脆陛X综合征的细胞遗传学研究

本研究从10个X连锁智力低下家系中，经细胞遗传学检查．检测出5个Fra(X)综合征家系，共15名患者和携带者检查发现：1、不同成份培养液对脆性X表达有影响。2、活性X染色体Xq27迟复制与Fra(X)综合征患者智力密切相关。3、Fra(X)染色体的活性与女性携带者的智力有一定的关系。     

先天性智力低下的遗传学研究

为探索先天性智力低下的遗传异质性,对２４０例先天性智力低下患者进行Ｇ显带分析和低叶酸诱导脆性Ｘ染色体检测,并以先证者为核心进行家系调查。发现先天性智力低下患者中,Ｄｏｗｎ综合征占１０．４２％,Ｆｒａ（Ｘ）综合征占５．４２％,染色体倒位、易位及缺失共占３．７５％,染色体正常８０．４２％。表明先天性智力低下具有多种遗传学病因和不同的复发风险率。     

脆性X综合征的临床和遗传方式探讨

脆性Ｘ综合征是非特异性Ｘ连锁智力低下综合征。本文通过二个家系２４ 人的调查分析,将智力低下、语言障碍、多动,视作脆性Ｘ 综合征最明显的临床特征。本病遗传有其特殊的遗传方式：（１）脆Ｘ 综合征是由表型正常的男性传递。（２） 表型正常的男性携带者通常是男性患者的外祖父。（３） 脆Ｘ综合征家系中,智力低下男性患者比予期的约少２０ ％ ,低于Ｘ连锁基因所予期的数值。（４）本综合征患儿母亲几乎均是携带者。（５） 表型异常的女性ｆｒａ（ｘ）来自母亲而非来自父亲。（６）同胞中外显程度不一致。对患者及携带者的确切诊断是依靠染色体显示Ｘｑ２７ ．３ 位置的脆位点。     

唾液口腔粘膜上皮细胞FMR1基因突变的PCR检测

本文采用ＰＣＲ技术对５个已确诊为脆性Ｘ综合征〗Ｆｒａ（Ｘ）【家系的１５名成员唾液中口腔粘上皮细胞ＦＭＲ１基因进行了分析，并与其外周血ＰＣＲ结果进行了比较，发现６例全突变患者有３例两种组织的结果出现了明显关 ，而５全本、４例前突变携带者及另３例全突变患者两种组织的ＰＣＲ结果完全一致，提示唾液中口腔粘膜上皮细胞同样可用于检测ＦＭＲ１基因突变，同时也表明Ｆｒａ（Ｘ）患者体内ＦＭＲ１基因突变存在着组织间的     

DNA分析技术在脆性X综合征临床诊断和遗传咨询中的应用

ＤＮＡ分析技术在脆性Ｘ综合征临床诊断和遗传咨询中的应用孙玉洁脆性Ｘ综合征［Ｆｒａ（Ｘ）］是一种常见的Ｘ连锁智力障碍，其发病率仅次于Ｄｏｗｍ综合征。临床上Ｆｒａ（Ｘ）以不同程度的智力障碍（ＭＲ）为特征，同时伴有长脸、耳异常、大睾丸和多动等症状，因其表型...     

含人脆性X染色体的杂交细胞系的建立与分析

建立了含人脆性Ｘ染色体的人－（中国）仓鼠染交细胞系，用细胞遗传学的Ｇ６ＰＤ同功酶电泳等方法进行了鉴定。克隆的４个杂交细胞系用３种诱导方法对其Ｆｒａ（Ｘ）的表达进行了分析，结果表明这些杂交细胞系的Ｆｒａ（Ｘ）频率不同，咖啡因可增加表达率，并证明Ｆｒａ（Ｘ）的表达不取决于任何其它人染色体的存在。这些种细胞系有助于对脆生Ｘ综合征的细胞遗传学和分子基础的研究。     

35例智力低下儿童染色体脆性部位分析

３５例智力低下儿童染色体脆性部位分析张晓珍，余继英，霍晓春，饶兆英近年来，对脆性Ｘ综合征的研究引起了医学遗传学界的广泛关注。脆性Ｘ染色体（ＦｒａＸ）与Ｘ连锁智力低下（ｍｅｎｔａｌｒｅｔａｒｄａｔｉｏｎ，ＭＲ）有关，进而使人们对罕见型脆性位点发生极大兴...     

FRAXA与FRAXE位点的快速基因筛查

Ｘ染色体长臂末端罕见脆性位点Ａ与Ｅ与分别由一个可遗传的三核苷酸重复序列的延长所致二种脆 性位占在细胞遗传学水平难以区别。为了建立快速筛查ＦＲＡＸＡ与ＦＲＡＸＥ位点的基因诊断法，本文采用毛细管ＰＣＲ－序列胶银染显示法对正常人，脆性Ｘ综合征家系及智力儿童三组样本进行了检测，结果显示正常人群的Ｐ（ＣＧＧ）ｎ与Ｐ（ＧＣＣ）ｎ均呈多态分面     

脆性X综合征的遗传学研究

为研究脆性Ｘ综合征的遗传学特征,提高诊断和遗传咨询水平,积极有效地治疗,降低复发风险。本实验采用低叶酸ＴＣ１９９培养基诱导脆性Ｘ染色体的方法,对具有Ｆｒａ ＸＳ临床特征的智低患儿４５０名进行ＦｒａＸ检测,发现ＦｒａＸＳ９５名,检出率２１．１１％,检测智低患儿母亲３２０名,有ＦｒａＸ表达者４８名。结果提示,ＦｒａＸＳ经临床筛选后有较高检出率,其智低程度与ＦｒａＸ表达频率有关;分析和探讨了ＦｒａＸＳ动     

脆性X综合征的研究进展

脆性Ｘ综合征［ｆｒａｇｉｌｅＸｓｙｎｄｒｏｍｅ,Ｆｒａ（Ｘ）］是最常见的Ｘ连锁智力低下性疾病,因其遗传方式独特,引起了医学界及分子生物学界的广泛关注。１９９１年Ｖｅｒｋｅｒｋ等［１］分离并克隆出该病的致病基因—脆性Ｘ智力低下１号基因（ｆｒａｇｉｌｅＸ...     

Parental origin of the fra(X) gene is a major determinant of the cytogenetic expression and the CGG repeat length in female carriers.

The fragile X [fra(X)] syndrome is the most frequent form of inherited mental retardation, and co-segregates with a fragile site at Xq27.3 as well as with insertion of a variable number of trinucleotide repeats in the 5'-end of the FMR-1 gene. As the fra(X) gene is transmitted by females as well as males, we have investigated whether the parental origin of the fra(X) gene has an effect upon the cytogenetic expression and CGG repeat length. An increased fragment length of 0.2-0.6 kb appeared to be associated with a very low expression or even complete absence of the fragile site as well as with a normal phenotype, and was seen mostly in cases of paternal inheritance. However, in most female carriers with the maternally inherited fra(X) gene we found dispersed fragments ranging from 1.4-6.5 kb or even complete absence of a hybridization signal. Within the group of female carriers with the maternally inherited fra(X) gene we found a statistically significant correlation between the level of the cytogenetic expression and the PstI restriction fragment length encompassing the CGG repeat. These data can be taken as indirect evidence that CGG repeat length and cytogenetic expression are causally related.     

Chromosome lesions which could be interpreted as “fragile sites” on the distal end of Xq

Chromosome lesions which could be interpreted as “fragile sites” on the distal end of the long arm of the X chromosome were identified during a cytogenetic study of 160 mentally retarded adult males with no apparent cause of their mental retardation and one normal adult female with a family history of fra (X) syndrome. Peripheral blood samples were cultured in either M199 or RPMI 1640 medium with FUdR or BrdU. Metaphases were examined for chromosome lesions or fragile sites on the distal end of Xq and 3 distinct sites were observed: Xq26, Xq27.2, and Xq27.3. Other chromosome lesions at Xq28 were observed and interpreted as nonspecific telomeric structural changes. Chromosome lesions were observed in cells from 14 of the 161 individuals. These included: 5 patients with an Xq26 site, 2 with the recently reported Xq27.2 site, 4 with the Xq27.3 site (characteristic of the fra (X) syndrome), 2 with nonspecific telomeric structural changes, and one individual with 2 lesions (a nonspecific telomeric structural change and an Xq26 site). Additional research is necessary to determine the frequency and clinical significance, if any, of lesions occurring in this region of the X chromosome and to distinguish among heritable fragile sites, constitutive fragile sites, and nonspecific telomeric structural changes.     

Chromosome lesions which could be interpreted as "fragile sites" on the distal end of Xq

Chromosome lesions which could be interpreted as "fragile sites" on the distal end of the long arm of the X chromosome were identified during a cytogenetic study of 160 mentally retarded adult males with no apparent cause of their mental retardation and one normal adult female with a family history of fra (X) syndrome. Peripheral blood samples were cultured in either M199 or RPMI 1640 medium with FUdR or BrdU. Metaphases were examined for chromosome lesions or fragile sites on the distal end of Xq and 3 distinct sites were observed: Xq26, Xq27.2, and Xq27.3. Other chromosome lesions at Xq28 were observed and interpreted as nonspecific telomeric structural changes. Chromosome lesions were observed in cells from 14 of the 161 individuals. These included: 5 patients with an Xq26 site, 2 with the recently reported Xq27.2 site, 4 with the Xq27.3 site (characteristic of the fra (X) syndrome), 2 with nonspecific telomeric structural changes, and one individual with 2 lesions (a nonspecific telomeric structural change and an Xq26 site). Additional research is necessary to determine the frequency and clinical significance, if any, of lesions occurring in this region of the X chromosome and to distinguish among heritable fragile sites, constitutive fragile sites, and nonspecific telomeric structural changes.     

Fragile (X)(q27) sites in a pedigree with female carriers showing mild to severe mental retardation.

A pedigree showing the fragile site at Xq27 in a severely retarded female and in other less retarded carriers is described. Two of the four moderately retarded males with the fra(X)(q27) show macro-orchidism, and a variety of other features usually used to support the effects of the fra(X)(q27) are also inconsistent. A second fragile site at (10)(q23) is also present and in the two oldest females its frequency is not decreased, whereas the fra(x)(q27) is not detectable in these females although probably present. It is concluded that pedigrees showing mentally retarded females and probable X linkage should be included in studies of the fra(X)(q27).     

The fragile X syndrome in a large family. I. Cytogenetic and clinical investigations.

Cytogenetic and clinical investigations were performed in 85 members of a large family, in which 18 males and seven females were mentally retarded. In the male patients the fragile site Xq27 was found in 6 to 44% (mean 22.5%) of peripheral blood lymphocytes. One non-retarded male expressed the cytogenetic abnormality in 6% of his cells. In 21 females the fra(X) was found in 3 to 28% (mean 8.7%) of their cells. Two obligate carriers did not express the fragile site. A significant difference in expression between the seven retarded (mean 16.7%) and seven non-retarded female carriers of corresponding age (mean 6.3%) was found (alpha = 0.01). No significant correlation between expression and age could be established, either in males or in females. The cytogenetic results appeared to be consistent. To avoid false positives, a cut-off point was chosen: males were considered to be fra(X) negative if no more than one in 100 cells showed the abnormality; for females the cut-off point was two in 100 cells. Segregation analysis did not detect significant deviations from the expected ratios. The putative presence of a transmitting male is discussed. The results of recombinant DNA analysis will be published elsewhere. Clinical investigations confirmed the findings of others. CT scans showed an enlargement of the ventricular system that exceeded the expected age changes.     

X chromosome inactivation in fibroblasts of mentally retarded female carriers of the fragile site Xq27.3: application of the probe M27 beta to evaluate X inactivation status.

Over 30% of female carriers of the fragile X [fra(X)] syndrome are clinically affected. A nonrandom X chromosome inactivation in these cases could be a plausible explanation. A review of previous studies addressing this question showed inconclusive results; thus, we analysed the X inactivation pattern in fibroblasts of 4 unrelated, mentally retarded fra(X) carriers with a high expression of the fragile site Xq27.3. Using Southern analysis with a highly polymorphic probe M27 beta that recognizes methylation differences between the active and inactive X chromosome we found a 50/50 inactivation pattern in 2 cases and skewed patterns in the other 2. As biased patterns were also observed in control females we conclude that at present no evidence exists for a nonrandom X chromosome inactivation in the fra(X) syndrome in females.     

Frequency of tri- or multiradial configurations in fragile X identification

Using the FUdR system for fragile X induction, we have observed no triradial or bisatellited configurations at fra (X) (q27.3) in over 5,000 fra(X) chromosomes examined from over 150 fra(X) individuals. Based on our observations, and those of Turner and Jacobs (1983) and Daniel et al (1984), we hypothesize that triradial configurations may not occur at Xq27 with FUdR induction. To test this hypothesis we cultured whole blood simultaneously in parallel folate-deficient and FUdR fra(X) induction systems, and systematically examined fra(X) chromosomes for triradials. Neither autosomes nor X chromosomes exhibited any apparent triradial figures in the FUdR system, while 1.4% of the fra(X) chromosomes in TC 199 exhibited a triradial. Also we observed one autosomal triradial at 4q35. We conclude that triradial configurations occur in low frequencies in the folate deficient system and seldom if ever in the FUdR system.     

Differential expression of fragile site Xq27 in cultured fibroblasts from hemizygotes and heterozygotes and its implications for prenatal diagnosis

Expression of the fragile site Xq27 (fraXq27) was studied in metaphases derived from fibroblasts of 8 hemizygotes and 2 heterozygotes, cultured in 2 different media containing reduced concentrations of folic acid. The proportion of fra(X) (q27)-positive metaphases ranged from 1.0 to 14%, which is considerably lower than in lymphocyte cultures from the same individual, but differed with respect to the culture medium used. Four hemizygotes showed a higher proportion of fra(X)-positive cells in medium 199 than in methotrexate-exposed cultures. No fra(X)-negative cultures were observed when the folic acid inhibitor methotrexate was added to medium 199. Thus, in all 10 individuals carrying the fra(X), the fragile site could be detected in fibroblast cultures. We conclude that the expression of fra(X) (q27) in cultured fibroblasts should be studied using at least 2 types of culture conditions, because familial, i.e. genetic differences may influence the expression of this fragile site in fibroblasts. The implications for prenatal diagnosis are discussed on the basis of investigations in 15 pregnancies at risk for the trait.     

Simultaneous expression of the rare and common fragile sites on the X chromosome

The fragile X [fra(X)] syndrome is the most common inherited form of X-linked mental retardation and is associated with a rare folate sensitive fragile site on the X chromosome at band Xq27.3. Recently, a common fragile site located at chromosome band Xq27.2 was delineated (Sutherland & Baker 1990). In order to confirm the previous findings and to further investigate the conditions required for induction of both types of fragile sites, we studied the use of four experimental protocols. Samples from a control male, two fra(X) males and a fra(X) carrier female were studied. Both common and rare fragile sites were seen in the samples from the fra(X) subjects. Up to 4% of cells showed both common and rare fragile sites on the same X chromosome at the 500 band level. The rare and common fragile sites on the X chromosome could be clearly distinguished. From 1 to 3% of the control cells exhibited the common fragile site, while none exhibited the rare fragile site. These protocols should be useful in resolving questionable fra(X) syndrome diagnoses.     

Prenatal diagnosis of fragile X syndrome: results from parallel molecular and cytogenetic studies.

Since 1985, we have provided coordinated DNA-based and cytogenetic prenatal analysis for couples at risk for offspring afflicted with the fragile X [fra(X)] syndrome. To date, 40 pregnancies have been studied (22 males, 18 females). There were 5 males and 3 females identified to be at high risk by DNA but only 2 males and one female were demonstrated to be cytogenetically expressing the fra(X) prenatally. Of the other 3 males, one was a cytogenetic false negative (i.e. confirmed fra(X)+ at termination of pregnancy). The other 2 remain fra(X)- and are developing normally (undetected recombinants or non-penetrant male carriers). All fetuses at low risk were carried to term and are reported to be normal.