Constitutive fragile sites 1p31, 3p14, 6q26, and 16q23 and their use as controls for false-negative results with the fragile(X)

Cytogenetic guidelines for fragile X studies tested in routine practice

Several organizations have proposed guidelines for fra(X) studies on peripheral blood lymphocytes. To evaluate these guidelines, we reviewed 1,033 consecutive specimens referred for fra(X) analysis. Each specimen was cultured with medium 199 and RPMI 1640 with 5-fluorodeoxyuridine or excess thymidine. The karyotype and expression of fra(X) were established from 20 GTL- or QFQ-banded cells and by screening of up to 130 more banded cells. We found anomalies other than fra(X) in 37 (3.6%) of the patients. We found 4% or more fra(X) cells in 38 (3.7%) cases from 36 unrelated families, including 33 (3.9%) of 850 males and 5 (2.7%) of 183 females. Another 4 females had 1 to 3% fra(X) cells. Six specimens were fra(X)-positive in only one stress system, and 32 were positive in 2 systems. To find the first 2 fra(X) cells in males, we needed to study up to 36 cells in 31 cases, 50 in one case, and 57 in another. To find the first 2 fra(X) cells in females, we needed to study up to 17 cells in 4 cases and 57 in another. A strong family history of fra(X) occurred in 5 patients, and each one was fra(X)-positive. Some manifestations of the fragile X syndrome occurred in 507 cases, 17 (3%) of which were fra(X)-positive. Abnormalities considered unlikely to be the fragile X syndrome occurred in 103 cases, 3 (3%) of which were fra(X)-positive. Use of chromosome breakage and fra(3)(p14) as quality control indicators of the fra(X) stress systems was found to be unreliable.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosome fragility in the Lennox-Gastaut epilepsy syndrome

Chromosome fragility was sought in a well-defined cohort of patients with Lennox-Gastaut epilepsy syndrome. Twenty-five patients plus 25 age- and sex-matched normal controls had cytogenetic studies performed. All patients were taking sodium valproate, and four were also on hydantoin. Blood cultures from both patients and controls were set up simultaneously in an appropriate medium designed to elicit fragile-sites. Harvesting took place after 96 h by standard techniques. In addition to routine banded analysis, at least 50 cells were scored for chromosome breaks and gaps from each patient and control. Results showed no difference between the patients and the control group in the overall occurrence of fragility or the type of aberration detected. No fragile-X syndrome was detected. This study found no effect due to sodium valproate on the occurrence of chromosome aberrations.

Early prenatal diagnosis of the fragile site at Xq27.3 associated with Martin-Bell syndrome

Early prenatal diagnosis of the fragile X was attempted in 44 pregnancies, including one twin pregnancy at risk of Martin-Bell (MB) syndrome. The sex ratio was 24M:21F. The fragile site was reproducibly demonstrated in cultured chorionic villus (CV) cells in eight male and five female fetuses. Six of the male and three of the female fetuses were terminated. Simultaneous RFLP analysis provided confirmative data with flanking DNA markers in 3 of 13 analysed cases. Recombination and/or non-informativeness at available distal and/or proximal loci were found in nine cases. In one male fetus, discordance between the haplotype and cytogenetics (fragile-X-negative) suggested the presence of a normal male transmitter, a double meiotic cross-over within the region, or a false-negative cytogenetic diagnosis. However, discordance between prenatal and post-termination/postnatal cytogenetic findings was not observed in this series. The use of excess thymidine for induction of the fragile X in cultured CV cells provided in the majority of cases a safe and rapid method for cytogenetic diagnosis, with options for early induced termination in fragile-X-positive pregnancies, for simultaneous RFLP analysis, and for subsequent second-trimester analysis of fetal blood in complicated cases.

Autosomal folate sensitive fragile sites in normal and mentally retarded individuals in Greece

The frequencies of autosomal folate sensitive fragile sites were compared in populations of mentally retarded fra(X) negative (N = 220) and normal children (N = 76) in Greece. In addition, the frequency of autosomal fragile sites was studied in 20 known fra(X) children in order to test if the fra(X) syndrome is associated with general chromosome instability. The frequencies of both common and rare autosomal fragile sites did not differ significantly between the mentally retarded and the normal children, although the rate of expression was considerably higher in the retarded group. Autosomal fragile sites were not increased in the fra(X) patients. Fra(3)(p14) was by far the most frequent one in all groups. The frequency of fra(6)(q26) was found to be considerably higher among the mentally retarded children, this difference being almost statistically significant. Further cytogenetic studies of normal and retarded individuals are required in order to elucidate this point further.

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.

Distribution of autosomal fragile sites in specimens cultured for prenatal fragile X diagnosis

We reviewed the distribution of autosomal fragile sites (FS) and spontaneous chromosome breaks or gaps (CB) at chromosome locations other than those recognized as FS from 100 amniotic fluid samples (AF), 19 chorionic villus samples (CVS), and 5 percutaneous umbilical blood samples (PUBS) referred for fragile X [fra(X)] analysis. We present data on the degree of expression of autosomal fragility in AF, CVS, and PUBS samples, and the relationship between degree of expression and induction system. The most common observed FS were: 3p14, 9p32, and 6q26 in AF; 9q32, 3q27, and 8q22 in CVS; and 3p14, Xq22, and 16q23 in PUBS cases. Distribution of FS and CB, when compared by induction system, was not found to be identical. Our data also indicate that the presence of any particular FS cannot be used as an indicator for the effectiveness of the fra(X) induction system in prenatal samples.

Possible association of rare autosomal folate sensitive fragile sites and idiopathic mental retardation: a blind controlled population study

The expression of folate sensitive fragile sites (FS) was assessed in cord blood lymphocyte cultures obtained from 790 newborns (NB) and in peripheral blood lymphocyte cultures from 326 institutionalized mentally retarded residents (MR). The mean rate of expression of common FS and the occurrence of rare FS was significantly higher in the MR population. Age, sex and history of chronic medication use did not appear to influence common FS expression in the MR population, 3/790 (0.38%) NB and 5/326 (1.53%) MR exhibited rare autosomal folate sensitive FS, a 4-fold difference in incidence (P = 0.009, Poisson test). Four of the five MR who expressed rare FS were considered to have idiopathic MR (4/179 or 2.2%). The occurrence of rare FS in 1/147 (0.68%) MR with known etiology is not significantly different from the frequency of occurrence in the NB population (P = 0.428, Poisson test). In this population, rare FS appear to be overrepresented in the idiopathic etiology MR group.

Missed prenatal diagnosis of fragile-X syndrome

An account is given of a pregnancy in an obligatory carrier of the fragile-X syndrome, in whom examination of chorionic villus cells and fetal blood cells showed the presence of a male fetus who lacked the fragile-X chromosome. However, at 3 months of age he had 14 per cent of fragile-X cells in his blood. Reasons are suggested for this error in diagnosis. The empirical risk for an error of this sort is 3 per cent.

Familial and individual variation in chromosome fragility

An extremely high frequency of fra 6q26 (25%) was detected during a routine cytogenetic investigation of a 9-year-old girl. This prompted us to perform an extensive study of fragile site expression in her cells and those of her parents and sister. The very high frequency of fragility at 6q26 which had been discovered initially in the proband was not detected in the first repeat culture under the same experimental conditions. However, in the second repeat culture fragility at 6q26 was clearly present again. In the 4 members of this family fragile site expression was found to vary significantly between repeat samples from the same person. Also, a specific order of individual fragile site expression appeared to be present. This order was the same for the different culture conditions used.

Population cytogenetics of folate-sensitive fragile sites. II. Autosomal rare fragile sites

The frequencies of folate-sensitive autosomal rare fragile sites (ARFS) were compared in populations of mentally retarded, mentally subnormal, and mentally normal children and of patients referred for diagnostic chromosome study. The frequencies did not differ significantly. Altogether, an autosomal rare fragile site was found in 16 of 1,445 individuals (1 in 90). Of six different folate-sensitive ARFS detected, the most common one was FRA9A, with a frequency of 1 in 241 individuals. In addition, FRA17A, classified as a distamycin A-inducible fragile site, was found with a frequency of 1 in 206. It was regarded as a spontaneously expressive fragile site. In 19 families in which transmission of an autosomal rare fragile site was studied, the mother was the carrier in 16 families and the father, in one family. The mean percentage (+/- SD) of cells expressing ARFS in 55 individuals was 19% (+/- 11.4). The age did not affect the rate of expression. When the rate of expression was calculated separately in a group of mentally retarded (mean = 23.4%) and in a group of mentally normal individuals (mean = 16.0%), the difference was statistically significant.

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.

Constitutive fragile sites in fra(X) individuals

Recently, it was proposed that the constitutive fragile site at 3p14 be used as an "internal control" to indicate the effectiveness of the FUdR fragile site induction system. We have tested this hypothesis by determining the frequency of constitutive fragile sites at 1p31, 3p14, and 16q23 in cultures from 42 known fra(X) individuals. At least 50 cells were analyzed from each case. Seventy-four percent (31/42), 95% (40/42) and 90% (38/42) of the fra(X) individuals exhibited frequencies of less than 4% at constitutive fragile sites 3p14, 1p31 and 16q23, respectively. Of the 42 individuals tested, 12 or 28.6% showed no fragility at any of the 3 sites studied. On the other hand, at least one constitutive fragile site was observed in 50 cells studied from over 70% of the 42 people studied. It is suggested that "positive controls" continue to be used, while at the same time recording all fragile sites to identify a combination of constitutive fragile sites that may serve as an internal control indicator, and that DNA marker studies be used to complement cytogenetic testing.

The predictive value of dermatoglyphic anomalies in the diagnosis of fra(X)-positive Martin-Bell syndrome (MBS)

In a representative group of 160 institutionalized mentally retarded males without Down syndrome, prospective dermatoglyphic-cytogenetic studies were performed in order to assess the utility of the dermatoglyphic index system of Rodewald [1986] for an efficient ascertainment of patients with Martin-Bell syndrome (MBS). A negative (abnormal) score was found in 32 men (20 +/- 3%), 14 of whom (predictive value: 44 +/- 9%) were fra(X)-positive. This prevalence of 14/160 = 9 +/- 2% patients with fra(X)-positive MBS indicates that in our study most, if not all, MBS patients have been detected by the simple pre-screening of dermatoglyphics. In the MBS patients, there was no correlation between the dermatoglyphic scores and percentage of fra(X)-positive cells.

Normal blood lymphocytes from patients with adipose tissue tumors with rearrangements at 12q13-q14 do not express the fragile site fra(12)(q13.1)

An association between chromosomal fragile sites and cancer-specific breakpoints has been found to be statistically significant. Cancer patients have been shown to be carriers of fragile sites in chromosome regions involved in rearrangements in malignant cells. Based on these observations it has been hypothesized that fragile sites may be involved in the pathogenesis of human tumors. We have recently described a new recurrent cancer breakpoint at chromosomal region 12q13-q14 in adipose tissue tumors. The possible involvement in these tumors of the rare folate-sensitive fragile site 12q13.1 has been investigated in PHA-stimulated peripheral blood cells from three patients carrying the t(12;16)(q13;p11) in their liposarcoma cells and one patient with the t(3;12)(q28;q14) in his lipoma cells. No expression of the fragile site 12q13.1 could be detected in the blood lymphocytes of any of the patients. The involvement of the fragile site 12q13.1 in the pathogenesis of adipose tissue tumors with a 12q13-q14 breakpoint remains to be established.

Fragile sites, cancer chromosome breakpoints, and oncogenes all cluster in light G bands

Fragile sites tend to be bands where breaks occur in cancer chromosome rearrangements that can involve oncogenes. The locations of fragile sites, cancer breakpoints, and oncogenes were therefore charted. All were predominantly in light G bands. Specifically, 78 of 89 (88%) fragile sites were in light G bands including the large group of common fragile sites inducible with aphidicolin (p less than 0.001). Of 61 cancer breakpoints, 50 (82%) were in light bands including translocation breakpoints (p less than 0.001). Thirteen of 14 (93%) oncogenes localized to light bands. The sharing of chromosome bands can stem from a biologically meaningful relationship, as between cancer breakpoints and oncogenes. Joint occupancy of chromosome bands can also reflect independent reasons to be in the same sector of the genome. Thus, fragile sites may well be in light bands because they are associated with active genes. This clearly does not rule out a biologic relationship between specific fragile sites and specific cancer breakpoints.

Fragile sites induced by FUdR, caffeine, and aphidicolin. Their frequency, distribution, and analysis

The frequencies of common fragile sites (c-fra) induced in peripheral blood lymphocytes by fluorodeoxyuridine (FUdR), aphidicolin, or caffeine, in eight healthy controls were studied. There was a significantly higher frequency of breaks (P less than 0.05) in the latter two treatments than the former. Also, significant variation in total number of breaks was observed among the eight individuals within the three treatments. The relative frequency of a fragile site in relation to the total number of fragile sites in an individual rather than its expression in total cells was considered important. Use of a frequency of 4% or more of total fragile sites was proposed to eliminate apparent "random" breaks that were observed. Using these criteria, a total of 31 c-fra were observed in the three treatments. The distribution of the fragile sites was different in FUdR-treated cells as opposed to caffeine- and aphidicolin-treated cells. Sites 3p14 and 16q23 and Xp22 were the three most frequently observed c-fra. The higher frequency of expression of some fragile sites in normal controls, as observed here, suggests that any relationship between fragile sites and neoplastic transformation has to be carefully evaluated. A classification based on frequency in the population, rather than mode of induction, is suggested.

The effect of hydroxyurea on the expression of the common fragile site at 3p14

Hydroxyurea (HU) is an inhibitor of DNA synthesis, which can inhibit the enzyme ribonucleotide reductase, reduce the syntheses of all four deoxyribonucleoside diphosphates (dNDP), and disturb the balance of the dNTP pool. We have studied the effect of HU on the common fragile site at 3p14 (FRA3B) and have found that G2 treatment with HU increased not only the frequency of chromosomal aberration but also the expression of FRA3B in both complete and folate deficient media. There is a synergistic effect between HU and growth in folate deficient medium on the induction of FRA3B. Our results suggest that the inhibition of DNA repair, including the inhibition in G2 phase, plays an important role in the expression of FRA3B, supporting other authors' data on the effect of other DNA repair inhibitors, such as aphidicolin, caffeine, 1-beta-D-arabinofuranosylcytosine, and 5-fluorodeoxyuridine, on the expression of FRA3B.

Variation in the expression of aphidicolin-induced fragile sites in human lymphocyte cultures

A correlation between specific fragile sites and cancer breakpoints has been suggested raising the question of fragile site expression as a predisposing factor in the occurrence of cancer in some persons. Before addressing the question of increased fragility among patients at high risk for cancer, we analyzed the variability of aphidicolin-induced fragile sites among nine normal persons and also among repeated samples from three of these individuals. Considerable variation in both the frequency and location of these fragile sites was observed and the data strongly suggest the significant variation of 6 of the 16 selected sites to be primarily due to sampling differences. These findings indicate that the use of fragile sites as a screening tool for patients at high risk of cancer should be carefully monitored relative to the variation inherent in both culture and individual expression.

Prospective risk in reciprocal translocation heterozygotes at amniocentesis as determined by potential chromosome imbalance sizes. Data of the European Collaborative Prenatal Diagnosis Centres

The Date of the European Cooperative Prenatal Diagnosis Laboratories (Boué and Gallano, 1984) of 596 prenatal (amniocyte) diagnoses of familial rcp was examined as to relationships between balanced/unbalanced result and ascertainment, carrier parent and chromosome imbalance size (percentage haploid autosome length). Each rearrangement was graphed once with actual (unbalanced result) or potential (normal or balanced result) imbalances plotted with trisomy as the ordinate and monosomy as the abscissa. The graphed data was divided into 15 regions, each of 2.0 per cent trisomy and 0.75 per cent monosomy and the rate of unbalanced pregnancies determined for each region. The highest rates of chromosomally unbalanced progeny (excluding regions with inadequate data) were found closest to the origin (i.e. associated with the smallest imbalances) and these were for ascertainment category 1 (previous rcp unbalanced child) 22.3 per cent for maternal carriers and 39 per cent for paternal carriers. Overall in pooled data for this ascertainment category (without reference to the imbalance graphs) there were for paternal carriers 28.6 per cent unbalanced pregnancies and for maternal carriers 18.1 per cent. The graphed data, therefore, revealed the higher rates associated with some of the rcp with small potential (combined duplication/deficiency) imbalances. Lesser rates were observed for ascertainment category 2 (carrier parent with a history of recurrent miscarriage) with overall percentages of imbalanced progeny ranging from 2.7 (paternal carriers) to 4.7 (maternal carriers). Again, higher rates were revealed in graphed data for small potential imbalances. All unbalanced results for this group (ascertainment category 2) plotted in the region closest to the origin with rates of 16 per cent (maternal carriers) and 9.5 per cent (paternal carriers) in this region. Remarkably in both ascertainment groups 1 and 2 there was no significant difference in the size of the imbalanced segments for unbalanced progeny. In ascertainment group 1 this was (dup/def; mean +/- S.D.): 1.09 +/- 0.77/0.47 +/- 0.45 and in ascertainment group 2: 1.09 +/- 0.80/0.66 +/- 0.71. From the graphed data which arguably denote viability relationships, a trisomy was approximately 2.7 times as likely to survive until amniocentesis as a monosomy of equivalent size. It is proposed that given further data, risk estimates could be determined for rcp heterozygotes using the present approach where empiric data (from the family history or an analysed series of similar rcp) is not available.

The most common fragile site in man is 3p14

In man a common fragile site is known to occur at 3p14. We studied the expression of this fragility in a group of 70 normal healthy subjects. Chromosome breaks, chromatid breaks and gaps at 3p14 could be observed in every examined individual, and in a total of 7000 metaphases they were seen in a mean of 4% of cells. Fluorescence studies in ten persons with chromosome No. 3 polymorphism showed that in all cases both Nos. 3 were about equally liable to breakage. A considerable variation in the fra 3p14 expression was found between individuals as well as in repeated cultures from the same person. Neither sex nor age influences could be detected. Cultures with a high percentage of lesions at 3p14 tended to have also a high number of lesions at other sites. Methotrexate and fluorodeoxyuridine markedly enhanced the expression of fra 3p14 and other fragilities. It is concluded that the chromosomal region at 3p14 represents man's most common fragile site, the expression of which seems to be influenced by environmental and heritable factors.

Clinical implications and classification of the constitutive fragile sites

Constitutive fragile sites (c-fra) comprise the more prevalent but less recognised suite of fragile sites in eukaryotes. They differ from the heritable (rare) suite of fragile sites (h-fra) in several significant ways. In the present report, data concerning the c-fra so far recognised are reviewed in connection with their origin, classification, use as positive controls for cell culture conditions inducing the fra(X), and their presumptive relationships to the characteristic breakpoints in the neoplasias and in constitutional chromosome rearrangements.

Mouse chromosome fragility

When cultures of fibroblast-like cells from inbred mouse strains RBC/Dn and AEJ/GnRk were exposed to 5-fluorodeoxyuridine (FUdR), non-random strain-specific distributions of chromosome gaps, breaks and exchanges were observed. Throughout the genomes there appeared to be specific sites at which lesions occurred preferentially. Two strain-specific fragile sites were identified in strain RBC/Dn at G-band 15A2, and at G-band 19B in strain AEJ/GnRk. Constitutive fragile sites at G-bands 12A2 and 18A2 were identified in both strains. A strain-specific marker at G-band 9B was found in strain AEJ/GnRk. The fragile sites reported here provide an animal model for the study of chromosome fragility as well as polymorphic markers for linkage studies.

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.

Absence of significant autosomal lesions in Huntington's disease

Peripheral blood from six patients with Huntington's disease (HD) and six controls were cultured in three types of media known to produce fragile sites. A total of 3000 metaphases per group were scrutinized in a blind coded study. No significantly specific 'hot-spot' was found capable of differentiating between HD patients and controls.

Genetic linkage heterogeneity in the fragile X syndrome

Genetic linkage between a factor IX DNA restriction fragment length polymorphism (RFLP) and the fragile X chromosome marker was analyzed in eight fragile X pedigrees and compared to eight previously reported pedigrees. A large pedigree with apparently full penetrance in all male members showed a high frequency of recombination. A lod score of -7.39 at theta = 0 and a maximum score of 0.26 at theta = 0.32 were calculated. A second large pedigree with a nonpenetrant male showed tight linkage with a maximum lod score of 3.13 at theta = 0, a result similar to one large pedigree with a nonpenetrant male previously reported. The differences in lod scores seen in these large pedigrees suggested there was genetic heterogeneity in linkage between families which appeared to relate to the presence of nonpenetrant males. The combined lod score for the three pedigrees with nonpenetrant males was 6.84 at theta = 0. For the 13 other pedigrees without nonpenetrant males the combined lod score was -21.81 at theta = 0, with a peak of 0.98 at theta = 0.28. When lod scores from all 16 families were combined, the value was -15.14 at theta = 0 and the overall maximum was 5.13 at theta = 0.17. To determine whether genetic heterogeneity was present, three statistical tests for heterogeneity were employed. First, a "predivided-sample" test was used. The 16 pedigrees were divided into two classes, NP and P, based upon whether or not any nonpenetrant males were detected in the pedigree. This test gave evidence for significant genetic heterogeneity whether the three large pedigrees with seven or more informative males (P less than 0.005), the eight pedigrees with three informative males (P less than 0.001), or all 16 pedigrees (P less than 0.001) were included in the analysis. Second, Morton's large sample test was employed. Significant heterogeneity was present when the analysis was restricted to the three large pedigrees (P less than 0.025), or to the eight pedigrees with informative males (P less than 0.05) but not when smaller, less informative pedigrees were also included. Third, an "admixture" test for heterogeneity was employed which tests for linkage versus no linkage. A trend toward significance was seen (0.05 less than P less than 0.10) which increased when the analysis was restricted to the larger, more informative pedigrees.(ABSTRACT TRUNCATED AT 400 WORDS)

Reduction of fragile X expression in blood after cryopreservation

Frequency of fragile X expression was investigated before and after cryopreservation (-196 degrees C) in the blood of 4 affected males, 3 fragile X carriers and in a fibroblast cell strain from a fragile X male fetus. The results indicate that there is a significant decrease (p less than 0.05) in the frequency of the fragile X expression in lymphocytes after cryopreservation, as compared to the fresh blood, but not in fibroblasts. This suggests that cryopreserved blood specimens may not be suitable for fragile X analysis.

New classes of common fragile sites induced by 5-azacytidine and bromodeoxyuridine

Two new classes of common fragile site seen in chromosomes from blood lymphocyte cultures are reported. The first class is induced in bands 1q42 and 19q13 by 5-azacytidine (5-AZA). Maximum induction of these fragile sites occurs when the 5-AZA is added 5-8h prior to harvest. The second class is induced in bands 6q13, 9p21, and 10q21 by bromodeoxyuridine (BrdU). In this instance maximum induction occurred if the BrdU was added 4-6h prior to harvest. The known fragile sites, both rare and common, are summarised.

Interstitial deletion of chromosome 3p: report of a patient and delineation of a proximal 3p deletion syndrome

We report on a patient with a de novo interstitial deletion of the proximal portion of the short arm of chromosome 3 (p12----14.2). The deleted portion excludes the constitutive fragile site assigned to band 3p14. The phenotype of the patient, together with that of three previously reported cases, seems to be sufficiently characteristic to allow the delineation of a proximal 3p deletion syndrome.