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

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 comprehensive review of iPS cell line-based disease modelling of the polyglutamine spinocerebellar ataxias 2 and 3: a focus on the research outcomes

Spinocerebellar ataxias (SCAs) are a rare autosomal dominant neurodegenerative disorder. To date, approximately 50 different subtypes of SCAs have been characterized. The prevalent types of SCAs are usually of PolyQ origin, wherein the disease pathology is a consequence of multiple glutamine residues being encoded onto the disease proteins, causing expansions. SCAs 2 and 3 are the most frequently diagnosed subtypes, wherein affected patients exhibit certain characteristic physiological manifestations, such as gait ataxia and dysarthria. Nevertheless, other clinical signs were exclusive to these subtypes. Recently, multiple molecular diagnostic methods have been developed to identify and characterize these subtypes. Despite these advancements, the molecular pathology of SCAs remains unknown. To further understand the mechanisms involved in neurodegenerative SCAs 2 and 3, patient-derived induced pluripotent stem cell (iPSC)-based modelling is a compelling avenue to pursue. We cover the present state of iPSC-based in-vitro illness modelling of SCA subtypes 2 and 3 below, along with a list of cell lines created, and the relevance of research outcomes to personalized autologous therapy.

Hereditary Ataxias: From Bench to Clinic, Where Do We Stand?

Cerebellar ataxias are a wide heterogeneous group of movement disorders. Within this broad umbrella of diseases, there are both genetics and sporadic forms. The clinical presentation of these conditions can exhibit a diverse range of symptoms across different age groups, spanning from pure cerebellar manifestations to sensory ataxia and multisystemic diseases. Over the last few decades, advancements in our understanding of genetics and molecular pathophysiology related to both dominant and recessive ataxias have propelled the field forward, paving the way for innovative therapeutic strategies aimed at preventing and arresting the progression of these diseases. Nevertheless, the rarity of certain forms of ataxia continues to pose challenges, leading to limited insights into the etiology of the disease and the identification of target pathways. Additionally, the lack of suitable models hampers efforts to comprehensively understand the molecular foundations of disease's pathophysiology and test novel therapeutic interventions. In the following review, we describe the epidemiology, symptomatology, and pathological progression of hereditary ataxia, including both the prevalent and less common forms of these diseases. Furthermore, we illustrate the diverse molecular pathways and therapeutic approaches currently undergoing investigation in both pre-clinical studies and clinical trials. Finally, we address the existing and anticipated challenges within this field, encompassing both basic research and clinical endeavors.

A Novel co‐existence of SCA1 and SCA2 mutations in Indian patients

Background

Spinocerebellar ataxia 1 (SCA1) and SCA2 are dominantly inherited ataxias caused due to CAG expansion mutation in ATXN1 (CAG≥39) and ATXN2 (CAG≥32) genes located at 6p22.3 and 12q24.12 loci, respectively, with key manifestations of progressive limb and gait ataxia and with or without brain stem and pyramidal tract involvement. Both SCA1 and SCA2 are quite prevalent subtypes among the SCAs. There are very few reports that describe a combinatorial SCA subtype mutation in a single patient.

Cases

Here, we report a novel co-occurrence of SCA1 and SCA2 mutations in two unrelated patients. Case-1 was observed to carry ATXN1-CAG (30/40) and ATXN2-CAG (23/45), while case-2 harbored ATXN1-CAG (29/42) and ATXN2-CAG (23/41). Overall, the clinical outcome was complex with probable early onset than expected in Case-1 and in Case-2, we observed a significant delayed onset of the disease than expected.

Conclusion

These cases highlight the probabilistic interactive outcome of two unrelated genetic events towards a converging phenotype.

Common and Founder Mutations for Monogenic Traits in Sub-Saharan African Populations

This review highlights molecular genetic studies of monogenic traits where common pathogenic mutations occur in black families from sub-Saharan Africa. Examples of founder mutations have been identified for oculocutaneous albinism, cystic fibrosis, Fanconi anemia, and Gaucher disease. Although there are few studies from Africa, some of the mutations traverse populations across the continent, and they are almost all different from the common mutations observed in non-African populations. Myotonic dystrophy is curiously absent among Africans, and nonsyndromic deafness does not arise from mutations in GJB2 and GJB7. Locus heterogeneity is present for Huntington disease, with two common triplet expansion loci in Africa, HTT and JPH3. These findings have important clinical consequences for diagnosis, treatment, and genetic counseling in affected families. We currently have just a glimpse of the molecular etiology of monogenic diseases in sub-Saharan Africa, a proverbial “ears of the hippo” situation.

A study of Huntington disease-like syndromes in black South African patients reveals a single SCA2 mutation and a unique distribution of normal alleles across five repeat loci

Huntington disease (HD) is a progressive neurodegenerative disease, characterised by a triad of movement disorder, emotional and behavioural disturbances and cognitive impairment. The underlying cause is an expanded CAG repeat in the huntingtin gene. For a small proportion of patients presenting with HD-like symptoms, the mutation in this gene is not identified and they are said to have a HD "phenocopy". South Africa has the highest number of recorded cases of an African-specific phenocopy, Huntington disease-like 2 (HDL2), caused by a repeat expansion in the junctophilin-3 gene. However, a significant proportion of black patients with clinical symptoms suggestive of HD still test negative for HD and HDL2. This study thus aimed to investigate five other loci associated with HD phenocopy syndromes - ATN1, ATXN2, ATXN7, TBP and C9orf72. In a sample of patients in whom HD and HDL2 had been excluded, a single expansion was identified in the ATXN2 gene, confirming a diagnosis of Spinocerebellar ataxia 2. The results indicate that common repeat expansion disorders do not contribute significantly to the HD-like phenotype in black South African patients. Importantly, allele sizing reveals unique distributions of normal repeat lengths across the associated loci in the African population studied.

Neurogenomics in Africa: Perspectives, progress, possibilities and priorities

The understanding of the genetic basis of neurological disorders has grown rapidly in the last two decades. Despite the genomic heterogeneity within African populations, large-scale candidate gene or linkage and exome studies are lacking. However, current knowledge on neurogenetics in African populations is limited and geographically very uneven. Isolated reports indicate the existence of autosomal dominant or recessive conditions incorporating cerebrovascular, movement, neuromuscular, seizure and motor neuron disorders in Africans. In addition, few African families with neurodegenerative disorders associated with dementia have been characterized in North, West and South Africa. The current insurgency in genomic research triggered by among others the Human Health and Heredity (H3) Africa Initiative indicates that there are unique opportunities to advance our knowledge and understanding of the influence of genomic variation on the pattern, presentations and prognosis of neurological disorders in Africa. These have enormous potential to unmask novel genes and molecular pathways germane to the neurobiology of brain disorders. It would facilitate the development of novel diagnostics, preventative and targeted treatments in the new paradigm of precision medicine. Nevertheless, it is crucial to strike a balance between effective traditional public health strategies and personalized genome based care. The translational barriers can be overcome through robust stakeholder engagement and sustainable multilevel, multigenerational and multidisciplinary capacity building and infrastructural development for genomic medicine in Africa.

Medical genetics and genomic medicine in Rwanda

Medical genetics and genomic medicine in Rwanda.

Epidemiology of neurodegenerative diseases in sub-Saharan Africa: a systematic review

BACKGROUND

Sub-Saharan African (SSA) countries are experiencing rapid transitions with increased life expectancy. As a result the burden of age-related conditions such as neurodegenerative diseases might be increasing. We conducted a systematic review of published studies on common neurodegenerative diseases, and HIV-related neurocognitive impairment in SSA, in order to identify research gaps and inform prevention and control solutions.

METHODS

We searched MEDLINE via PubMed, 'Banque de Données de Santé Publique' and the database of the 'Institut d'Epidemiologie Neurologique et de Neurologie Tropicale' from inception to February 2013 for published original studies from SSA on neurodegenerative diseases and HIV-related neurocognitive impairment. Screening and data extraction were conducted by two investigators. Bibliographies and citations of eligible studies were investigated.

RESULTS

In all 144 publications reporting on dementia (n = 49 publications, mainly Alzheimer disease), Parkinsonism (PD, n = 20), HIV-related neurocognitive impairment (n = 47), Huntington disease (HD, n = 19), amyotrophic lateral sclerosis (ALS, n = 15), cerebellar degeneration (n = 4) and Lewy body dementia (n = 1). Of these studies, largely based on prevalent cases from retrospective data on urban populations, half originated from Nigeria and South Africa. The prevalence of dementia (Alzheimer disease) varied between <1% and 10.1% (0.7% and 5.6%) in population-based studies and from <1% to 47.8% in hospital-based studies. Incidence of dementia (Alzheimer disease) ranged from 8.7 to 21.8/1000/year (9.5 to 11.1), and major risk factors were advanced age and female sex. HIV-related neurocognitive impairment's prevalence (all from hospital-based studies) ranged from <1% to 80%. Population-based prevalence of PD and ALS varied from 10 to 235/100,000, and from 5 to 15/100,000 respectively while that for Huntington disease was 3.5/100,000. Equivalent figures for hospital based studies were the following: PD (0.41 to 7.2%), ALS (0.2 to 8.0/1000), and HD (0.2/100,000 to 46.0/100,000).

CONCLUSIONS

The body of literature on neurodegenerative disorders in SSA is large with regard to dementia and HIV-related neurocognitive disorders but limited for other neurodegenerative disorders. Shortcomings include few population-based studies, heterogeneous diagnostic criteria and uneven representation of countries on the continent. There are important knowledge gaps that need urgent action, in order to prepare the sub-continent for the anticipated local surge in neurodegenerative diseases.

[Variation of CAG repeats in coding region of ATXN2 gene in different ethnic groups]

Toinvestigate CAG repeats variation of ATXN2 gene coding region in six ethnic groups that live in comparatively different environments, to evaluate whether these variations are under positive selection, and to find factors driving selection effects, 291 unrelated healthy individuals were collected from six ethnic groups and their STR geneotyping was performed. The frequencies of alleles and genotypes were counted and thereby Slatkin's linearized Fst values were calculated. The UPGMA tree against this gene was constructed. The MDS analysis among these groups was carried out as well. The results from the linearized Fst values indicated that there were significant evolutionary differences of the STR in ATXN2 gene between Hui and Yi groups, but not among the other 4 groups. Further analysis was performed by combining our data with published data obtained from other groups. These results indicated that there were significant differences between Japanese and other groups including Hui, Hani, Yunnan Mongolian, and Inner Mongolian. Both Hui and Mongolian from Inner Mongolia were significantly different from Han. In conclusion, the six ethnic groups had their own distribution characterizations of allelic frequencies of ATXN2 STR, and the potential cause of frequency changes in rare alleles could be the consequence of positive selection.

Clinical and genetic analysis of spinocerebellar ataxia in Mali

BACKGROUND

Autosomal dominant cerebellar ataxia, currently denominated spinocerebellar ataxia (SCAs), represents a heterogeneous group of neurodegenerative disorders affecting the cerebellum and its connections. We describe the clinical and molecular findings in 16 patients originating from Malian families, who suffer from progressive cerebellar ataxia syndrome.

METHODS AND RESULTS

Molecular analysis allows genetic profiles of SCA to be distinguished. In seven patients, SCA type 2 (CAG) mutation was expanded from 39 to 43 repeats. SCA type 7 (CAG) mutation was confirmed in six patients. Mutations were expanded from 49 to 59 repeats. In three patients, SCA type3 was diagnosed and CAG mutation was expanded to 73 repeats.

CONCLUSIONS

Our data suggest that the most frequent types of SCA are SCA2 and SCA7. However, further studies are needed to confirm these preliminary results.

[Gene diagnosis and CAG repeat analysis of spinocerebellar ataxia cases of Guangxi region]

To characterize the distributions and subtypes of the spinocerebellar ataxias (SCA) in Guangxi region, the SCAl, SCA2, SCA3/MJD, SCA6, SCA7 and SCA12 (CAG)n mutations were analyzed by polymerase chain reaction (PCR) and capillary electrophoresis (CE). The SCA3/MJD mutation was detected in a total of 21 SCA patients and 19 presymptomatic individuals from 6 SCA families and their CAG repeat numbers were 59-70 and 60-73, respectively. No (CAG)n mutations of SCA1, SCA2, SCA6, SCA7 and SCA12 were detected. This study showed that SCA in Guangxi region is mostly SCA3/MJD subtype and the CAG repeats are smaller than those reported in other regions previously.