Similarities and differences in the phenotype, genotype and pathogenesis of different spinocerebellar ataxias.

Historically, the differential diagnosis of the autosomal ataxias (ADCAs) has been difficult. In 1983 Harding proposed a useful clinical classification. Since 1983 ADCAs have been increasingly characterized in terms of their genetic locus and are referred to as spinocerebeller ataxia (SCA). The overlap between the SCA phenotypes and the high variability within SCA subgroups means that, for individual patients, the underlying mutation cannot be predicted reliable purely on the basis of clinical symptoms and so diagnosis should be made on the genotype. However, for executing DNA analyses in order of clinical likelihood, neurologists may try to deduce the underlying mutation by using a clinical algorithm. In this article we not only describe such an algorithm but also plot the pathway from clinical presentation, genetic classification and mutation, abnormal protein to common neuropathology in these disorders.     

Clinical and genetic analysis of a four-generation family with a distinct autosomal dominant cerebellar ataxia

The autosomal dominant cerebellar ataxias (ADCAs) are a heterogeneous group of neurodegenerative disorders characterised by progressive cerebellar dysfunction in combination with a variety of other associative features. Since 1993 ADCAs have been increasingly characterised in terms of their genetic mutation and are referred to as spinocerebellar ataxias (SCAs). Some families with ADCA cannot be assigned to any of the known genotypes, which implies further genetic heterogeneity. We investigated the clinical symptoms of 12 patients of a four-generation family with ADCA and carried out mutation and genetic linkage studies. The family showed a relatively mild cerebellar ataxic syndrome with congitive impairment, poor performance on the Wisconsin Card Sorting Test, myoclonus, and a postural irregular tremor of slow frequency. Age at disease onset and severity of cerebellar signs and symptoms suggest anticipation. The genetic loci implicated in ADCA were excluded by mutation analyses (SCA 1,2,3,6,7,8,12) and genetic linkage (SCA 4,5,6,10,11). We conclude that this family represents a clinically and genetically distinct form of SCA. Received: 31 March 2000 / Received in revised form: 14 July 2000 / Accepted: 12 August 2000     

Identification of five Spinocerebellar Ataxia Type 2 pedigrees in patients with autosomal dominant cerebellar ataxia in Taiwan

OBJECTIVES: The autosomal dominant cerebellar ataxias (ADCAs) are a group of genetically diverse neurological conditions linked by progressive deterioration in balance and coordination. Spinocerebellar Ataxia Type 2 (SCA2) is one of the ADCAs and also belongs to a special group caused by the expansion of an unstable CAG repeat encoding a polyglutamine tract. We aimed to investigate the frequency of SCA2 mutation in the ataxia patients referred to the clinic. MATERIALS AND METHODS: We screened 58 families with inherent cerebellar ataxia and 57 normal individuals by the use of radioactive genomic polymerase chain reaction (PCR) method. A simple non-radioactive PCR for rapid detection of the expanded SCA2 alleles via agarose gel electrophoresis was also employed. RESULTS: Eight SCA2 affected patients and 1 at-risk individual in 5 unrelated SCA2 families were identified. The CAG repeats of normal alleles in the sample studied range in size from 16 to 30 repeat units, while those of SCA2 chromosomes are expanded to 34 to 49 repeat units. Our results also showed that unlike SCA 1 and SCA3/MJD, the size distribution of the normal alleles showed few polymorphisms, with the 22 repeat allele accounting for 90.1%. Homozygosity in normal individuals was 80.2%. No overlap in ataxin-2 allele size between normal and expanded chromosomes was observed. CONCLUSION: This is the first report of the SCA2 gene distributions in the population of Taiwan. The SCA2 mutation accounts for 8.6% of ADCA type I families referred to us, intermediate between SCA1(1.7%) and SCA3/MJD (24%) of the ADCA type I families in our collection.     

Clinical and genetic analysis of spinocerebellar ataxia type 11

The autosomal dominant cerebellar ataxias (ADCAs) are a genetically heterogeneous group of disorders. Clinical classification of the ADCAs into three types has facilitated defining phenotypes and in turn, linkage analysis, which has led to the discovery of 30 loci and 16 genes. The type III ADCAs are ‘pure’ spinocerebellar ataxias (SCA), those that appear to elude neurological features outside of the cerebellum. At present 3 ADCA type III SCA genes have been published, SCA5, SCA6, and SCA14, these three genes appear to have various roles suggesting involvement in both different and possibly overlapping neurodegenerative pathways. The known ADCAIII genes are thought to have such roles as involvement in signal transduction, cell proliferation, synaptic transmission, and channel regulation. Here we update readers on the current progress on SCA11 and the identification of the disease gene. We discuss the clinical, genetic, and pathological details of SCA11 – a locus at chromosome 15q14-q21.3 in a Caucasian family of British ancestry. We also discuss the refining of this region, and methods used to prioritize the screening of the over 130 candidate genes in this genomic region.     

Spinocerebellar Ataxia Type 28 (SCA28) is an Uncommon Cause of Dominant Ataxia Among Chinese Kindreds

ABSTRACT Autosomal dominant cerebellar ataxias (ADCAs) are a clinically and genetically heterogeneous group of neurodegenerative disorders primarily affecting the cerebellum. Nearly 33 genetically distinct subtypes have been defined, and 19 seemingly unrelated disease genes have been identified so far. Recently, mutations in the ATPase family gene 3-like 2 (AFG3L2) gene were presented to cause SCA28 subtype. In order to define the frequency of SCA28 mutation in Chinese mainland, we performed molecular genetic analysis in 67 unrelated affected individuals with ADCA. At last, we did not find AFG3L2 gene mutation, except for three known single nucleotide polymorphisms (SNP)s. It suggests that SCA28 subtype is very rare in Chinese mainland.     

Cognitive impairment in SCA-19

The autosomal dominant cerebellar ataxias (ADCAs) are a heterogeneous group of neurodegenerative disorders characterised by progressive cerebellar dysfunction in combination with various associated features. Since 1993, ADCAs have been increasingly characterised in terms of their genetic mutation and are currently referred to as spinocerebellar ataxias (SCAs). The discovery of genetic abnormalities offers the opportunity to study the possible interaction between the identified gene mutation and cognitive function. In this study, we focus on the neuropsychological abnormalities in a Dutch ADCA family, in which a new locus was recently identified (SCA-19). The family members showed frontal-executive dysfunction, with global cognitive impairment occurring in some of the more severely affected patients. Interestingly, the neuropsychological profile of this new family seems to overlap that of individuals with various other SCAs. Apparently, similar pattern of neuronal degeneration in various SCA subtypes accounts for the neuropsychological dysfunction, which is thus not genotype specific.     

Frequency of spinocerebellar ataxia types 1, 2, 3, 6, 7 and dentatorubral pallidoluysian atrophy mutations in Korean patients with spinocerebellar ataxia

Autosomal dominant cerebellar ataxias (ADCAs) are a heterogeneous group of disorders characterized by degenerative symptoms in the cerebellum, spinal cord, and brain stem. Six different genes have been reported to be associated with ADCA, and the length of trinucleotide repeats of these genes is correlated with the age at onset and severity of symptoms. Although there are strong hereditary effects in these disorders, most of the studies carried out in heterogeneous populations and in small groups obscure the true incidence of these diseases. We examined the frequency of six types of ADCAs in 87 unrelated Korean patients with progressive ataxia and compared the results to the frequencies in other ethnic groups. Spinocerebellar ataxia (SCA) type 2 was the most frequent hereditary ataxia (12.6%) and types 3 and 6 accounted for 4.6% and 6.9% of ataxia patients, respectively. Dentatorubral pallidoluysian atrophy was also found in three patients (3.4%). No instances of SCA types 1 or 7 were detected. These findings show the striking contrast to the white population and a difference from Japanese findings. Our results demonstrate that dentatorubral pallidoluysian atrophy should be included in the differential diagnosis of Korean patients with spinocerebellar ataxia, and that there are strong hereditary effects in patients with ADCAs. Received: 6 March 1998 Received in revised form: 8 July 1998 Accepted: 18 August 1998     

A genetic epidemiological study of spinocerebellar ataxias in Tottori prefecture, Japan

We investigated the genotype frequencies of patients with spinocerebellar ataxias (SCA), using a community-based prevalence study among 613,349 inhabitants in Tottori prefecture, Japan. Prevalence date was April 1, 1998. On this date, 109 SCA patients were identified in this community. The prevalence of SCA was 17.8 per 100,000 individuals. The most common cause of inherited SCA was a mutation at the SCA6 locus (25%), followed by mutation at the SCA1 locus (15%), SCA3 locus (5%) and dentatorubral-pallidoluysian atrophy locus (5%). None of the expanded alleles was found in SCA2, SCA7 or Friedreich's ataxia. Mutation at SCA6 was also the most common form of sporadic SCA at 11%. Prevalences per 100,000 individuals were as follows: SCA6, 2.40; SCA1, 0.48; DRPLA, 0.32, and SCA3, 0.16.     

The genetic aetiology of late-onset chronic progressive cerebellar ataxia

Background   An increasing number of dominant and recessive disorders have been associated with late onset chronic progressive ataxia (LOCA) complicating the formulation of a rational diagnostic strategy. Furthermore, there is marked geographic and ethnic variation in the relative importance of these individual disorders and the cause of such observed variation remains unexplained. Methods   We have systematically investigated a populationbased cohort of patients with chronic progressive LOCA for SCA 1,2,3,6,7,8,10,12,17, FXTAS and FRDA. In addition we have examined repeat length polymorphism in chromosomes from a genetically homogeneous and representative control population to investigate the association of high-normal repeats and disease prevalence. Results   A total of 178 patients including 55 familial cases segregating in 38 kindreds and 123 sporadic were investigated. Pathological expansions were identified in 11/38 (28.9 %) of families and in 5/123 (4.1 %) of sporadic patients. The most frequent diagnoses were SCA6 (6 families and 1 sporadic patient), DRPLA (4 families) and SCA8 (1 family). In addition, one elderly female patient was identified with “possible FXTAS”. Six (2 %) control patients were noted to have expanded SCA8 alleles. Conclusions   SCA6 and DRPLA were the most frequent genetic diagnoses identified. Patterns of highnormal allele frequency in this UK population were distinct compared to other ethnic groups but this was poorly predictive of the distribution of disease in this region. The relative contribution of new mutation formation and founder effects to the prevalence of familial ataxia is uncertain, and further exploration of these factors will require detailed analysis of disease allele haplotypes and meiotic instability of intermediate length alleles. Electronic Supplementary Material  The online version of this article (DOI) contains supplementary material, which is available to authorized users.     

Clinical and molecular analysis of 11 Sicilian SCA2 families: influence of gender on age at onset

Autosomal dominant cerebellar ataxias (ADCAs) are a complex group of slowly progressive neurodegenerative disorders characterized by gait and stance ataxia, dysarthria and other symptoms of nervous system involvement. ADCA type I is the commonest form and is genetically heterogeneous; several loci have been identified. Spinocerebellar ataxia type 2 (SCA2) has been mapped to chromosome 12, with expanded cytosine-adenine-guanine (CAG) repeats being identified as the mutational cause of the disease. We investigated 15 families, all originating from mid-eastern Sicily, with ADCA type I; molecular studies performed in 12 families showed the SCA2 mutation to be present in 11 of them (91.6%) - the highest occurrence so far reported in the literature. The CAG repeat of the affected alleles varied between 34 and 44 repeats. Age at onset and repeat length revealed an inverse correlation. Mean age at onset was 37.32 +/- 16. 74 years, and occurred earlier in males than in females. There were no differences in mean CAG repeat units between the sexes. However, a higher instability of CAG repeats was observed for paternal transmission than for maternal transmission. Age at onset and anticipation were not related to parental transmission. Our data suggest that in SCA2 an unknown sex-linked factor may play a role in the modulation of toxic effects of the polyglutamine tract.     

Genetic and clinical analysis of spinocerebellar ataxia type 8 repeat expansion in Italy.

BACKGROUND: The spinocerebellar ataxias (SCAs) are clinically heterogeneous disorders caused by triplet repeat expansions in the sequence of specific disease genes. Spinocerebellar ataxia type 8 (SCA8), originally described in a family characterized by pure cerebellar ataxia with slow disease progression, presents with expansion of combined CTA/CTG repeats. OBJECTIVE: To perform SCA8 repeat expansion analysis in a heterogeneous group of ataxic patients, to determine the prevalence of this mutation in our patients and establish the frequency of expanded CTA/CTG repeats in a large group of control subjects. PATIENTS: One hundred sixty-seven patients affected by sporadic, autosomal dominant and recessive hereditary ataxia were clinically examined and analyzed for SCA8 expansion. We further studied 161 control subjects and 125 patients with psychiatric disorders. RESULTS: We found abnormally expanded CTA/CTG repeats in 5 ataxic patients, 3 of them characterized by pure cerebellar ataxia. One patient had vitamin E deficiency and 1 patient with a sporadic case was affected by gluten ataxia. No evidence of expanded alleles was found in healthy control subjects and in patients with psychiatric disorders. CONCLUSIONS: Our data support the evidence that CTG expansions may be linked to SCA8, since the pathogenic expansions have been found only among patients with genetically unidentified forms of hereditary and sporadic ataxia. Patients carrying expanded alleles present peculiar phenotypic features, thus suggesting that unknown additional factors could probably predispose to the disease.     

The molecular biology of the autosomal-dominant cerebellar ataxias.

Autosomal-dominant cerebellar ataxias (ADCA) may present as progressive or paroxysmal disorders. While the progressive ataxias have been named spinocerebellar ataxias (SCA), the paroxysmal disorders are designated episodic ataxias (EA). Until now, three different mutational mechanisms resulting in distinctive pathogenesis have been identified. The first type of mutation present in SCA1, SCA2, SCA3, and SCA7 is an expanded CAG repeat in genes of unknown function that are translated into proteins with expanded polyglutamine tracts. A common ultrastructural feature of these disorders is the formation of neuronal intranuclear inclusions (NII) harboring the expanded disease proteins and a variety of other proteins. The pathogenic role of these inclusions has yet to be clarified. A second group of disorders is the result of mutations in genes that code for ion channels. In EA-1, a disorder characterized by episodes of ataxia provoked by movement and startle, missense mutations in a potassium channel gene, KCNA1, have been found. Patients with EA-2, another form of paroxysmal ataxia, carry nonsense mutations of the gene encoding the alpha1A voltage-dependent calcium channel subunit, CACNA1A, that are predicted to result in truncated channel proteins. In SCA6, a progressive ataxia, an expanded CAG repeat in the 3' translated region of the CACNA1A gene, has been found. The third type of mutation is an untranslated CTG expansion resembling the mutation found in myotonic dystrophy. It is associated with a progressive ataxia, SCA8.     

Hereditary ataxias in Akita prefecture]

To provide a genetic survey of hereditary ataxia, we performed PCR screening of SCA1, SCA2, MJD1 (SCA 3), SCA6, DRPLA, with 71 patients in 61 families living in Akita prefecture (1,205,571 population in 1997) in Japan. Of 71 patients in 61 families, 18 MJD1, 14 SCA6, 5 DRPLA, 1 SCA1 and 1 SCA2 patients were detected. Eighty percent of autosomal dominant inherited spinocerebellar degeneration (AD-SCD) including 7 spoladic patients genetically diagnosed as AD-SCD was MJD1 (45.7%) and SCA6 (34.3%). These suggest the prevalence rate of hereditary ataxias in Akita prefecture; 1.5 and 1.2/100,000 of MJD1 and SCA6, respectively. Only one patient of SCA1 was detected, which was frequently reported in Hokkaido and Tohoku area in Japan.     

Spinocerebellar ataxia type 1 in China: molecular analysis and genotype-phenotype correlation in 5 families

BACKGROUND: Twelve genetic types of autosomal dominant hereditary ataxia have been recently identified and the genes responsible for most of them cloned. Molecular identification of the type of ataxia is important to determine the disease prevalence and its natural history in various populations. OBJECTIVES: To perform molecular analysis of 75 Chinese families affected with spinocerebellar ataxia (SCA) and to evaluate the spectrum of mutations in these genes and the correlation between genotypes and phenotypes in Chinese patients. SETTING: Neurogenetics Unit, China-Japan Friendship Hospital, Beijing, China. METHODS: One hundred nine patients from 75 kindreds diagnosed as having autosomal dominant SCA, 16 patients with sporadic SCA or spastic paraplegia, 280 control chromosomes of the Chinese population, and 120 control chromosomes of the Sakha population were selected for this study. We conducted detailed mutational analysis by direct sequencing of polymerase chain reaction products amplified from genomic DNA. RESULTS: Spinocerebellar ataxia type 1 (SCA1) was identified in 5 families with 12 studied patients. All affected family members were heterozygous for a CAG repeat expansion in the SCA1 gene containing 51 to 64 trinucleotide repeats. Normal alleles had 26 to 35 repeats. Spinocerebellar ataxia type 1 accounted for 7% of the studied Chinese families with ataxia. In addition, we determined the frequency of a single vs double CAT interruption in 120 control chromosomes of the Siberian Sakha population, which has the highest known prevalence of SCA1, and compared this with 280 control chromosomes from the Chinese populations. The results show that 64.7% of the Siberian normal alleles contain a single CAT interruption, whereas 92% of the Chinese had more than 1 interruption. CONCLUSIONS: Spinocerebellar ataxia type 1 is responsible for 7% of affected families in the Chinese population. A correlation between the prevalence of SCA1 and the number of CAT interruptions in the trinucleotide chain suggests that a CAT-to-CAG substitution may have been the initial event contributing to the generation of expanded alleles and influencing relative prevalence of SCA1.     

Analysis of trinucleotide repeats in different SCA loci in spinocerebellar ataxia patients and in normal population of Taiwan

Objective – To identify various subtypes of spinocerebellar ataxias (SCAs) among autosomal dominant cerebellar ataxia (ADCA) patients referred to our research center, SCA1, SCA2, SCA3/MJD (Machado–Joseph disease), SCA6, SCA7, SCA8 and SCA12 loci were assessed for expansion of trinucleotide repeats.
Patients and methods – A total of 211 ADCA patients, including 202 patients with dominantly inherited ataxia from 81 Taiwanese families and nine patients with sporadic ataxia, were included in this study and subjected to polymerase chain reaction (PCR) analysis. The amplified products of all loci were analyzed on both 3% agarose gels and 6% denaturing urea-polyacrylamide gels. PCR-based Southern blots were also applied for the detection of SCA7 locus.
Results – The SCA1 mutation was detected in six affected individuals from one family (1.2%) with expanded alleles of 50–53 CAG repeats. Fourteen individuals from nine families (11%) had a CAG trinucleotide repeat expansion at the SCA2 locus, while affected SCA2 alleles have 34–49 CAG repeats. The SCA3/MJD CAG trinucleotide repeat expansion in 60 affected individuals from 26 families (32%) was expanded to 71–85 CAG repeats. As for the SCA7 locus, there were two affected individuals from one family (1.2%) possessed 41 and 100 CAG repeats, respectively. However, we did not detect expansion in the SCA6, SCA8 and SCA12 loci in any patient.
Conclusions – The SCA3/MJD CAG expansion was the most frequent mutation among the SCA patients. The relative prevalence of SCA3/MJD in Taiwan was higher than that of SCA2, SCA1 and SCA7.     

Spinocerebellar ataxia associated with a mutation in the fibroblast growth factor 14 gene (SCA27): A new phenotype.

Autosomal dominant cerebellar ataxias (ADCAs) are genetically classified into spinocerebellar ataxias (SCAs). We describe 14 patients of a Dutch pedigree displaying a distinct SCA-phenotype (SCA27) associated with a F145S mutation in the fibroblast growth factor 14 (FGF14) gene on chromosome 13q34. The patients showed a childhood-onset postural tremor and a slowly progressive ataxia evolving from young adulthood. Dyskinesia was often present, suggesting basal ganglia involvement, which was supported by functional imaging in 1 patient. Magnetic resonance imaging (MRI) of the brain showed only moderate cerebellar atrophy in the 2 eldest patients. Neuropsychological testing indicated low IQ and deficits in memory and executive functioning. Behavioral problems were also observed. Further investigations will have to determine the role of FGF14 in the pathogenesis of neurodegeneration and the frequency of this FGF14 mutation in SCA. (c) 2005 Movement Disorder Society.     

Fine mapping of 16q-linked autosomal dominant cerebellar ataxia type III in Japanese families

The autosomal dominant cerebellar ataxias (ADCAs) are a clinically and genetically heterogeneous group of disorders. To date, at least 11 genes and 13 additional loci have been identified in ADCAs. Despite phenotypic differences, spinocerebellar ataxia 4 (SCA4) and Japanese 16q-linked ADCA type III map to the same region of 16q22.1. We report four Japanese families with pure cerebellar ataxia and a disease locus at 16q22.1. Our families yielded a peak lod score of 6.01 at marker D16S3141. To refine the candidate region, we carried out genetic linkage studies in four pedigrees with a high density set of DNA markers from chromosome 16q22.1. Our linkage data suggest that the disease locus for 16q-ADCA type III is within the 1.25-Mb interval delineated by markers 17msm and CTTT01. We screened for mutations in 36 genes within the critical region. Our critical region lies within the linkage interval reported for SCA4 and for Japanese 16q-ADCA type III. These data suggest that the ADCA that we have characterized is allelic with SCA4 and Japanese 16q-linked ADCA type III.     

Polyneuropathy in autosomal dominant cerebellar ataxias: phenotype-genotype correlation.

Autosomal dominant cerebellar ataxias (ADCAs) are clinically and genetically heterogeneous neurodegenerative disorders. The aim of this study was to evaluate electrophysiologically peripheral nervous system involvement in each of the groups studied and its correlation with the number of CAG repeats. Forty patients with ADCA were clinically and electrophysiologically investigated. Thirty-five patients belonged to the ADCA type I group (SCA1, 12; SCA2, 10; SCA3, 13) and five to the ADCA type II group. Axonal sensory or sensorimotor polyneuropathy was found in 42% of the SCA1 patients, 80% of the SCA2 patients, and 54% of the SCA3 patients, whereas electrophysiological studies were normal in all those with ADCA type II. The number of CAG repeats was significantly higher in SCA1 patients with polyneuropathy than in those without polyneuropathy (P = 0.01), whereas the reverse was observed in SCA3/MJD (Machado-Joseph disease) patients (P = 0.05). We conclude that axonal polyneuropathy is often associated with ADCA type I, but its frequency varies according to factors such as the locus responsible and the number of CAG repeats.