Relative frequencies of CAG expansions in spinocerebellar ataxia and dentatorubropallidoluysian atrophy in 116 Italian families

Two hundred and forty-eight patients from 116 Italian families with dominant ataxia were studied for CAG expansion within SCA1, 2, 3, 6, 7 (spinocerebellar ataxia) and DRPLA (dentatorubropallidoluysian atrophy) genes. Fifty-six percent of the families originated from Southern, 19% from Central and 25% from Northern Italy. SCA2 was the commonest mutation, accounting for 47% of the families, followed by SCA1 (24%), SCA6 (2%), SCA7 (2%) and DRPLA (1%). No SCA3 family was found. Twenty-four percent of the families carried a still unidentified mutation. When occurrence of mutations was evaluated according to the geographic origin, SCA1 was the commonest in Northern (72%), whereas SCA2 was prevalent (63%) in Southern Italy. The number of CAG repeats in SCA1 normal alleles was higher in Northern than in Central-Southern Italy.     

两遗传性脊髓小脑型共济失调7型家系的临床特征和基因突变研究

目的 探讨遗传性脊髓小脑型共济失调(SCA)7型(SCA7)的临床特征和基因突变.方法 采用聚合酶链反应(PCR)和琼脂糖凝胶电泳(AGE)等技术,检测临床诊断为SCA的5个家系26例患者和37例表型正常的家系成员的SCA7基因内CAG三核苷酸重复次数,对异常等位基因片段进行DNA测序,分析临床表现和基因突变的关系. 结果 2个SCA7家系患者的SCA7等位基因内CAG重复数目为44～50次;临床表现主要为共济失调、视力下降及视网膜色素变性.该家系内表型正常的家系成员SCA7等位基因CAG重复数目为10～30. 结论 CAG过度扩增为SCA7的致病原因,分子遗传学分析有助于SCA7的诊断.     

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.     

Clinical features and ATTCT repeat expansion in spinocerebellar ataxia type 10

BACKGROUND: Spinocerebellar ataxia type 10, an autosomal dominant disease characterized by ataxia and seizures, is caused by a large expansion of an unstable ATTCT pentanucleotide repeat. OBJECTIVES: To characterize the phenotypic expression of spinocerebellar ataxia type 10 and to examine the genotype-phenotype correlations in 2 large families. DESIGN: Clinical characterization and genotype-phenotype correlation. SETTING: Studies at 2 medical schools with private practice referral. PATIENTS: Twenty-two affected individuals from 2 large Mexican American pedigrees. RESULTS: Of the 22 individuals, ataxia was the initial symptom in 21; seizure disorders developed in 11, mostly within several years following the onset of ataxia. The seizure frequency was different in the 2 families: 3 (25%) of 12 had seizures in family 1, and 8 (80%) of 10 had seizures in family 2 (P =.01). A brain magnetic resonance imaging or computed tomographic scan showed cerebellar atrophy in all patients examined. An electroencephalogram demonstrated epileptiform discharges in 4 of 8 patients studied. Although anticipation was apparent in both families, only family 1 showed a strong inverse correlation between age of onset and repeat number (r(2) = 0.79, P =.001). In family 1, 8 transmissions, of which 7 were paternal, resulted in an average gain of 1940 repeats. In contrast, despite anticipation, 2 affected male subjects transmitted their expanded alleles to 8 progenies, with an average loss of 755 repeats, in family 2. CONCLUSIONS: Seizure is an integral part of the spinocerebellar ataxia type 10 phenotype, with documented morbidity and mortality. Family-dependent factors may alter the frequency of the seizure phenotype and the pattern of intergenerational repeat size changes, making the genotype-phenotype correlation complex.     

遗传性脊髓小脑型共济失调患者SCA1基因突变检测分析

检测中国人遗传性脊髓小脑型共济失调（ＳＣＡ）患者的ＳＣＡ１基因突变［（ＣＡＧ）ｎ］。方法应用聚合酶链（ＰＣＲ）技术，检测了２７个ＳＣＡ家系中４４例ＳＣＡ患者的ＳＣＡ１（ＣＡＧ）ｎ。结果首次发现１个家系２例患者及１位“正常者”均有１个ＳＣＡ１异常等位基因扩增片段。患者Ⅲ５与其１位兄弟（“正常者”）的异常等位基因扩增片段，长度为２７２ｂｐ，三核苷酸ＣＡＧ重复数为５３次，患者Ⅲ２的异常等位基因扩增片段，长度为２９９ｂｐ，ＣＡＧ重复数为６２次，均超出正常范围。另２６个家系４２例患者的等位基因扩增片段长度范围在１６４～２１８ｂｐ之间，ＣＡＧ重复数在１７～３５次间，属于正常范围。结论来自１家系２例ＳＣＡ患者的基因分型为ＳＣＡ１型，“正常者”可能是未到发病年龄的无症状ＳＣＡ１患者，余２６个家系４２例患者不是ＳＣＡ１型。     

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.     

CTG18.1 and ERDA-1 CAG/CTG repeat size in bipolar disorder.

Several groups have reported association between large CAG/CTG repeat sequences in the genome and bipolar disorder using the Repeat Expansion Detection (RED) method. Unfortunately, the RED method cannot identify the specific repeat(s) responsible for these findings but it has recently been proposed that around 90% of the large CAG/CTG repeats detected by RED can be explained by repeat size at either CTG18.1, which maps to 18q21.1, or ERDA-1 (also known as Dir 1), which maps to 17q21.3. These data suggest that the previous associations between bipolar disorder and large CAG/CTG repeats might be explained at least in part by a specific association between bipolar disorder and either or both of these loci. However, using a case control study design, we find no evidence for such associations. Thus we conclude that in our sample, the previous RED associations are not a result of large CAG/CTG repeats at CTG18.1 or ERDA-1.     

遗传性脊髓小脑型共济失调7型一家系的临床及基因突变分析

目的研究中国人遗传性脊髓小脑型共济失调7型(SCA7)的基因突变和临床特征。方法应用聚合酶链反应(PCR)、聚丙烯酰胺凝胶电泳(PAGE)等技术对一个表现为共济失调、视力下降、视网膜变性的家系(6位成员,包括2个患者)的SCA7基因内CAG三核苷酸重复序列进行检测,并对异常等位基因片段进行DNA直接测序,分析基因型和表型之间的关系。结果检测出该家系内2个患者的SCA7等位基因CAG重复数目为71,而该家系内其他表型正常的SCA7等位基因CAG重复数目为7～9。结论CAG过度扩增为SCA7的致病原因,分子遗传学分析有助于SCA7的诊断以及症状前患者的预测。     

Clinical and genetic findings in Finnish ataxia patients with the spinocerebellar ataxia 8 repeat expansion

Spinocerebellar ataxia 8 (SCA8) is caused by a CTG repeat expansion in an untranslated region of a recently cloned gene on 13q21. The pathogenic role of this trinucleotide repeat was evaluated by examining 154 Finnish ataxia patients and 448 controls. Expansions ranging from 100 to 675 repeats were present in 9 (6%) unrelated patients and in 13 (3%) controls. There was a threefold excess of shorter expansions (<204 repeats) in the ataxia series, and the expansions tended to cluster in patients with a family history for the disease. Clinical and genetic data were subsequently collected from 15 patients. Common initial symptoms included gait instability, dysarthria, and tremor. A marked cerebellar atrophy in magnetic resonance imaging or computed tomography was found in all patients. Pyramidal affection was often seen, and various kinds of cognitive impairment were evident in 40% of patients. Disease progression was slow, and fluctuation of symptoms was commonly observed. A maternal penetrance bias was not seen, nor was there any clear-cut negative correlation between age of onset and repeat number. Meiotic but not mitotic instability of the repeat expansion was evident. Haplotype analysis suggests multiple origins for the Finnish spinocerebellar ataxia 8 repeat expansions.     

遗传性脊髓小脑型共济失调6型两个家系的临床特征及基因突变研究

目的 研究中国人遗传性脊髓小脑型共济失调6型(SCA6)的基因突变和临床特征。方法 应用聚合酶链反应(PCR)、聚丙烯酰胺凝胶电泳(PAGE)等技术，检测临床诊断脊髓小脑型共济失调(SCA)的120个家系210例患者和47例散发SCA患者的SCA6基因内CAG三核苷酸重复序列，并对异常等位基因片段进行DNA测序。结果 检出2个家系(4例患者)为SCA6，阳性率为1，7％，测序证实其异常等位基因的CAG重复数目为25和26。另253例SCA患者的SCA6等位基因CAG重复数目为7-17，健康人SCA6等位基因CAG重复数目为5-16。2个家系均存在遗传早现现象，异常扩展的CAG序列呈代间稳定性。结论 从临床及基因诊断方面首次确认中国大陆存在SCA6家系；CAG过度扩增为SCA6的致病原因。     

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     

马查多-约瑟夫病/脊髓小脑型共济失调Ⅲ型患者(CAG)n拷贝数与临床特征

目的探讨马查多约瑟夫病基因１（ＭＪＤ１）ＣＡＧ三核苷酸动态突变及其拷贝数与ＭＪＤ／脊髓小脑型共济失调Ⅲ型（ＳＣＡ３）患者临床特征的相关关系。方法应用聚合酶链式反应、变性聚丙烯酰胺凝胶电泳和银染技术,对９个ＭＪＤ／ＳＣＡ３家系１０９名成员进行ＭＪＤ１基因（ＣＡＧ）ｎ拷贝数分析。结果发现异常扩增的（ＣＡＧ）ｎ拷贝数与发病年龄呈负相关,并在一定程度上影响病情严重程度;主要临床症状、体征与异常扩增的（ＣＡＧ）ｎ拷贝数无关,而是受病程影响。同时发现１７例症状前患者。结论异常扩增的（ＣＡＧ）ｎ拷贝数对疾病表型有影响,但不能完全作为临床特征的预测指标     

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 of SCA1, SCA2, SCA3/MJD, SCA6, SCA7, and DRPLA CAG trinucleotide repeat expansion in patients with hereditary spinocerebellar ataxia from Chinese kindreds

OBJECTIVE: To assess the frequency of SCA1 (spinocerebellar ataxia type 1), SCA2, SCA3/MJD (spinocerebellar ataxia type 3/Machado-Joseph disease), SCA6, SCA7, and DRPLA (dentatorubropallidoluysian atrophy) CAG trinucleotide repeat expansions [(CAG)n] among persons diagnosed with hereditary SCA from Chinese families. PATIENTS AND METHODS: Spinocerebellar ataxia type 1, SCA2, SCA3/MJD, SCA6, SCA7, and DRPLA (CAG)n mutation were detected with the polymerase chain reaction, highly denaturing polyacrylamide gel electrophoresis, and silver staining technique in 167 patients with autosomal dominant SCA from 85 Chinese families and 37 patients with sporadic SCA. RESULTS: Spinocerebellar ataxia type 1 (CAG)n mutation in 7 patients from 4 kindreds (4.70%) was expanded to 53 to 62 repeats. Spinocerebellar ataxia type 2 (CAG)n mutation in 12 patients from 5 kindreds (5.88%) was expanded to 42 to 47 repeats. Spinocerebellar ataxia type 3/Machado-Joseph disease (CAG)n mutation in 83 patients from 41 kindreds (48.23%) was expanded to 68 to 83 repeats. Sixty-five patients from 35 kindreds (41.19%) and 37 patients with sporadic SCA did not test positive for SCA1, SCA2, SCA3/MJD, SCA6, SCA7, or DRPLA. There was a predictable inverse relationship between the number of CAG repeats and the age at onset for SCA3/MJD and SCA2. Clinically, dementia and hyporeflexia were more frequent in patients with SCA2, while spasticity, hyperreflexia, and Babinski signs were more frequent in patients with SCA3/ MJD, and those might be helpful in clinical work to primarily distinguish patients with SCA3/MJD and SCA2 from others with different types of SCA. CONCLUSIONS: The frequency of SCA3/MJD is substantially higher than that of SCA1 and SCA2 in patients with autosomal dominant SCA from Chinese kindreds, who are non-Portuguese. Clinical expressions of the various types of SCAs overlap one another; therefore, for clinical study it is important to make a gene diagnosis and genetic classification for patients with SCA.