不明原因智力低下儿童脆性X综合征的筛查和基因诊断

目的建立一种快速分析脆性X综合征智力低下基因1(Fragile X mental retardation gene 1,FMR-1)突变的方法,对不明原因智力低下儿童进行脆性X综合征的筛查和诊断。方法应用7-deza-dGTP的PCR法一次性扩增FMR-1基因的(CGG)n的重复区,检测CGGn的重复序列的大小判断FMR-1基因状态(正常、突变前、突变后),对脆性X综合征可疑患儿快速筛查。结果在101例不明原因的先天性智力低下惠儿中,我们发现脆性X综合征患儿13例(男性10例,女性3例)。结论采用7-deza-dGTP扩增GC富集区的PCR法可对高危患儿进行快速筛查,确定携带者和患者。     

甲基化特异性三重PCR检测FMR1基因突变的研究

目的探讨甲基化特异性三重PCR检测FMR1基因不同突变类型的价值。方法用甲基化特异性三重PCR方法检测了99例病人的FMR1基因,并用半巢式PCR和Southern印迹杂交方法进行比较。结果用甲基化特异性三重PCR检测出70例男性正常基因型、27例女性正常基因型,1例男性全突变基因型,1例女性前突变基因型,与半巢式PCR和Southern印迹杂交方法的检测结果相符。结论甲基化特异性三重PCR能准确检测FMR1突变的不同类型,适用于对脆性X综合征的临床筛查和诊断。     

先天性智力低下儿童脆性X综合征的分子流行病学调查

目的根据脆性X综合征的两个分子生物学标志,建立在先天性智力低下患儿中快速分析脆性X综合征智力低下基因1(Fragile X mental retardation gene 1,FMR1)突变的方法,对先天性智力低下儿童进行脆性X综合征的大面积筛查和诊断,调查智力低下儿童中脆性X综合征的发病率。方法应用复式PCR方法检测FMR1基因的(CGG)n重复区CGG重复序列的大小,判断FMR1基因状态(正常、前突变、全突变),快速筛查脆性X综合征可疑患儿。用甲基化特异性PCR方法,检测FMR1基因启动子区CpG岛的异常甲基化情况,进一步诊断脆性X综合征患者,并用Southern印迹技术进行验证。结果1248例先天性智力低下患儿中,筛查出149名不明原因的智低儿童进行了FMR1基因分析,检出脆性X综合征携带者(FMR1基因前突变者)32例(10男22女),脆性X综合征患者(FMR1基因全突变者)12例(9男3女),脆性X综合征检出率为8.05%。结论复式PCR法灵敏、快速、简便,适应于临床和基层开展脆性X综合征筛查。脆性X综合征在先天性智力低下儿童中的发病率高,应对先天性智力低下儿童进行脆性X综合征FMR1基因的分析。     

脆性X综合征分子诊断研究进展

脆性X智力低下1基因(fragile X mental retardation l gene,FMRI)是脆性X综合征的致病基因,其产物脆性X智力低下蛋白(fragile X mental retardation protein,FMRP)与大脑神经元的发育密切相关.自FMR1基因被鉴定以来,以PCR和Southern印迹杂交为主的分子诊断方法已成为脆性X综合征实验室诊断的主流技术.本文就脆性X综合征分子诊断方法的最新研究进展作一综述.     

脆性X综合征3个家系的基因诊断

采用快速毛细管ＰＣＲ非同位素检测及Ｓｏｕｔｈｅｒｎ印迹杂交技术，对３个脆性综合征家系１８名成员进行了基因型鉴定，其检出全突变患者４例，前突变女性携者４例及正常男性传递者２例，结果显示直接基因诊断方法较细胞遗传学检查更灵敏，对３个家系进行系谱分析证实其遗传特点符合Ｓｈｅｒｍａｎ推论与Ｓｍｉｔｈｓ的观察，同时提供了一种更加快速筛查脆性Ｘ综合征的非同位素ＰＣＲ诊断方法。     

脆性X综合征FMR1基因CpG岛的甲基化程度分析

目的 建立用甲基化敏感性限制性内切酶定量聚合酶链反应(methylation-sensitiverestriction enzymes-based quantitative PCR,MSRE-qPCR)分析FMR1基因CpG岛甲基化程度的方法,并探讨其对脆性X综合征的诊断价值.方法 以常规PCR初筛存在FMR1基因5′(CGG)n异常扩增的30例智力低下男童和20名母亲作为研究对象,用Eag Ⅰ酶消化DNA样品,针对FMR1基因CpG岛设计引物,定量PCR扩增Eag Ⅰ酶切前、后DNA,用2-△△Ct法计算CpG岛甲基化程度;以Southern印迹杂交确诊的3例患儿和正常体检男、女各30例DNA样品为质控样本,从而建立优化的MSRE-qPCR方法.结果 确立了正常甲基化、部分异常甲基化、全甲基化的区间值,并明确30例常规PCR初筛异常患儿中3例存在部分甲基化,27例为全甲基化,其中3例经Southern印迹杂交验证;13例母亲处于正常甲基化,7例存在异常甲基化.结论 MSRE-qPCR可以对FMR1基因CpG岛的甲基化程度进行快速可靠分析,为脆性X综合征的分子诊断提供新的策略.     

应用PCR快速筛查脆性X综合征患儿

目的应用PCR快速筛查脆性X综合征患儿。方法采用PCR和聚丙烯酰胺凝胶电泳技术,对24例不明原因智力低下患儿的脆性X基因（CGG）n重复序列进行检测。结果在24例不明原因智力低下患儿中,筛查出1例脆性X综合征患者。结沦采用PCR技术扩增脆性X基因的（CGG）n重复序列,可对脆性X综合征患者进行快速筛查。     

应用PCR对脆性X综合征进行产前筛查与诊断

目的对脆性X综合征进行产前基因筛查与诊断。方法采用聚合酶链式反应（polymerase chain reaction,PCR）和聚丙烯酰胺凝胶电泳技术,对46例孕妇及其胎儿的脆性X基因（CGG）n重复序列进行检测,同时采用PCR扩增牙幼基因对胎儿性别进行鉴定。结果在46例孕妇及其胎儿中,检出2例前突变携带者孕妇,2例男性患者胎儿。结论采用PCR扩增脆性X基因（CGG）n重复序列,结合扩增牙幼基因进行性别鉴定,可对脆性X综合征进行产前筛查与诊断。     

脆性X综合征的分子机制

脆性X智力低下基因(FMR-1)克隆后,特别是1993年以来,在FMR-1精细结构与功能及脆性X综合征发病机制等方面的研究有了重要发现。现已知FMR-1有17个外显子,分布在38kb范围内,而不是当初推测的80kb以上,FMR-1的表达产物为一种RNA结合蛋白;FMR-1异常甲基化的研究支持X失活印迹假说;染色体奠基突变是导致FMR-1突变的原因;在三核苷酸动态突变的疾病中,只有(CGG)n序列拷贝数变化可能与脆性位点表达有关。     

脆性X综合征的概况

脆性X综合征(fragile X syndrome,Fra(X)S)是X连锁不完全显性遗传病,该病由X染色体上的FMR-1基因改变引起FMRP表达异常造成.本文就脆性X综合征的遗传特征,FMR-1基因的致病机理,FMRP的功能,脆性X综合征的临床筛查与诊断等的国内外最新报道作一综述.     

脆性X综合征的筛查及基因诊断

目的：建立一种简便快速初步筛查脆性X综合征智力缺陷基因FMR－1突变的方法。方法：采用套式PCR技术对新生儿及婴幼儿的足跟血X染色体上基因FMR－1CGG重复序列进行扩增,通过以其拷贝数的鉴定筛查其突变型。结果：共筛查5200全新生儿和婴幼儿,查出1例男婴患者,其母亲是携带者。结论：套式PCR能简便快速地初筛出人群中携带者和可疑患者,对脆性X综合征的早期诊断和产前诊断有应用价值。     

Molecular screening for fragile X syndrome in mentally handicapped children in Korea.

Fragile X syndrome is one of the most common forms of inherited mental retardation and is caused by the expansion of the CGG trinucleotide repeats in the FMR-1 gene. This study was aimed to facilitate the molecular screening of fragile X syndrome in Korean children with mental retardation of unknown etiology. The subjects were tested by Expand Long Template PCR system in the presence of 7-deaza-dGTP, and then by Southern blot analysis. The PCR method provided rapid and reliable results for the identification of fragile X negative and positive patients. One hundred one mentally retarded children (78 males and 23 females) were screened by PCR amplification, which detected only one abnormal sample. The PCR-positive case was confirmed by the CGG repeat expansion on Southern blot analysis with a positive cytogenetic result. In conclusion, Expand Long Template PCR may be used as the first screening test for detecting the fragile X syndrome.     

Segregation of the fragile X mutation from an affected male to his normal daughter.

We report here a family in which the fragile X mutation segregates from an affected grandfather through his normal daughter to an affected grandson. The grandson shows clinical and cytogenetic expression of fragile X syndrome due to a full mutation (large methylated insertion) in the fragile X gene (FMR-1). The mother shows a premutation (small unmethylated insertion) in her FMR-1 gene as the sole manifestation of the fragile X syndrome. The grandfather expresses the fragile X syndrome at the clinical and cytogenetic level, whereas he is mosaic for a methylated full mutation and an unmethylated premutation. The absence of expression of the fragile X mutation when transmitted through an expressing male might present further evidence for genomic imprinting of the FMR-1 gene. Alternatively, it is possible that the grandfather transmitted his premutation to his daughter due to germline mosaicism with both the premutation and the full mutation present in his sperm.     

Segregation of the fragile X mutation from a male with a full mutation: Unusual somatic instability in the FMR-1 locus

Fragile X syndrome is associated with an unstable CGG-repeat in the FMR-1 gene. There are few reports of affected males transmitting the FMR-1 gene to offspring. We report on a family in which the propositus and his twin sister each had a full mutation with abnormal methylation. Their mother had an FMR-1 allele in the normal range and a large premutation, with normal methylation. The maternal grandmother had two normal FMR-1 alleles. The maternal grandfather had an unusual somatic FMR-1 pattern, with allele size ranging from premutation to full mutation. No allele was detectable by PCR analysis. Multiple Southern blot analyses identified a hybridization pattern that originated at a distinct premutation band and extended into the full mutation range. Methylation studies revealed a mosaic pattern with both unmethylated premutations and methylated full mutations. This individual declined formal evaluation but did not finish high school and has difficulty in reading and writing. The size of the premutation FMR-1 allele passed to his daughter is larger than his most prominent premutation allele. This is most likely due to gonadal mosaicism similar to that in his peripheral lymphocytes. Alternatively, this expansion event may have occurred during his daughter's early embryonic development and this large premutation allele is mitotically unstable. This pattern of FMR-1 alleles in a presumably mildly affected male is highly unusual. These findings are consistent with the absence of transmission of a full fragile X mutation through an expressing male. Studies of tissue specific FMR-1 allele expansion and FMR-1 protein expression on this individual should help to determine the correlation of the molecular findings with the phenotypic effects. © 1996 Wiley-Liss, Inc.     

Expand Long PCR for fragile X mutation detection

Fragile X mutation detection by DNA analysis enables accurate diagnosis of the fragile X syndrome. The mutation involves the expansion of CGG repeats in the FMR1 gene and has been primarily detected by the Southern blotting method. In this study we present a novel, efficient and reliable PCR protocol that is more convenient for routine diagnosis of the fragile X syndrome. This method is based on the use of the Expand Long PCR System, which enables the amplification of normal, premutated and full-mutated alleles, and therefore provides complete CGG repeat analysis of the FMR1 gene. Normal alleles were easily detected by ethidium bromide staining of the agarose gels, suggesting that this assay could be used as a screening test for a large number of referrals. The amplified premutations and full mutations were identified by hybridization with a digoxigenin-labeled 5'-(CGG)_5–3' probe, followed by chemiluminescent detection. The accuracy of our Expand Long PCR protocol was confirmed by Southern blot analysis, illustrating that the Expand Long PCR results concur with those of Southern blotting. In this paper we propose a new strategy for molecular diagnosis of the fragile X syndrome in which our Expand Long PCR assay is used as the first screening test for fragile X mutation detection.     

Prenatal diagnosis of fragile X syndrome by direct detection of the dynamic mutation due to an unstable DNA sequence

Yamauchi M, Nagata S, Seki N, Toyama Y, Harada N, Niikawa N, Masuno I, Kajii T, Hori T. Prenatal diagnosis of fragile X syndrome by direct detection of the dynamic mutation due to an unstable DNA sequence.
Clin Genet 1993: 44: 169–172. © Munksgaard, 1993
The fragile X syndrome is the most common familial form of mental retardation. The mutation causing the syndrome is dynamic mutation due to an unstable DNA (CCG)n repeat localized at Xq27.3. We have previously reported a PCR procedure to prepare a diagnostic probe, pPCRfx1, which can be used to determine the genotype of fragile X mutation individuals by Southern blot analysis. In the present study, pPCRfx1 was applied to the prenatal diagnosis, using chorionic villus cells, of a fetus which was at risk of having fragile X syndrome. In the PstI assay, the Southern blot showed the typical pattern of a female carrier with the full mutation. Analysis of the DNA methylation patterns by EcoRI + EagI assay showed that the EagI restriction site was not methylated on the mutated X chromosome of chorionic villi, but the sites were totally methylated in the brain and other tissues of the fetus. Thus the fetus was diagnosed to be a heterozygous female carrier of the dynamic mutation involved in the fragile X syndrome.     

Development of a novel, accurate, automated, rapid, high-throughput technique suitable for population-based carrier screening for Fragile X syndrome.

PURPOSE: To develop a high-throughput, automated, accurate method suitable for population-based carrier detection of fragile X syndrome. METHODS: We developed a new method called capillary Southern analysis that allows automated high-throughput screening for expanded fragile X mental retardation 1 (FMR1) alleles. Initially samples are analyzed by a multiplex polymerase chain reaction that contains an internal control to establish gender. All females heterozygous for two normal alleles are reported as normal without further analysis. All females homozygous at the FMR1 locus (24% of all analysis) are then analyzed by capillary Southern analysis. Theoretically this method can detect expansion as high as 2000 CGG repeats, although in our series the largest nonmosaic FMR1 present was 950 CGG repeats. After assay development, we performed capillary Southern analysis on 995 female and 557 male samples submitted for fragile X syndrome testing by polymerase chain reaction and Southern blot. RESULTS: The polymerase chain reaction/capillary Southern analysis technique identified 100% of six female premutation carriers, seven full mutation carrier females, one premutation male, and five affected males. There was only one discrepancy between analysis by polymerase chain reaction/Southern blot and analysis by polymerase chain reaction/capillary Southern analysis. A single female sample appeared to be heterozygous for a premutation allele by polymerase chain reaction/capillary Southern analysis but was negative by Southern blot. It is possible this patient is a mosaic for the premutation allele, but because samples were deidentified, we were unable to determine whether this was a true false positive. CONCLUSION: We have developed an automated, high-throughput technique capable of detecting carriers of fragile X syndrome with 100% sensitivity and at least 99.5% specificity. This should allow population-based carrier detection for the most commonly inherited form of mental retardation.