Spinocerebellar ataxia type 8: molecular genetic comparisons and haplotype analysis of 37 families with ataxia

Spastic paraplegia is the main manifestation of a spinocerebellar ataxia type 8 lineage in China: a case report and review of literature

The diagnosis and treatment of cerebellar atrophy remain challenging owing to its nonspecific symptoms and laboratory indicators. Three patients with spinocerebellar ataxia type 8 caused by ATXN8OS were found among the 16 people in the studied family. The clinical manifestations of the patients included progressive spastic paraplegia of the lower extremities, mild ataxia, mild cognitive impairment, and cerebellar atrophy. After administering antispasmodic rehabilitation treatment, using oral drugs, botulinum toxin injection, baclofen pump, and other systems in our hospital, the patients' lower extremity spasticity was significantly relieved. To our knowledge, till date, this is the first domestic report of spinocerebellar ataxia type 8 affecting a family, caused by ATXN8OS with spasticity onset in early childhood. Manifestations of the disease included spastic dyskinesia (in early disease stages) and cerebellar atrophy. Through systematic rehabilitation, the daily life of patients with this movement disorder was improved. This case report adds to the literature on spinocerebellar ataxia type 8 by summarizing its features.

Between Order and Chaos: Understanding the Mechanism and Pathology of RAN Translation

Repeat-associated non-AUG (RAN) translation is a pathogenic mechanism in which repetitive sequences are translated into aggregation-prone proteins from multiple reading frames, even without a canonical AUG start codon. Since its discovery in spinocerebellar ataxia type 8 (SCA8) and myotonic dystrophy type 1 (DM1), RAN translation is now known to occur in the context of 12 disease-linked repeat expansions. This review discusses recent advances in understanding the regulatory mechanisms controlling RAN translation and its contribution to the pathophysiology of repeat expansion diseases. We discuss the key findings in the context of Fragile X Tremor Ataxia Syndrome (FXTAS), a neurodegenerative disorder caused by a CGG repeat expansion in the 5' untranslated region of FMR1.

CCG•CGG interruptions in high-penetrance SCA8 families increase RAN translation and protein toxicity

Spinocerebellar ataxia type 8 (SCA8), a dominantly inherited neurodegenerative disorder caused by a CTG•CAG expansion, is unusual because most individuals that carry the mutation do not develop ataxia. To understand the variable penetrance of SCA8, we studied the molecular differences between highly penetrant families and more common sporadic cases (82%) using a large cohort of SCA8 families (n = 77). We show that repeat expansion mutations from individuals with multiple affected family members have CCG•CGG interruptions at a higher frequency than sporadic SCA8 cases and that the number of CCG•CGG interruptions correlates with age at onset. At the molecular level, CCG•CGG interruptions increase RNA hairpin stability, and in cell culture experiments, increase p-eIF2α and polyAla and polySer RAN protein levels. Additionally, CCG•CGG interruptions, which encode arginine interruptions in the polyGln frame, increase toxicity of the resulting proteins. In summary, SCA8 CCG•CGG interruptions increase polyAla and polySer RAN protein levels, polyGln protein toxicity, and disease penetrance and provide novel insight into the molecular differences between SCA8 families with high vs. low disease penetrance.

Conventional MRI findings in hereditary degenerative ataxias: a pictorial review

Purpose

Cerebellar ataxias are a large and heterogeneous group of disorders. The evaluation of brain parenchyma via MRI plays a central role in the diagnostic assessment of these conditions, being mandatory to exclude the presence of other underlying causes in determining the clinical phenotype. Once these possible causes are ruled out, the diagnosis is usually researched in the wide range of hereditary or sporadic ataxias.

Methods

We here propose a review of the main clinical and conventional imaging findings of the most common hereditary degenerative ataxias, to help neuroradiologists in the evaluation of these patients.

Results

Hereditary degenerative ataxias are all usually characterized from a neuroimaging standpoint by the presence, in almost all cases, of cerebellar atrophy. Nevertheless, a proper assessment of imaging data, extending beyond the mere evaluation of cerebellar atrophy, evaluating also the pattern of volume loss as well as concomitant MRI signs, is crucial to achieve a proper diagnosis.

Conclusion

The integration of typical neuroradiological characteristics, along with patient’s clinical history and laboratory data, could allow the neuroradiologist to identify some conditions and exclude others, addressing the neurologist to the more appropriate genetic testing.

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

Spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominant inherited diseases that share the degeneration of the cerebellum and its connections as their main feature. We performed a detailed description of the natural history of the main SCAs, focusing on epidemiology, progression, haplotype analysis and its correlation with founder effect, and perspective of future treatments. References for this review were identified by an in-depth literature search on PubMed and selected on the basis of relevance to the topic and on the authors' judgment. More than 40 SCAs have been described so far. SCA3 is the most common subtype worldwide, followed by SCA2 and 6. To evaluate the natural history and to estimate the progression of the main SCAs, consortiums were created all over the globe. Clinical rating scales have been developed to provide an accurate estimation of cerebellar clinical deficits, evaluating cerebellar and non-cerebellar signs. Natural history studies revealed that SCA1 patients' functional status worsened significantly faster than in other SCA subtypes, followed by SCA3, SCA2, SCA6, and SCA10. Number of CAG repeats, age of onset, and ataxia severity at baseline are strong contributors to the risk of death in most SCAs. Understanding the natural history of SCAs is extremely important. Although these are rare diseases, the impact they have on the affected individual are enormous. The advances in the field of genetics are helping understand neuronal functions and dysfunctions and allowing the study and development of possible therapies.

The First Case of Spinocerebellar Ataxia Type 8 in Monozygotic Twins

Spinocerebellar ataxia type 8 (SCA8) is a rare hereditary cerebellar ataxia showing mainly pure cerebellar ataxia. We herein report cases of SCA8 in Japanese monozygotic twins that presented with nystagmus, dysarthria, and limb and truncal ataxia. Their ATXN8OS CTA/CTG repeats were 25/97. They showed similar manifestations, clinical courses, and cerebellar atrophy on magnetic resonance imaging. Some of their pedigrees had nystagmus but not ataxia. These are the first monozygotic twins with SCA8 to be reported anywhere in the world. Although not all subjects with the ATXN8OS CTG expansion develop cerebellar ataxia, these cases suggest the pathogenesis of ATXN8OS repeat expansions in hereditary cerebellar ataxia.

Antibody Therapy Targeting RAN Proteins Rescues C9 ALS/FTD Phenotypes in C9orf72 Mouse Model

The intronic C9orf72 G4C2 expansion, the most common genetic cause of ALS and FTD, produces sense- and antisense-expansion RNAs and six dipeptide repeat-associated, non-ATG (RAN) proteins, but their roles in disease are unclear. We generated high-affinity human antibodies targeting GA or GP RAN proteins. These antibodies cross the blood-brain barrier and co-localize with intracellular RAN aggregates in C9-ALS/FTD BAC mice. In cells, α-GA₁ interacts with TRIM21, and α-GA₁ treatment reduced GA levels, increased GA turnover, and decreased RAN toxicity and co-aggregation of proteasome and autophagy proteins to GA aggregates. In C9-BAC mice, α-GA₁ reduced GA as well as GP and GR proteins, improved behavioral deficits, decreased neuroinflammation and neurodegeneration, and increased survival. Glycosylation of the Fc region of α-GA₁ is important for cell entry and efficacy. These data demonstrate that RAN proteins drive C9-ALS/FTD in C9-BAC transgenic mice and establish a novel therapeutic approach for C9orf72 ALS/FTD and other RAN-protein diseases.

PSP-Phenotype in SCA8: Case Report and Systemic Review

Spinocerebellar ataxia type 8 (SCA8) is a rare autosomal dominant neurodegenerative disease caused by expanded CTA/CTG repeats in the ATXN8OS gene. Many patients had pure cerebellar ataxia, while some had parkinsonism, both without causal explanation. We analyzed the ATXN8OS gene in 150 Japanese patients with ataxia and 76 patients with Parkinson's disease or related disorders. We systematically reassessed 123 patients with SCA8, both our patients and those reported in other studies. Two patients with progressive supranuclear palsy (PSP) had mutations in the ATXN8OS gene. Systematic analyses revealed that patients with parkinsonism had significantly shorter CTA/CTG repeat expansions and older age at onset than those with predominant ataxia. We show the imaging results of patients with and without parkinsonism. We also found a significant inverse relationship between repeat sizes and age at onset in all patients, which has not been detected previously. Our results may be useful to genetic counseling, improve understanding of the pathomechanism, and extend the clinical phenotype of SCA8.

Noncoding repeat expansions for ALS in Japan are associated with the ATXN8OS gene

Objective

To assess the contribution of noncoding repeat expansions in Japanese patients with amyotrophic lateral sclerosis (ALS).

Methods

Sporadic ALS in Western countries is frequently associated with noncoding repeat expansions in the C9ORF72 gene. Spinocerebellar ataxia type 8 (SCA8) is another noncoding repeat disease caused by expanded CTA/CTG repeats in the ATXN8OS gene. Although the involvement of upper and lower motor neurons in SCA8 has been reported, a positive association between SCA8 and ALS remains unestablished. Spinocerebellar ataxia type 36 is a recently identified disease caused by noncoding repeat expansions in the NOP56 gene and is characterized by motor neuron involvement. We collected blood samples from 102 Japanese patients with sporadic ALS and analyzed the ATXN8OS gene by the PCR–Sanger sequencing method and the C9ORF72 and NOP56 genes by repeat-primed PCR assay.

Results

Three patients with ALS (3%) had mutations in the ATXN8OS gene, whereas no patient had a mutation in the C9ORF72 or NOP56 gene. The mutation-positive patients were clinically characterized by neck weakness or bulbar-predominant symptoms. None of our patients had apparent cerebellar atrophy on MRI, but 2 had nonsymptomatic abnormalities in the white matter or putamen.

Conclusions

Our finding reveals the importance of noncoding repeat expansions in Japanese patients with ALS and extends the clinical phenotype of SCA8. Three percent seems small but is still relatively large for Japan, considering that the most commonly mutated genes, including the SOD1 and SQSTM1 genes, only account for 2%–3% of sporadic patients each.

Paradigm for disease deconvolution in rare neurodegenerative disorders in Indian population: insights from studies in cerebellar ataxias

Cerebellar ataxias are a group of rare progressive neurodegenerative disorders with an average prevalence ranges from 4.8 to 13.8 in 100,000 individuals. The inherited disorders affect multiple members of the families, or a community that is endogamous or consanguineous. Presence of more than 3000 mutations in different genes with overlapping clinical symptoms, genetic anticipation and pleiotropy, as well as incomplete penetrance and variable expressivity due to modifiers pose challenges in genotype-phenotype correlation. Development of a diagnostic algorithm could reduce the time as well as cost in clinicogenetic diagnostics and also help in reducing the economic and social burden of the disease. In a unique research collaboration spanning over 20 years, we have been able to develop a paradigm for studying cerebellar ataxias in the Indian population which would also be relevant in other rare diseases. This has involved clinical and genetic analysis of thousands of families from diverse Indian populations. The extensive resource on ataxia has led to the development of a clinicogenetic algorithm for cost-effective screening of ataxia and a unique ataxia clinic in the tertiary referral centre in All India Institute of Medical Sciences. Utilizing a population polymorphism scanning approach, we have been able to dissect the mechanisms of repeat instability and expansion in many ataxias, and also identify founders, and trace the mutational histories in the Indian population. This provides information for genetic testing of at-risk as well as protected individuals and populations. To dissect uncharacterized cases which comprises more than 50% of the cases, we have explored the potential of next-generation sequencing technologies coupled with the extensive resource of baseline data generated in-house and other public domains. We have also developed a repository of patient-derived peripheral blood mononuclear cells, lymphoblastoid cell lines and neuronal lineages (derived from iPSCs) for ascribing functionality to novel genes/mutations. Through integrating these technologies, novel genes have been identified that has broadened the diagnostic panel, increased the diagnostic yield to over 75%, helped in ascribing pathogenicity to novel mutations and enabled understanding of disease mechanisms. It has also provided a platform for testing novel molecules for amelioration of pathophysiological phenotypes. This review through a perspective on CAs suggests a generic paradigm fromdiagnostics to therapeutic interventions for rare disorders in the context of heterogeneous Indian populations.

Frequency of SCA8, SCA10, SCA12, SCA36, FXTAS and C9orf72 repeat expansions in SCA patients negative for the most common SCA subtypes

BACKGROUND

Spinocerebellar ataxia (SCA) subtypes are often caused by expansions in non-coding regions of genes like SCA8, SCA10, SCA12 and SCA36. Other ataxias are known to be associated with repeat expansions such as fragile X-associated tremor ataxia syndrome (FXTAS) or expansions in the C9orf72 gene. When no mutation has been identified in the aforementioned genes next-generation sequencing (NGS)-based diagnostics may also be applied. In order to define an optimal diagnostic strategy, more information about the frequency and phenotypic characteristics of rare repeat expansion disorders associated with ataxia should be at hand.

METHODS

We analyzed a consecutive cohort of 440 German unrelated patients with symptoms of cerebellar ataxia, dysarthria and other unspecific symptoms who were referred to our center for SCA diagnostics. They showed alleles in the normal range for the most common SCA subtypes SCA1-3, SCA6, SCA7 and SCA17. These patients were screened for expansions causing SCA8, SCA10, SCA12, SCA36 and FXTAS as well as for the pathogenic hexanucleotide repeat in the C9orf72 gene.

RESULTS

Expanded repeats for SCA10, SCA12 or SCA36 were not identified in the analyzed patients. Five patients showed expanded SCA8 CTA/CTG alleles with 92-129 repeats. One 51-year-old male with unclear dementia symptoms was diagnosed with a large GGGGCC repeat expansion in C9orf72. The analysis of the fragile X mental retardation 1 gene (FMR1) revealed one patient with a premutation (>50 CGG repeats) and seven patients with alleles in the grey zone (41 to 54 CGG repeats).

CONCLUSIONS

Altogether five patients showed 92 or more SCA8 CTA/CTG combined repeats. Our results support the assumption that smaller FMR1 gene expansions could be associated with the risk of developing neurological signs. The results do not support genetic testing for C9orf72 expansion in ataxia patients.

Repeat expansion diseases

More than 40 diseases, most of which primarily affect the nervous system, are caused by expansions of simple sequence repeats dispersed throughout the human genome. Expanded trinucleotide repeat diseases were discovered first and remain the most frequent. More recently tetra-, penta-, hexa-, and even dodeca-nucleotide repeat expansions have been identified as the cause of human disease, including some of the most common genetic disorders seen by neurologists. Repeat expansion diseases include both causes of myotonic dystrophy (DM1 and DM2), the most common genetic cause of amyotrophic lateral sclerosis/frontotemporal dementia (C9ORF72), Huntington disease, and eight other polyglutamine disorders, including the most common forms of dominantly inherited ataxia, the most common recessive ataxia (Friedreich ataxia), and the most common heritable mental retardation (fragile X syndrome). Here I review distinctive features of this group of diseases that stem from the unusual, dynamic nature of the underlying mutations. These features include marked clinical heterogeneity and the phenomenon of clinical anticipation. I then discuss the diverse molecular mechanisms driving disease pathogenesis, which vary depending on the repeat sequence, size, and location within the disease gene, and whether the repeat is translated into protein. I conclude with a brief clinical and genetic description of individual repeat expansion diseases that are most relevant to neurologists.

Deregulation of RNA Metabolism in Microsatellite Expansion Diseases

RNA metabolism impacts different steps of mRNA life cycle including splicing, polyadenylation, nucleo-cytoplasmic export, translation, and decay. Growing evidence indicates that defects in any of these steps lead to devastating diseases in humans. This chapter reviews the various RNA metabolic mechanisms that are disrupted in Myotonic Dystrophy-a trinucleotide repeat expansion disease-due to dysregulation of RNA-Binding Proteins. We also compare Myotonic Dystrophy to other microsatellite expansion disorders and describe how some of these mechanisms commonly exert direct versus indirect effects toward disease pathologies.

Intrinsic Disorder in Proteins with Pathogenic Repeat Expansions

Intrinsically disordered proteins and proteins with intrinsically disordered regions have been shown to be highly prevalent in disease. Furthermore, disease-causing expansions of the regions containing tandem amino acid repeats often push repetitive proteins towards formation of irreversible aggregates. In fact, in disease-relevant proteins, the increased repeat length often positively correlates with the increased aggregation efficiency and the increased disease severity and penetrance, being negatively correlated with the age of disease onset. The major categories of repeat extensions involved in disease include poly-glutamine and poly-alanine homorepeats, which are often times located in the intrinsically disordered regions, as well as repeats in non-coding regions of genes typically encoding proteins with ordered structures. Repeats in such non-coding regions of genes can be expressed at the mRNA level. Although they can affect the expression levels of encoded proteins, they are not translated as parts of an affected protein and have no effect on its structure. However, in some cases, the repetitive mRNAs can be translated in a non-canonical manner, generating highly repetitive peptides of different length and amino acid composition. The repeat extension-caused aggregation of a repetitive protein may represent a pivotal step for its transformation into a proteotoxic entity that can lead to pathology. The goals of this article are to systematically analyze molecular mechanisms of the proteinopathies caused by the poly-glutamine and poly-alanine homorepeat expansion, as well as by the polypeptides generated as a result of the microsatellite expansions in non-coding gene regions and to examine the related proteins. We also present results of the analysis of the prevalence and functional roles of intrinsic disorder in proteins associated with pathological repeat expansions.

Sequence configuration of spinocerebellar ataxia type 8 repeat expansions in a Japanese cohort of 797 ataxia subjects

Spinocerebellar ataxia type 8 (SCA8), an autosomal dominant neurodegenerative disorder showing slowly progressive cerebellar ataxia, is caused by a tri-nucleotide CTG repeat expansion (CTGexp) in the SCA8 gene. As the CTGexp is not fully penetrant, the significance of screening CTGexp in ataxia subjects remains obscure. We tested SCA8 CTGexp in a cohort of 797 ataxia subjects, and if present, its sequence configuration was analyzed. CTGexp was found in 16 alleles from 14 individuals, 2 of which was homozygous for CTGexp. Nucleotide sequencing disclosed 3 types of CTGexp sequence configurations: uninterrupted CTGexp, tri-nucleotide CTA interruption and CCG interruption. The 2 individuals with homozygous expansions were both sporadic cases with clinical features compatible with SCA8, supporting gene dosage effect. Seven out of 14 CTGexp-positive subjects were also carriers of other SCA expansions [Machado-Joseph disease (n=1), SCA6 (n=3) and SCA31 (n=3)], whereas 7 others were not complicated with such major SCAs. Ages of onset in subjects with pure CTGexp tended to be earlier than those with interrupted CTGexp among the 7 subjects not complicated by major SCAs, suggesting that pure CTGexp have stronger pathogenic effect than interrupted CTGexps. The present study underscores importance of disclosing sequence configuration when testing SCA8.

Unstable repeat expansion in major psychiatric disorders: two decades on, is dynamic DNA back on the menu?

For a period in the mid-1990s, soon after the discovery of the involvement of trinucleotide repeat expansions in fragile-X syndrome (both A and E), Huntington's disease, myotonic dystrophy, and a number of hereditary ataxias, there was a clear sense that this new disease mechanism might provide answers for psychiatric disorders. Given the then failures to replicate initial genetic linkage findings for schizophrenia (SCZ) and bipolar disorder (BD), a greater emphasis was placed on the role of complex and non-Mendelian mechanisms, and repeat instability appeared to have the potential to provide adequate explanations for numerous apparently non-Mendelian features such as anticipation, incomplete penetrance, sporadic occurrence, and nonconcordance of monozygotic twins. Initial molecular studies using a ligation-based amplification method (repeat expansion detection) appeared to support the involvement of CAG•CTG repeat expansion in SCZ and BD. However, subsequent studies that dissected the large repeats responsible for much of the positive signal showed that there were three main loci where CAG•CTG repeat expansion was occurring (on 13q21.33, 17q21.33-q22, and 18q21.2). None of the expansions at these loci appeared to segregate with SCZ or BD, and research into repeat expansions in psychiatric illness petered out in the early 2000s. The 13q expansion occurs within a noncoding RNA and appears to be associated with spinocerebellar ataxia 8 (SCA8), but with a still unexplained dichotomy in penetrance - either very high or very low. The 17q expansion occurs within an intron of the carbonic anhydrase-like gene, CA10. The 18q expansion is located within an intron of the TCF4 gene. Mutations in TCF4 are a known cause of Pitt-Hopkins syndrome. Also, pertinently, genome-wide association studies have shown a well-replicated association between TCF4 and SCZ. Two decades on, in 2016, it appears to be an appropriate juncture to reflect on what we have learned, and, with the arrival of newer technologies, whether there is any mileage to be made in revisiting the unstable DNA hypothesis for psychiatric illness.

The Repeat Expansion Diseases: The dark side of DNA repair

DNA repair normally protects the genome against mutations that threaten genome integrity and thus cell viability. However, growing evidence suggests that in the case of the Repeat Expansion Diseases, disorders that result from an increase in the size of a disease-specific microsatellite, the disease-causing mutation is actually the result of aberrant DNA repair. A variety of proteins from different DNA repair pathways have thus far been implicated in this process. This review will summarize recent findings from patients and from mouse models of these diseases that shed light on how these pathways may interact to cause repeat expansion.

Searching for Grendel: origin and global spread of the C9ORF72 repeat expansion

Recent advances are uncovering more and more of the genetic architecture underlying amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative condition that affects ~6,000 Americans annually. Chief among these was the discovery that a large repeat expansion in the C9ORF72 gene is responsible for an unprecedented portion of familial and sporadic ALS cases. Much has been published on how this expansion disrupts neuronal homeostasis and how gene-based therapy might be an effective treatment in the future. Nevertheless, it is instructive to look back at the origins of this important mutation. In this opinion piece, we attempt to answer three key questions concerning C9ORF72. First, how many times did the expansion occur throughout human history? Second, how old is the expansion? And finally and perhaps most importantly, how did the expansion spread throughout Europe? We speculate that the expansion occurred only once in the past, that this event took place in the Finnish population and that the Vikings and their descendants were responsible for disseminating this mutation throughout the rest of the continent.

Non-Ataxic Phenotypes of SCA8 Mimicking Amyotrophic Lateral Sclerosis and Parkinson Disease

Background

Spinocerebellar ataxia (SCA) type 8 (SCA8) is an inherited neurodegenerative disorder caused by the expansion of untranslated CTA/CTG triplet repeats on 13q21. The phenomenology of SCA8 is relatively varied when compared to the other types of SCAs and its spectrum is not well established.

Case Report

Two newly detected cases of SCA8 with the nonataxic phenotype and unusual clinical manifestations such as dopaminergic-treatment-responsive parkinsonism and amyotrophic lateral sclerosis (ALS) are described herein. Family A expressed good dopaminergic treatment-responsive parkinsonism as an initial manifestation and developed mild cerebellar ataxia with additional movements, including dystonic gait and unusual oscillatory movement of the trunk, during the disease course. The proband of family B presented as probable ALS with cerebellar atrophy on brain MRI, with a positive family history (a brother with typical cerebellar ataxia) and genetic confirmation for SCA8.

Conclusions

Our findings support that the non-ataxic phenotypes could be caused by a mutation of the SCA8 locus which might affect neurons other than the cerebellum.

Spinocerebellar ataxias type 8, 12, and 17 and dentatorubro-pallidoluysian atrophy in Czech ataxic patients

Spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders currently associated with 27 genes. The most frequent types are caused by expansions in coding CAG repeats. The frequency of SCA subtypes varies among populations. We examined the occurrence of rare SCAs, SCA8, SCA12, SCA17 and dentatorubro-pallidoluysian atrophy (DRPLA), in the Czech population from where the data were missing. We analyzed causal gene expansions in 515 familial and sporadic ataxic patients negatively tested for SCA1-3 and SCA6-7. Pathogenic SCA8 and SCA17 expansions were identified in eight and five patients, respectively. Tay-Sachs disease was later diagnosed in one patient with an SCA8 expansion and the diagnosis of multiple sclerosis (MS) was suspected in two other patients with SCA8 expansions. These findings are probably coincidental, although the participation of SCA8 expansions in the susceptibility to MS and disease progression cannot be fully excluded. None of the patients had pathogenic SCA12 or DRPLA expansions. However, three patients had intermediate SCA12 alleles out of the normal range with 36 and 43 CAGs. Amyotrophic lateral sclerosis (ALS) was probable in the patient with 43 CAGs. This coincidence is remarkable, especially in the context with the recently identified predisposing role of longer SCA2 alleles in ALS. Five families with SCA17 represent a significant portion of ataxic patients and this should be reflected in the diagnostics of SCAs in the Czech population. SCA8 expansions must be considered after careful clinical evaluation.

Genetic screening of Greek patients with Huntington’s disease phenocopies identifies an SCA8 expansion

Huntington’s disease (HD) is an autosomal dominant disorder characterized by a triad of chorea, psychiatric disturbance and cognitive decline. Around 1% of patients with HD-like symptoms lack the causative HD expansion and are considered HD phenocopies. Genetic diseases that can present as HD phenocopies include HD-like syndromes such as HDL1, HDL2 and HDL4 (SCA17), some spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA). In this study we screened a cohort of 21 Greek patients with HD phenocopy syndromes formutations causing HDL2, SCA17, SCA1, SCA2, SCA3,SCA8, SCA12 and DRPLA. Fifteen patients (71%) had a positive family history. We identified one patient (4.8% of the total cohort) with an expansion of 81 combined CTA/CTG repeats at the SCA8 locus. This falls within what is believed to be the high-penetrance allele range. In addition to the classic HD triad, the patient had features of dystonia and oculomotor apraxia. There were no cases of HDL2, SCA17, SCA1, SCA2, SCA3, SCA12 or DRPLA. Given the controversy surrounding the SCA8 expansion, the present finding may be incidental. However, if pathogenic, it broadens the phenotype that may be associated with SCA8 expansions. The absence of any other mutations in our cohort is not surprising, given the low probability of reaching a genetic diagnosis in HD phenocopy patients.

[A case of juvenile parkinsonism with expanded SCA8 CTA/CTG repeats]

A 31-year-old man was referred to our hospital because of progressive tremor and clumsiness in his limbs and trunk. His symptoms were started in the right leg then gradually spread to all extremities as well as his trunk for 2 years. Neurological examinations revealed muscle rigidity with resting tremor predominantly right limbs. Akinesia and retropulsion were positive. Neither pyramidal tract sign nor cerebellar ataxia was detected. Genetic testing showed the expansion of SCA8 CTA/CTG repeats as 28/141 repeats. Though moderate expansion (less than 92) of SCA8 repeats has been reported in healthy subjects and patients with various diseases, the extraordinary long expansion of CTA/CTG repeats in SCA8 gene in our patient could be significantly pathological. 600 mg/day of L-DOPA clearly improved his symptoms. Dedicate follow up of the clinical course of our patient and the accumulation of the further cases is essential.

Acoustic impairment is a distinguishable clinical feature of Asidan/SCA36

OBJECTIVE

To investigate acoustic function of Asidan/spinocerebellar ataxia type 36 (SCA36) in which sensorineural hearing loss may be found as one of extracerebellar symptom that can be a distinguishable feature from other degenerative ataxias.

METHODS

Acoustic function in the groups of normal control (n=31), Asidan/SCA36 (n=13), cortical cerebellar atrophy (CCA, n=28), multiple system atrophy of cerebellar predominance (MSA-C, n=48), SCA31 (n=4), and other forms of SCAs (n=14) was evaluated by pure tone average (PTA) calculated by the results of audiogram and brainstem auditory evoked potentials (BAEPs).

RESULTS

PTA was significantly decreased in Asidan/SCA36 in comparison to normal control and other ataxic groups, but not significant within other ataxic groups and normal control. In comparison to other groups, Asidan/SCA36 showed a constant depression at 7 different frequencies in audiogram, especially at 4000 and 8000 Hz. BAEPs in 2 Asidan/SCA36 cases suggested possible involvement in the inner ear or the peripheral part of the auditory system. PTA in Asidan/SCA36 cases significantly correlated with their severity of ataxia.

CONCLUSIONS

In addition to signs for motor neuron involvement, acoustic impairment in Asidan/SCA36 is another characteristic clinical feature that is distinguishable from other forms of SCAs.

Expanding the genetics of amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized clinically by rapidly progressive paralysis leading ultimately to death from respiratory failure. It is now recognized that ALS and frontotemporal lobar degeneration (FTLD) form a clinical spectrum of disease with overlapping clinical, pathological and genetic features. This past year, the genetic causes of ALS have expanded to include mutations in the genes OPTN, VCP, and UBQLN2, and the hexanucleotide repeat expansion in C9ORF72. The C9ORF72 repeat expansion solidifies the notion that ALS and FTLD are phenotypic variations of a disease spectrum with a common molecular etiology. Furthermore, the C9ORF72 expansion is the genetic cause of a substantial portion of apparently sporadic ALS and FTLD cases, showing that genetics plays a clear role in sporadic disease. Here we describe the progress made in the genetics of ALS and FTLD, including a detailed look at how new insights brought about by C9ORF72 have both broadened and unified current concepts in neurodegeneration.

ATXN8 -62 G/A promoter polymorphism and risk of Taiwanese Parkinson's disease

BACKGROUND AND PURPOSE

We recently reported a novel -62 G/A polymorphism within ataxin 8 (ATXN8) gene promoter region, with -62 G displaying significantly higher luciferase activity compared with -62 A. Phenotypic variability in spinocerebellar ataxia type 8 (SCA8) has been suggested, and large SCA8 repeats were found in patients with Parkinson's disease (PD). We aimed to investigate the association of ATXN8 -62 G/A polymorphism with the risk of Taiwanese PD, and identify the trans-acting factor modulating the ATXN8 promoter activity.

METHODS

A case-control study in a cohort of 569 PD cases and 547 ethnically matched controls was conducted by polymerase chain reaction (PCR) and restriction enzyme analysis. The trans-acting factor binding to the ATXN8 promoter was examined by chromatin immunoprecipitation (ChIP)-PCR assay, cDNA co-transfection and luciferase reporter assay.

RESULTS

When genotype distribution was calculated by comparing the rare AA genotype with the GG + GA genotypes (recessive model), a significant difference was found (P = 0.035, 1 df). Individuals carrying AA genotype exhibited a decreased risk of developing PD (odds ratio: 0.73; 95% CI: 0.55-0.98, P = 0.035). After stratification by age, individuals over 60 years of age carrying AA genotype demonstrated a further decrease in the risk of developing PD (odds ratio: 0.64; 95% CI: 0.43-0.96, P = 0.030). ChIP-PCR and cDNA over-expression revealed that CCAAT/enhancer-binding protein alpha binds to the ATXN8 proximal promoter to upregulate ATXN8 expression in neuroblastoma SK-N-SH cells.

CONCLUSIONS

Our data suggest that ATXN8 -62 G/A polymorphism plays a role in Taiwanese PD susceptibility.

The spinocerebellar ataxias: clinical aspects and molecular genetics

Spinocerebellar ataxias (SCAs) are a highly heterogeneous group of inherited neurological disorders, based on clinical characterization alone with variable degrees of cerebellar ataxia often accompanied by additional cerebellar and noncerebellar symptoms which in most cases defy differentiation. Molecular causative deficits in at least 31 genes underlie the clinical symptoms in the SCAs by triggering cerebellar and, very frequently, brain stem dysfunction. The identification of the causative molecular deficits enables the molecular diagnosis of the different SCA subtypes and facilitates genetic counselling. Recent scientific advances are shedding light into developing therapeutic strategies. The scope of this chapter is to provide updated details of the spinocerebellar ataxias with particular emphasis on those aspects aimed at facilitating the clinical and genetic diagnoses.

Comparisons of acoustic function in SCA31 and other forms of ataxias

OBJECTIVE

To investigate whether acoustic impairment can be one of the characteristic extracerebellar symptoms in sporadic and hereditary ataxias including spinocerebellar ataxia type 31 (SCA31).

METHODS

We investigated genotypes of dominant ataxia families, and determined a frequency of each form in our cohort of 154 families. Acoustic function in the groups of various forms of ataxia with multiple system atrophy of cerebellar predominance (MSA-C), cortical cerebellar atrophy (CCA), and hereditary ataxias including SCA31 was evaluated by using audiogram and brainstem auditory evoked potentials (BAEPs).

RESULTS

Genetic analysis of dominant ataxia families revealed that a frequency of SCA31 in our cohort was fewer than that reported from other areas of Japan, indicating that SCA31 is not widely distributed throughout Japan. Results of audiogram showed no significant difference of hearing levels among ataxic groups, and those of BAEPs did not support inner ear dysfunction in SCA31 in which hearing loss had initially been suggested as one of its characteristic symptoms.

CONCLUSION

This study suggests that acoustic impairment is neither specific to SCA31, MSA-C and CCA nor useful in making a differential diagnosis among them.

Autosomal dominant cerebellar ataxias

Cerebellar ataxias with autosomal dominant transmission (ADCA) are far rarer than sporadic cases of cerebellar ataxia. The identification of genes involved in dominant forms has confirmed the genetic heterogeneity of these conditions and of the underlying mechanisms and pathways. To date, at least 28 genetic loci and, among them, 20 genes have been identified. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes more complex multisystemic neurological deficits. Seven ADCA (SCA1, 2, 3, 6, 7, 17, and dentatorubro-pallido-luysian atrophy) are caused by repeat expansions in the corresponding proteins; phenotype-genotype correlations have shown that repeat size influences the progression of the disease, its severity and clinical differences among patients, including the phenomenon of anticipation between generations. All other ADCA are caused either by non-coding repeat expansions, conventional mutations or large rearrangements in genes with different functions. This review will focus on the genetic features of ADCA and on the clinical differences among the different forms.

Spinocerebellar degenerations

The spinocerebellar ataxias (SCA) are a large group of inherited disorders affecting the cerebellum and its afferent and efferent pathways. Their hallmark symptom is slowly progressive, symmetrical, midline, and appendicular ataxia. Some may also have associated hyperkinetic movements (chorea, dystonia, myoclonus, postural/action tremor, restless legs, rubral tremor, tics), which may aid in differential diagnosis and provide treatable targets to improve performance and quality of life in these progressive, incurable conditions. The typical dominant ataxias with associated hyperkinetic movements are SCA1-3, 6-8, 12, 14, 15, 17, 19-21, and 27. The common recessive ataxias with associated hyperkinetic movements are ataxia telangiectasia and Friedreich's ataxia. Fragile X tremor-ataxia syndrome (FXTAS) and multiple-system atrophy (a sporadic ataxia which is felt to have a genetic substrate) also have hyperkinetic features. A careful work-up should be done in all apparently sporadic cases, to rule out acquired causes of ataxia, some of which can cause hyperkinetic movements in addition to ataxia. Some testing should be done even in individuals with a confirmed genetic cause, as the presence of a secondary factor (nutritional deficiency, thyroid dysfunction) can contribute to the phenotype.

Consensus and controversies in best practices for molecular genetic testing of spinocerebellar ataxias

Many laboratories worldwide are offering molecular genetic testing for spinocerebellar ataxias (SCAs). This is essential for differential diagnosis and adequate genetic counselling. The European Molecular Genetics Quality Network (EMQN) started an SCA external quality assessment scheme in 2004. There was a clear need for updated laboratory guidelines. EMQN and EuroGentest organized a Best Practice (BP) meeting to discuss current practices and achieve consensus. A pre-meeting survey showed that 36 laboratories (20 countries) conducted nearly 18 000 SCA tests the year before, and identified issues to discuss. Draft guidelines were produced immediately after the meeting and discussed online for several months. The final version was endorsed by EMQN, and harmonized with guidelines from other oligonucleotide repeat disorders. We present the procedures taken to organize the survey, BP meeting, as well as drafting and approval of BP guidelines. We emphasize the most important recommendations on (1) pre-test requirements, (2) appropriate methodologies and (3) interpretation and reporting, and focus on the discussion of controversial issues not included in the final document. In addition, after an extensive review of scientific literature, and responding to recommendations made, we now produce information that we hope will facilitate the activities of diagnostic laboratories and foster quality SCA testing. For the main loci, this includes (1) a list of repeat sequences, as originally published; (2) primers in use; and (3) an evidence-based description of the normal and pathogenic repeat-size ranges, including those of reduced penetrance and those in which there is still some uncertainty. This information will be maintained and updated in http://www.scabase.eu.

Spinocerebellar ataxia 8: variable phenotype and unique pathogenesis

Spinocerebellar ataxia 8 (SCA8), a triplet repeat expansion disorder, is genetically distinct from the other inherited ataxias, but its unusually variable phenotype can make its diagnosis difficult. In this review we describe 3 new cases of genetically verified SCA8 to highlight the broad clinical spectrum of symptoms observed with this disorder and to draw attention to the features of myoclonus and migraine headaches, which in the context of cerebellar ataxia warrants the clinician to consider SCA8 as a potential diagnosis. We also address the controversy surrounding the genetic testing approach for diagnosing SCA8. Finally, we evaluate the evidence that SCA8 may affect calcium channel function and that the presentation of episodic ataxia and migraines suggests a clinical and pathogenic overlap of SCA8 with the channelopathies.

Bidirectional expression of the SCA8 expansion mutation: one mutation, two genes

Spinocerebellar ataxia type 8 (SCA8) is a dominantly inherited, slowly progressive neurodegenerative disorder caused by a CTG.CAG repeat expansion located on chromosome 13q21. The expansion mutation was isolated directly from the DNA of a single patient using RAPID cloning and subsequently shown to co-segregate with disease in additional ataxia families including a seven-generation kindred (the MN-A family). The size-dependent penetrance of the repeat found in the large MN-A kindred makes it appear as though some parts of the family have a dominant disorder while other parts of this same family have recessive or sporadic forms of ataxia. While the linkage and size-dependent penetrance of the SCA8 CTG.CAG expansion in the MN-A family argue that the SCA8 expansion causes ataxia, the reduced penetrance in other SCA8 families and the discovery of expansions in the general population have led to a controversy surrounding whether or not the SCA8 expansion is pathogenic. A recently reported mouse model in which SCA8 BAC-expansion but not BAC-control lines develop a progressive neurological phenotype now demonstrates the pathogenicity of the (CTG.CAG)(n) expansion. These mice show a loss of cerebellar GABAergic inhibition and, similar to human patients, have 1C2-positive intranuclear inclusions in Purkinje cells and other neurons. Additional studies demonstrate that the SCA8 expansion is expressed in both directions (CUG and CAG) and that a novel gene expressed in the CAG direction encodes a pure polyglutamine expansion protein (ataxin 8, ATXN8). Moreover, the expression of non-coding (CUG)(n) expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and the discovery of intranuclear polyglutamine inclusions suggest SCA8 pathogenesis may involve toxic gain-of-function mechanisms at both the protein and RNA levels. Our data, combined with the recently reported antisense transcripts spanning the DM1 repeat expansion in the CAG direction and the growing number of reports of antisense transcripts expressed throughout the mammalian genome, raises the possibility that bidirectional expression across pathogenic microsatellite expansions may occur in other expansion disorders, and that potential pathogenic effects of mutations expressed from both strands should be considered.

SCA8 repeat expansion: large CTA/CTG repeat alleles in neurological disorders and functional implications

Spinocerebellar ataxia type 8 (SCA8) involves bidirectional expression of CUG (ATXN8OS) and CAG (ATXN8) expansion transcripts. The pathogenesis of SCA8 is complex and the spectrum of clinical presentations is broad. In the present study, we assessed the SCA8 repeat size ranges in Taiwanese Parkinson's disease, Alzheimer's disease and atypical parkinsonism and investigated the genetic variation modulating ATXN8 expression. Thirteen large SCA8 alleles and a novel ATXN8 -62 G/A promoter SNP were found. There is a significant difference in the proportion of the individuals carrying SCA8 larger alleles in atypical parkinsonism (P = 0.044) as compared to that in the control subjects. In lymphoblastoid cells carrying SCA8 large alleles, treatment of MG-132 or staurosporine significantly increases the cell death or caspase 3 activity. Although expressed at low steady-state, ATXN8 expression level is significantly higher (P = 0.012) in cells with SCA8 large alleles than that of the control cells. The ATXN8 transcriptional activity was significantly higher in the luciferase reporter construct containing the -62G allele than that containing the -62A allele in both neuroblastoma and embryonic kidney cells. Therefore, our preliminary results suggest that ATXN8 gene -62 G/A polymorphism may be functional in modulating ATXN8 expression.

Spinocerebellar ataxia type 8 larger triplet expansion alters histone modification and induces RNA foci

BACKGROUND

Spinocerebellar ataxia type 8 (SCA8) involves the expression of an expanded CTG/CAG combined repeats (CR) from opposite strands producing CUG expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and a polyglutamine expansion protein (ataxin 8, ATXN8). The pathogenesis of SCA8 is complex and the spectrum of clinical presentations is broad.

RESULTS

Using stably induced cell models expressing 0, 23, 88 and 157 CR, we study the role of ATXN8OS transcripts in SCA8 pathogenesis. In the absence of doxycycline, the stable ATXN8OS CR cell lines exhibit low levels of ATXN8OS expression and a repeat length-related increase in staurosporine sensitivity and in the number of annexin positive cells. A repeat length-dependent repression of ATXN8OS expression was also notable. Addition of doxycycline leads to 25 approximately 50 times more ATXN8OS RNA expression with a repeat length-dependent increase in fold of ATXN8OS RNA induction. ChIP-PCR assay using anti-dimethyl-histone H3-K9 and anti-acetyl-histone H3-K14 antibodies revealed increased H3-K9 dimethylation and reduced H3-K14 acetylation around the ATXN8OS cDNA gene in 157 CR line. The repeat length-dependent increase in induction fold is probably due to the increased RNA stability as demonstrated by monitoring ATXN8OS RNA decay in cells treated with the transcriptional inhibitor, actinomycin D. In cells stably expressing ATXN8OS, RNA FISH experiments further revealed ribonuclear foci formation in cells carrying expanded 88 and 157 CR.

CONCLUSION

The present study demonstrates that the expanded CUG-repeat tracts are toxic to human cells and may affect ATXN8OS RNA expression and stability through epigenetic and post-transcriptional mechanisms.

Spinocerebellar ataxia type 8 in Scotland: frequency, neurological, neuropsychological and neuropsychiatric findings

OBJECTIVES

The objectives of this study were to: (i) establish whether the spinocerebellar ataxia type 8 (SCA 8) expansion is associated with ataxia in Scotland; (ii) test the hypothesis that SCA 8 is associated with neuropsychological impairment; and (iii) review neuroradiological findings in SCA 8.

METHODS

The methods included: (i) measurement of SCA 8 expansion frequencies in ataxic patients and healthy controls; (ii) comprehensive neuropsychological assessment of patients with SCA 8 and matched controls, neuropsychiatric interview; and (iii) comparison of patient and matched control magnetic resonance imaging (MRI) scans.

RESULTS

(i) 10/694 (1.4%) unrelated individuals with ataxia had combined CTA/CTG repeat expansions >100 compared to 1/1190 (0.08%) healthy controls (P < 0.0005); (ii) neuropsychological assessment revealed a dysexecutive syndrome among SCA 8 patients, not readily explained by motor or mood disturbance; neuropsychiatric symptoms occurred commonly; (iii) cerebellar atrophy was the only salient MRI abnormality in the patient group.

CONCLUSIONS

The SCA 8 expansion is associated with ataxia in Scotland. The disorder is associated with a dysexecutive syndrome.

White matter hyperintense lesions in genetically proven spinocerebellar ataxia 8

We report two brothers with a progressive cerebellar syndrome due to spinocerebellar ataxia type 8 (SCA8). In addition to severe cerebellar atrophy, both had prominent white matter hyperintensities on cranial MRI. This is the first report of white matter hyperintensities on cranial MRI in patients with SCA8. A disorder due to a similar molecular basis, myotonic dystrophy 1 (DM1), is known to have white matter hyperintensities on cranial MRI. Cognitive impairment is well described in DM1 and is being recognized in SCA8. The significance of these associations is discussed.