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PubMed1981

The 'fragile' X chromosome in the Martin-Bell-Renpenning syndrome and in males with other forms of familial mental retardation.

A clinical and cytogenetic study has been made of subjects from families who have possible X linked mental retardation. The families were distinguished as those with a clinical diagnosis of Renpenning syndrome and those with other behavioural or physical abnormalities obviating such a diagnosis. All subjects with REnpenning syndrome carried a fragile Xq27-28 chromosome in more than 4% of their blood lymphocytes. In addition, two other families who did not have Renpenning syndrome but had similar clinical features also carried the fragile site Xq27-28. A female age effect was observed and one possible carrier of Renpenning syndrome exhibited the fragile X in 10% of her lymphocytes but was also mentally retarded. Subjects within the same family did not always exhibit the fragile site on a comparable proportion of their cells.

Adult↗
PubMed1992

Evidence of founder chromosomes in fragile X syndrome.

The mutation responsible for fragile X syndrome and myotonic dystrophy involves the amplification of a simple trinucleotide repeat sequence, which increases in successive generations of affected pedigrees accounting for increasing penetrance of both disorders. This common molecular basis suggests that the two diseases may share other genetic features, but whereas myotonic dystrophy exhibits a significant founder chromosome effect, fragile X syndrome apparently has a very high mutation frequency. By haplotype analysis of microsatellite markers which flank the fragile X unstable element, we have uncovered evidence of founder chromosomes of the fragile X 'mutation'. Disorders caused by heritable unstable elements may therefore exhibit common genetic properties including anticipation and founder chromosomes.

Base Sequence↗
PubMed1990

Automatic detection of fragile X chromosomes using an X centromere probe.

In order to score for the fragile X syndrome, blood samples are prepared with absorption stain labeling by in situ hybridisation of the X chromosome centromeres. Metaphases are located, digitised at high resolution, and segmented fully automatically. A three stage adaptive classification scheme for labeled X chromosomes is then applied. This consists of a simple box classifier to identify plausible X and false positive X chromosomes, followed by a quadratic discriminant classifier that is re-trained for each sample. The modal number of X chromosomes is then determined for each sample and used to refine the classification. A simple fragile site detector is applied to the distal portion of the detected X chromosome long arms. From the results we estimate computer and operator time requirements for a screening system in which the operator reviews only the apparently fragile X chromosomes detected by the computer.

Biotin↗
PubMed1983

The strength of association between fragile (X) chromosome presence and mental retardation.

In order to obtain a quantitative estimate of the degree of association between presence of fragile X chromosome (fra(X] and mental retardation (MR), existing data from nonretarded males were analyzed. Clearly, fra(X) occurs less frequently among nonretarded compared to MR males. However, incidence estimates for fra(X) based upon existing data hold open the possibility that there may be significant numbers of nonretarded males with fra(X). Additional analyses of data from families with a pattern of fra(X) linked MR showed: (a) the probability that nonretarded male offspring will have fra(X) is very small, and (b) the probability that MR male offspring will have fra(X) is very large. Thus, accurate prognostic decisions can be based upon prenatal diagnosis of fra(X) presence, especially in families with a pattern of fra(X) linked MR.

Female↗
PubMed1984

Recurrent chromosomal defects are found in most patients with acute nonlymphocytic leukemia.

Using a methotrexate cell synchronization technique, we have successfully studied chromosome preparations of bone marrow biopsies from 49 of 51 patients with acute nonlymphocytic leukemia (ANLL). Clonal chromosomal abnormalities were detected in 46 patients, and one of eight types of recurrent chromosomal aberrations were found in 31 patients. One of these types represents a new chromosome defect [inv(16)(p13.1q22)], found in four patients with ANLL-M2, -M4. Chromosome preparations from cultured lymphocytes of two of the four patients were analyzed for the presence of chromosome fragile sites. Both cases showed a frequent break at band 16q22, an intriguing finding that suggests a possible correlation between a fragile site and predisposition to chromosomal rearrangement in human neoplasia.

Adolescent↗
PubMed1984

Familial autism and the fragile-X chromosome.

This report presents two male siblings in whom the diagnosis of infantile autism was found in association with a fragile site on the X chromosome. In addition to their marked autistic characteristics, formal examinations indicated that both boys were severely mentally retarded and had several physical features commonly observed in association with the fragile-X syndrome. The mother of these two siblings also gave birth to identical twin boys, who were developmentally delayed and showed several autistic features prior to their untimely death in a house fire. The possible role of the fragile-X chromosome as an etiological factor in families where there is a clustering of autism and related developmental disturbances is discussed.

Autistic Disorder↗
PubMed1988

The role of fluorinated pyrimidine analogues in the induction of the in vitro expression of the fragile X chromosome.

The modes of action of 5-fluoro-2'-deoxyuridine (FdUrd) and 5-fluoro-2'-deoxycytidine (FdCyd) were studied in PHA-stimulated lymphocytes from normal volunteer donors and a fragile X patient. In both cell types, FdUrd and FdCyd inhibited cell proliferation at concentrations of 3 x 10(-8) M. Thymidylate synthetase was identified as the decisive target for the action of both FdUrd and FdCyd, as judged from the following observations: First, addition of thymidine to the culture medium was able to counteract both FdUrd and FdCyd toxicities, whereas addition of dCyd had no observable effect. Second, inhibition of the in situ thymidylate synthetase activity measured as an increase in the level of [3H]-dThd incorporation coincided with the inhibition of cell proliferation. Third, the inhibition of the thymidylate synthetase-dependent incorporation of [3H]-dUrd into newly synthesized DNA coincided with the inhibition of cell proliferation. The effects of FdUrd and FdCyd on the in vitro expression of fragile site Xq27 of fragile X chromosomes was shown to be based on the depletion of the intracellular pool of thymidine-5'-monophosphate (dTMP), as judged from the following observations: First, both the FdUrd- and FdCyd-dependent induction of site Xq27 coincided with the antiproliferative effects of the respective fluoropyrimidines. Second, addition of thymidine (dThd) to the culture medium both prevented the expression of site Xq27 and neutralized the cytotoxicity of FdUrd and of FdCyd. On the basis of these findings, we provide further evidence for the concept that the fragile X site is located in an AT-rich region.

Base Composition↗
PubMed2004

The guanine-rich fragile X chromosome repeats are reluctant to form tetraplexes.

Using circular dichroism spectroscopy, UV absorption spectroscopy and polyacrylamide gel electrophoresis, we studied conformational properties of guanine-rich DNA strands of the fragile X chromosome repeats d(GGC)n, d(GCG)n and d(CGG)n, with n = 2, 4, 8 and 16. These strands are generally considered in the literature to form guanine tetraplexes responsible for the repeat expansion. However, we show in this paper that the repeats are reluctant to form tetraplexes. At physiological concentrations of either Na+ or K+ ions, the hexamers and dodecamers associate to form homoduplexes and the longer repeats generate homoduplexes and hairpins. The tetraplexes are rarely observed being relatively most stable with d(GGC)n and least stable with d(GCG)n. The tetraplexes are exclusively formed in the presence of K+ ions, at salt concentrations higher than physiological, more easily at higher than physiological temperatures, and they arise with extremely long kinetics (even days). Moreover, the capability to form tetraplexes sharply diminishes with the oligonucleotide length. These facts make the concept of the tetraplex appearance in this motif in vivo very improbable. Rather, a hairpin of the fragile X repeats, whose stability increases with the repeat length, is the probable structure responsible for the repeat expansion in genomes.

Base Sequence↗
PubMed1985

A community study of severe mental retardation in the West Midlands and the importance of the fragile X chromosome in its aetiology.

This paper describes a community based study of 156 boys with idiopathic, severe mental retardation. The boys were examined and a pedigree taken before the cytogenetic results were known. The prevalence of the fragile X chromosome among this group of boys was high: 9% in the whole group and 11% after 39 boys with specific features had been excluded. The fragile X syndrome is therefore an important cause of idiopathic, severe retardation. Its clinical features of large head, large testes, and IQ in the 35 to 70 range were often but not always present in the 14 boys identified in this study. In the whole group, the recurrence of severe mental subnormality was high: 1 in 8 for brothers and 1 in 25 for sisters. This high recurrence was partly due to the fragile X syndrome, partly to X linked mental retardation not accompanied by cytogenetic abnormalities, and partly due to autosomal recessive disease. Autosomal recessive disease was perhaps higher in the West Midlands than elsewhere (such as British Columbia, for example 1) because of the disproportionate contribution by Asian immigrants.

Adolescent↗
PubMedDate not supplied

Fragile X chromosome frequency is consistent temporally and within replicate cultures.

Fragile X frequencies differ widely between different fra(X)-positive individuals. The basis for this variation is unknown, but may reflect genetic differences or unknown environmental factors. To determine more fully the individual and familial variation in fra(X) frequencies, we studied 15 individuals. The present study showed that fra(X) frequency, with few exceptions, was consistent for the same individual both over time and within replicate cultures. This confirms previous observations by others on the consistency of fra(X) expression by others, and indicates the extent of expected variability within replicate cultures. Consideration of this variability should enable improved fra(X) identification.

Cells, Cultured↗
PubMed1996

Trinucleotide repeats at the FRAXF locus: frequency and distribution in the general population.

FRAXF, the third X-chromosomal fragile site to be cloned, has been shown to harbour a polymorphic compound triplet array: (GCCGTC)n (GCC)n. Expansion and methylation of the GCC-repeat and the neighbouring CpG-rich region result in chromosomal fragility. DNAs from 500 anonymous consecutive newborn males were examined to determine the incidence of various repeat numbers. The range of repeats was from 10-38, with the most common alleles having 14 (52.7%), 12 (16.6%), 21 (9.0%), and 22 (5.2%) triplets. Based on the distribution of repeat numbers, we suggest that the 21-repeat allele resulted from hairpin formation involving 7 GCC-repeats in a 14-repeat allele, accompanied by polymerase slippage. Examination of dinucleotide repeats near the FRAXF repeat will be important in testing this hypothesis. Since the clinical phenotype, if any, of FRAXF is unknown, this database will also be valuable for comparisons with repeat numbers in individuals from special populations.

Chromosome Fragile Sites↗
PubMedDate not supplied

Prenatal cytogenetic diagnosis of the fragile X chromosome: feasibility and speed of in situ clonal method in amniotic fluid cell tissue culture.

We have had experience with over 300 amniotic fluid specimens for prenatal diagnosis for the fragile X chromosome [fra(X)], and the flask method of tissue culture has been routinely utilized requiring extended tissue culture periods of 3-4 weeks. The use of the in situ clonal method of tissue culture for routine prenatal cytogenetic diagnosis of amniotic fluid cells has shortened tissue culture time and resulted in more rapid reporting; however, it has not been widely employed for fra(X) prenatal diagnosis. The simultaneous use of both methods of tissue culture has resulted in the detection of 2 cytogenetically fra(X) positive cases in amniotic fluid, with more rapid reporting and satisfactory expression of the fra(X) with the in situ clonal method. Thus, the use of the in situ clonal method of tissue culture for fra(X) prenatal diagnosis in amniotic fluid cells is feasible, faster and can serve as a more rapid cytogenetic adjunct to the newer DNA testing methods.

Amniotic Fluid↗
PubMed1983

Expression of the fragile (X) chromosome in an interspecific somatic cell hybrid.

Interspecific somatic cell hybrids were constructed between a Chinese hamster lung cell line deficient in hypoxanthine phosphoribosyltransferase and two lymphoblastoid cultures (GM 4025 and GM 3200) from unrelated males affected with the fragile (X) syndrome. Thirteen independent colonies survived selection in hypoxanthine-azaserine, while only one colony survived selection in hypoxanthine-aminopterin-thymidine. One hybrid formed from GM 4025 was found to contain a human X chromosome as the only detectable human chromosome in the majority of cells analyzed. Induction of fragile (X) expression in this hybrid at frequencies up to 20% was achieved by treatments with 5-fluoro-2'-deoxyuridine (5 X 10(-8) M or 1 X 10(-7) M) or methotrexate (5 X 10(-6) or 1 X 10(-5) for 12 h. Use of the somatic cell hybrid system may allow study of the fragile (X) from different patients on a homogeneous xenogeneic background and may provide a better system for characterization of the fragile (X) at the biochemical and molecular level.

Animals↗
PubMed1989

Fragile X chromosome in institutionalized male adults with mental retardation.

A clinical and cytogenetical study of mentally retarded male adults with an IQ of below 35 has been carried out in the Ranzan Colony for Mental Retardates, Saitama, Japan. The study showed one fragile X-positive retardate with IQ 23 in the 53 residential retarded patients, giving a hemizygote prevalence of 1.9% (1/53). Macroorchidism and elongated ears, practical markers for the clinical diagnosis of fragile X-linked mental retardation, were also detected in this 43-year-old subject with fra(X)(q27.3). He is amiable and no autistic behavior has been observed. The subject, however, has been suffering from epilepsy since childhood and has cataract in both eyes.

Adult↗
PubMed1989

The inactivation of the fragile X chromosome in female carriers of the Martin Bell syndrome as studied by two different methods.

Female heterozygotes for the fragile X syndrome show variable levels of mental handicap from normal to severely retarded. The degree to which they are affected may depend upon whether the fragile or the normal X chromosome is preferentially inactivated, but one of the problems with the use of BUdR for the study of Lyonisation in fragile-X heterozygotes is that it reduces the level of expression of the fragile site. Results obtained by this method will be biased if the suppression occurs preferentially in either the active or the inactive X chromosome. To confirm that BUdR does not preferentially cause repair of the fragile site on either the late or the early replicating X chromosome, a comparison was made between the percentage of active or early fragile-X obtained using BUdR, and that obtained using tritiated thymidine in cells from the same heterozygote.

Bromodeoxyuridine↗
PubMed1999

How many tumor suppressor genes are involved in human lung carcinogenesis?

To date, only a limited number of tumor suppressor genes have been identified as being inactivated in lung cancer. The p53 and RB genes are frequently inactivated by genetic alterations such as chromosomal deletions and loss-of-function mutations, while the p16 gene is inactivated not only by genetic alterations but also by transcriptional silencing due to hypermethylation. Recently, it was shown that the FHIT gene encompassing the chromosomal fragile site, FRA3B, is also inactivated in a large proportion of lung cancers. Several lines of evidence indicate the presence of additional tumor suppressor genes involved in lung carcinogenesis. Lung cancer cells often show deletions at multiple chromosomal regions, and deletion mapping studies have defined more than 30 regions dispersed on 21 different chromosome arms as candidate tumor suppressor loci. Several chromosomal regions hypermethylated in lung cancer cells and a number of chromosomal fragile sites have been mapped to the regions deleted in lung cancer. These chromosomal loci can harbor unknown tumor suppressor genes inactivated in lung cancer. Studies on the inherited susceptibility to lung cancer in mice have also indicated the presence of additional tumor suppressor genes for lung cancer. Further analyses of these loci should elucidate how many tumor suppressor genes are involved in human lung carcinogenesis. Molecular and functional analyses of those genes will make it possible to fully understand the molecular mechanism of lung carcinogenesis.

Acid Anhydride Hydrolases↗