients, which have an expanded cytosine‐adenine‐guanine (CAG) repeat mutation in both alleles of ATXN3, are extremely rare. Clinical features and genetic characteristics of them were seldom studied.

Methods

We analyzed seven newly homozygous SCA3 patients from five families and 14 homozygotes reported previously. An additional cohort of 30 heterozygous SCA3 patients were analyzed to compare age at onset (AAO).

Results

Two out of seven SCA3 homozygotes had the minimum CAG repeats reported so far (55/56 and 56/58). Five patients appeared peripheral neuropathy and two had mild cognitive impairment. The AAO was significantly inversely correlated with both the large and small expanded CAG repeats (r = −.7682, p < .0001). The AAO was significantly earlier in homozygous SCA3 than heterozygous ones (32.81 ± 11.86 versus. 49.90 ± 9.73, p < .0001). In addition, the AAO of our seven homozygotes is elder compared to those reported previously (41.29 years vs. 28.57 years), which may be related to the fewer CAG repeats in our seven patients.

Conclusion

Gene dosage effect may play an important role in the AAO and severity of disease, and homozygosity for ATXN3 enhances phenotypic severity. Our findings expand clinical features and genetic characteristics of homozygous SCA3 patients.

Selective Patterns of Cognitive Impairment in Spinocerebellar Ataxia Type 6 and Idiopathic Late-Onset Cerebellar Ataxia

Purpose

To determine cognitive impairment patterns in patients with spinocerebellar ataxia type 6 (SCA6) compared to patients with idiopathic late-onset cerebellar ataxia (ILOCA).

Methods

Neurocognitive testing was conducted on 21 SCA6, nine ILOCA, and 27 controls subjects. Intergroup differences were assessed using the Wilcoxon signed-ranked test or Student's t-test. Principal component analysis (PCA) was performed on nine cognitive variables, and Hotelling's T-squared test assessed group-specific differences. Pearson's correlations assessed changes in cognitive performance and disease progression. Intra-group differences among SCA6 were examined in a post-hoc analysis.

Results

SCA6 and ILOCA patients showed impairment in visuo-spatial executive function, phonemic verbal fluency, and semantic-verb word generation. ILOCA showed impairment in mental flexibility/response inhibition, verbal learning, semantic-noun verbal fluency, and forward numerical working memory. Within the first three principal components, SCA6 and ILOCA differed from controls and from each other. Verbal working and immediate visuo-spatial memory correlated with disease duration for SCA6. For ILOCA, Mini-Mental Status Exam and RCF copy correlated with disease duration.

Conclusion

Differing patterns of cognitive dysfunction were seen in SCA6 and ILOCA. PCA suggested that distinct SCA6 subgroups may exist, SCA61 with significant ILOCA overlap in several cognitive deficits, and SCA62 showing deficits in visuo-spatial performance only.

Genetic testing for clinically suspected spinocerebellar ataxias: report from a tertiary referral centre in India

Spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative syndromes, characterized by a wide range of muscular weakness and motor deficits, caused due to cerebellar degeneration. The prevalence of the syndromes of SCA varies across the world and is known to be linked to the instability of trinucleotide repeats within the high-end normal alleles, along with susceptible haplotype. We estimated sizes of the CAG or GAA repeat expansions at the SCA1, SCA2, SCA3, SCA12 and frataxin loci among 864 referrals of subjects to genetic counselling and testing (GCAT) clinic, National Institute of Mental Health and Neurosciences, Bengaluru, India, with suspected SCA. The most frequent mutations detected were SCA1 (n = 100 (11.6%)) and SCA2 (n = 98 (11.3%)) followed by SCA3 (n = 40 (4.6%)), FRDA (n = 20 (2.3%)) and SCA12 (n = 8 (0.9%)).

High Serum GFAP Levels in SCA3/MJD May Not Correlate with Disease Progression

Spinocerebellar ataxia type 3(SCA3), also known as Machado-Joseph disease (MJD), is the most frequent subtype of autosomal dominant inherited spinocerebellar ataxias, which caused by the expansion of CAG repeats in the ATXN3 gene. The number of CAG repeats of the abnormal allele determines the rate of disease progression in patients with SCA3/MJD. Markers to assess the clinical severity, to predict the course of illness and to monitor the efficacy of therapeutic measures, can be clinical, biological, and radiological. Here, we aimed to explore whether the serum glial fibrillary acidic protein (GFAP) may act as a biomarker in SCA3/MJD patients and to evaluate the correlation between some markers with the number of CAG repeats in SCA3/MJD patients. We showed that the serum levels of GFAP were significantly higher in SCA3/MJD patients than in controls. There was a strong positive correlation between the age-adjusted GFAP levels with the number of CAG repeats. Age-adjusted International Cooperative Ataxia Rating Scale (ICARS) scores and Scale for the Assessment and Rating of Ataxia (SARA) scores correlated with the number of CAG repeats. Raw scores and disease duration-adjusted GFAP levels, ICARS scores, and SARA scores were not correlated with the number of CAG repeats. Our results reveal novel evidence for the role of the triplet expansion in SCA3/MJD-associated neuronal damage.

Ataxias with Autosomal, X-Chromosomal or Maternal Inheritance

Heredoataxias are a group of genetic disorders with a cerebellar syndrome as the leading clinical manifestation. The current classification distinguishes heredoataxias according to the trait of inheritance into autosomal dominant, autosomal recessive, X-linked, and maternally inherited heredoataxias. The autosomal dominant heredoataxias are separated into spinocerebellar ataxias (SCA1-8, 10-15, 17-23, 25-30, and dentato-rubro-pallido-luysian atrophy), episodic ataxias (EA1-7), and autosomal dominant mitochondrial heredoataxias (Leigh syndrome, MIRAS, ADOAD, and AD-CPEO). The autosomal recessive ataxias are separated into Friedreich ataxia, ataxia due to vitamin E deficiency, ataxia due to Abeta-lipoproteinemia, Refsum disease, late-onset Tay-Sachs disease, cerebrotendineous xanthomatosis, spinocerebellar ataxia with axonal neuropathy, ataxia telangiectasia, ataxia telangiectasia-like disorder, ataxia with oculomotor apraxia 1 and 2, spastic ataxia of Charlevoix-Saguenay, Cayman ataxia, Marinesco-Sjögren syndrome, and autosomal recessive mitochondrial ataxias (AR-CPEO, SANDO, SCAE, AHS, IOSCA, MEMSA, LBSL CoQ-deficiency, PDC-deficiency). Only two of the heredoataxias, fragile X/tremor/ataxia syndrome, and XLSA/A are transmitted via an X-linked trait. Maternally inherited heredoataxias are due to point mutations in genes encoding for tRNAs, rRNAs, respiratory chain subunits or single large scale deletions/duplications of the mitochondrial DNA and include MELAS, MERRF, KSS, PS, MILS, NARP, and non-syndromic mitochondrial disorders. Treatment of heredoataxias is symptomatic and supportive and may have a beneficial effect in single patients.

**Please see page 424 for abbreviation list.

Consensus paper: pathological mechanisms underlying neurodegeneration in spinocerebellar ataxias

Intensive scientific research devoted in the recent years to understand the molecular mechanisms or neurodegeneration in spinocerebellar ataxias (SCAs) are identifying new pathways and targets providing new insights and a better understanding of the molecular pathogenesis in these diseases. In this consensus manuscript, the authors discuss their current views on the identified molecular processes causing or modulating the neurodegenerative phenotype in spinocerebellar ataxias with the common opinion of translating the new knowledge acquired into candidate targets for therapy. The following topics are discussed: transcription dysregulation, protein aggregation, autophagy, ion channels, the role of mitochondria, RNA toxicity, modulators of neurodegeneration and current therapeutic approaches. Overall point of consensus includes the common vision of neurodegeneration in SCAs as a multifactorial, progressive and reversible process, at least in early stages. Specific points of consensus include the role of the dysregulation of protein folding, transcription, bioenergetics, calcium handling and eventual cell death with apoptotic features of neurons during SCA disease progression. Unresolved questions include how the dysregulation of these pathways triggers the onset of symptoms and mediates disease progression since this understanding may allow effective treatments of SCAs within the window of reversibility to prevent early neuronal damage. Common opinions also include the need for clinical detection of early neuronal dysfunction, for more basic research to decipher the early neurodegenerative process in SCAs in order to give rise to new concepts for treatment strategies and for the translation of the results to preclinical studies and, thereafter, in clinical practice.

Genotype-specific patterns of atrophy progression are more sensitive than clinical decline in SCA1, SCA3 and SCA6

Spinocerebellar ataxias are dominantly inherited disorders that are associated with progressive brain degeneration, mainly affecting the cerebellum and brainstem. As part of the multicentre European integrated project on spinocerebellar ataxias study, 37 patients with spinocerebellar ataxia-1, 19 with spinocerebellar ataxia-3 and seven with spinocerebellar ataxia-6 were clinically examined and underwent magnetic resonance imaging at baseline and after a 2-year follow-up. All patients were compared with age-matched and gender-matched healthy control subjects. Magnetic resonance imaging analysis included three-dimensional volumetry and observer-independent longitudinal voxel-based morphometry. Volumetry revealed loss of brainstem, cerebellar and basal ganglia volume in all genotypes. Most sensitive to change was the pontine volume in spinocerebellar ataxia-1, striatal volume in spinocerebellar ataxia-3 and caudate volume in spinocerebellar ataxia-6. Sensitivity to change, as measured by standard response mean, of the respective MRI measures was greater than that of the most sensitive clinical measure, the Scale for the Assessment and Rating of Ataxia. Longitudinal voxel-based morphometry revealed greatest grey matter loss in the cerebellum and brainstem in spinocerebellar ataxia-1, in the putamen and pallidum in spinocerebellar ataxia-3 and in the cerebellum, thalamus, putamen and pallidum in spinocerebellar ataxia-6. There was a mild correlation between CAG repeat length and volume loss of the bilateral cerebellum and the pons in spinocerebellar ataxia-1. Quantitative volumetry and voxel-based morphometry imaging demonstrated genotype-specific patterns of atrophy progression in spinocerebellar ataxias-1, 3 and 6, and they showed a high sensitivity to detect change that was superior to clinical scales. These structural magnetic resonance imaging findings have the potential to serve as surrogate markers, which might help to delineate quantifiable endpoints and non-invasive methods for rapid and reliable data acquisition, encouraging their use in clinical trials.

Alterations in cortical excitability and central motor conduction time in spinocerebellar ataxias 1, 2 and 3: a comparative study

INTRODUCTION

Spinocerebellar ataxias 1, 2 and 3 (SCA1, SCA2 and SCA3) are CAG repeat disorders. The prevalence of changes in the cortical excitability and central motor conduction time (CMCT) in these disorders is largely unknown, and there are few studies which have compared these findings in the subtypes of SCA. The objectives of this study were to measure the cortical resting motor threshold (RMT) and CMCT using transcranial magnetic stimulation in patients with SCA1, SCA2, and SCA3.

METHODS

The subjects of this study were 32 genetically confirmed patients with SCA (SCA1 = 15, SCA2 = 11, SCA3 = 6). Transcranial magnetic stimulation (TMS) was performed using a figure-of-eight coil attached to Magstim 200 stimulator. Motor evoked potentials were recorded from first dorsal interosseous at rest. RMT was determined using standard techniques and the CMCT by 'F' wave method. Comparison was made with data from 32 healthy controls.

RESULTS

Compared to controls, the patients with SCA had significantly higher mean RMT as well as CMCT (RMT: 49.9 ± 9.1 vs. 41.5 ± 6.6, p < 0.0001; CMCT: 7.7 ± 2.3 ms vs. 4.8 ± 0.6 ms; p < 0.0001). When compared separately with the controls, while all the three subtypes of SCAs had significantly prolonged CMCT, only SCA1 and SCA3, but not SCA2 had significantly greater RMT. RMT and CMCT between patients with SCA2 and SCA3, and between SCA1 and SCA3 did not differ significantly, while SCA1 had significantly higher RMT and CMCT than SCA2.

CONCLUSIONS

Patients with SCA have reduced cortical excitability and prolonged central motor conduction time, which was most evident in SCA1 and least in SCA2.

CAG repeats determine brain atrophy in spinocerebellar ataxia 17: a VBM study

Background

Abnormal repeat length has been associated with an earlier age of onset and more severe disease progression in the rare neurodegenerative disorder spinocerebellar ataxia 17 (SCA17).

Methodology/Principal Findings

To determine whether specific structural brain degeneration and rate of disease progression in SCA17 might be associated with the CAG repeat size, observer-independent voxel-based morphometry was applied to high-resolution magnetic resonance images of 16 patients with SCA17 and 16 age-matched healthy controls. The main finding contrasting SCA17 patients with healthy controls demonstrated atrophy in the cerebellum bilaterally. Multiple regression analyses with available genetic data and also post-hoc correlations revealed an inverse relationship again with cerebellar atrophy. Moreover, we found an inverse relationship between the CAG repeat length and rate of disease progression.

Conclusions

Our results highlight the fundamental role of the cerebellum in this neurodegenerative disease and support the genotype-phenotype relationship in SCA17 patients. Genetic factors may determine individual susceptibility to neurodegeneration and rate of disease progression.