Molecular genetics of hereditary spinocerebellar ataxia: mutation analysis of spinocerebellar ataxia genes and CAG/CTG repeat expansion detection in 225 Italian families

BACKGROUND: Autosomal dominant cerebellar ataxias are a clinical and genetically heterogeneous group of progressive neurodegenerative diseases, at present associated with 22 loci (spinocerebellar ataxia [SCA] 1-SCA8, SCA10-SCA19, SCA21, SCA22, fibroblast growth factor 14 [FGF14]-SCA, and dentatorubral-pallidoluysian atrophy [DRPLA]). The relevant gene has been identified in 12 cases (SCA1-3, SCA6-8, SCA10, SCA12, FGF14, and DRPLA), and in all but the recently identified SCA14, SCA17, PRKCG and FGF14 genes, the defect consists of the expansion of a short nucleotide repeat. OBJECTIVES: To investigate the relative prevalence of SCA1-3, SCA6-8, SCA10, SCA12, and SCA17 gene expansions in Italian families with hereditary ataxia, specifically to verify the occurrence of SCA10, SCA12, and SCA17 in Italy; and to analyze samples from probands with negative test results at the initial screening by means of the repeat expansion detection technique to identify CAG/CTG expansions in novel loci.Patients Two hundred twenty-five unrelated Italian index cases with hereditary ataxia, most (n = 183) of whom presented with a clear dominantly transmitted trait. RESULTS: We found that SCA1 and SCA2 gene mutations accounted for most cases (21% and 24%, respectively). We found SCA3, SCA6, SCA7, SCA8, and SCA17 to be very rare (approximately 1% each), and no case of SCA10 or SCA12 was identified. Half of the index cases (113/225) were negative for expansions in the known SCA genes. Repeat expansion detection analysis performed on 111 of these cases showed a CAG/CTG repeat expansion of at least 50 triplets in 22 (20%). Twenty-one of 22 expansions could be attributed to length variation at 2 polymorphic loci (expanded repeat domain CAG/CTG 1 [ERDA1] or CTG repeat on chromosome 18q21.1 [CTG18.1]). In 1 patient, the expansion was assigned to the DRPLA gene. CONCLUSIONS: The distribution of SCA1-3 and SCA6-7 gene mutations is peculiar in Italy. We found a relatively high frequency of SCA1 and SCA2 gene expansions; SCA3, SCA6, and SCA7 mutations were rare, compared with other European countries. No SCA10 or SCA12 and only a few SCA8 (2/225) and SCA17 (2/225) families were detected. In patients negative for defects in known SCA genes, repeat expansion detection data strongly suggest that, at least in our population, CAG/CTG expansions in novel genes should be considered an unlikely cause of the SCA phenotype.     

Pontine atrophy in spinocerebellar ataxia type 6

To investigate the clinical range of spinocerebellar ataxia type 6 (SCA6), we screened CAG repeat expansion in the voltage-dependent alpha 1A calcium channel gene (CACNL1A4) in 71 ataxic patients in 60 families; 54 patients in 43 families with hereditary ataxia and 17 sporadic patients. Thirteen patients with SCA6 were detected to have elongated CAG in CACNL1A4. Of these, 7 patients had been diagnosed as having hereditary cerebellar cortical atrophy, and 6 patients had been found to have sporadic occurrence. One patient showed distinct pontine atrophy with prominent horizontal or oblique gaze nystagmus which is an unusual feature in sporadic olivopontocerebellar atrophy. For the efficient screening of SCA6, we would propose testing CAG repeat expansion in CACNL1A4, in patients with one of two markers: (1) horizontal or oblique gaze nystagmus without other eye movement disorders, (2) pure cerebellar atrophy, even if occurrence is sporadic. We should note that the pontine atrophy could also be caused by CAG repeat expansion in CACNL1A4.     

CAG repeat expansions in patients with sporadic cerebellar ataxia

CAG repeat expansions cause spinocerebellar ataxia type 1 (SCA1), SCA2, SCA3, SCA6 and dentatorubral-pallidoluysian atrophy (DRPLA). So far these expansions have been examined mainly in ataxia patients with a family history. However, some sporadic cases with SCA have recently been reported. To elucidate the frequency and characteristics of sporadic SCAs, we screened 85 Japanese ataxia patients without a family history for the SCA1, SCA2, SCA3, SCA6 and DRPLA mutations. As a result, 19 patients (22%) were found to have expanded CAG repeats. Among sporadic SCAs, the SCA6 mutation was most frequently observed. The sporadic SCA6 patients had smaller CAG repeats and a later age of onset than SCA6 patients with an established family history. We also identified one father-child pair in which intermediate sized CAG repeats expanded into the SCA2 disease range during transmission. These findings suggest that patients with ataxia even without a family history should be examined for a CAG repeat expansion.     

Refinement of the spinocerebellar ataxia type 4 locus in a large German family and exclusion of CAG repeat expansions in this region

Spinocerebellar ataxia type 4 (SCA4) is an autosomal dominant disorder mapped to chromosome 16q22.1 in a large Utah kindred. The clinical phenotype is characterized by cerebellar ataxia with sensory neuropathy. We describe a five-generation family from northern Germany with similar clinical findings linked to the same locus. Haplotype analyses refined the gene locus to a 3.69 cM interval between D16S3019 and D16S512. Analysis of nine CAG/CTG tracts in this region revealed no evidence for a repeat expansion. Received: 28 October 2002, Received in revised form: 16 December 2002, Accepted: 19 December 2002 Correspondence to: Dr. Yorck Hellenbroich     

Spinal cord atrophy in spinocerebellar ataxia type 3 and 6

Objective   

To quantify spinal cord atrophy and its impact on clinical disability in spinocerebellar ataxia (SCA) type 3 and 6.     

Dementia, ataxia, extrapyramidal features, and epilepsy: phenotype spectrum in two Italian families with spinocerebellar ataxia type 17

Abstract. We observed two families with a dominantly inherited complex neurological syndrome with onset in adulthood. Family F included 9 affected in four generations. One patient showed prominent anticipation of onset age. Onset was with cerebellar signs followed by dementia, psychiatric symptoms, seizures, and extrapyramidal features. Family M included 14 affected individuals in five generations. Presenting symptoms were either psychiatric and cognitive impairment or a cerebellar syndrome. Extrapyramidal features, dysphagia, incontinence, seizures, and myoclonus may occur. In both families magnetic resonance imaging showed marked atrophy of the brain and cerebellum. Molecular analyses demonstrated an expanded CAG/CAA repeat in the in the TATA box-binding protein (TBP) gene (SCA17).     

A clinical and molecular genetic study of dentatorubropallidoluysian atrophy in four european families

Dentatorubropallidoluysian atrophy is a neurodegenerative disorder with characteristic pathology, chiefly described in reports from Japan, and is associated with an unstable CAG trinucleotide repeat in a gene on chromosome 12. We describe four European families, three British and one Maltese, with this mutation. All exhibited autosomal dominant inheritance, and there was evidence for anticipation associated with an increase of the expansion with paternal transmission in two families. Affected chromosomes from patients with dentatorubropallidoluysian atrophy had CAG expansions of 58 to 74 repeats, compared to 7 to 26 in control chromosomes, and the size of repeat was significantly inversely correlated with age of onset. The clinical features were diverse, even within individual families, and comprised a combination of a movement disorder (chorea, myoclonus, dystonia, or parkinsonism), cerebellar ataxia, epilepsy, psychosis, and dementia. A clinical diagnosis of Huntington's disease had been made in affected individuals from all families. Neuropathological examination of 2 patients showed no specific abnormality in one and degenerative changes predominantly affecting the spinal cord in the other. Investigation of 55 patients who might represent sporadic examples of dentatorubropallidoluysian atrophy did not detect any expanded alleles. Dentatorubropallidoluysian atrophy is likely to be more common than previously recognized in non-Japanese populations, and should be considered in any patient with a dominantly inherited neurodegenerative disorder with the above-mentioned clinical features.     

Brain regional differences in the expansion of a CAG repeat in the spinocerebellar ataxias: Dentatorubral-pallidoluysian atrophy,machado-joseph disease,and spinocerebellar ataxia type 1

Three autosomal dominant spinocerebellar ataxias, dentatorubral-pallidoluysian atrophy (DRPLA), Machado-Joseph disease (MJD), and spinocerebellar ataxia type 1 (SCA1), are associated with the expansion of a CAG repeat in the respective genes. To investigate the association between CAG repeat expansion and neuropathological findings, we analyzed several brain regions from 9 cases of DRPLA, 3 cases of MJD, and 1 case of SCA1. We found that the expanded alleles were smaller in the cerebellar cortex than in other brain regions, such as the frontal cortex, in these three diseases. The discrepancy in the expanded CAG repeat length between cerebellar cortex and other tissues was most prominent in DRPLA, and especially in cases of adult-onset DRPLA. A significant correlation was found between the age at onset of DRPLA and the size of the CAG repeat expansion. Cerebella of DRPLA patients were microscopically dissected into three layers, the molecular and granularlayers and the white matter, which were analyzed separately. The lower level of CAG repeat expansion in DRPLA cerebella was representative of CAG repeat expansion in the granule cells. The microdissected samples of the granular layer of the hippocampal formation, which is densely packed with neuronal cells, revealed that the degree of CAG repeat expansion in this layer was similar to that in the cerebellum. These observations suggest that granule cells in the cerebellum and hippocampus have low levels of CAG repeat expansion, and that other types of cells exhibit a higher level of CAG repeat expansion, in spinocerebellar ataxias.     

Clinical phenotype of Brazilian families with spinocerebellar ataxia 10

Spinocerebellar ataxia type 10 (SCA10) is an autosomal dominant ataxia caused by an ATTCT repeat expansion in an intron of the SCA10 gene. SCA10 has been reported only in Mexican families, in which the disease showed a combination of cerebellar ataxia and epilepsy. The authors report 28 SCA10 patients from five new Brazilian families. All 28 patients showed cerebellar ataxia without epilepsy, suggesting that the phenotypic expression of the SCA10 mutation differs between Brazilian and Mexican families.     

Mosaicism of unstable CAG repeats in the brain of spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of unstable CAG repeats within the coding region of the novel gene, ataxin-2, on chromosome 12q24.1. We analyzed CAG repeat size of the SCA2 allele in two deceased patients (father and daughter) to investigate the repeat mosaicism in CNS regions. The CAG repeat size was examined using lymphoblastoid cell lines, frozen brain tissues, and paraffin-embedded tissues. In each patient the major repeat size of the expanded allele varied within the brain or spinal cord (father, 39–42; daughter, 39–47 repeats), and was smaller by three to eight repeats in the cerebellum than in other CNS regions. Our results are in agreement with the findings in other polyglutamine disorders showing somatic mosaicism. Received: 7 August 1998 Received in revised form: 20 January 1999 Accepted: 19 March 1999     

CAG repeat length and clinical features in three Italian families with spinocerebellar ataxia type 2 (SCA2): early impairment of Wisconsin Card Sorting Test and saccade velocity

We report on the clinical, neuropsychological, neurophysiological, computerized eye movement, magnetic resonance imaging (MRI) and molecular findings from 17 individuals affected with spinocerebellar ataxia type 2 (SCA2) belonging to three families. The average age at onset of the symptoms was 35.6, 11.9 (mean, SD) years. The mean age at onset of the symptoms in the parents was 44.8, 8.2 years, and in the offspring it was 28.7, 7.2 years. In 12 parent-child pairs, the mean anticipation was –15.75, 9.1 years (range –8.1 to –23.3 years, t = –4.9, P = < 0.002). The mutated SCA2 alleles ranged from 38 to 42 CAG repeats, while the normal alleles ranged from 22 to 24 repeats, with 97% of the alleles having 22 repeats. Small differences in the number of CAG repeats influenced the age at onset and rate of progression of the disease considerably. Indeed, patients presenting with their first symptom at an age of 35 years or later with a slower course of the disease harboured between 38 and 39 repeats. In contrast, patients carrying ≥ 40 CAG repeats manifested the disease prior to 30 years of age and had a faster disease progression toward incapacity. The presenting symptom was always gait ataxia. Slow saccades occured from the beginning of the disease despite normal delay, accuracy and smooth pursuit eye movements. The neuropsychological study showed early and selective impairment of conceptual reasoning ability, as detected by the Wisconsin Card Sorting Test (WCST). It is noteworthy that a significant mutual relationship was observed between performance on the WCST and saccade velocity. All of these findings favour the hypothesis that the disease process of SCA2 in regions other than the cerebellum and brain stem affects severely and early those cortical structures involved in the control of both visually guided saccades and WCST performance. Received: 13 October 1997 Received in revised form: 23 February 1998 Accepted: 20 March 1998     

Frequency of spinocerebellar ataxia mutations in patients with multiple system atrophy

Clinical Autonomic Research - Investigate single nucleotide variants and short tandem repeats in 39 genes related to spinocerebellar ataxia in clinical and pathologically defined cohorts of...     

Genotype-phenotype correlation in 667 Chinese families with spinocerebellar ataxia type 3

IntroductionDue to diverse symptoms of spinocerebellar ataxia type 3 (SCA3) and the high prevalence of SCA3 in China, a more in-depth study of Chinese SCA3 patients in a large cohort is well merited.MethodsDuring the last 10 years, 730 patients and 133 premanifest individuals from 667 SCA3 families genetically confirmed to have SCA3 were enrolled from three leading academic hospitals in China. The clinical profile and genotype-phenotype correlation were analyzed.ResultsA quadratic equation best explained the relationship between the logarithmically transformed age at onset (AAO) and expanded CAG repeats (expCAGs) (r² = 0.634, p < 0.001). The expCAG and AAO in Asian populations and western populations were compared with the Chinese population. SCA3 individuals had shorter normal CAG repeats (norCAGs) than healthy controls (Mann-Whitney, p < 0.0001). Most (92.1%) SCA3 patients had gait-ataxia onset. Their AAO and expCAGs were not significantly different from SCA3 patients with non-gait-ataxia onset. Limb ataxia and pyramidal impairment occurred less in patients with disease duration >10 years. Intriguingly, onset after parturition happened in 10 female patients with the AAO of 26.7 ± 4.3 years and the expCAG of 77.4 ± 1.4 repeats. Five out of 12 patients with subtype V and larger expCAGs (78.8 ± 4.8 repeats) suffered from spastic gait initially, and 10 out of 12 showed no limb ataxia. Nystagmus happened most frequently (10.5%) in premanifest individuals.ConclusionWe demonstrated the genotype-phenotype correlation in the largest cohort of SCA3 individuals to date, and interestingly found some new phenomena in Chinese SCA3 individuals.     

Coincident trinucleotide repeat expansions in a patient with myotonic dystrophy type 1 and spinocerebellar ataxia

This is a case report of a patient with confirmed myotonic dystrophy type 1 and spinocerebellar ataxia type 6. The coexistence of two trinucleotide repeat expansions in this family illustrates the importance of continued and vigilant diagnostic inquiry when a patient with a confirmed genetic abnormality has an atypical presentation. The coincidence of two trinucleotide repeat expansions in this patient may suggest an underlying error in DNA metabolism.     

中国大陆南方汉族正常人群齿状核红核苍白球路易体萎缩基因三核苷酸重复变异研究

目的研究中国大陆南方正常人群齿状核红核苍白球路易体萎缩(DRPLA)基因(以CAG)n正常变异范围,以及DRPLA基因(CAG)n扩展突变在中国大陆脊髓小脑型共济失调(SCA)患者中的分布。方法应用荧光PCR,毛细管电泳等技术,对67个已经排除了SCA1、SCA2、SCA3、SCA6、SCA7的常染色体显性遗传SCA家系的先证者和66个散发SCA患者以及94个南方正常汉族人进行DRPLA基因CAG重复次数分析。结果未发现DRPLA基因(CAG)n扩展突变；DRPLA基因(CAG)n正常变异范围为5～21个拷贝,15个拷贝最多见,杂合频率为89．13%,共14种等位基因。结论DRPLA在中国大陆为罕见的SCA亚型,DRPLA基因(CAG)n正常变异范围存在地区和种族差异,中国大陆DRPLA发病率低可能同正常国人较大重复次数的等位基因少见有关。     

Spinocerebellar ataxia type 12 identified in two Italian families may mimic sporadic ataxia

SCA12 is an autosomal dominant cerebellar ataxia characterized by onset in the fourth decade of life with action tremor of arms and head, mild ataxia, dysmetria, and hyperreflexia. The disease is caused by an expansion of ≥51 CAGs in the 5′ region of the brain‐ specific phosphatase 2 regulatory subunit B‐beta isoform (PPP2R2B) gene. SCA12 is very rare, except for a single ethnic group in India. We screened 159 Italian ataxic patients for SCA12 and identified two families that segregated an expanded allele of 57 to 58 CAGs, sharing a common haplotype. The age at onset, phenotype, and variability of symptoms were compatible with known cases. In one family, the disease was apparently sporadic due to possible incomplete penetrance and/or late age at onset. Our data indicate that SCA12 is also present in Italian patients, and its genetic testing should be applied to both sporadic and familial ataxias. © 2010 Movement Disorder Society