The incidence of unstable chromosome aberrations in peripheral blood lymphocytes from unirradiated control subjects was analyzed using cytogenetic data obtained from 9 cytogenetic laboratories located in Moscow, St.-Petersburg, Obninsk, and Dubna (Russia). The objective of this study was to estimate the level and spectrum of spontaneous chromosome aberrations in human lymphocytes. 1140 blood samples were taken from 1112 subjects (594 men and 546 women) aged 1 to 72. The total metaphase number was 466795. The uniform Giemsa method for peripheral blood lymphocyte cultures was used. After counting 466795 metaphases, 4288 chromosomal aberrations of various types were classified. The most frequent types of aberrations were acentrics and chromatid deletions. They made up 90% of the total number of aberrations. The remaining 10% were exchange aberrations. The number of chromosome exchanges (dicentrics and centric rings) was twice the number of chromatid exchanges. Overall, the portion ofcells with chromosomal or (and) chromatid aberrations was 0.89 +/- 0.01%; the frequency of acentrics was 0.29 +/- 0.01; the frequency of dicentrics was 0.046 +/- 0.003; the frequency of unstable chromosome aberrations was 0.35 +/- 0.01; and the frequency of chromatid aberrations was 0.57 +/- 0.01 per 100 cells.

Analysis of birth defect (BD) rates in regions of nuclear power plant locations in comparison with control regions has been performed using the BD monitoring database for 2000–2007. It has been shown that the BD rates in these regions do not differ from BD rates in control regions, for the Russia Federation on the whole and for some other countries. The results indicate that the work of nuclear power plants does not lead to an increase in the BD frequencies in these regions.

The results of radiation genetics studies are reviewed. The first series of studies concerned the role of heterogeneity of the human population for radiosensitivity of chromosomes in determining the pattern of dose-response relationships; correctness of extrapolation of averaged experimental data to low doses was demonstrated. In the second series of experiments, the radiation-induced adaptive response and the contribution of different factors, including genetic ones, to its formation in human cells were studied. A conclusion was made about impossibility of extrapolating data obtained for cell cultures to an organism as a whole or to a population. The third part of the study was of applied character: cytogenetic methods of biological dosimetry were used to estimate the doses of internal and external irradiation of children living on the territory of the Bryansk oblast contaminated after the Chernobyl accident. The results are discussed in the context of the present-day concepts of genetic control of sensitivity to environmental factors.

Based on published data on the occurrence of GST genes in various groups and populations, the authors have analyzed the potential role of polymorphism in the process of adaptation. The estimated dynamics of the occurrence of normal or deleted alleles makes it possible to assess a selection factor (S) in favor of heterozygotes / homozygotes by normal alleles. Its value can be 0.2-0.3.

The paper provides the results of calculating the risks to human health in the cities of Seversk and Tomsk. The cancer risk from man-caused radiation is 2 orders of magnitude lower than that from air pollution with chemical carcinogens. Air contamination of classical chemical pollutants presents a major hazard to human health.

Lymphocytes were characterized by cytogenetic, cytochemical and immune phenotype parameters. The stratification of the children population was demonstrated: in lymphocytes of children living on more contaminated territories (over 15 Ci/square km), radiation-induced aberrations ape often, and judging by environment-dependent cytochemical lymphocyte markers, these children have a higher risk of the possible foreseen accident consequences. 5.5 per cent of children-residents of Krasnogorsk district have accumulated inside their bodies dangerous amounts of cesium 137, producing additional internal irradiation at annual dose of over 1 mZv. The majority of these so called "accumulator" children live on the territories where soil contamination with Cs-137 exceeds 15 Ci/square km; (and even 40 Ci/square km). Significantly more radiation-induced chromosome aberrations, decreased absolute lymphocytes number (CD2+, CD4+ subsets also decreased), and significantly lower number of lymphocytes with point nonspecific esterase (the marker of mature T-lymphocytes) were observed in these "accumulator" children. While analyzing cytochemical lymphocytograms in 1994-1995 we revealed some unfavorable trends implying probable enhancement of thyroid cancer and other chronic pathologies against the background of weakened immunity.

Experimental evidence for the existence of local spontaneous DNA synthesis in PHA-stimulated human lymphocytes at the G(1) phase (G(1) process) is presented. This process is associated with the appearance of single-stranded DNA breaks and their subsequent reparation. DNA sequences involved in the G(1) process were characterized in terms of their nucleotide composition and association with the nuclear matrix. It was shown that the G(1) process occurs in chromosome regions in which radiation-induced exchange-type chromosome aberrations arise. The results of the study are regarded as evidence in favor of a molecular version of the primary contact theory of chromosomal mutagenesis. A possible role of G(1) process disturbances in pathogenesis of chromosome instability syndromes in humans is discussed.

Experimental evidence for the existence of local spontaneous DNA synthesis in PHA-stimulated human lymphocytes at the G1 phase (G1 process) is presented. This process is associated with the appearance of single-stranded DNA breaks and their subsequent reparation. DNA sequences involved in the G1 process were characterized in terms of their nucleotide composition and association with the nuclear matrix. It was shown that the G1 process occurs in chromosome regions in which radiation-induced exchange-type chromosome aberrations arise. The results of the study are regarded as evidence in favor of a molecular version of the primary contact theory of chromosomal mutagenesis. A possible role of G1 process disturbances in pathogenesis of chromosome instability syndromes in humans is discussed.

The frequency of chromosome aberrations (CA) was studied in peripheral blood lymphocytes from healthy children and children with thyreopathology living in the city of Klintsy, Bryansk Province (contamination level up to 5 Ci/km2), and two Moscow groups, respectively. We have observed the elevated number of dicentrics and acentric fragments in cell from children with thyreopathology with respect to those from healthy children living in Klintsy. This fact cannot be explained by influence of disease because there was no difference in cytogenetical markers between the groups of healthy children and children with thyreopathology from Moscow. The number of dicentrics was increased in cells from children with high level of internal contamination (more than 400 nCi) living in Krasnaya Gora (15-40 Ci/km2). It is proposed that the internal irradiation is more important for the CA induction. The symmetrical translocation analysis using the method of fluorescence in situ hybridisation (FISH) has shown the absence of this type of aberrations in cells from children with high level of internal irradiation whereas the translocations frequency in cells from control children was (1.1 +/- 0.4) per 1000 cells.

The number of unstable chromosome aberrations was determined in peripheral blood lymphocytes from 15 children with thyreopathology living in Klintsy (Bryansk Province); the mean age was 14 years. The number of dicentric chromosome is determined to be (0.18 +/- 0.07) per 100 cells and is significantly higher than that in cells from healthy children of Klintsy and Moscow (control). There was no differences in the frequency of other types of chromosome aberrations as well as of aberrant cells.

In studying the radioprotective action of natural and synthesised antioxydants a decreased yield of chromosome aberrations with respect to those in untreated cells was noted in normal cells irradiated in phase G1 whereas no radioprotective effect was found in cells irradiated in G0. The addition of antioxydants into the cell cultures from patients with Turner's syndrome did not change their radiosensitivity. No adaptive response was induced in lymphocytes from patients with Down's syndrome cultivated with vitamin E.

The adaptive syndrome and response (AR) in lymphocytes from 6 patients with Down syndrome (DS) were investigated. No AR was found to occur in all cases in DS cells pre-exposed to 3 rad of X-rays in S phase of cell cycle and then irradiated with 150 rad of gamma rays in G2 whereas the chromosome aberrations yield in cells from control donors was decreased twice under such conditions of the experiment.

Presented are the results of an investigation of the dose-response relationship for the yield of chromosome aberrations in peripheral blood lymphocytes of persons with some hereditary diseases which represent the high risk group with respect to the increased incidence of malignant tumors and decreased life span. Despite substantially different absolute radiosensitivities of chromosomes, the variations of the alpha/beta ratio determining the extrapolation of experimental dose-response relationships to low doses did not prove to be too high, the mean deviation from the control being 15%. This points to the possible practical use of the dose-response relationships averaged over the human population as a whole.

The authors review both their own findings and literature data about chromosomal instability in neurologic diseases. The genetic mechanisms responsible for the development of chromosomal instability and its role in the pathogenesis of different diseases of the nervous system are discussed.

A study was made of the yield of chromosome aberrations in gamma-irradiated G0 peripheral blood lymphocytes from 6 patients with different forms of Down's syndrome. The doses used were from 0.25 to 3.0 Gy. Seven healthy donors of different age made the control group. There was a significant increase in the yield of chromosome exchanges in lymphocytes from all the patients as compared to control. The spontaneous level of chromosome aberrations and the frequency of radiation-induced fragments did not differ from the control values. The yield of exchanges in diploid and trisomic cells from patients with the mosaic form of Down's syndrome did not change significantly as the time of cultivation was raised. The origin of DNA repair defects leading to the increased chromosome radiosensitivity in Down's syndrome is discussed.