武汉地区CAG扩增突变致青少年发病的亨廷顿舞蹈病的家系分析(英文)

目的对青少年发病的亨廷顿舞蹈病(Huntington disease)家系进行致病IT15基因早期诊断分析,为家系成员提供遗传咨询, 并为后续的HD发病机制及实验治疗研究提供依据。方法按照知情同意原则抽取家系成员外周血,提取基因组DNA,采用改良的降落PCR方法扩增IT15基因致病区域,DNA测序检测异常等位基因(CAG) n 三核苷酸重复次数。结果在该家系三代25名成员中,共发现8名致病IT15基因携带者,其中,III10、III12、III14、IV3和V2 CAG三核苷酸的拷贝数均为48,IV11和IV12均为(CAG) 67, IV14为(CAG) 63,而对照组35名正常人的CAG三核苷酸的拷贝数为8-25,两者之间没有重叠。结论家系中第四代致病基因携带者IV14与第三代患者III10比较,CAG三核苷酸重复次数增加15次,即本家系IT15基因在传递过程中发生了扩增突变。同时,扩增突变导致该家系出现青少年发病及遗传早现现象。     

Huntington病两家系基因分析

目的 建立准确而快速的IT15基因胞嘧啶-腺嘌呤-鸟嘌呤(CAG)重复序列检测方法,并应用于Huntington病患者的基因诊断及症状前诊断.方法 应用聚合酶链反应、聚丙烯酰胺凝胶电泳及DNA测序技术对Huntington病两家系中的15名成员进行IT15基因CAG重复数目的检测及分析.结果 两家系中共计检出8名成员携带异常的IT15基因,其中2例先证者CAG重复序列存在异常扩增,1例(AⅡ4)出现Huntington病临床表现,其余5例尚未出现Huntington病临床症状与体征.结论 IT15基因CAG重复序列的异常扩增是Huntington病的发病基础,应用上述检测方法对IT15基因CAG重复序列进行检测可对Huntington病患者进行准确的基因诊断及症状前诊断.     

亨廷顿病的发病机制和治疗进展

亨廷顿病（HD）为遗传性进行性神经变性疾病,以异常的自主运动、认知功能障碍和精神疾病为临床特征,中老年发病,发病后10～15年死亡。已知致病基因为IT15基因,其1号外显子含有一段多态性三核苷酸[胞嘧啶．腺嘌呤．鸟嘌呤（CAG）]重复序列,当CAG重复拷贝数大于36次即引起发病。     

亨廷顿舞蹈病的临床特点与基因诊断(附一个家系报告)

目的对一个临床拟诊为亨廷顿舞蹈病(Huntington′s disease,HD)家系进行IT15基因诊断,探讨IT15基因中CAG的重复拷贝数与发病年龄、临床特征之间的关系,提供遗传咨询并综述亨廷顿舞蹈病治疗的最新进展。方法收集该家系详细的临床资料,抽取该家系成员外周静脉血提取DNA,采用PCR、电泳技术以及DNA直接测序方法 ,并进行文献复习。结果家系调查发现该家族共28人,有6例患者,男3例,女3例,平均起病年龄54.3岁。呈父系遗传,第Ⅰ代起病年龄71岁,第Ⅱ代平均起病年龄59岁,第Ⅲ代平均起病年龄39岁。6例均以不自主舞蹈样动作起病,逐渐加重,其中4例晚期伴痴呆。有11例成员参与基因测序,包含2名有症状成员Ⅱ9和Ⅲ4(Ⅱ9起病年龄为62岁,Ⅲ4起病年龄为43岁)。实验结果发现参与成员中有3例(Ⅱ9、Ⅲ4和1例无症状成员Ⅳ1)PCR扩增后电泳显示两条扩增带,一条长约220 bp,另一条长约300 bp,Ⅱ9、Ⅲ4和Ⅳ1的CAG重复数目分别为17/40、17/45、16/48;其他8名成员显示一条扩增带,长约220 bp左右,CAG重复数目在20次以下。结论该家系根据临床表现和基因检测可确诊为亨廷顿舞蹈病,有1例症状前患者,建议该患者将来孕前期行产前基因检测。发病年龄与IT 15基因中CAG的重复拷贝数呈负相关,父系遗传有遗传早现现象。     

少年型亨廷顿病临床与基因突变分析

研究背景亨廷顿病是一种常染色体显性遗传性神经系统退行性疾病.临床主要表现为舞蹈样动作、进行性认知功能减退及精神症状,神经影像学检查显示尾状核和大脑皮质萎缩.其致病基因IT15定位于4p16.3,由67个外显子组成编码亨廷顿蛋白,在其第1个外显子内存在一段多态胞嘧啶.腺嘌呤-鸟嘌呤(CAG)三核苷酸重复序列,正常范围为6～35次、异常36～250次.亨廷顿病多于成年期发病,具有外显不完全和延迟外显现象,而青少年型亨廷顿病临床较为少见.本研究针对一例少年期发病的亨廷顿病患者临床表型及其家系IT15基因CAG重复动态突变特征进行细致分析.方法 采用聚合酶链反应结合荧光标记毛细管电泳片段分析方法,对115例临床拟诊为亨廷顿病家系的先证者进行IT15基因CAG重复次数分析,经pMD18-T载体克隆测序验证部分阳性或携带中间重复等位基凶的样本.结果 经基因分析共发现109例患者携带异常扩展的IT15基因CAG重复序列,其中一例为少年期发病患者,临床以认知功能障碍和运动功能减退为首发症状,其父母临床表型正常.基因片段分析显示,患者IT15基因CAG重复次数为15/68次;其父母分别为17/37次和15117次.结论 (1)少年期发病的亨廷顿病与成年型临床表型不同,后者临床表现以舞蹈样运动、智能减退和精神异常为主,而少年型患者大多以认知功能障碍发病.(2)IT15基因扩展CAG重复序列在代问传递过程中会出现动态突变.引起发病年龄逐代提前,症状加重,即遗传早现.该家系患者之父携带中间等位基因37次重复,遗传给患者成为68次重复.在代间传递过程中发生了大幅度扩展,使CAG三核苷酸重复次数增加了31次,提示重复序列在父系遗传更不稳定.     

多聚谷氨酰胺病CAG重复序列动态突变机制研究进展

多聚谷氨酰胺病是一类中枢神经系统退行性疾病,由致病基因外显子内胞嘧啶腺嘌呤鸟嘌呤(CAG)三核苷酸重复序列拷贝数异常扩增导致其编码的多聚谷氨酰胺链异常延长,引起多聚谷氨酰胺扩展突变型蛋白积聚而致病。迄今为止,共发现9种因多聚谷氨酰胺扩展突变型蛋白积聚引起的遗传性神经退行性疾病。CAG重复序列在代间传递过程中发生动态突变(拷贝数不断扩增),进而导致发病年龄提前和疾病严重程度增加。     

舞蹈病家系临床、影像学特征及基因突变分析

目的明确一个无明显痴呆的舞蹈病家系的临床、影像学特征及IT15、DRPLA、JPH3、TBP基因突变情况。方法对5例已发病患者的临床及脑影像学特征进行分析;用聚合酶链反应技术、8%变性聚丙烯酰胺凝胶电泳及直接测序等方法,对18名家系成员的IT15、DRPLA、JPH3、TBP基因的三核苷酸(CAG/CTG)重复序列进行分析。结果5例患者主要表现为舞蹈样不自主运动;3例患者头颅磁共振成像无明显尾状核萎缩,其中1例头颅单光子发射计算机断层显像(SPECT)提示双侧基底节血流受损,比健康人血流灌注减少;检测到9例(5例患者,4例症状前患者)分别有一(CAG)n重复拷贝数大于40次的IT15基因,无DRPLA、JPH3、TBP基因的突变。结论根据临床和影像学特征该家系在临床上不能确诊为亨廷顿舞蹈病,但经基因突变分析确定了IT15基因中(CAG)n重复拷贝数的异常扩展导致该家系发生了亨廷顿舞蹈病。     

青少年型亨廷顿病10例临床表型及基因突变分析

目的总结青少年型亨廷顿病患者临床表型及IT15基因胞嘧啶-腺嘌呤-鸟嘌呤(CAG)重复突变特点。方法采用聚合酶链反应结合荧光标记毛细管电泳片段分析方法,对159个亨廷顿病家系272名成员进行IT15基因CAG重复序列检测,并对其中10例青少年期发病患者的临床表现、影像学特征以及临床表型与基因型相关性进行分析。结果经基因检测共发现211例携带异常扩展的IT15基因CAG重复序列,其中10例为青少年型亨廷顿病患者,临床表现各异,主要以不自主运动和认知功能障碍为主;发病年龄平均(12.50±4.55)岁,IT15基因CAG重复序列平均(63.70±14.83)个,Pearson相关分析显示,二者呈负相关关系(r=-0.865,P=0.001)。结论青少年型亨廷顿病与成年型亨廷顿病患者临床表现不同,前者主要表现为认知功能障碍;对于无明确家族史、临床表现疑似亨廷顿病的患者,基因检测是明确诊断的依据;亨廷顿病发病年龄与IT15基因CAG重复次数呈负相关,但不能完全解释发病年龄的变异性,尤以青少年型亨廷顿病患者显著,可能存在其他遗传调节因素。     

脊髓小脑共济失调2型、3型患者10例基因突变与临床表型分析

目的探讨脊髓小脑共济失调（SCA）2型、3型患者的基因突变特点及临床表型。方法总结4个SCAs家系的9例患者和1例散发患者的临床表现，对全部患者、43名家系成员及60名健康对照，采用PCR、荧光PCR、毛细管电泳等技术检测分析SCA2、3基因内CAG三核苷酸重复序列的长度及拷贝数。结果3个家系中的6例患者、1例散发患者存在SCA3／MJD（CAG）n扩展突变，CAG重复数为68—75次；1个家系的3例患者存在SCA2（CAG）n扩展突变，CAG重复数为39—41次。两型患者的临床表现有重叠之处，但在发病年龄、病程进展、神经系统受累部位等方面有明显差异。结论SCA3／MJD型与SCA2型在临床表现上存在一定差异性，有助于鉴别和分型，但基因检测是明确诊断的惟一方法。     

脊髓小脑性共济失调2型的分子遗传学诊断及临床分析

目的:研究分析脊髓小脑性共济失调2型(SCA2)的分子遗传学诊断、应用以及临床表现特征。方法:对来自广西地区临床诊断为SCA的1个家系2例患者和8名"健康"家系成员,以及35名正常对照人员,通过聚合酶链式反应、琼脂糖电泳等技术检测SCA2基因位点内CAG三核苷酸重复扩增次数,并对异常等位基因片段进行DNA测序。结果:我国广西正常人群SCA2等位基因CAG重复数为20～29次,1家系中2例患者与1例症状前患者存在SCA2(CAG)n扩展突变,拷贝数分别为42、45、55次。结论:首次发现广西SCA2,利用分子遗传学分析可进行SCA2基因诊断,为症状前诊断及遗传咨询提供依据。     

Expansion of a (CAG)n repeat region in a sporadic case of HD

The genetic mutation underlying Huntington's disease (HD) has been identified as an expansion and instability of a specific CAG repeat sequence in a gene on chromosome 4. A simple polymerase chain reaction assay has been used for the assessment of the (CAG)n expansion in a 72-year-old woman with typical HD symptoms, but no family history of the disorder. The DNA analysis showed that the patient had an allele with 41 repeat units, in the size range seen in HD chromosomes. Therefore, HD diagnosis is confirmed in this seemingly sporadic case and the disease is newly diagnosed in a large family. The risk of inheriting this unstable expanded allele is discussed. Introduction– The discovery of an expansion of a trinucleotide (CAG) repeat region in the IT 15 gene on the short arm of chromosome 4 has identified the mutational mechanism causing Huntington's disease (HD) and enables the direct diagnosis of affected subjects based on DNA analysis alone. Here a 72-year-old woman with typical HD symptoms, but no family history of the disorder, has been unambiguously diagnosed by using a quick DNA analysis. This is relevant because the disease is newly diagnosed in a large family. Material and methods– A labelled polymerase chain reaction (PCR) test has been used to amplify the repeat region of the IT 15 gene and DNA fragments were analyzed by Polyacrylamide gel electrophoresis. Results– The number the CAG repeats in the proband displayed two alleles of 23 and 41 repeats, respectively. Since normal chromosomes are reported to contain 11–34 repeats, the clinical appearance of HD in the proband is explained by the presence of the repeat expansion. Discussion– The parents of the proposita both died aged over 80 y apparently without neurological signs referable to HD. Hence, this is presumably a sporadic case of the disease. Because of the length of 41 repeats of this HD chromosome, offspring of this proband could inherit the expanded allele with 37 repeats, as expected for the reversal of the trinucleotide expansion. A subject with this intermediate allele could be affected, but would not be affected if the HD IT gene with reduced triplets had recovered its normal function. Thus, in a seemingly sporadic case like the one reported here, despite the PCR analysis, the risk of transmission of HD to her offspring may remain uncertain.     

Molecular diagnosis of Huntington disease in Brazilian patients

Huntington disease (HD) is a progressive neurodegenerative disorder with autosomal dominant inheritance, characterized by choreiform movements and cognitive impairment. Onset of symptoms is around 40 years of age and progression to death occurs in approximately 10 to 15 years from the time of disease onset. HD is associated with an unstable CAG repeat expansion at the 5' and of the IT15 gene. We have genotyped the CAG repeat in the IT15 gene in 44 Brazilian individuals (42 patients and 2 unaffected family members) belonging to 34 unrelated families thought to segregate HD. We found one expanded CAG allele in 32 individuals (76%) belonging to 25 unrelated families. In these HD patients, expanded alleles varied from 43 to 73 CAG units and normal alleles varied from 18 to 26 CAGs. A significant negative correlation between age at onset of symptoms and size of the expanded CAG allele was found (r=0.6; p=0.0001); however, the size of the expanded CAG repeat could explain only about 40% of the variability in age at onset (r2=0.4). In addition, we genotyped 25 unrelated control individuals (total of 50 alleles) and found normal CAG repeats varying from 16 to 33 units. The percentage of heterozigocity of the normal allele in the control population was 88%. In conclusion, our results showed that not all patients with the "HD" phenotype carried the expansion at the IT15 gene. Furthermore, molecular diagnosis was possible in all individuals, since no alleles of intermediate size were found. Therefore, molecular confirmation of the clinical diagnosis in HD should be sought in all suspected patients, making it possible for adequate genetic counseling.     

Maternal transmission in sporadic Huntington's disease.

Huntington's disease is an autosomal dominant neurodegenerative disorder caused by the expansion of a (CAG)n repeat in the IT15 gene. Three per cent of cases are sporadic and in those in which family studies have been performed, the origin of the mutation was always paternal. The first sporadic case of Huntington's disease is presented in which a premutated maternal allele of 37 CAG repeats was transmitted expanded to the proband (43 CAG repeats). Molecular analysis of the IT15 gene is extremely important in sporadic cases of Huntington's disease, providing correct diagnosis of the disorder and facilitating genetic counselling to the family members.     

Analysis of CAG repeat expansion in Huntington's disease gene (IT 15) in a Hungarian population

Huntington's disease (HD) is a neurodegenerative disorder with autosomal dominant inheritance. The genetic defect is a CAG trinucleotide repeat expansion at the 5' end of the IT 15 gene on chromosome 4. This gene has not been analyzed in the Hungarian population yet. To obtain data DNA from 26 HD patients, 18 members of their families and 70 normal controls was amplified in the involved region by polymerase chain reaction. The CAG repeat numbers varied from 37 to 70 (median: 43) in HD patients and asymptomatic carriers, while individuals of the normal control group had 10-36 CAG repeat numbers (median: 18). The length of CAG repeat expansion in Hungarian HD patients was similar to that reported from other countries. The group of normal controls had the same CAG repeat expansion as populations reported from Western European countries. It is a useful piece of data for population genetics to prove that the population of Hungary is a mélange of different nations that influenced the history of the country in the last 11 centuries. As opposed to this, the only closely related nation, the Finnish, was genetically more isolated during this time, so the frequency of HD (and also the number of CAG repeats in normal individuals) proved to be exceptionally low.     

CAG/CTG repeat expansions at the Huntington's disease-like 2 locus are rare in Huntington's disease patients

The authors report a large series of patients with Huntington disease (HD)-like phenotype without CAG repeat expansions in the IT15 gene that were screened for the newly identified CAG/CTG expansion in the gene encoding junctophilin-3. Normal alleles in controls had from 8 to 28 repeats. A single patient of North African origin with typical HD carried an allele with 50 uninterrupted repeats, representing approximately 2% of the non-IT15 HD patients tested. Therefore, further genetic heterogeneity is expected in HD.     

Co-segregation of Huntington disease and hereditary spastic paraplegia in 4 generations

INTRODUCTION: Huntington disease (HD) is an autosomal dominant neurodegenerative disease characterized by choreic hyperkinesias, cognitive decline, and psychiatric manifestations, caused by an increased number of CAG repeats in the IT15 gene on chromosome 4p16.3. Silver syndrome is a rare autosomal dominant form of complicated hereditary spastic paraplegia, characterized by lower limb spasticity in addition to amyotrophy of the small muscles of the hands. In addition to the previously identified locus SPG17 on chromosome 11q12-q14, a new locus (SPG38) on chromosome 4p16-p15 has been recently identified, a region that includes the HD gene. REPORT OF THE CASES: We present a Greek family with 5 members diagnosed with HD in 4 generations. All affected members also presented with clinical features of Silver syndrome showing severe spastic paraplegia and prominent atrophy of all small hand muscles bilaterally. None of the other family members showed features of either HD or spastic paraplegia. CONCLUSIONS: The reported coexistence of Silver syndrome with HD in 4 generations is not fortuitous, suggesting that these 2 distinct genetic disorders are in linkage disequilibrium. Although rare, it is reasonable to expect additional similar cases. Clinical neurologists should perhaps investigate this possibility in cases combining features of HD and involvement of the upper and lower motor neurons.     

Genetically confirmed clinical Huntington's disease with no observable cell loss

Huntington's disease (HD) results from neurodegeneration of the neostriatum. The mutation on chromosome 4 is an expansion in a triplet repeat (CAG)(n) located within the IT15 gene. Only six patients have been reported with clinical features of HD in association with limited neuropathology. Of these, only one has had the diagnosis confirmed by genetic (DNA) testing. We describe a patient with the clinical phenotype and genetically confirmed HD but unexpected limited neuropathology. The patient was seen because of aggressive behaviour and memory problems of two years duration. The differential diagnosis included HD although there was no family history. DNA testing was positive for the HD mutation. Clinical follow up three months later confirmed classic features of HD. Progression of the disease was rapid with death three years later. Neuropathology revealed a largely intact neostriatum with bilateral ischaemic damage and cell loss in the external globus pallidus. Such pathology alone could explain the clinical features of HD. This is only the second report of genetically confirmed clinically manifest HD with little evidence of HD neuropathology. There are several unusual features which could not have been predicted by the clinical picture, in particular the progressive course of bilateral ischaemic changes restricted to the external globus pallidus. The potential to miss other HD cases at post-mortem examination, and the implications of this for family members, are discussed.