Sister-chromatid exchange in childhood in relation to age and sex

Cell proliferation kinetics and genotoxicity in lymphocytes of smokers living in Mexico City

Genotoxicity caused by tobacco smoke was assessed in peripheral blood lymphocytes of smokers living in Mexico City by determining sister chromatid exchange (SCE), cell proliferation kinetics (CPK), replication index (RI) and mitotic index (MI). Nicotine levels, and its major metabolite cotinine, were also estimated in urine samples using gas-chromatography-mass spectrometry to quantify smoking intensity. The outcome of the analysis and the comparison of the 77-smoker group with a non-smoking control group showed that moderate and heavy smokers exhibited significant differences (P < 0.001 and P < 0.05, respectively) in CPK, with an underlying delay in the cellular cycle; similarly, RI was significantly different in these groups (P < 0.001 and P < 0.0001, respectively). There were significant correlations (P < 0.05) between age and number of years the subject had been smoking, as well as between RI and nicotine and cotinine levels and between CPK (M1, M2 and M3) and nicotine and cotinine levels. Smokers were classified for the analysis according to the nicotine levels (it is in relation to number of cigarettes smoked per day) found in urine (ng/mL) as: light (10-250), moderate (251-850) and heavy (851-4110). Significant differences in CPK were found (P < 0.05) between moderate and heavy smokers and non-smokers. Significant differences in RI were found between moderate (P < 0.001) and heavy smokers (P < 0.0001) and non-smokers, but not for the light smoking group. MI was determined in 57 of the smokers, whereas SCE frequency was only recorded in 34 smokers. Both parameters yielded no significant differences, nor correlations with any of the assessed variables. In conclusion, cytokinetic and cytostatic effects were mainly detected in heavy and moderate smokers. Cell cycle delay and RI decrease were found in all ;healthy' smokers. The nicotine and cotinine exposure (causing oxidative damage to DNA) may have implications in the decrease in cell replication due to direct damage to DNA and/or a decrease in the DNA repair mechanisms. Alternatively, nicotine and cotinine may possibly induce apoptosis.

Propofol anesthesia in children does not induce sister chromatid exchanges in lymphocytes

BACKGROUND

Propofol is frequently used for general anesthesia in children although little is known about possible genotoxic effects in humans. We investigated the formation of sister chromatid exchanges (SCE) in metaphase chromosomes of T-lymphocytes of children as a marker for possible genotoxocity following total intravenous anesthesia with propofol for minor surgical procedures.

METHODS

40 children ASA classification I-III were included (ASA I n=34, ASA II n=5, ASA III n=1) in the study. Anesthesia was induced by propofol (3mg/kg) and alfentanil. Succinylcholine or rocuronium were administered for muscle relaxation. After tracheal intubation anesthesia was maintained by continuous propofol infusion at 12 mg/(kgh). Blood samples were drawn before induction and after termination of anesthesia. Following a 72 h cell culture period, 25 T-lymphocyte metaphases per blood sample for all children were analyzed for SCE frequencies.

RESULTS

Total intravenous anesthesia with propofol on children did not influence SCE rates in metaphase chromosomes of T-lymphocytes. No SCE differences could be detected between blood samples before initiation and after termination of anesthesia (Wilcoxon signed rank test). Slightly elevated SCE rates were obtained in T-lymphocytes of girls compared to boys, but these differences did not reach statistical significance.

CONCLUSIONS

Propofol anesthesia under the chosen conditions did not induce the formation of SCE in children in vivo. No genotoxic effect of a short term exposure to propofol during pediatric anesthesia had been observed.

Variation of micronucleated erythrocytes in peripheral blood of Sciurus aureogaster in relation to age: an increment of micronucleated polychromatic erythrocytes after the administration of colchicine

In some species, in which the human is included, the influence of age in the variation in the number of micronucleated erythrocytes (MNE) is known. In the present work we show how the process of aging influences the number of spontaneous MNE in the gray squirrel (Sciurus aureogaster). Because of the difficulty of knowing the age of each animal, 69 animals were weighed at their arrival to the laboratory and at the start of sample taking, with the supposition that the heaviest animals were the oldest and those with the lightest weight were the youngest. The major number of MNE was found in the younger animals, whereas the adults displayed less MNE (P < 0.0001). A group of 11 animals were sampled every 15 days over a period of 6 months, and the number of MNE were found to decrease with an increment in the weight in conformity with the time elapsed. These results showed that in the gray squirrel, the number of spontaneous MNE in peripheral blood depend on age. An additional interesting datum about the increment of MNE after the administration of colchicine is shown.

Induction of micronuclei in the domestic cat (Felis domesticus) peripheral blood by colchicine and cytosine-arabinoside

One advantage of bioassays over other kinds of tests is the processing or metabolism of the compound by the organism. In a previous work, in which we reported the number of micronucleated erythrocytes (MNE) in the peripheral blood of 35 species, the cat was one of the species with the highest number of micronuclei (MN). Cats have a low level of circulating polychromatic erythrocytes (PCE), i.e. 0.05%, which is much lower than in the laboratory mouse, but higher than in species such as cows, donkeys, sheep, goats and horses. Thus, MN were scored in total blood erythrocytes. In the present work, we assess the cat as a test system for MN induction. Three doses of a colchicine-cytosine arabinoside mixture were administered to young cats during 4 days; then, the numbers of MNE in blood collected before the first injection and 48 and 96 h later were compared. The number of MNE increased with time, reaching the highest values in the samples taken 96 h after the administration of the micronucleogenic agents.

Sister chromatid exchange and micronucleus frequency in human lymphocytes of 1,650 subjects in an Italian population: II. Contribution of sex, age, and lifestyle

Sister chromatid exchange (SCE) and micronuclei (MN) analysis was carried out on 1,650 healthy individuals living in Pisa and in two nearby small cities, Cascina and Navacchio (Ca-Na). The effect of smoking on SCEs was linearly correlated with the number of cigarettes per day, and an increase of 7.3% SCEs was detectable for as few cigarettes as 1-10/day. Ex-smokers showed intermediate mean values of SCEs (8.09 +/- 1.88) in comparison with never smokers (7.54 +/- 1.61) and current smokers (8.45 +/- 1.94). Mean values of SCEs of ex-smokers decreased linearly with time of smoking cessation, reaching the mean values of never smokers within 8 years. The extent of SCE decrease was inversely proportional to the number of cigarettes previously smoked. No interaction between smoking habits and coffee or alcohol drinking on SCEs was observed. A borderline (P = 0.053) increase in mean SCE values in coffee drinkers (more than 3 cups/day) was found. The age effect on SCEs was remarkable in Ca-Na, but not in Pisa donors. Job type was not associated with significant modification of mean values of SCEs. Multiple logistic regression analysis revealed a statistically significant association between the proportion of high frequency cells (HCF) outliers and coffee consumption. Age and sex appeared to be by far the most important variables associated with modifications in MN frequency, which increased by 0.04 per thousand and 0.02 per thousand per year in males and females, respectively. Children and young donors (age < or = 40 years) showed lower MN frequency regardless of sex, whereas sex appeared to determine a significantly higher increase of MN only in females older than 40 years. In contrast, in males the MN rate by age tended to level off after the age of 30-50. MN frequencies of Pisa blue- and white-collar workers were statistically significantly higher than in students (+0.71 and +0.55 per thousand, respectively). Smoking did not determine any increase of MN frequency. A total lack of correlation (P = 0.913) between MN and SCEs was observed.

Modulating factors of individual sensitivity to diepoxybutane: sister chromatid exchanges induced in vitro in human lymphocytes

Spontaneous and diepoxybutane (DEB)-induced sister chromatid exchanges (SCEs) were examined in cultured peripheral lymphocytes (PBL) from 122 healthy donors. SCE-inducing activity under defined experimental conditions and individual sensitivity to genotoxic stress were assessed. SCE means distribution appeared asymmetrical, identifying about 22% of subjects characterized by a 'high-respondent' phenotype with more than 111 SCEs/cell. Confounding factors, such as smoking habit, wine and coffee consumption, work activity and hematological factors, showed a limited capacity to affect individual SCE responsiveness, however hemoglobin and uric acid seemed to antagonize DEB genotoxicity.

Cytogenetic biomonitoring of a population of children allegedly exposed to environmental pollutants. Phase 2: Results of a three-year longitudinal study

Our previous cytogenetic biomonitoring of a group of inhabitants in a village (Mellery, Belgium) where exposure to a mixture of toxic environmental pollutants, (probably originating from a neighbouring chemical waste disposal site) was suspected, showed that difference in the SCE and HFC bioassays was more pronounced for children. The results of follow-up study in 1992 confirmed this surprising conclusion by an even higher incidence. As very few studies have been performed on the levels of children's biomarkers, this group of exposed populations needed to be explored further. Do children residing in the vicinity of hazardous waste sites indeed represent a population at higher risk? In the present study, we compare the performance of various bioassays (SCE, HFC, SSB and MN) in extended exposed and reference children's groups. Simultaneously, in the exposed group, we followed variation in the lymphocyte SCE frequencies as a function of time. Reversibility of the latter biomarker was ascertained subsequent to a preliminary technical remediation of the disposal site. We compared these data with those obtained from a synchronous cross-sectional study on a group of children living near a similar chemical disposal site. The two exposed populations did not differ from the reference population regarding to the SCE and HFC mean levels. Comparisons of the mean levels of the two other biomarkers, SSB and MN, showed no difference between the Mellery exposed children and the reference group from Wavre whereas significant differences appeared when the Hensies group is compared either to the Mellery or to the Wavre reference group.

Increased rate of spontaneous mitotic recombination in T lymphocytes from a Bloom's syndrome patient using a flow-cytometric assay at HLA-A locus

Bloom's syndrome (BS) is an autosomal recessive disorder conferring high propensity for cancer and displaying a high degree of genetic instability; the frequency of sister chromatid exchange is characteristically 10 times above background. The symmetrical four-armed chromatid interchanges are much more readily detected in peripheral blood lymphocytes of BS patients, suggesting that the frequency of somatic recombination is also increased. In the present study, the rate of spontaneous loss of HLA-A allele expression was estimated following fluctuation analysis in cultured T lymphocytes using a flow-cytometric assay. It was found to be 10 times or more higher than normal in lymphocytes from a BS patient. Molecular and chromosome analyses showed that all 13 independent variants from the patient were most likely derived from somatic recombinations. Further tests for loss of heterozygosity at a closely linked proximal locus, HLA-DQA1, showed that as many as half of the recombinants retained heterozygosity irrespective of the donor. The results suggest that the HLA region is hyperrecombinogenic in somatic cells and that the elevated recombination rate in BS cells results from the general increase at ordinary sites and not from random creation of unusual sites for recombination.

No significant increase in sister-chromatid exchanges in cultured blood lymphocytes from workers in a large oil refinery

In order to assess the potential genotoxic effects of occupational exposure to petrochemicals, the incidence of sister-chromatid exchanges (SCE) in cultured lymphocytes was studied. Blood samples were taken from 233 individuals (184 exposed and 49 worksite controls) in an oil refinery and from 47 community control persons. The data showed a non-significant elevation of SCE frequency in occupationally exposed workers when compared to non-exposed individuals. The mean SCE frequency per cell ranged from 7.55 +/- 0.55 in blood of lube oil blending and canning (LOBC) workers to 9.13 +/- 0.71 in catalytic cracking and water treatment (CCWT) workers. The control values were 6.2 +/- 0.67 and 7.21 +/- 0.45 in the community and worksite individuals, respectively. Furthermore, the SCE frequencies were influenced neither by age nor by smoking.

Cytogenetic monitoring of a village population potentially exposed to a low level of environmental pollutants. Phase 1:SCE analysis

By analogy to the techniques applied for monitoring biological effects of exposure to genotoxic agents in occupational populations, we have carried out cytogenetic monitoring in a group of inhabitants of a village (Mellery, Belgium) suspected to have been exposed to a variety of toxic environmental pollutants. These pollutants probably originated from a neighboring chemical wastes site. A group of 51 environmentally exposed and 52 reference persons (including children) were examined for the frequency of sister-chromatid exchanges (SCE) in their peripheral blood lymphocytes. The technique was further refined by using a high frequency cells (HFC) analysis. Analysis of the reference subgroups showed a significant difference between non-smoking adults and children. The influence of tobacco was clear, too. In the exposed group, no significant differences could be demonstrated between either the smokers or the non-smokers or the children. Furthermore, not only were the mean frequencies of SCE higher than in the respective reference subgroups but comparison between the two groups also showed a higher number of individuals presenting a HFC level above the background in the exposed group. Surprisingly, the difference was more pronounced for the children. A follow-up of the same exposed population carried out 18 months later and after remediation of the atmospheric chemical release, the previously observed tendencies in the exposure parameter remained unmodified.

A cytogenetic study of cows from a highly industrial or an agricultural region

An examination was made of the frequency of chromosomal aberrations and sister-chromatid exchange in the blood lymphocytes of cows from an industrial region (aluminium smelting plant, lignite quarries, briquette factory, electric plants, mechanical plants. The control group consisted of cows from an agricultural region. In cows from the industrial region a significantly higher level of chromosomal aberrations was observed than in cows from the agricultural region (5.82 +/- 0.46 vs. 2.11 +/- 0.31 per 100 cells). In older, 7-12-year-old cows from the industrial region a slightly higher level of chromosomal aberrations was observed, and a significantly higher level of gaps than in younger cows. The frequency of SCE in the blood lymphocytes of cows from the industrial region was also higher and reached 7.47 +/- 2.33 per cell, while in cows from the agricultural region it was only 6.38 +/- 1.88, but these differences were not significant statistically. However, significant differences were observed in the number of SCE between the age groups within the industrial region P < or = 0.001) in favour of the younger animals. The results obtained indicate that the industrial pollution emitted into the environment may have a genotoxic character. Thus cytogenetic examination of cattle may be a useful test for monitoring industrial pollution.

Baseline frequency of sister-chromatid exchanges in 142 persons of the general Korean population

Baseline frequencies of sister-chromatid exchange (SCE) were measured in lymphocytes of 142 healthy Koreans ranging in age from newborn infants to the fifties. The overall mean frequency of SCE was 8.78 +/- 0.24/cell. However, highly significant differences were found between individuals. The mean SCE values of the newborn babies and small children less than 10 years old were significantly lower than those of other age groups. No age effect was, however, observed in adolescent and adult subjects. Females had statistically higher SCE levels than males. The mean SCE frequencies of smokers, measured in male subjects more than 10 years old, were slightly, but statistically significantly, higher than those of non-smokers.

Sister-chromatid exchange rates in XX and XY cells of ten chimeric Callithrix jacchus individuals

In order to ascertain whether or not sister-chromatid exchange (SCE) differs in relation to sex, SCE rates in XX and XY cells from 10 specimens of marmoset (Callithrix jacchus) were examined. The choice of this primate is particularly suitable for three reasons: most individuals have a chimeric constitution, the X chromosome is quite large and the Y chromosome is particularly small. Therefore, the influence of possible differences in their exposure to the external environment can be eliminated. The results obtained did not reveal any significant difference between SCE rates in male and female cells in any of the examined individuals.

Chromosomal alterations and sister chromatid exchanges induced by zirconium oxychloride in human lymphocytes in vitro with relation to age of donors

Aqueous solutions of zirconium oxychloride were added to human peripheral blood lymphocyte culture. Cultures were set up from healthy donors of both sexes belonging to age groups of 0-10, 11-20, 21-30, 31-40, 41-50 and 51-60 years. Airdried Giemsa schedule was followed for preparation of chromosomal aberrations and micronuclei count. Flourescence plus Giemsa staining techniques were applied for the study of sister chromatid exchange. The endpoints screened were chromosome and chromatid breaks, dicentrics and rearrangements. The frequencies of chromosomal aberrations and sister chromatid exchanges induced were compared between the samples of different age groups. The frequency of CA could not be related to age of the donor. However, the frequency of SCE increased with increase in age of female donor.

The effect of aging on cell-cycle kinetics and X-ray-induced chromosome aberrations in cultured lymphocytes from patients with Down syndrome

To evaluate the effects of aging on cytogenetic characteristics of lymphocytes from Down syndrome (DS), cell-cycle kinetics after PHA stimulation and chromosome-type aberration frequencies after X-ray exposure were investigated in vitro in the lymphocytes derived from 4 (or 3 for X-ray treatment) age groups of DS patients and age-matched controls. The results clearly showed higher mitotic and proliferation index levels in younger groups compared to older groups at the various culture intervals, whether the lymphocytes were from the DS patients or controls. The age-related changes of the proliferation index were mainly attributed to a delayed response to PHA as age increased. The changes of PHA responses seemed to be particularly marked during adolescence. Nonetheless, no significant differences were observed between the DS patients and age-matched controls for each age group. In all age groups, frequencies of both chromosome-type exchanges and deletions were elevated in the DS patients by about 1.3 times in comparison with the controls. The magnitude of radiosensitivity, however, seemed to decrease slightly in the 40-49-year group. To our knowledge, the present study is the first report in the literature to deal with the effect of aging on the greater radiosensitivity of DS lymphocytes.

Sister-chromatid exchanges in cannabis smokers

The genotoxicity of cannabis smoking was evaluated by means of the sister-chromatid exchange (SCE) test. The SCE test is considered to be a sensitive tool for the discovery of genotoxic agents in the environment. Twenty-two tobacco smokers and 22 persons smoking both tobacco and cannabis were compared. Our findings showed that smoking in itself enhanced the SCE level significantly (18.5%) compared to a group of non-smokers, but adding smoking of cannabis to tobacco smoking did not affect the SCE level further. Based on our observations cannabis smoking could not be considered genotoxic.

Micronucleated lymphocytes in people occupationally exposed to potential environmental contaminants: the age effect

This work is part of a research project on 2 groups of tannery workers (i.e., workers employed in the tanning process and those employed in the finishing department), and 2 control groups consisting of individuals paired with each exposed person according to sex, age and smoking habit. The whole study included the evaluation of micronuclei as well as of chromosomal aberrations and sister-chromatid exchanges in peripheral blood lymphocytes. Data on micronucleus analysis in both controls and exposed persons are shown in this paper. There was no statistically significant difference between MN frequencies in the 2 groups of exposed and controls, nor any positive correlation with smoking habit. The effect of age on basal frequency of micronucleated cells clearly emerges in the present study: both controls and exposed show an increase in MN frequency due to age. This could be correlated with a higher sensitivity to breaks, rearrangements or aneuploidogenic events of circulating lymphocytes in aged people.

Cytogenetic effects of phenytoin and/or carbamazepine on human peripheral leukocytes

The cytogenetic effects of phenytoin (PHT) and/or carbamazepine (CBZ) were studied to determine clastogenic potential. Comparative analysis of chromosome breakage and sister chromatid exchange (SCE) was performed between 18 patients with epilepsy receiving PHT and/or CBZ and 10 healthy nontreated controls. These studies failed to detect a significant increase in chromosome aberrations or SCEs in groups of treated individuals as compared with controls. No correlation was observed between the rate of either chromosome damage or SCEs and age, sex, drug blood level, or daily dose. The results indicate no detectable chromosome damaging effects of PHT alone, CBZ alone, or a combination of these two antiepileptic drugs (AEDs).

Lack of sister chromatid exchange induction in phenytoin-treated patients with epilepsy

Phenytoin (PHT) has been suspected of having a mutagenic effect with chronic administration, but the existing evidence is equivocal. Contradictory results have been obtained using different testing systems. Sister chromatid exchange (SCE), a sensitive indicator of genotoxic environmental influences, has been used in only a few limited studies of PHT users, with varying results. The present study was designed to evaluate the potential mutagenicity of PHT in a more objective and reliable way than has been done previously. Following careful screening procedures, 16 adult male patients with epilepsy receiving long-term PHT monotherapy and 16 healthy controls were selected for a study of SCE frequencies in peripheral lymphocytes. The patients and controls were matched for sex, age, and smoking habits. Strict exclusionary criteria were observed, including all factors known to affect or suspected of affecting the SCE frequencies. Statistical analyses did not reveal any significant differences between the SCE rates of PHT-treated patients and controls, indicating a lack of PHT mutagenicity as expressed by induction of SCE in adults.

Sister chromatid exchange in human chromosomes from normal individuals and epileptic patients on combinations of anticonvulsants

Sister chromatid exchange (SCE) frequency, a sensitive indicator in mutagenicity testing, and mitotic index (MI) have been studied to observe genotoxic effects in epileptic patients on routine combinations of anticonvulsant therapy. All patients, both male and female and from various age groups, revealed an increased frequency of SCE per metaphase and a low MI (P less than 0.001) with respect to controls. A nonsignificant decrease in SCE frequency has been observed with an increase in the age of onset of epilepsy. Although the SCE frequency increased and the MI decreased in some groups with respect to the duration of epilepsy, there was no difference observed in SCE frequency with the duration of therapy.

Variation in the human lymphocyte sister-chromatid exchange frequency: results of a long-term longitudinal study

The variation in lymphocyte sister-chromatid exchange (SCE) frequency as a function of time was investigated in nonsmokers and smokers. The smokers were divided into 3 groups depending on their smoking status. The group termed 'smokers' participated in a program to stop smoking but did not reduce or eliminate their use of tobacco; 'smoke enders' successfully completed the smokending program and remained free of tobacco for the duration of the study, while the 'variable' group stopped smoking for a limited time but then resumed smoking. 8 or more blood samples per person were obtained over a period of at least 12 months. The SCE frequencies for each of these groups were compared with each other and with those of two previous longitudinal study groups from our laboratory. The proportion of high-frequency cells (HFCs) was also determined for each sample. The results confirm our previous finding that SCE frequencies and the proportion of HFCs observed in separate samples from the same individual are more likely to be different as the time between samples increases. We also show that smokers have significantly more SCEs and HFCs than do nonsmokers, that SCE frequencies in smokers do not decline for at least 12 months when smoking is stopped, and that among smokers, significant seasonal variation in the SCE frequency occurs. These results provide useful information concerning the effects of smoking upon SCE frequencies, and will be helpful in designing and interpreting the results of long-term human population cytogenetic studies.

A further assessment of factors influencing measurements of thioguanine-resistant mutant frequency in circulating T-lymphocytes

We have used the T-Lymphocyte cloning technique as a method of monitoring the human population for somatic cell mutant frequency. We present a statistical analysis of the experimental factors which may influence the observed mutant frequency. We have obtained consistently high plating efficiencies of T-cells from the mononuclear cell fraction from donor blood samples (mean of 56%, based on 123 observations from 70 individuals). Nevertheless, an inverse correlation of mutant frequency with plating efficiency was observed, and some experimental factors (serum and interleukin-2 batch, and worker) may have a significant effect on the observed mutant frequency. We discuss the difficulties that these possible effects present in establishment of a reference database and design of long-term studies. No significant effect of donor sex on mutant frequency was observed, but age (1.3% increase per year for normal adults) and smoking (56% increase over normal non-smokers) both significantly increased the mutant frequency. We discuss the utility of the assay for the monitoring of populations for heritable DNA damage, and we compare the results to those obtained with lymphocytes using other endpoints, e.g. chromosome aberrations, micronuclei and sister-chromatid exchange.

Chromosomal aberration and sister-chromatid exchange frequencies in peripheral blood lymphocytes of a large human population sample

In order to assess the potential of cytogenetic determinations on peripheral blood lymphocytes as a means of monitoring human populations subject to low level occupational and environmental exposures to chemical mutagens and carcinogens, accurate baseline data are required. Accordingly, we have determined mean frequencies of chromosomal aberrations and of sister-chromatid exchanges, their variances, and the sources of this variance in a cohort of 353 healthy employees of the Brookhaven National Laboratory. A detailed protocol was adopted for blood sampling, lymphocyte culture, cytogenetic preparation and scoring in order to minimize variation from these potential sources. Scoring was divided between the Oak Ridge and the Brookhaven groups with duplicate scoring sufficient to evaluate and minimize the effect of any differences between laboratories or between individual scorers. In all, the data include 71,950 cells scored for chromosomal aberrations and 16,898 cells scored for sister-chromatid exchanges. The mean unadjusted frequency of sister-chromatid exchanges was 8.29 +/- 0.08/cell. As reported in other studies, cigarette smoking very significantly influenced sister-chromatid exchange frequencies; in our study the mean for smokers was 9.0 +/- 0.2, while that for non-smokers was 8.1 +/- 0.1/cell. The mean frequency was statistically higher in females than in males, regardless of smoking status. On the other hand, age of the subject did not significantly influence sister-chromatid exchange frequencies. Curiously, the subject's total white cell count did influence sister-chromatid exchange frequency. No other source of variation was found. The frequencies of chromosomal aberrations of all types were determined. The frequency of the most common unequivocal chromatid type, the chromatid deletion, was 0.81 +/- 0.05%, that of the most common unequivocal chromosome type, the dicentric, was 0.16 +/- 0.02%. No statistically significant influence was found of age or sex, nor of any other parameter tested, on the frequency of any chromosomal aberration type, with the single exception of long acentric fragments, often "supernumerary", believed to represent X chromosomes precociously separated at the centromere. Such fragments were significantly more frequent in samples from females than those from males, and showed a significant positive regression on age.

Sister-chromatid exchanges in lymphocytes from patients with Schistosoma hematobium

Sister-chromatid exchange (SCE) frequencies were studied in peripheral blood lymphocytes from 19 patients (13 males and 6 females) with Schistosoma hematobium, prior to the initiation of chemotherapy. The mean frequency of SCE per metaphase for the patients (both sexes) was 10.4 +/- 4.2 which was significantly higher (P less than 0.01) than the mean SCE (6.4 +/- 1.1) score for 35 healthy controls. A highly significant reduction in lymphocyte division and delay in cell-cycle progression as a result of infection were also noticed. These data indicate that infection with S. hematobium could increase SCEs in the host somatic cells.