Clinical characteristics of combined cases of spinocerebellar ataxia types 6 and 31

This study reports the first family in which spinocerebellar ataxia type 6 (SCA6) and spinocerebellar ataxia type 31 (SCA31) mutations were seen. An index patient first presented to our hospital due to gait and speech disturbances. Subsequent clinical investigation of this patient and her family members revealed consistent pure cerebellar ataxia transmitted in an autosomal-dominant manner. Genetic examination unexpectedly demonstrated that two of the five affected individuals had expansions of SCA6 and SCA31, while two others had SCA31 alone and the remaining had SCA6. Clinical manifestations were more severe in individuals with combined mutations relative to those with single mutation, suggesting that the SCA6 and SCA31 mutations have a cumulative pathogenic effect.     

一个遗传性脊髓小脑型共济失调大家系的致病基因分析

目的探讨一个遗传性脊髓小脑型共济失调（SCA）大家系的遗传特点和基因突变分析。方法对一个遗传性脊髓小脑型共济失调（SCA）大家系进行家系调查,绘制系谱图,抽取家系成员外周血,采用聚合酶链反应和毛细管电泳对致病基因进行分析检测。结果该家系的遗传性脊髓小脑型共济失调（SCA）为常染色体显性遗传,6代45人中有15人为SCA患者,4人为携带致病基因的无症状患者。患者ATX3基因的CAG三核苷酸重复65-73次。结论该家系为常染色体显性遗传的SCA3型（SCA/MJD）,患者基因突变检测分析显示异常扩增的CAG突变数与发病年龄呈明显的负相关。基因突变检测在疾病诊断和早期发现无症状患者方面有重要作用,从遗传生殖角度阻断该病的遗传有重要意义。     

A Novel GBA2 Gene Missense Mutation in Spastic Ataxia

Autosomal recessive cerebellar ataxias (ARCA) encompass a heterogeneous group of rare diseases that affect the cerebellum, the spinocerebellar tract and/or the sensory tracts of the spinal cord. We investigated a consanguineous Cypriot family with spastic ataxia, aiming towards identification of the causative mutation. Family members were clinically evaluated and studied at the genetic level. Linkage analysis at marker loci spanning known ARCA genes/loci revealed linkage to the APTX locus. Thorough investigation of the APTX gene excluded any possible mutation. Whole genome linkage screening using microsatellite markers and whole genome SNP homozygosity mapping using the Affymetrix Genome‐Wide Human SNP Array 6.0 enabled mapping of the disease gene/mutation in this family to Chromosome 9p21.1‐p13.2. Due to the large number of candidate genes within this region, whole‐exome sequencing of the proband was performed and further analysis of the obtained data focused on the mapped interval. Further investigation of the candidate variants resulted in the identification of a novel missense mutation in the GBA2 gene. GBA2 mutations have recently been associated with hereditary spastic paraplegia and ARCA with spasticity. We hereby report a novel GBA2 mutation associated with spastic ataxia and suggest that GBA2 mutations may be a relatively frequent cause of ARCA.     

脊髓小脑性共济失调12型维吾尔族一家系的基因突变及临床特点

目的 研究新疆地区维吾尔族脊髓小脑性共济失调12亚型(spinocerebellar ataxia type 12,SCA12)致病基因的CAG三核苷酸病理重复次数范围及临床特点.方法 依据Harding标准,收集一个维吾尔族家系,应用聚合酶链反应、琼脂糖凝胶电泳、T载体分子克隆技术并结合酶切鉴定、直接测序等技术对其中6例患者、54例家系"健康"个体进行分子遗传学诊断,基因诊断为SCA12型,同时对致病基因CAG三核苷酸病理重复次数进行突变分析.结果 发现该家系SCA12型患者6例,症状前患者13例.5例经基因重组检测发现:患者异常等位基因CAG重复数目分别是47次、51次、52次、53次;症状前患者是48次;其中在连续CAG重复中间有单个碱基C、A、G的互相替换.结论 SCA12型的47次CAG病理重复次数为国内外报道的最小CAG病理重复次数;国内首次对维吾尔族SCA12型的基因突变特点进行分析,从而对于该类疾病的准确分类、病因探讨、治疗、产前诊断等具有重要的意义.     

脊髓小脑性共济失调12型维吾尔族一家系的基因突变及临床特点

目的 研究新疆地区维吾尔族脊髓小脑性共济失调12亚型(spinocerebellar ataxia type 12,SCA12)致病基因的CAG三核苷酸病理重复次数范围及临床特点.方法 依据Harding标准,收集一个维吾尔族家系,应用聚合酶链反应、琼脂糖凝胶电泳、T载体分子克隆技术并结合酶切鉴定、直接测序等技术对其中6例患者、54例家系"健康"个体进行分子遗传学诊断,基因诊断为SCA12型,同时对致病基因CAG三核苷酸病理重复次数进行突变分析.结果 发现该家系SCA12型患者6例,症状前患者13例.5例经基因重组检测发现:患者异常等位基因CAG重复数目分别是47次、51次、52次、53次;症状前患者是48次;其中在连续CAG重复中间有单个碱基C、A、G的互相替换.结论 SCA12型的47次CAG病理重复次数为国内外报道的最小CAG病理重复次数;国内首次对维吾尔族SCA12型的基因突变特点进行分析,从而对于该类疾病的准确分类、病因探讨、治疗、产前诊断等具有重要的意义.     

脊髓小脑性共济失调12型维吾尔族一家系的基因突变及临床特点

目的 研究新疆地区维吾尔族脊髓小脑性共济失调12亚型(spinocerebellar ataxia type 12,SCA12)致病基因的CAG三核苷酸病理重复次数范围及临床特点.方法 依据Harding标准,收集一个维吾尔族家系,应用聚合酶链反应、琼脂糖凝胶电泳、T载体分子克隆技术并结合酶切鉴定、直接测序等技术对其中6例患者、54例家系"健康"个体进行分子遗传学诊断,基因诊断为SCA12型,同时对致病基因CAG三核苷酸病理重复次数进行突变分析.结果 发现该家系SCA12型患者6例,症状前患者13例.5例经基因重组检测发现:患者异常等位基因CAG重复数目分别是47次、51次、52次、53次;症状前患者是48次;其中在连续CAG重复中间有单个碱基C、A、G的互相替换.结论 SCA12型的47次CAG病理重复次数为国内外报道的最小CAG病理重复次数;国内首次对维吾尔族SCA12型的基因突变特点进行分析,从而对于该类疾病的准确分类、病因探讨、治疗、产前诊断等具有重要的意义.

Abstract：

Objective To investigate the CAG trinucleotide repeat expansion and clinical characteristics of a Chinese Uygur family with spinocerebellar ataxia type 12 (SCA12) in Xinjiang Uygur Autonomous Region. Methods In the Uygur SCA12 family, 6 patients and 54 "healthy" members were analyzed by polymerase chain reaction, agarose gel electrophoresis, recombinant DNA technology by T-Vector cloning and restriction enzyme digestion, and direct sequencing. The diagnosis of SCA12 was confirmed. The CAG trinucleotide expansion was also analyzed. Results Six members in the family were diagnosed as SCA12 patients and 13 were presymptomatic. Five of them were successfully detected by sequencing. The CAGrepeat numbers of 4 patients were 47, 51, 52 and 53, respectively, and 48 in the presymptomatic patient.We also observed that in the CAG repeat region there was replacement of single nucleotide C, A or G.Conclusion Forty-seven CAG repeats of SCA12 has been reported as the shortest known causative expanded alleles. The present study is the first report of the characteristics of SCA12 gene mutation in Chinese. It will provide basis for the accurate classification, disease etiology, treatment and prenatal diagnosis of this disease.     

Early onset and slow progression of SCA28, a rare dominant ataxia in a large four-generation family with a novel AFG3L2 mutation

Autosomal dominantly inherited spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders primarily affecting the cerebellum. Genetically, 26 different loci have been identified so far, although the corresponding gene has not yet been determined for 10 of them. Recently, mutations in the ATPase family gene 3-like 2 gene were presented to cause SCA type 28. To define the frequency of SCA28 mutations, we performed molecular genetic analyses in 140 unrelated familial cases with ataxia. Among other variations, we found a novel missense mutation at an evolutionarily conserved amino-acid position using a single-strand conformation polymorphism approach, followed by DNA sequencing. This amino-acid exchange p.E700K was detected in a four-generation German family and was not observed in a survey of 400 chromosomes from healthy control individuals.     

东北地区正常汉族人群 SCA1及 SCA3/MJD基因内CAG重复变异研究

目的　对东北地区 110名汉族正常人 SCA1及 SCA3/ MJD基因 (CAG) n拷贝进行检测 ,探讨其正常变异范围 ,并对临床诊断为遗传型脊髓小脑共济失调的 8个家系的 2 5例患者和 6个散发病例进行基因分型评价和症状前及产前诊断。方法　应用荧光 - PCR方法测定不同基因型片段长度 ,并进行 DNA序列分析。结果　 SCA3/ MJD基因 (CAG) n正常变异范围为 14～ 38个拷贝 ,集中于 14个拷贝 ,其等位基因频率为 39.5 5 % ,杂合频率为 78.18% ,共 13种等位基因。检出一个家系先证者携带有 (CAG) 6 8的 SCA3/ MJD基因 ,并对该家系成员进行了症状前诊断 ,没有发现 (CAG) n拷贝异常突变 ;SCA1基因内 (CAG) n正常变异范围 2 0～ 39拷贝 ,集中于 2 6及 2 7次 ,等位基因频率分别为 34.0 9%和 2 0 .91% ,杂合频率为 84 .5 5 % ,共 13种等位基因 ;散发病例未检出 CAG扩展性突变。结论　 SCA1及 SCA3/ MJD基因中 (CAG) n正常变异范围存在地区和种族差异 ,SCAs基因分型是该病症状前及产前诊断的首选策略。     

Analysis of spinocerebellar ataxia types 1, 2, 3, and 6, dentatorubral-pallidoluysian atrophy, and Friedreich''s ataxia genes in spinocerebellar ataxia patients in the UK.

Accurate clinical diagnosis of the spinocerebellar ataxias (SCAs) can be difficult because of overlap in phenotype with other disorders and variation in clinical manifestations. Six SCA loci have been mapped and four disease causing genes identified, in addition to the causative gene for Friedreich's ataxia (FA). All of the identified mutations are expansions of trinucleotide repeat tracts. The SCA2 and SCA6 genes were published recently. The extent of the normal CAG size ranges at these loci and the relative frequencies of the known causes of SCA in the UK are not known. This study first investigated the normal size ranges of the SCA2 and SCA6 loci by genotyping control populations of West African and South African subjects, since African populations generally show the greatest allelic diversity. We found one allele larger than the previously determined normal range for SCA2, and our results at the SCA6 locus agreed with the previously reported normal range. The second component of the study assessed the relative frequencies of the SCA1, 2, 3, and 6, DRPLA, and FA trinucleotide repeat mutations in 146 patients presenting with SCA-like symptoms referred to genetic diagnostic laboratories in the UK. We detected mutations in 14% of patients referred with a diagnosis of autosomal dominant SCA, and in 15% of patients referred with spinocerebellar ataxia where we did not have sufficient family history data available to allow categorisation as familial or sporadic cases. Friedreich's ataxia accounted for 3% of the latter category of cases in our sample, but the most common causes of SCA were SCA2 and SCA6.     

Spinocerebellar ataxia type 6 and episodic ataxia type 2 in a Korean family.

Spinocerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2) and familial hemiplegic migraine (FHM) have been known as allelic disorders, which are caused by the alteration of the alpha1A voltage-dependent calcium channel subunit. Expansions of the CAG repeat in the CACNA1A gene on the short arm of the chromosome 19 induce SCA6, and point mutations in the same gene are responsible for EA2 and FHM. In recent studies, both SCA6 and EA2 have been concurrently found in families with 26 CAG repeats without previously reported point mutations either in coding sequences or in intron-exon junctions. We describe a Korean family with CAG26 repeats in the CACNA1A gene. Some of the affected family members had progressive ataxia typical of SCA6 whereas others had episodic vertigo responsive to acetazolamide typical of EA2. Our family support that SCA6 and EA2 are allelic disorders with a high phenotypic variability.     

Trinucleotide expansions in the SCA7 gene in a large family with spinocerebellar ataxia and craniocervical dystonia

Spinocerebellar ataxia type 7 is a rare autosomal dominant cerebellar ataxia (ADCA). Herein, we describe the molecular and clinical findings in patients within six generations of a large Chinese family with spinocerebellar ataxia. To identify the genetic cause(s), 4 affected patients and 26 asymptomatic relatives were recruited for the study. Molecular screening of the SCA1 and SCA7 genes was carried out by subcloning and direct PCR-sequencing methods. Both neurological and ophthalmic examinations were performed to investigate the clinical characteristics of the disease. The patients had typical cerebellar ataxia, achromatopsia and macular degeneration, and displayed a rare phenotype manifesting as a combination of cerebellar ataxia and craniocervical dystonia. Mutational analysis of the SCA7 genes demonstrated expanded CAG-repeats in the four patients. In conclusion, we identified expanded CAG-repeats in the SCA7 gene within members of a large Chinese family with spinocerebellar ataxia. The defined phenotypic characteristics of the patients may be helpful for clinical diagnosis and genetic typing of new patients.     

Analysis of SCA1, DRPLA,MJD, SCA2, and SCA6 CAG repeats in 48 portuguese ataxia families

The spinocerebellar ataxias (SCAs) are clinically and genetically a heterogeneous group of neurodegenerative disorders. To date, eight different loci causing SCA have been identified: SCA1, SCA2, Machado-Joseph disease (MJD)/SCA3, SCA4, SCA5, SCA6, SCA7, and dentatorubropallidoluysian atrophy (DRPLA). Expansion of a CAG repeat in the disease genes has been found in five of these disorders. To estimate the relative frequencies of the SCA1, DRPLA, MJD, SCA2, and SCA6 mutations among Portuguese ataxia patients, we collected DNA samples from 48 ataxia families and performed polymerase chain reaction (PCR) amplification of the CAG repeat mutations on chromosomes 6p, 12p, 14q, 12q, and 19p, respectively. Fifty-five individuals belonging to 34 dominant families (74%) had an expanded CAG repeat at the MJD gene. In five individuals from two kindreds with a dominant pattern of inheritance (4%), an expanded CAG repeat at the SCA2 gene was found. In MJD patients, the normal allele size ranged from 13 to 41, whereas the mutant alleles contained 65 to 80 repeats. For the SCA2 patients, normal alleles had 22 or 23, while expanded alleles had between 36 and 47 CAG units. We did not find the SCA1, DRPLA, or SCA6 mutations in our group of families. The MJD mutation remains the most common cause of SCA in Portugal, while a small number of cases are caused by mutations at the SCA2 gene, and 22% are due to still unidentified genes. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 81:134–138, 1998. © 1998 Wiley-Liss, Inc.     

Spinocerebellar ataxia type 23 is an uncommon SCA subtype in the Chinese Han population

The spinocerebellar ataxias (SCAs) are a clinically and genetically heterogeneous group of neurodegenerative diseases. In 2010, four missense mutations in the prodynorphin (PDYN) gene were found in two families and two sporadic cases of SCA type 23 (SCA23) from the Netherlands. In addition, one missense mutation in PDYN was also found in one sporadic SCA23 case in America in 2012. To date, there have been no reports of PDYN gene mutations in mainland China. To investigate the frequency of SCA23 among the Chinese Han population, we performed polymerase chain reaction (PCR) and DNA direct sequencing of the PDYN gene in 305 unrelated ataxia patients. Although no SCA23 mutation was identified, one novel single nucleotide polymorphism (c.255G>A, p.Lys85Lys) in exon 4 of the PDYN gene was found. This suggests that SCA23 is a rare form of dominant ataxia in the Chinese Han population.     

Molecular genetic analysis of a new form of spinocerebellar ataxia in a Chinese Han family

The pathological changes of spinocerebellar ataxias (SCAs), mainly include the degeneration of the cerebellum, spinal cord and brainstem. To investigate the genotype of a three-generation Chinese Han pedigree with an autosomal dominant SCA for clinical diagnosis and genetic counseling, direct mutation test and linkage analysis were performed. SCA1–8, SCA10–14, SCA17, SCA27 and dentatorubral-pallidoluysian atrophy (DRPLA) were excluded by mutation analysis while SCA15/16/29, SCA18, SCA19/22, SCA20, SCA21, SCA23, SCA25, SCA26, SCA28 and SCA30 were excluded by linkage analysis. Therefore, we excluded all of the previously identified SCA-associated genes and loci. Interestingly, one patient (III-13) had a novel mutation of the pleckstrin homology domain containing, family G (with RhoGef domain) member 4 gene (PLEKHG4), and another patient (II-7) had a novel mutation of the β-III spectrin gene (SPTBN2) (Genbank accession numbers FJ905766 and FJ811850, respectively). However, mutations of the PLEKHG4 gene and the SPTBN2 gene are not the causes of SCAs in this family. We conclude that this autosomal dominant cerebellar ataxia family is likely a new genotype of SCAs.     

浙江沿海一家系脊髓小脑性共济失调的基因突变检测与临床表现

目的 探讨浙江沿海脊髓小脑性共济失调的基因突变检测与临床表现.方法 对该家系18例患者的临床表现、头颅MRI等辅助检查资料分析,并与10名家系中未发病成员及12名非血缘的健康人进行SCA31MJD基因CAG三核苷酸重复数目比较.结果 家系18例患者均为SCA3/MJD型,同时检测出家系中未发病对照组有2例为SCA31MJD型基因携带者.产物测序结果家系对照组与健康对照组CAG重复数为14～27次;SCA患者CAG重复数为67～82次;SCA3/MJD携带者CAG重复数为28～45次.在现存三代18例患者中,每代均有患者,男女均受累,起病年龄平均38岁,以行走不稳、动作笨拙和言语含糊为突出表现,MRI检测结果小脑、脑干明显萎缩.结论 在我国沿海存在SCA3/MJD家系遗传.临床均以共济失调和构音障碍为突出,CAG重复数目检测可为基因诊断和症状前诊断提供依据.     

Exome Sequencing as a Diagnostic Tool for Pediatric‐Onset Ataxia

Ataxia demonstrates substantial phenotypic and genetic heterogeneity. We set out to determine the diagnostic yield of exome sequencing in pediatric patients with ataxia without a molecular diagnosis after standard‐of‐care assessment in Canada. FORGE (Finding Of Rare disease GEnes) Canada is a nation‐wide project focused on identifying novel disease genes for rare pediatric diseases using whole‐exome sequencing. We retrospectively selected all FORGE Canada projects that included cerebellar ataxia as a feature. We identified 28 such families and a molecular diagnosis was made in 13; a success rate of 46%. In 11 families, we identified mutations in genes associated with known neurological syndromes and in two we identified novel disease genes. Exome analysis of sib pairs and/or patients born to consanguineous parents was more likely to be successful (9/13) than simplex cases (4/15). Our data suggest that exome sequencing is an effective first line test for pediatric patients with ataxia where a specific single gene is not immediately suspected to be causative.     

A novel heterozygous variant p.(Trp538Arg) of SYNM is identified by whole‐exome sequencing in a Chinese family with dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a relatively frequent myocardial disease that may lead to heart failure, syncope, and sudden cardiac death. Genetic factors play important roles in the etiology of the disease. To date, at least 50 genes have been identified in patients with DCM, among them, only three mutations have been reported in Synemin (SYNM) gene. In this study, we investigate a Chinese family of three generations with four patients with DCM. Employing whole‐exome sequencing (WES) and bioinformatics strategies, a novel heterozygous missense mutation p.(Trp538Arg) of SYNM was identified and cosegregated with the affected family members. The missense mutation locates in the C‐terminal domain of SYNM and leads to a substitution of tryptophan by arginine and may cause the structure change of synemin protein. In conclusion, we employed WES to detect the mutations of DCM patients and identified a novel likely pathogenic mutation in SYNM gene. Our study not only expands the spectrum of SYNM mutations, it further confirms that mutations in SYMN may underlie nonfamilial DCM, and offers genetic testing information to additional DCM patients.     

Autosomal dominant SCA5 and autosomal recessive infantile SCA are allelic conditions resulting from SPTBN2 mutations

Although many genes have been identified for the autosomal recessive cerebellar ataxias (ARCAs), several patients are unlinked to the respective loci, suggesting further genetic heterogeneity. We combined homozygosity mapping and exome sequencing in a consanguineous Egyptian family with congenital ARCA, mental retardation and pyramidal signs. A homozygous 5-bp deletion in SPTBN2, the gene whose in-frame mutations cause autosomal dominant spinocerebellar ataxia type 5, was shown to segregate with ataxia in the family. Our findings are compatible with the concept of truncating SPTBN2 mutations acting recessively, which is supported by disease expression in homozygous, but not heterozygous, knockout mice, ataxia in Beagle dogs with a homozygous frameshift mutation and, very recently, a homozygous SPTBN2 nonsense mutation underlying infantile ataxia and psychomotor delay in a human family. As there was no evidence for mutations in 23 additional consanguineous families, SPTBN2-related ARCA is probably rare.     

Novel mutations in typical and atypical genetic loci through exome sequencing in autosomal recessive cerebellar ataxia families

Nearly a thousand mutations mapping to 60 different loci have been identified in cerebellar ataxias. However, almost 50% of the cases remain genetically uncharacterized and there is a difference in prevalence as well as in the phenotypic spectrum of ataxia among various geographical regions. This poses a challenge for setting up a genetic panel for screening ataxia. In our ataxic cohort of 1014 families, 61% are genetically uncharacterized (UC). We investigated the potential of whole exome sequencing in conjunction with homozygosity mapping (HM) to delineate the genetic defects in three uncharacterized families with recessive inheritance each manifesting some unusual phenotype: (i) infantile onset ataxia with hearing loss (IOAH), (ii) Juvenile onset cerebellar ataxia with seizures (JCS) and (iii) Friedreich ataxia‐like (FA‐like). We identified a novel missense mutation in c10orf2 in the family with IOAH, compound heterozygous mutations in CLN6 in the family with JCS and a homozygous frame‐shift mutation in SACS in the FA‐like patient. Phenotypes observed in our families were concordant with reported phenotypes of known mutations in the same genes thus obviating the need for functional validation. Our study revealed novel variations in three genes, c10orf2, CLN6, and SACS, that have so far not been reported in India. This study also demonstrates the utility of whole exome screening in clinics for early diagnosis.