Genetic background of apparently idiopathic sporadic cerebellar ataxia

The 'hot cross bun' sign in the patients with spinocerebellar ataxia

BACKGROUND AND PURPOSE

The 'hot cross bun' sign (HCBS), typically seen in the patients with multiple system atrophy, refers to a cruciform hyperintensity in the pons on T2-weighted MRI. Little is known about its pathological basis and prevalence in other degenerative cerebellar diseases and healthy population. We investigate the frequency of HCBS in the patients with spinocerebellar ataxia (SCA) and healthy controls.

METHODS

The presence of HCBS on T2-weighted axial MRIs from 138 SCA patients (three SCA1, 35 SCA2, 76 SCA3, 18 SCA6, one SCA7, three SCA8, and two SCA17) and 102 healthy controls was evaluated retrospectively.

RESULTS

The overall prevalence of HCBS in the SCA patients is 8.7%, but the frequency varies in different subtypes: 25.7% in SCA2, 1.3% in SCA3, and none in SCA6 or healthy controls. Notably, one patient with SCA7 and one with SCA8 were also found to have HCBS.

CONCLUSIONS

The differential list of HCBS should be expanded to include SCA7 and SCA8. The elucidation of frequency of HCBS in various SCA subtypes may help prioritize the genetic testing in late-onset dominant ataxia.

The clinical diagnosis of autosomal dominant spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are a heterogeneous group of autosomal dominantly inherited progressive ataxia diseases. Up to now, almost 30 different gene loci have been found. In 14 of them, the underlying mutations have been identified. The more common SCAs, SCA1, 2, 3 and 6 are due to translated CAG repeat expansions that code for an elongated polyglutamine tract within the respective proteins. These diseases belong to a larger group of polyglutamine disorders that also includes Huntington's disease. Epidemiological studies conducted in different European regions found prevalence rates of SCAs ranging from 0.9 to 3.0:100,000. In all SCAs, ataxia is the prominent symptom. However, the majority have a complex phenotype in which ataxia is accompanied by varying non-ataxia symptoms. In all ataxia patients with proven or suspected autosomal dominant mode of inheritance, the available molecular genetic tests for SCA mutations should be performed. Depending on the geographical origin of the family, these tests will lead to positive diagnostic results in at least half of the families.

A previously undiagnosed case of Gerstmann-Sträussler-Scheinker disease revealed by PRNP gene analysis in patients with adult-onset ataxia

Ataxia is a frequently reported symptom in prion diseases (PD) and it is characteristic of Gerstmann-Sträussler-Scheinker syndrome (GSS), a genetic PD mainly related to the P102L mutation in the PRNP gene. Our aim was to screen for the P102L and other six known PRNP gene mutations (P105L, A117V, Y145X, E200K, D202N, and V210I) a group of 206 consecutive patients diagnosed with adult-onset cerebellar ataxia of unknown origin. The patients, negative for the most common acquired and genetic forms, were analyzed using a combination of restriction endonuclease digestion and pyrosequencing; eight, affected by ataxia and cognitive dysfunction, were also sequenced for the PRNP gene. One patient resulted to be heterozygous for the P102L mutation. Retrospectively, the clinical picture was consistent with a "classical" GSS phenotype. In conclusion, the screening for the P102L mutation, or even the sequencing of the PRNP gene should be taken in consideration in patients with late-onset ataxia (>50 years).

CTA/CTG expansions at the SCA 8 locus in multiple system atrophy

OBJECTIVE

Spinocerebellar ataxia type 8 (SCA 8) is an autosomal dominant disorder characterized by cerebellar ataxia with additional features, such as upper motor neuron signs, urinary incontinence and dysphagia. From a clinical standpoint, SCA 8 and the cerebellar form of multiple system atrophy (MSA-C) share several common features.

METHODS

We studied the presence of expanded SCA 8 alleles in 10 sporadic patients with probable MSA-C.

RESULTS

We found 1 patient with a heterozygous CTA/CTG repeat expansion in the pathological range. Clinically this subject presented no features that differed from the other subjects carrying smaller repeat sizes.

CONCLUSIONS

We believe that the association of SCA 8 repeat expansions with sporadic, atypical and heterogeneous phenotypes is debatable and should be interpreted with caution. Our personal conclusion is that testing in such patients may become a source of diagnostic confusion.

The autosomal dominant cerebellar ataxias are hereditary neurodegenerative diseases

Az autoszomális domináns cerebellaris ataxiák örökletes neurodegeneratív betegségek. Az ataxiák még néhány évtizeddel ezelőtt is a legkevésbé megértett idegi rendellenességek közé tartoztak, de molekuláris hátterük tisztázása mára lehetőséget teremtett a pontos diagnózis megállapítására, és segítséget nyújtott számos olyan különös jelenség értelmezésében is, mint például a családon belül változatosan megjelenő fenotípus. A spinocerebellaris ataxiák patogenezisének megismerése esélyt kínálhat sikeres terápiák kifejlesztésére, a jelenlegi, pusztán tüneti kezelések helyett. A gyors egymásutánban felfedezett gének és génlocusok, valamint a kialakított ataxiaaltípusok azonban zavart is okozhatnak a betegség pontos meghatározásában. Célunk rövid betekintést nyújtani e neurodegeneratív kórképek genetikai hátterébe, és a fontosabb ataxiaaltípusok jellemzésével megkönnyíteni az egyértelmű diagnózis felállítását.

Diagnosis and management of early- and late-onset cerebellar ataxia

Cerebellar ataxias represent a heterogeneous group of neurodegenerative disorders. Two main categories are distinguished: hereditary and sporadic ataxias. Sporadic ataxias may be symptomatic or idiopathic. The clinical classification of hereditary ataxias is nowadays being replaced by an expanding genotype-based classification. A large spectrum of degenerative and metabolic disorders may also present with ataxia early or late in the course of disease. We present a diagnostic algorithm for the adult patient presenting with subacute cerebellar ataxia, based on family history and straightforward clinical characteristics of the patient. Along with the algorithm, an overview of the autosomal dominant, autosomal recessive, X-linked, mitochondrial, symptomatic and idiopathic subtypes of cerebellar ataxia is presented. An appropriate diagnosis is of utmost importance to such considerations as prognosis, genetic counselling and possible therapeutic implications.

Common mitochondrial DNA and POLG1 mutations are rare in the Chinese patients with adult-onset ataxia on Taiwan

BACKGROUND AND PURPOSE

Spinocerebellar ataxia (SCA) is a heterogeneous group of neurodegenerative disorders with common features of adult-onset cerebellar ataxia. Many patients with clinically suspected SCA are subsequently diagnosed with common SCA gene mutations. Previous reports suggest some common mitochondrial DNA (mtDNA) point mutations and mitochondrial DNA polymerase gene (POLG1) mutations might be additional underlying genetic causes of cerebellar ataxia. We tested whether mtDNA point mutations A3243G, A8344G, T8993G, and T8993C, or POLG1 mutations W748S and A467T are found in patients with adult-onset ataxia who did not have common SCA mutations.

METHODS

Four hundred seventy-six unrelated patients with suspected SCA underwent genetic testing for SCA 1, 2, 3, 6, 7, 8, 10, 12, 17, and DRPLA gene mutations. After excluding these SCA mutations and patients with paternal transmission history, 265 patients were tested for mtDNA mutations A3243G, A8344G, T8993G, T8993C, and POLG1 W748S and A467T mutations.

RESULTS

No mtDNA A3243G, A8344G, T8993G, T8993C, or POLG1 W748S and A467T mutation was detected in any of the 265 ataxia patients, suggesting that the upper limit of the 95% confidence interval for the prevalence of these mitochondrial mutations in Chinese patients with adult-onset non-SCA ataxia is no higher than 1.1%.

CONCLUSIONS

The mtDNA mutations A3243G, A8344G, T8993G, T8993C, or POLG1 W748S and A467T are very rare causes of adult-onset ataxia in Taiwan. Routine screening for these mutations in ataxia patients with Chinese origin is of limited clinical value.

Ataxias

Gait disorders in elderly individuals are a major cause of falls and their attendant morbidities. Ataxia is one of the neurologic components of fall risk, as are inattention or confusion, visual impairment, vestibular impairment, subcortical white matter disease, parkinsonism, weakness, sensory loss, orthostasis or arrhythmia with alterations in blood pressure, pain, medication use, and environmental hazards. Ataxia in the geriatric population has many causes. Correctly identifying them can improve clinicians' ability to offer treatment and management strategies to patients and their families. The goals should be safe mobility and preserved activities of daily living.

Centres of Excellence for the care of people with progressive ataxias

This article provides a description of the progressive ataxias and how such a diagnosis impacts on a person's life. The nurse's role in helping these patients, who can face numerous difficulties in everyday life, is highlighted. Moreover, the authors discuss the development of Ataxia Specialist Centres of Excellence for the diagnosis and management of people with ataxia, and the benefits believe these centres will bring to the care of these patients.

Very late-onset Friedreich's ataxia with minimal GAA1 expansion mimicking multiple system atrophy of cerebellar type

Very late-onset Friedreich's ataxia (VLOFA) is characterized by symptomatic onset after 40 years of age and, usually, a benign phenotype. We describe a sporadic case with onset at 53 years of age and a novel VLOFA phenotype mimicking multiple system atrophy (MSA) of cerebellar type associated with minimal GAA1 expansion. We detected several atypical features for a diagnosis of MSA, which should alert to the possibility of an inherited ataxia.

Adult onset spinocerebellar ataxia in a Canadian movement disorders clinic

BACKGROUND

The spinocerebellar ataxias (SCAs) are a genetically and clinically heterogeneous group of neurodegenerative disorders. Relative frequencies vary within different ethnic groups and geographical locations.

OBJECTIVES

1) To determine the frequencies of hereditary and sporadic adult onset SCAs in the Movement Disorders population; 2) to assess if the fragile X mental retardation gene 1 (FMR1) premutation is found in this population.

METHODS

A retrospective chart review of individuals with a diagnosis of adult onset SCA was carried out. Testing for SCA types 1, 2, 3, 6, 7, and 8, Dentatorubral-pallidoluysian atrophy (DRPLA), Friedreich ataxia and the FMR1 expansion was performed.

RESULTS

A total of 69 patients in 60 families were identified. Twenty-one (35%) of the families displayed autosomal dominant and two (3.3%) showed autosomal recessive (AR) pattern of inheritance. A positive but undefined family history was noted in nine (15%). The disorder appeared sporadic in 26 patients (43.3%). In the AD families, the most common mutation was SCA3 (23.8%) followed by SCA2 (14.3%) and SCA6 (14.3%). The SCA1 and SCA8 were each identified in 4.8%. FA was found in a pseudodominant pedigree, and one autosomal recessive pedigree. One sporadic patient had a positive test (SCA3).Dentatorubral-pallidoluysian atrophy and FMR1 testing was negative.

CONCLUSION

A positive family history was present in 53.3% of our adult onset SCA patients. A specific genetic diagnosis could be given in 61.9% of dominant pedigrees with SCA3 being the most common mutation, followed by SCA2 and SCA6. The yield in sporadic cases was low. The fragile X premutation was not found to be responsible for SCA.

Meiotic CAG repeat instability in spinocerebellar ataxia type 6: Maternally transmitted elongation in a presumed sporadic case

Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominantly inherited disorder characterized by cerebellar ataxia, dysarthria and nystagmus. The molecular background for the disorder is a CAG repeat expansion in the CACNA1A gene located on chromosome 19. The size of SCA6 expanded alleles is usually stable, and variation in repeat size over successive generations is rare. We report a Danish family with one case of SCA6 resembling a sporadic case of spinocerebellar ataxia. Analysis of the CACNA1A gene showed meiotic CAG repeat instability in the transmission from a 70-year-old woman with no subjective symptoms to her symptomatic son. The CAG repeat size expanded from 22 repeats in the mother to 23 repeats in the proband. This case demonstrates maternal repeat instability and clinical anticipation in a family with SCA6.

Frequency analysis and clinical characterization of different types of spinocerebellar ataxia in Serbian patients

The relative frequencies of different spinocerebellar ataxias (SCAs) vary widely among different ethnic groups, presumably due to a founder effect. We investigated the relative prevalence of SCA1-3, 6-8, 12, 17; dentate-rubro-pallidoluysian atrophy; and Friedreich's ataxia (FRDA) in Serbian patients with adult-onset (>20 years of age) hereditary and sporadic SCAs, and compared clinical features of patients with genetically confirmed SCAs. A total of 108 patients from 54 families (38 apparently dominant [ADCA] and 16 apparently recessive) with adult-onset hereditary ataxia and 75 apparently sporadic patients were assessed. Of 38 families with ADCA, 13 (34%) were positive for an expansion in an SCA1 and 5 families (13%) for an expansion in an SCA2 allele. In 20 families (53%), no expansions have been identified in any of the analyzed genes. Gaze palsy, spasticity, and hyperreflexia were significantly more common in SCA1, whereas slow saccades, hypotonia, hyporeflexia, and dystonia prevailed in SCA2 patients. Among the 16 families with an apparently recessive mode of ataxia inheritance, 4 (25%) were identified as having the FRDA mutation. Ataxia-causing mutations were identified in 8 (10.6%) of patients with apparently sporadic adult-onset ataxia.

Olivopontocerebellar atrophy: Toward a better nosological definition

Olivopontocerebellar atrophy (OPCA) is a pathological label implying not only olivopontocerebellar changes, but also cases with more widespread lesions involving the CNS. This polytopic pathological background accounts for clinical complexity, essentially defined as cerebellar-plus syndrome. The term "OPCA" is applicable to an increasing number of neurodegenerative syndromes, including autosomal dominant ataxia, complicated spastic paraplegia, multiple-system atrophy (MSA), and many cases of idiopathic late-onset cerebellar ataxia (ILOCA), some of whom also turn out to have MSA. OPCA may also be part of the pathological hallmark of other disorders, such as prion disorders, mitochondrial encephalomyopathies, and hereditary metabolic diseases. Sporadic OPCA and ILOCA with cerebellar-plus presentation and neuroimaging evidence of brainstem and cerebellar atrophy may represent interchangeable eponyms. Just a quarter of such cases evolve to MSA within 5 years of the onset of symptoms. Therefore, the assumption that MSA and sporadic OPCA necessarily are one and the same disease is no longer tenable. Our review suggests that the label "OPCA" is useful to designate a clinicopathological syndrome that has a variety of etiologies carrying a poor prognosis, particularly if associated with autonomic failure as occurs in MSA.

Late-onset pure cerebellar ataxia: Differentiating those with and without identifiable mutations

Late onset cerebellar ataxia can be caused by several genetic mutations but a large percentage of patients remain undiagnosed. Thirty-eight patients with onset of slowly progressive, pure cerebellar ataxia >or=40 years-of-age were identified from a large ataxia database. Their clinical findings and quantitative oculomotor tests were reviewed; all were screened for SCA1, SCA2, SCA3, SCA6, SCA8, SCA14, and the Fragile X premutation (FMR1). All 47 exons of CACNA1A were screened for mutations. Genetic analysis uncovered a mutation in 11 patients. The SCA6 mutation was present in 8 patients (repeats 22-23). Three additional genetic mutations were found: SCA1 (42 repeats), SCA3 (66 repeats), and SCA8 (121 repeats). Patients without identified genetic mutations were characterized by 1) a later age of onset, 2) truncal without extremity ataxia, 3) and down beat nystagmus. Although only a third of these idiopathic late onset ataxia patients had a positive family history, this homogeneous syndrome probably represents a yet to be identified genetic disorder.

Spinocerebellar ataxia type 2 (SCA2) with white matter involvement

Two sisters presented with olivopontocerebellar atrophy, neuronal loss in the substantia nigra, intranuclear ubiquitin-, ataxin-2-positive inclusions in neurons, and severe demyelination and axon loss of the cerebral white matter with no accompanying inflammatory pathology. The genetic study demonstrated a 22/36 CAG triplet expansion in the SCA2 gene in one of the sisters; SCA1, SCA3, SCA6, SCA7, SCA8, SCA12, SCA17 and DRPL were ruled out in this patient. The present report shows that severe cerebral white matter pathology may occur in the context of SCA2.

The occurrence of dominant spinocerebellar ataxias among 251 Finnish ataxia patients and the role of predisposing large normal alleles in a genetically isolated population

OBJECTIVES

Frequency and distribution of dominant ataxias caused by dynamic mutations may vary in different populations, which has been explained on the basis of relative frequency of predisposing normal alleles. The aim of the study was to evaluate the occurrence of spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA) in Finland, and to investigate the role of predisposing normal alleles in a genetically homogenous population.

MATERIAL AND METHODS

Mutation analyses for SCA1, 2, 3, 6, 7, 8, 10, 12, 17, and DRPLA and frataxin genes were performed for 251 unrelated Finnish patients who presented with progressive ataxia disorder.

RESULTS

Expansions of SCA1, SCA2, SCA6, SCA7, SCA8, and SCA17 genes were detected in 2, 1, 1, 7, 22, and 1 patients, respectively. Altogether, 39 and 7% of dominant and sporadic SCA patients, respectively, harboured expansions at some of the investigated loci. Normal variation, collected from 477 to 502 chromosomes at each disease loci, revealed that Finns were different from the Japanese but largely similar to other Caucasians.

CONCLUSIONS

Lack of SCA3 and excess of SCA8 are characteristic to the Finnish population. Homozygosity for the SCA8 expansion increases penetrance. Frequencies of large normal alleles at the SCA loci predict poorly prevalence of the respective diseases in Finland. Prioritization in DNA testing, based on ethnic origin and geographical location, is recommendable in Finland, and analogous approach may be applied to other countries as well.

Population based study of late onset cerebellar ataxia in south east Wales

OBJECTIVE

To determine the prevalence and causation of late onset cerebellar ataxia (LOCA) in south east Wales, United Kingdom.

METHODS

A population based study of LOCA was conducted in a defined geographical region with a total population of 742,400. Multiple sources of ascertainment were used to identify all cases prevalent on 1 January 2001. The inclusion criteria were: a predominantly progressive cerebellar ataxia with onset of symptoms at age > or = 18 years; and disease duration of > or = 1 year. Cases with known acquired ataxias, ataxic syndromes with associated prominent autonomic dysfunction and/or atypical parkinsonism suggestive of multiple system atrophy and disorders with ataxia as a minor feature were excluded.

RESULTS

We identified 76 index cases of LOCA, of whom 63 were sporadic, idiopathic LOCA (ILOCA) and 13 were familial LOCA, of whom six had either spinocerebellar ataxia type 6, Friedreich's ataxia or dominant episodic ataxia. The mean annual incidence rate for the period 1999-2001 was 0.3/100,000 population/year. The crude prevalence rates were 8.4 per 100,000 (95% CI 7.2 to 11.6) for ILOCA and 1.8 per 100,000 (95% CI 0.8 to 2.7) for inherited LOCA. Of the 54/63 (85.7%) patients with ILOCA who were assessed, mean (SD) age at onset of symptoms was 53.8 (14.1) years (range 19 to 78) with a male:female ratio of 2.1:1. The mean disease duration was 8.7 (6.3) years (range 1 to 31). The most frequent presenting complaint was disturbance in gait (90.7%). One-third had a relatively pure cerebellar syndrome (33.3%) and two-thirds (66.7%) had additional extracerebellar neurological features. The majority (92%) were ambulant but only 9.3% were independently self-caring.

CONCLUSION

This population based study provides insight into LOCA within a defined region and will inform decisions about the rational use of healthcare resources for patients with LOCA.

Autosomal dominant cerebellar ataxias: clinical features, genetics, and pathogenesis

Autosomal dominant cerebellar ataxias are hereditary neurodegenerative disorders that are known as spinocerebellar ataxias (SCA) in genetic nomenclature. In the pregenomic era, ataxias were some of the most poorly understood neurological disorders; the unravelling of their molecular basis enabled precise diagnosis in vivo and explained many clinical phenomena such as anticipation and variable phenotypes even within one family. However, the discovery of many ataxia genes and loci in the past decade threatens to cause more confusion than optimism among clinicians. Therefore, the provision of guidance for genetic testing according to clinical findings and frequencies of SCA subtypes in different ethnic groups is a major challenge. The identification of ataxia genes raises hope that essential pathogenetic mechanisms causing SCA will become more and more apparent. Elucidation of the pathogenesis of SCA hopefully will enable the development of rational therapies for this group of disorders, which currently can only be treated symptomatically.

Detection of large pathogenic expansions in FRDA1, SCA10, and SCA12 genes using a simple fluorescent repeat-primed PCR assay

At least 18 human genetic diseases are caused by expansion of short tandem repeats. Here we describe a successful application of a fluorescent PCR method for the detection of expanded repeats in FRDA1, SCA10, and SCA12 genes. Although this test cannot give a precise estimate of the size of the expansion, it is robust, reliable, and inexpensive, and can be used to screen large series of patients. It proved useful for confirming the presence of large expansions in the Friedreich ataxia gene following an ambiguous result of long-range PCR, as well as rapid pre-screening for large repeat expansions associated with Friedreich ataxia and SCA10 and the shorter repeat expansions associated with SCA12.

Dominant spinocerebellar ataxias: a molecular approach to classification, diagnosis, pathogenesis and the future

The capacity to use molecular techniques to establish the genetic diagnoses of the autosomal dominant ataxias has revolutionized the field. It is now possible to systematically classify these disorders according to the nature of the causative mutation, with implications for diagnostic testing, analysis of pathogenesis and therapeutic strategies. Here, the disorders are grouped into ataxias caused by CAG repeat expansions that encode polyglutamine, ataxias caused by mutations in ion channels, ataxias caused by repeat expansions that do not encode polyglutamine, and ataxias caused by point mutations. The clinical, pathological, genetic and pathogenic features of each disorder are considered and the current status and future of diagnosis and therapy are reviewed in light of this classification scheme.

Pure cerebello-olivary degeneration of Marie, Foix, and Alajouanine presenting with progressive cerebellar ataxia, cognitive decline, and chorea

Parenchymatous cerebellar cortical atrophy (CCA) usually presents with a "pure" cerebellar ataxia. We describe a patient with a sporadic, late-onset progressive cerebellar ataxia plus cognitive decline and chorea who had CCA at post mortem. We discuss this unique case in the current context of classification of idiopathic cerebellar ataxia.

Structures of trinucleotide repeats in human transcripts and their functional implications

Among the goals of RNA structural and functional genomics is determining structures and establishing the functions of a rich repertoire of simple sequence repeats in transcripts. These repeats are present in transcripts from their 'birth' in the nucleus to their 'death' in cytoplasm and have the potential of being involved in many steps of RNA regulation. The knowledge of their structural features and functional roles will also shed more light on the postulated mechanisms of RNA pathogenesis in a growing list of neurological diseases caused by simple sequence repeat expansions. Here, we discuss several different lines of research to support the hypothesis that the mechanism of RNA pathogenesis may be a more common phenomenon triggered or modulated also by abundant long normal repeats. We propose structures of the repeat regions in transcripts of genes involved in Triplet Repeat Expansion Diseases. We have classified the polymorphic repeat alleles of these genes according to their ability to form hairpin structures in transcripts, and describe the distribution of different structural forms of the repeats in the human population. We have also reported the results of a systematic survey of the human transcriptome to identify mRNAs containing triplet repeats and to classify them according to structural and functional criteria. Based on this knowledge, we discuss the putative wider role of triplet repeat RNA hairpins in human diseases. A hypothetical model is proposed in which long normal RNA hairpins formed by the repeats may also be involved in pathogenesis.

Why is SCA12 different from other SCAs?

Spinocerebellar ataxia type 12 (SCA12), now described in European-American and Asian (Indian) pedigrees, is unique among the SCAs from clinical, pathological, and molecular perspectives. Clinically, the distinguishing feature is early and prominent action tremor with variability in other signs. Pathologically, brain MRIs also suggest variability, with prominent cortical as well as cerebellar atrophy. Genetically, SCA12 is caused by a CAG repeat expansion that does not encode polyglutamine; we speculate that the mutation may affect expression of the gene PPP2R2B, which encodes a brain-specific regulatory subunit of the protein phosphatase PP2A.

State of the art review: molecular diagnosis of inherited movement disorders. Movement Disorders Society task force on molecular diagnosis

This review is designed to provide practical help for the clinical neurologist to make appropriate use of the possibilities of molecular diagnosis of inherited movement disorders. Huntington's disease, Parkinson's disease and parkinsonian syndromes, ataxias, Wilson disease, essential tremor, dystonias, and other genetic diseases associated with a variety of movement disorders are considered separately.

Frequency of spinocerebellar ataxia mutations in the Kinki district of Japan

OBJECTIVES

To determine the frequencies of spinocerebellar ataxias (SCAs) in the Kinki district, the western part of the main island of Japan.

MATERIAL AND METHODS

One hundred and forty-three families with dominantly inherited ataxia and 220 patients with apparently sporadic cerebellar ataxia were examined for the SCA1, SCA2, SCA3/Machado-Joseph disease (MJD), SCA6, SCA7, SCA8, SCA12 and dentatorubral-pallidoluysian atrophy (DRPLA) mutations.

RESULTS

Among the dominant families, SCA1 accounted for 3%, SCA2 for 4%, SCA3/MJD for 24%, SCA6 for 31% and DRPLA for 12%. Neither SCA7 nor SCA12 mutations were detected. Among the apparently sporadic patients, 15% were found to have expanded triplet repeats. Of these, the SCA6 mutation was most frequently detected.

CONCLUSION

SCA6 is the most common SCA in the Kinki district of Japan. Comparison of our results with those from other regions of Japan and different countries shows geographic and ethnic variation in the frequency of SCAs.

DNA instability and human disease

It is now well established that non-Mendelian examples of DNA instability are associated with human disease. Most malignancies are associated with various chromosomal instabilities, such as aneuploidy, gene amplification, and chromosomal deletion. Furthermore, widespread microsatellite instability (MSI) is associated with a variety of tumors, and instability at specific dynamic repeat expansions underlies a family of neurologic disorders. Inactivation of DNA mismatch repair genes results in genomic instabilities affecting microsatellite regions. Mutations in genes involved in DNA polymerization or Okazaki fragment processing are also associated with MSI. Such instabilities convey a 'mutator' phenotype which is pathogenic. The mechanisms controlling trinucleotide repeat expansions are less well understood. Why this type of genomic instability is particularly pathogenic to neurons is also not clear. An understanding of what normally maintains stability is the first step towards preventing such loss of control and maintaining health.

The spinocerebellar ataxias: order emerges from chaos

In the past decade, the genetic etiologies accounting for most cases of adult-onset dominant cerebellar ataxia have been discovered. This group of disorders, generally referred to as the spinocerebellar ataxias (SCAs), can now be classified by a simple genetic nosology, essentially a sequential list in which each new SCA is given a number. However, recent advances in the elucidation of SCA pathogenesis provide the opportunity to subclassify the disorders into three discrete groups based on pathogenesis: 1) the polyglutamine disorders, SCAs 1, 2, 3, 7, and 17, which result from proteins with toxic stretches of polyglutamine; 2) the channelopathies, SCA6 and episodic ataxia types 1 and 2 (EA1 and EA2), which result from disruption of calcium or potassium channel function; and 3) the gene expression disorders, SCAs 8, 10, and 12, which result from repeat expansions outside of coding regions that may quantitatively alter gene expression. SCAs 4, 5, 9, 11, 13-16, 19, 21, and 22 are of unknown etiology, and may or may not fit into one of these three groups. At present, most diagnostic and therapeutic strategies apply equally to all of the SCAs. Therapy specific for individual diseases or types of diseases is a realistic goal in the foreseeable future.

The aetiology of sporadic adult-onset ataxia

The nosology and aetiology of sporadic adult-onset ataxia are poorly understood. The aim of the present study was to answer the following questions: (i) How many sporadic ataxia patients have a genetic cause? (ii) How many sporadic ataxia patients suffer from multiple system atrophy (MSA)? (iii) Is there a specific association between sporadic ataxia and serum anti-glutamic acid decarboxylase (GAD) or antigliadin antibodies? and (iv) What are the clinical features of patients with unexplained sporadic ataxia? The study was performed in 112 patients who met the following inclusion criteria: (i) progressive ataxia; (ii) onset after 20 years; (iii) informative and negative family history (no similar disorders in first- and second-degree relatives; parents older than 50 years); and (iv) no established symptomatic cause. Thirty-two patients (29%) met the clinical criteria of possible (7%) or probable (22%) MSA. The Friedreich's ataxia mutation was found in five patients (4%), the spinocerebellar ataxia (SCA) 2 mutation in one (1%), the SCA3 mutation in two (2%) and the SCA6 mutation in seven (6%). The disease remained unexplained in 65 patients (58%). We did not detect anti-GAD antibodies in any of our patients. Antigliadin antibodies were present in 14 patients, 10 patients with unexplained ataxia (15%) and 4 patients with an established diagnosis (9%). Patients with unexplained sporadic ataxia had a median disease onset of 56.0 years. Decreased vibration sense (62%), decreased or absent ankle reflexes (40%), increased ankle reflexes (39%), dysphagia (38%) and extensor plantar responses and/or spasticity (34%) were the most frequent extracerebellar symptoms. Compared with MSA, disease progression was significantly slower.