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PubMed1991

Changes of common fragile sites on chromosomes according to the menstrual cycle.

The frequencies of chromosomal breaks and sister chromatid exchanges (SCE) are influenced by pregnancy, oral hormonal contraceptives and the menstrual cycle. The changes in the number and sites of spontaneous and aphidicolin-induced breaks on chromosomes from peripheral blood lymphocytes during the menstrual cycle were examined in 8 healthy women. Menstrual cycle was determined by menstruation and the quantity of serum estrogen, progesterone and luteinizing hormone. The number of spontaneous breaks at the follicular phase, the interval phase (which includes ovulation) and the luteal phase were 3.1 +/- 1.1, 2.7 +/- 2.3 and 3.9 +/- 2.6 per 100 mitoses, respectively. The frequencies of aphidicolin-induced breaks in the same phases were 95.8 +/- 23.3, 90.6 +/- 14.3 and 122.7 +/- 20.1 per 100 mitoses, respectively. The higher frequency at the luteal phase was statistically significant compared with the other phases. In the luteal phase, bands 2q32, 3q27, 6q26 and 16q23 had higher frequencies of breaks (P less than 0.05); however, breaks at band 9q32 decreased significantly. SCE showed considerable variation, but with no statistical significance.

Adult↗
PubMed1985

High resolution ultrasound of macro-orchidism in mental retardation.

Asymptomatic testicular enlargement is common in mentally retarded males. This enlargement includes males with non-specific forms of mental retardation as well as a subgroup of males who have a chromosomally recognizable feature involving the X-chromosome ("fragile X" chromosome). We examined the testes of a group of 25 mentally retarded males with macro-orchidism including both fragile X and non-fragile X patients. Apart from large size, the testes scanned were all normal in appearance. In particular, there was no evidence for neoplasia. There were no distinguishing features between the fragile X and the non-fragile X groups.

Evaluation Studies as Topic↗
PubMed1994

Chromosome sensitivity to bleomycin-induced mutagenesis in lymphocytes from colorectal cancer patients under 40 years of age.

PURPOSE: The incidence of colorectal cancer in young adults (under 40 years of age) is rare. The reason for the occurrence in these patients may lie in their genetic background. METHODS: We studied chromosomal fragility in peripheral blood lymphocytes of patients under the age of 40 with large bowel cancer. Lymphocytes from 24 subjects were examined: 10 untreated large bowel cancer patients under the age of 40 and 14 age-matched and sex-matched controls. RESULTS: The mean number of spontaneous chromosomal breaks per cells (b/c) was significantly higher in the right-sided large bowel cancer patients (0.23 +/- 0.12 b/c) compared with the control group (0.09 +/- 0.04 b/c; P < 0.01), but with no significant difference between the left-sided colorectal cancer patients and the control group. Lymphocytes exposed to the radiomimetic agent, bleomycin, were arrested in methaphase and analyzed for chromosome fragility. Mean chromosome breaks per cell in the left-sided colorectal cancer patients (1.60 +/- 0.49 b/c) were significantly higher than in either the controls (0.72 +/- 0.31 b/c; P < 0.001) or the right-sided, large bowel cancer patients (0.91 +/- 0.24 b/c; P < 0.05). CONCLUSIONS: The increased spontaneous chromosomal breaks in the right colon, as opposed to the increased mutagen-induced chromosomal breaks in the left colon, might indicate that in young colon cancer patients the occurrence of right-sided colon cancer is more likely to be genetically determined, whereas in left-sided colon cancer, environmental carcinogens might play a greater role.

Adenocarcinoma↗
PubMed1986

Low frequencies of apparently fragile X chromosomes in normal control cultures: a possible explanation.

Low frequencies of apparently fragile X [fra(X)] chromosomes have been reported in normal control, short-term, whole blood cultures, and they have been noted in both amniocyte and fetal blood cultures. However, there is currently no universal agreement on the lowest frequency for fra(X)(q27) that is diagnostic for the fragile X syndrome. Here, we present our observations on low levels of apparently fra(X) chromosomes in normal samples. We observed frequencies of 0.5% in short-term whole blood cultures and 0.9% in amniotic fluid cell cultures. In 1982, Steinbach et al. described nonspecific telomeric structural changes (TSC) and suggested that such low frequencies of apparently fra(X) chromosomes in normal material may be occurring by the same mechanism that is responsible for TSC formation. To determine if TSC formation can explain the significant baseline frequencies of fra(X) in normal controls, 10,457 cells were screened from 178 individuals referred for fra(X) analysis. Our findings indicated that TSC are not randomly distributed across chromosomes but tend to occur at specific sites. Based on our observations, we offer the hypothesis that the low frequency of apparent fra(X) in normal individuals may be due to nonrandom TSC distribution.

Amnion↗
PubMed1997

A variable domain of delayed replication in FRAXA fragile X chromosomes: X inactivation-like spread of late replication.

The timing of DNA replication in the Xq27 portion of the human X chromosome was studied in cells derived from normal and fragile X males to further characterize the replication delay on fragile X chromosomes. By examining a number of sequence-tagged sites (STSs) that span several megabases of Xq27, we found this portion of the normal active X chromosome to be composed of two large zones with different replication times in fibroblasts, lymphocytes, and lymphoblastoid cells. The centromere-proximal zone replicates very late in S, whereas the distal zone normally replicates somewhat earlier and contains FMR1, the gene responsible for fragile X syndrome when mutated. Our analysis of the region of delayed replication in fragile X cells indicates that it extends at least 400 kb 5' of FMR1 and appears to merge with the normal zone of very late replication in proximal Xq27. The distal border of delayed replication varies among different fragile X males, thereby defining three replicon-sized domains that can be affected in fragile X syndrome. The distal boundary of the largest region of delayed replication is located between 350 and 600 kb 3' of FMR1. This example of variable spreading of late replication into multiple replicons in fragile X provides a model for the spread of inactivation associated with position-effect variegation or X chromosome inactivation.

Cell Cycle↗
PubMed2001

The role of folic acid and Vitamin B12 in genomic stability of human cells.

Folic acid plays a critical role in the prevention of chromosome breakage and hypomethylation of DNA. This activity is compromised when Vitamin B12 (B12) concentration is low because methionine synthase activity is reduced, lowering the concentration of S-adenosyl methionine (SAM) which in turn may diminish DNA methylation and cause folate to become unavailable for the conversion of dUMP to dTMP. The most plausible explanation for the chromosome-breaking effect of low folate is excessive uracil misincorporation into DNA, a mutagenic lesion that leads to strand breaks in DNA during repair. Both in vitro and in vivo studies with human cells clearly show that folate deficiency causes expression of chromosomal fragile sites, chromosome breaks, excessive uracil in DNA, micronucleus formation and DNA hypomethylation. In vivo studies show that Vitamin B12 deficiency and elevated plasma homocysteine are significantly correlated with increased micronucleus formation. In vitro experiments indicate that genomic instability in human cells is minimised when folic acid concentration in culture medium is >227nmol/l. Intervention studies in humans show: (a) that DNA hypomethylation, chromosome breaks, uracil misincorporation and micronucleus formation are minimised when red cell folate concentration is >700nmol/l folate; and (b) micronucleus formation is minimised when plasma concentration of Vitamin B12 is >300pmol/l and plasma homocysteine is <7.5micromol/l. These concentrations are achievable at intake levels in excess of current RDIs i.e. more than 200-400microgram folic acid per day and more than 2microgram Vitamin B12 per day. A placebo-controlled study with a dose-response suggests that based on the micronucleus index in lymphocytes, an RDI level of 700microgram/day for folic acid and 7microgram/day for Vitamin B12 would be appropriate for genomic stability in young adults. Dietary intakes above the current RDI may be particularly important in those with extreme defects in the absorption and metabolism of these Vitamins, for which ageing is a contributing factor.

Cells, Cultured↗
PubMed1988

A cytogenetic study of mentally retarded school children in Taiwan with special reference to the fragile X chromosome.

A cytogenetic study was made on 341 mentally retarded children in the Provincial Nantou Rehabilitation Center for the Mentally Retarded and the St. Raphael Opportunity Center in Tainan. Of the 89 mentally retarded children with chromosomal abnormalities, 63 had Down syndrome, 13 had the fragile X [fra(X)] syndrome, and the remaining had other aneuploid constitutions. Family studies were possible for 2 of the 13 fra(X) probands. The results of this study illustrate the contribution of chromosomal abnormalities to the pathogenesis of mental retardation in children.

Chromosome Banding↗
PubMed1983

The fragile X chromosome in a large Indian kindred.

A large Indian kindred in which the fragile X chromosome is segregating has been investigated in Cape Town. Eight male hemizygotes and four female heterozygotes were mentally retarded. There is suggestive evidence that one deceased male of reportedly normal intelligence may have been a hemizygote. The existence of the fragile X syndrome in a number of different ethnic groups supports the contention that the gene controlling the phenotype and the fragile site are the same, or at least overlap.

Adolescent↗
PubMed2002

The X chromosome and fragile X mental retardation.

Fragile X syndrome represents the most common inherited cause of mental retardation. It is caused by a stretch of CGG repeats within the fragile X gene, which increases in length as it is transmitted from generation to generation. Once the repeat exceeds a threshold length, no protein is produced, resulting in the fragile X phenotype. Both X chromosome inactivation and inactivation of the FMR1 gene are the result of methylation. X inactivation occurs earlier than inactivation of the FMR1 gene. The instability to a full mutation is dependent on the sex of the transmitting parent and occurs only from mother to child. For most X-chromosomal diseases, female carriers do not express the phenotype. A clear exception is fragile X syndrome. It is clear that more than 50% of the neurons have to express the protein to ensure a normal phenotype in females. This means that a normal phenotype in female carriers of a full mutation is accompanied by a distortion of the normal distribution of X inactivation.

Chromosomes, Human, X↗
PubMed1982

[Fragile X chromosome and X-linked mental retardation (author's transl)].

In males affected by a special form of X-linked mental retardation a characteristic chromosomal abnormality can be demonstrated, - i.e. a fragile site on the long arm of the X chromosome, fra(X) (q27 or 28) (marker-X chromosome). Male carriers are physically normal, but in most cases show macroorchidism. The demonstration of the marker-X chromosome requires special cell culture conditions, above all a folic acid-deficient medium. The frequency of cells with fragile X chromosome varies interindividually, ranging from 2 to 50%. In female heterozygous carriers the number of cells with fra(X) decreases with age and cannot be demonstrated in some cases. Distribution and frequency of X-linked mental retardation with marker-X chromosome and macro-orchidism are discussed, as well as possibilities of prenatal diagnosis of this disorder.

Adolescent↗
PubMed1979

The constitutional fragility of chromosome 12 in a case of 46,XX,var(12)(gh',RHG,CAG,CBG).

The constitutional fragility of chromosome no. 12 in a female infant with unspecific clinical signs is described. RHG, GAG, and CBG methods were used to localize the fragile point. The breaks seem to be in 12q1.3, and always within an R band. A possible correlation between the phenotypic modifications and the chromosome variant is discussed.

Chromosome Aberrations↗
PubMed1986

The frequency of the fragile X chromosome among schoolchildren in Coventry.

A population study has been carried out among schoolchildren in the City of Coventry in order to ascertain the frequency of mental retardation associated with the fragile X chromosome. The prevalence of the fragile X mental retardation syndrome in the 11 to 16 year age group (the age of greatest ascertainment) was about 1.0 per 1,000 and therefore indicates that the syndrome is a major cause of mental retardation.

Adolescent↗
PubMedDate not supplied

Guidelines for the preparation and analysis of the fragile X chromosome in lymphocytes.

The following guidelines were adopted by an Ad Hoc Committee convened at the Fourth International Workshop on the Fragile X Syndrome and X-Linked Mental Retardation to establish minimum cytogenetic standards for the preparation and analysis of the fragile X chromosome. The intention of the committee was to develop and provide practical standards for the routine cytogenetic detection of the fragile X. The guidelines describe reasonable criteria for effective tissue culture methods for eliciting the Xq27.3 fragile site in vitro and for the analysis of such chromosome preparations.

Cells, Cultured↗