中国汉族人群SCA1、2、3、6、7、8、10、12、17亚型和齿状核-红核-苍白球-路易体萎缩亚型频率分布

目的 研究中国汉族人群中脊髓小脑性共济失调(SCAs)不同基因亚型的频率分布.方法 运用聚合酶链反应、变性聚丙烯酰胺凝胶电泳、Southern blot、T载体克隆重组DNA技术结合直接测序等技术对559例临床诊断为SCA的患者(363例常染色体显性遗传先证者,196例散发患者)进行了SCA1、SCA2、SCA3/MJD、SCA6、SCA7、SCA8、SCA10、SCA12、SCA17和齿状核-红核-苍白球-路易体萎缩(DRPLA)致病基因多核苷酸病理重复突变检测分析.结果 在363个常染色体显性遗传的SCA(AD-SCA)家系中,发现有15个SCA1家系(4.13%),26个SCA2家系(7.16%),187个SCA3/MJD家系(51.52%),6个SCA6家系(1.65%),7个SCA7家系(1.93%),1个SCA12家系(0.28%)和1个SCA17家系(0.28%),120个SCA家系未明确基因分型(33.06%);在196例散发SCA患者中,发现有2例SCAI患者(1.02%),3例SCA2患者(1.53%),15例SCA3/MJD患者(7.65%),3例SCA6患者(1.53%),173例SCA患者未明确基因分型(88.27%);未发现SCA8、SCA10和DRPLA型患者.结论 在中国汉族人群中SCA3/MJD为最常见的SCA亚型,其次为SCA2、SCA1、SCA7和SCA6,SCA12和SCA17比较少见,SCA8、SCA10和DRPLA罕见,SCA17亚型为国内首次报道.部分AD-SCA家系存在其他致病基因的作用,大部分散发SCA患者除遗传因素外还存在其他致病因素.     

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.     

Distinct distribution of autosomal dominant spinocerebellar ataxia in the Mexican population.

Dominant ataxias show wide geographic variation. We analyzed 108 dominant families and 123 sporadic ataxia patients from Mexico for mutations causing SCA1-3, 6-8, 10, 12, 17 and DRPLA. Only 18.5% of dominant families remained undiagnosed; SCA2 accounted for half (45.4%), followed by SCA10 (13.9%), SCA3 (12%), SCA7 (7.4%), and SCA17 (2.8%). None had SCA1, 6, 8, 12 or DRPLA. Among sporadic cases, 6 had SCA2 (4.9%), and 2 had SCA17 (1.6%). In the SCA2 patients we identified 6 individuals with the rare (CAG)(33) allele, 2 of whom showed early onset ataxia. The distribution of dominant ataxia mutations in Mexicans is distinct from other populations.     

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.     

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.     

Autosomal dominant cerebellar ataxia: frequency analysis and clinical characterization of 45 families from Portugal

Background and purpose:  The relative frequency of the different autosomal dominant cerebellar ataxia (ADCA) varies widely amongst different geographic locations. Here we describe a series of 45 ADCA families from Portugal.
Methods:  Patients with progressive cerebellar dysfunction of autosomal dominant transmission underwent a clinical examination protocol and genetic testing for spinocerebellar ataxia (SCA)1 to Machado-Joseph disease (MJD)/SCA3, SCA6, SCA7, SCA10, SCA12, SCA17 and dentatorubral-pallidoluysian atrophy (DRPLA). We registered the clinical characteristics and frequency of each type of ataxia.
Results:  MJD/SCA3 was the most frequent ADCA (26 families, 57.8% of all families), followed by DRPLA (5 families, 11.2%), SCA7 (2 families, 4.4%), SCA2 and SCA1 (1 family each, 2.2% each); 10 families (22.2%) had no molecular diagnosis. SCA1 and SCA7 patients had African ancestry. DRPLA patients had Portuguese ancestry and were characterized by prominent anticipation and a variable combination of epilepsy, extra-pyramidal symptoms and dementia. Ophtalmoparesis, slow saccades and retinopathy were most distinctive of SCA3, SCA2 and SCA7 cases, respectively.
Conclusions:  MJD/SCA3 was the most common ADCA in this group of families. The high frequency of DRPLA and presence of SCA1 and SCA7 cases was unexpected. The presence of these rarer ADCA types probably reflects migration phenomena, posing a challenge for differential diagnosis.     

A survey of spinocerebellar ataxia in South Brazil – 66 new cases with Machado-Joseph disease, SCA7, SCA8, or unidentified disease–causing mutations

Background The autosomal dominant spinocerebellar ataxias (SCAs) are a clinical and genetically heterogeneous group of debilitating, neurodegenerative diseases, related to fourteen different loci– SCAs 1, 2, 4, 5, 6, 7, 8, 10, 11, 12, 13 and 14, Machado-Joseph disease (MJD/SCA 3), and DRPLA. Objectives (1) to verify the frequency of SCA1, SCA2, MJD, DRPLA, SCA6, SCA7 and SCA8 in a series of new SCA patients from South Brazil and (2) to compare their molecular and clinical characteristics with other patients previously described. Methods sixty-six cases were included in the present study: 52 were familial and 14 sporadic. Molecular analysis of the trinucleotide repeat loci were performed according to methods in the literature. Results 92 % of families with autosomal dominant inheritance segregated the MJD1 mutation, 2 % of families segregated the SCA7 mutation and 6 % remained undiagnosed. Among 14 isolated cases, one showed the SCA8 mutation. Clinical and molecular findings were similar to those already described in the literature, but revealed (1) one SCA7 patient with eyelid retraction, a sign usually related to MJD; and (2) one sporadic case of SCA8. Conclusions The proportion of MJD cases was very high, probably reflecting an Azorean founder effect. The estimated frequency of affected individuals with MJD, in our region, was 1.8 / 100,000, and of SCAs other than MJD, 0.2/100,000. Received: 13 February 2001, Received in revised form: 6 April 2001, Accepted: 9 April 2001     

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.     

Prevalence of triplet repeat expansion in ataxia patients from Hokkaido, the northernmost island of Japan

Approximately 44% of cases of spinocerebellar ataxia (SCA) in Hokkaido, the northernmost island of Japan, were estimated to be inherited. To determine the prevalence of triplet repeat expansion in hereditary SCA patients, we genotyped seven genetically defined dominant SCAs in 349 patients, including 266 patients from 77 families, 78 probands from unrelated families with hereditary late-onset SCA, and five patients in whom a family history of SCA was not demonstrated. The frequency of each disorder in a total of 155 unrelated families was 23.9% for Machado-Joseph disease (MJD), 29.0% for SCA6, 9.7% for SCA1, 7.7% for SCA2, and 2.6% for dentatorubral-pallidoluysian atrophy. Abnormal expansion of triplet repeats for SCA7 and SCA8 was not detected. A total of 27.1% of the patients had still unknown SCA mutations. In addition, the GAA repeat in the frataxin gene was not abnormally expanded in 13 early-onset SCA patients with clinical features similar to those of Friedreich ataxia. Comparison of our results with those from other centers handling SCA showed that MJD is prevalent throughout Japan, but the frequencies of other dominant SCAs differ considerably even within Japan.     

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.     

Analysis of spinocerebellar ataxias due to expanded triplet repeats in Greek patients with cerebellar ataxia

The relative frequency of different autosomal dominant cerebellar ataxias, commonly referred to as spinocerebellar ataxias (SCAs), varies considerably among populations of different ethnic origin. No data exist at present on the frequency of different SCAs in the Greek population. In the present study we investigated the presence of triplet repeat expansion SCAs (SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, SCA12, SCA17 and DRPLA) in a cohort of 83 Greek patients with slowly progressive cerebellar ataxia. Twenty patients came from autosomal dominant (AD) pedigrees, seven displayed recessive or unclear inheritance and 56 were sporadic. We found four patients with pathological SCA expansions, all from AD pedigrees. Two patients had SCA1, one SCA2 and one SCA7 (10.0, 5.0 and 5.0% of the AD group, respectively). The clinical features of these patients were within the expected spectrum. In total, a pathological expansion was detected in 20% of patients from AD pedigrees. Interestingly, no cases of SCA3 or SCA6 were detected in the AD group. No expansions were found in other familial cases or in sporadic patients. Overall, no cases of SCA3, SCA6, SCA12, SCA17 or DRPLA were identified in the Greek population. In conclusion, SCA1, SCA2 and SCA7 are present in Greek patients with AD cerebellar ataxia in frequencies similar to those observed in other populations. SCA3 and SCA6 appear however to be rare in Greece. The genetic cause for the majority of AD ataxias remains to be identified.     

Dentatorubro-Pallidoluysian Atrophy (DRPLA) among 700 Families with Ataxia in Brazil

Dentatorubro-pallidoluysian atrophy (DRPLA) is a spinocerebellar ataxia (SCA) very rare in non-Asian populations. To date, DRPLA was undetected in the general Brazilian population. Adult-onset ataxic patients have been recruited from several Brazilian neurology and neurogenetics centers. CAG lengths at SCA1, SCA2, SCA3/MJD, SCA6, SCA7, SCA12, SCA17 and DRPLA associated genes, and ATTCT expansions at SCA10 gene were studied. A single DRPLA case detected is reported. Proband was a 69-year-old Brazilian woman of mixed ancestry, with a late-onset pure ataxia: her alleles at the associated gene, ATN1, presented 14/52 CAG repeats. History of gait ataxia and dementia was observed in two out of six siblings but was absent in her parents. This was the single DRPLA diagnosis obtained from 700 Brazilian unrelated cases with adult-onset ataxia, 487 of them with clear autosomal dominant inheritance. DRPLA accounted for 0.14% of all adult-onset ataxia cases and for 0.2% of families with autosomal dominant inheritance. Normal CAG repeats at ATN1 had a median (range) of 14 (5–20) repeats in other 410 Brazilian chromosomes. DRPLA is quite rare in Brazilian SCA families, which is consistent with the lack of large normal alleles in our population.     

Spinocerebellar ataxia type 17 in the Yugoslav population

OBJECTIVES: (1) Analysis of Spinocerebellar ataxia type 17 (SCA17) locus in a group of ataxic patients excluded on other known SCAs; (2) assessment of frequency distributions of SCA17 alleles in the Yugoslav population. MATERIAL AND METHODS: Study includes 115 non-related Yugoslav patients belonging to autosomal-dominant cerebellar ataxias or to sporadic idiopathic adult-onset ataxia and 115 controls. Analysis of SCA17 locus was performed using polymerase chain reaction. RESULTS: None of the analyzed patients show the presence of mutation in SCA17 locus. In the group of patients 12 different alleles in the range of 30-42 repeats were observed, while in healthy population eight alleles in the range of 30-40 repeats were detected. CONCLUSION: (1) None of 115 non-related Yugoslav ataxic patients belong to any known SCAs nor to DRPLA gene; (2) the distribution of SCA17 alleles in the Yugoslav population is consistent with the distribution in other populations and (3) the paucity of alleles with more than 39 repeats could suggest that SCA17 is very rare in the Yugoslav population.     

宁夏地区回、汉族脊髓小脑共济失调家系SCA3/MJD基因突变研究

目的通过对宁夏地区临床诊断为脊髓小脑共济失调的3个家系(2个汉族家系、1个回族家系)进行SCA3/MJD基因检测,探讨脊髓小脑共济失调的发病机制与临床特点,以为临床应用提供依据。方法对3家系受试者进行神经系统检查和系谱调查,部分行头部MRI和肌电图检查,以及SCA3/MJD基因胞嘧啶-腺嘌呤-鸟嘌呤(CAG)重复数目检测。结果3家系中共计8例脊髓小脑共济失调患者(汉族家系1中6例、汉族家系2中1例和回族家系中1例),符合常染色体显性遗传特点,以共济失调与构音障碍为主要表现,其次为眼外肌麻痹、眼球震颤、慢眼动、锥体束征等。其中汉族家系1和回族家系明确诊断为SCA3/MJD家系,两家系中7例患者(汉族家系1中6例、回族家系中1例)及2例临床表型正常亲属(两家系中各1例)检测出SCA3/MJD异常等位基因,其CAG重复数目为66～81次。汉族家系2中1例患者及汉族家系1中4例临床表型正常亲属SCA3/MJD基因CAG重复数目为20～33次。正常等位基因与异常等位基因CAG重复数目差异有统计学意义(t=5.309,P=0.000)。结论宁夏地区回、汉族脊髓小脑共济失调患者中存在SCA3/MJD基因型,基因检测分析有利于明确诊断脊髓小脑共济失调且能够检出症状前患者。     

Autosomal dominant cerebellar ataxia type I in Morocco: presence of the SCA1 and SCA3/MJD mutations

We searched for CAG repeat expansions at the SCA1 and SCA3/MJD loci in nine families, including 15 examined patients, with autosomal dominant cerebellar ataxia type I from Morocco. Expansion of the CAG repeat was found in one family at the SCA1 and two at the SCA3/MJD locus, demonstrating the existence of genetic heterogeneity among ADCA type I families in Morocco. Instability during transmission was observed at both loci as in other unstable mutations. The phenotypes of the SCA1 and SCA3/MJD patients were similar.     

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.     

High prevalence of spinocerebellar ataxia type 1 (SCA1) in an isolated region of Japan

Autosomal dominant cerebeller ataxias (ADCAs) are a heterogeneous group of neurodegenerative disorders that differ in both the clinical manifestations and modes of inheritance. At present, eight different genes causing ADCAs have been found: spinocerebeller ataxia type 1 (SCA1), SCA2, SCA3/Machado-Joseph disease (MJD), SCA6, SCA7, SCA8, SCA12 and dentatorubropallidoluysian atrophy (DRPLA). The relative prevalence of each mutation varies according to race and native place. We studied 117 unrelated ADCA families that originated from the Tohoku District in the northernmost part of Honshu Island in Japan (mainly Miyagi Prefecture in the central part of Tohoku District). The SCA1 mutation was the most frequent among the known disorders (24.8% of all such families). The relative prevalence of SCA1 in the Tohoku District is very high compared with the values already reported from other regions in the world. Because the population of this area had seldom moved, the alleles with SCA1 mutations (including alleles with an intermediate CAG repeat number) are assumed to have been present in this area for a long time.     

Regional differences in genetic subgroup frequency in hereditary cerebellar ataxia, and a morphometrical study of brain MR images in SCA1, MJD and SCA6.

Molecular genetic assessments of 69 individuals in 44 families with hereditary cerebellar ataxia (HCA) were made to determine the relative frequencies of subtypes of HCA in Yamagata, Japan. Fifteen families (34%) had SCA1, none had SCA2, nine (20%) had MJD, five (11%) had SCA6 and nine (20%) had DRPLA. These findings differ markedly from those in other regions of Japan and the rest of the world. A morphometrical study of the brain MR images also was made on 38 individuals with SCA1 (n = 14), MJD (n = 8) or SCA6 (n = 16). In SCA1, the ventral pons was atrophic in proportion to the amount of cerebellar atrophy. In MJD, both the pons and the cerebellum were atrophic, cerebellar atrophy being less pronounced than that in SCA1 and SCA6. While both the major and minor axes of the ventral pons were proportionally decreased in SCA1, the minor axis was more decreased than the major axis in MJD. In SCA6, a mild reduction in the ratio of the ventral pontine area to the posterior fossa area (Pv/PF) was observed as well as obvious cerebellar atrophy. These findings indicate that in MR images SCA1, MJD and SCA6 show different atrophic features of the cerebellum and brainstem.     

Differential diagnosis of spinocerebellar ataxia]

Spinocerebellar ataxia (SCA) is a group of heterogeneous disorders. In Japan, approximately 60% of SCA consist of sporadic disorders, and the rest mostly consists of a variety of late-onset dominant disorders. In the latter, MJD, SCA6, DRPLA, SCA1 and SCA2 are frequent in this order, and others are rare. All these disorders are caused by unstable expansion of CAG repeat in the coding region of each responsible gene. Among those disorders, SCA6 manifests late-onset pure cerebellar ataxia and frequently associated with positioning vertigo. In other disorders, phenotype variation, clinical severity, and onset of age are known to correlate inversely with the CAG repeat size. Such variation even in a given disorder is often difficult to apply single criteria to diagnose the disorder based on its clinical findings alone. MSA is a major disorder of sporadic SCA. Signs of cerebellar ataxia, parkinsonism, autonomic disturbance are incorporated into current diagnostic criteria. However, cases meeting the criteria of autonomic disturbances are confined to the advanced stage of the illness or rare cases starting with obvious dysautonomia. These problems indicate that the criteria need further adjustment.     

Trinucleotide repeats in 202 families with ataxia: a small expanded (CAG)n allele at the SCA17 locus

BACKGROUND: Ten neurodegenerative disorders characterized by spinocerebellar ataxia (SCA) are known to be caused by trinucleotide repeat (TNR) expansions. However, in some instances the molecular diagnosis is considered indeterminate because of the overlap between normal and affected allele ranges. In addition, the mechanism that generates expanded alleles is not completely understood. OBJECTIVE: To examine the clinical and molecular characteristics of a large group of Portuguese and Brazilian families with ataxia to improve knowledge of the molecular diagnosis of SCA. PATIENTS AND METHODS: We have (1) assessed repeat sizes at all known TNR loci implicated in SCA; (2) determined frequency distributions of normal alleles and expansions; and (3) looked at genotype-phenotype correlations in 202 unrelated Portuguese and Brazilian patients with SCA. Molecular analysis of TNR expansions was performed using polymerase chain reaction amplification. RESULTS: Patients from 110 unrelated families with SCA showed TNR expansions at 1 of the loci studied. Dominantly transmitted cases had (CAG)(n) expansions at the Machado-Joseph disease gene (MJD1) (63%), at SCA2 (3%), the gene for dentatorubropallidoluysian atrophy (DRPLA) (2%), SCA6 (1%), or SCA7 (1%) loci, or (CTG)(n) expansions at the SCA8 (2%) gene, whereas (GAA)(n) expansions in the Freidreich ataxia gene (FRDA) were found in 64% of families with recessive ataxia. Isolated patients also had TNR expansions at the MJD1 (6%), SCA8 (6%), or FRDA (8%) genes; in addition, an expanded allele at the TATA-binding protein gene (TBP), with 43 CAGs, was present in a patient with ataxia and mental deterioration. Associations between frequencies of SCA2 and SCA6 and a frequency of large normal alleles were found in Portuguese and Brazilian individuals, respectively. Interestingly, no association between the frequencies of DRPLA and large normal alleles was found in the Portuguese group. CONCLUSIONS: Our results show that (1) a significant number of isolated cases of ataxia are due to TNR expansions; (2) expanded DRPLA alleles in Portuguese families may have evolved from an ancestral haplotype; and (3) small (CAG)(n) expansions at the TBP gene may cause SCA17.