Microsatellite mutations show no increases in the children of the Chernobyl liquidators

A systematic review of human evidence for the intergenerational effects of exposure to ionizing radiation

PURPOSE

To provide a synthesis of the published evidence pertaining to the intergenerational health effects of parental preconceptional exposure to ionizing radiation in humans.

METHODS

The study populations are the descendants of those who were exposed to ionizing radiation prior to conception. A Boolean search identified publications for review in accordance with Office of Health Assessment and Translation guidelines. Initially, a risk of bias assessment was conducted for each published study and relevant data extracted. Information was organized into adverse health outcome groups and exposure situations. To make an assessment from the body of evidence within each group, an initial confidence rating was assigned, before factors including inconsistencies between studies, magnitude of effect, dose response and confounders were considered. From this, 'an effect', 'no effect' or whether the evidence remained 'inadequate' to determine either effect or no effect, was ascertained. This assessment was based primarily upon the author's conclusions within that evidence-base and, by binomial probability testing of the direction of effect reported.

RESULTS

2441 publications were identified for review which after screening was reduced to 127. For the majority of the adverse health groups, we find there to be inadequate evidence from which to determine whether the health effect was, or was not, associated with parental preconceptional radiation exposure. This was largely due to heterogeneity between individual study's findings and conclusions within each group and, the limited number of studies within each group. We did observe one health grouping (congenital abnormalities) in occupationally exposed populations, where an increase in effect relative to their controls or large magnitude of effects, were reported, although it is noted that the authors of these studies interpreted their findings as most likely not to be associated with parental radiation exposure.

CONCLUSIONS

We find there to be a lack of evidence to enable the formal assessment of radiation-related adverse effects in offspring of exposed humans. This is not the same as there being no clear evidence that effects may occur but does infer that if adverse health effects do arise in children of exposed parents, then these effects are small and difficult to reproducibly measure. Inconsistencies in designing studies are unavoidable, however we highlight the need for an element of standardization and, more sharing of primary datasets as part of open access initiatives, in order for future reviews to make reasonable conclusions. Overall, there is a need for future work to ensure comparable measures between studies where possible.

Field Study of the Possible Effect of Parental Irradiation on the Germline of Children Born to Cleanup Workers and Evacuees of the Chornobyl Nuclear Accident

Although transgenerational effects of exposure to ionizing radiation have long been a concern, human research to date has been confined to studies of disease phenotypes in groups exposed to high doses and high dose rates, such as the Japanese atomic bomb survivors. Transgenerational effects of parental irradiation can be addressed using powerful new genomic technologies. In collaboration with the Ukrainian National Research Center for Radiation Medicine, the US National Cancer Institute, in 2014-2018, initiated a genomic alterations study among children born in selected regions of Ukraine to cleanup workers and/or evacuees exposed to low-dose-rate radiation after the 1986 Chornobyl (Chernobyl) nuclear accident. To investigate whether parental radiation exposure is associated with germline mutations and genomic alterations in the offspring, we are collecting biospecimens from father-mother-offspring constellations to study de novo mutations, minisatellite mutations, copy-number changes, structural variants, genomic insertions and deletions, methylation profiles, and telomere length. Genomic alterations are being examined in relation to parental gonadal dose, reconstructed using questionnaire and measurement data. Subjects are being recruited in exposure categories that will allow examination of parental origin, duration, and timing of exposure in relation to conception. Here we describe the study methodology and recruitment results and provide descriptive information on the first 150 families (mother-father-child(ren)) enrolled.

Chronic radiation exposure at Chernobyl shows no effect on genetic diversity in the freshwater crustacean, Asellus aquaticus thirty years on

Analysis of genetic diversity represents a fundamental component of ecological risk assessments in contaminated environments. Many studies have assessed the genetic implications of chronic radiation exposure at Chernobyl, generally recording an elevated genetic diversity and mutation rate in rodents, plants, and birds inhabiting contaminated areas. Only limited studies have considered genetic diversity in aquatic biota at Chernobyl, despite the large number of freshwater systems where elevated dose rates will persist for many years. Consequently, the present study aimed to assess the effects of chronic radiation exposure on genetic diversity in the freshwater crustacean, Asellus aquaticus, using a genome-wide SNP approach (Genotyping-by-sequencing). It was hypothesized that genetic diversity in A. aquaticus would be positively correlated with dose rate. A. aquaticus was collected from six lakes in Belarus and the Ukraine ranging in dose rate from 0.064 to 27.1 µGy/hr. Genotyping-by-sequencing analysis was performed on 74 individuals. A significant relationship between geographical distance and genetic differentiation confirmed the Isolation-by-Distance model. Conversely, no significant relationship between dose rate and genetic differentiation suggested no effect of the contamination gradient on genetic differentiation between populations. No significant relationship between five measures of genetic diversity and dose rate was recorded, suggesting that radiation exposure has not significantly influenced genetic diversity in A. aquaticus at Chernobyl. This is the first study to adopt a genome-wide SNP approach to assess the impacts of environmental radiation exposure on biota. These findings are fundamental to understanding the long-term success of aquatic populations in contaminated environments at Chernobyl and Fukushima.

The protective function of noncoding DNA in genome defense of eukaryotic male germ cells

Peripheral and abundant noncoding DNA has been hypothesized to protect the genome and the central protein-coding sequences against DNA damage in somatic genome. In the cytosol, invading exogenous nucleic acids may first be deactivated by small RNAs encoded by noncoding DNA via mechanisms similar to the prokaryotic CRISPR-Cas system. In the nucleus, the radicals generated by radiation in the cytosol, radiation energy and invading exogenous nucleic acids are absorbed, blocked and/or reduced by peripheral heterochromatin, and damaged DNA in heterochromatin is removed and excluded from the nucleus to the cytoplasm through nuclear pore complexes. To further strengthen the hypothesis, this review summarizes the experimental evidence supporting the protective function of noncoding DNA in the genome of male germ cells. Based on these data, this review provides evidence supporting the protective role of noncoding DNA in the genome defense of sperm genome through similar mechanisms to those of the somatic genome.

Radioactively contaminated areas: Bioindicator species and biomarkers of effect in an early warning scheme for a preliminary risk assessment

Concerns about the impacts on public health and on the natural environment have been raised regarding the full range of operational activities related to uranium mining and the rest of the nuclear fuel cycle (including nuclear accidents), nuclear tests and depleted uranium from military ammunitions. However, the environmental impacts of such activities, as well as their ecotoxicological/toxicological profile, are still poorly studied. Herein, it is discussed if organisms can be used as bioindicators of human health effects, posed by lifetime exposure to radioactively contaminated areas. To do so, information was gathered from several studies performed on vertebrates, invertebrate species and humans, living in these contaminated areas. The retrieved information was compared, to determine which are the most used bioindicators and biomarkers and also the similarities between human and non-human biota responses. The data evaluated are used to support the proposal for an early warning scheme, based on bioindicator species and on the most sensitive and commonly shared biomarkers, to perform a screening evaluation of radioactively contaminated sites. This scheme could be used to support decision-making for a deeper evaluation of risks to human health, making it possible to screen a large number of areas, without disturbing and alarming local populations.

Follow-up studies on genome damage in children after Chernobyl nuclear power plant accident

As children are more susceptible to ionizing radiation than adults, each nuclear accident demands special attention and care of this vulnerable population. The Chernobyl nuclear disaster occurred in a region populated with a large number of children, but despite all efforts and expertise of nuclear specialists, it was not possible to avoid casualties. As vast regions of Ukraine, Belarus and Russia were exposed to doses of ionizing radiation, which are known to be related with different diseases, shortly after the accident medical surveillance was launched, which also included analysis of genome damage. Child population affected by internal and external radiation consisted of subjects exposed prenatally, postnatally (both evacuated and non-evacuated), born by irradiated fathers who worked as liquidators, and parents exposed environmentally. In all groups of children during the last 30 years who were exposed to doses which were significantly higher than that recommended for general population of 1 mSv per year, increased genome damage was detected. Increased genome damage includes statistically higher frequency of dicentric and ring chromosomes, chromated and chromosome breaks, acentric fragments, translocations, and micronuclei. The presence of rogue cells confirmed internal contamination. Genome instability and radiosensitivity in children was detected both in evacuated and continuously exposed children. Today the population exposed to ionizing radiation in 1986 is in reproductive period of life and follow-up of this population and their offspring is of great importance. This review aims to give insight in results of studies, which reported genome damage in children in journals without language restrictions.

Irradiation of rainbow trout at early life stages results in trans-generational effects including the induction of a bystander effect in non-irradiated fish

The bystander effect, a non-targeted effect (NTE) of radiation, which describes the response by non-irradiated organisms to signals emitted by irradiated organisms, has been documented in a number of fish species. However transgenerational effects of radiation (including NTE) have yet to be studied in fish. Therefore rainbow trout, which were irradiated as eggs at 48h after fertilisation, eyed eggs, yolk sac larvae or first feeders, were bred to generate a F1 generation and these F1 fish were bred to generate a F2 generation. F1 and F2 fish were swam with non-irradiated bystander fish. Media from explants of F1 eyed eggs, F1 one year old fish gill and F1 two year old fish gill and spleen samples, and F2 two year old gill and spleen samples, as well as from bystander eggs/fish, was used to treat a reporter cell line, which was then assayed for changes in cellular survival/growth. The results were complex and dependent on irradiation history, age (in the case of the F1 generation), and were tissue specific. For example, irradiation of one parent often resulted in effects not seen with irradiation of both parents. This suggests that, unlike mammals, in certain circumstances maternal and paternal irradiation may be equally important. This study also showed that trout can induce a bystander effect 2 generations after irradiation, which further emphasises the importance of the bystander effect in aquatic radiobiology. Given the complex community structure in aquatic ecosystems, these results may have significant implications for environmental radiological protection.

Chernobyl cleanup workers from Estonia: cohort description and related epidemiological research

The Estonian study of Chernobyl cleanup workers was one of the first investigations to evaluate the possible health consequences of working in the Chernobyl area (the 30 km exclusion zone and/or adjacent territories) after the 1986 reactor accident. The cohort consists of 4831 men who were dispatched in 1986-1991 for tasks involving decontamination, construction of buildings, transport, radiation measurement, guard duty or other activities. By 31 December 2012, the follow-up of the cohort yielded 102 158 person-years of observation. Exposure and health data were collected by postal questionnaires, biodosimetry evaluations, thyroid screenings, and record-linkages with cancer, causes of death and health insurance reimbursement registers and databases. These data cover socio-demographic factors, employment history, aspects of health behaviour, medical history, work and living conditions in the Chernobyl area, biomarkers of exposure, cancer and non-cancer disease occurrence and causes of death. Cancer incidence data were obtained for 1986-2008, mortality data for 1986-2011 and non-cancer morbidity data for 2004-2012. Although the cohort is relatively small, it has been extensively examined and benefited from comprehensive nationwide population and health registers. The major finding was an increased risk of suicide. Thyroid examinations did not reveal an association with thyroid nodular disease and radiation dose, but did indicate the importance of accounting for screening when making comparisons with unscreened populations. No risk of leukaemia was observed and risks higher than 2.5-fold could be excluded with 95% confidence. Biodosimetry included GPA analyses and chromosomal translocation analyses and indicated that the Estonian cleanup workers experienced a relatively low mean exposure of the order of 0.1 Gy. One value of the Estonian study is in the methodologic processes brought to bear in addressing possible health effects from the Chernobyl accident. Twenty-five years of research are summarised and opportunities for the future listed.

Fukushima simulation experiment: assessing the effects of chronic low-dose-rate internal 137Cs radiation exposure on litter size, sex ratio, and biokinetics in mice

To investigate the transgenerational effects of chronic low-dose-rate internal radiation exposure after the Fukushima Daiichi Nuclear Power Plant accident in Japan, 18 generations of mice were maintained in a radioisotope facility, with free access to drinking water containing (137)CsCl (0 and 100 Bq/ml). The (137)Cs distribution in the organs of the mice was measured after long-term ad libitum intake of the (137)CsCl water. The litter size and the sex ratio of the group ingesting the (137)Cs water were compared with those of the control group, for all 18 generations of mice. No significant difference was noted in the litter size or the sex ratio between the mice in the control group and those in the group ingesting the (137)Cs water. The fixed internal exposure doses were ∼160 Bq/g and 80 Bq/g in the muscles and other organs, respectively.

Single-molecule PCR analysis of an unstable microsatellite for detecting mutations in sperm of mice exposed to chemical mutagens

Single-molecule PCR (SM-PCR) analysis of long and repetitive DNA sequences, known as expanded simple tandem repeats (ESTRs), has been the most efficient method for studying germline mutation induction in endogenous sequences to date. However, the long length of these sequences makes mutation detection imprecise and laborious, and they have been characterized only in mice. Here, we explore the use of unstable microsatellite sequences that can be typed with high precision by capillary electrophoresis as alternative loci for detecting germline mutations. We screened 24 microsatellite loci across inbred mouse strains and identified Mm2.2.1 as the most polymorphic microsatellite locus. We then optimized SM-PCR of Mm2.2.1 to detect mutations in sperm. SM-PCR analysis of sperm from untreated B6C3F1 and Muta(™)Mouse samples revealed mutation frequencies that are consistent with rates derived from family pedigree analysis (∼ 5 × 10(-3)). To determine whether this locus can be used to detect chemically induced germline mutations, Muta(™)Mouse males were exposed by oral gavage to a single dose of 100mg/kg of N-ethyl-N-nitrosourea (ENU) or to 100mg/kg of benzo(a)pyrene (BaP) for 28 days alongside vehicle treated controls. Sperm were collected 10 weeks post-ENU exposure to sample sperm exposed as spermatogonial stem cells and 6 weeks post-BaP exposure to sample sperm that were dividing spermatogonia when the exposure was terminated. Both treatments resulted in a significant (approximately 2-fold) increase in mutation frequency in sperm compared to the control animals. The work establishes the utility of this microsatellite for studying mutation induction in the germ cells of mice. Because microsatellites are found in virtually every species, this approach holds promise for other organisms, including humans.

Germline minisatellite mutations in workers occupationally exposed to radiation at the Sellafield nuclear facility

Germline minisatellite mutation rates were investigated in male workers occupationally exposed to radiation at the Sellafield nuclear facility. DNA samples from 160 families with 255 offspring were analysed for mutations at eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern hybridisation. No significant difference was observed between the paternal mutation rate of 5.0% (37 mutations in 736 alleles) for control fathers with a mean preconceptional testicular dose of 9 mSv and that of 5.8% (66 in 1137 alleles) for exposed fathers with a mean preconceptional testicular dose of 194 mSv. Subgrouping the exposed fathers into two dose groups with means of 111 mSv and 274 mSv revealed paternal mutation rates of 6.0% (32 mutations in 536 alleles) and 5.7% (34 mutations in 601 alleles), respectively, neither of which was significantly different in comparisons with the rate for the control fathers. Maternal mutation rates of 1.6% (12 mutations in 742 alleles) for the partners of control fathers and 1.7% (19 mutations in 1133 alleles) for partners of exposed fathers were not significantly different. This study provides evidence that paternal preconceptional occupational radiation exposure does not increase the germline minisatellite mutation rate and therefore refutes suggestions that such exposure could result in a destabilisation of the germline that can be passed on to future generations.

Aspermy, sperm quality and radiation in Chernobyl birds

BACKGROUND

Following the Chernobyl nuclear power plant accident, large amounts of radionuclides were emitted and spread in the environment. Animals living in such contaminated areas are predicted to suffer fitness costs including reductions in the quality and quantity of gametes.

METHODOLOGY/PRINCIPAL FINDINGS

We studied whether aspermy and sperm quality were affected by radioactive contamination by examining ejaculates from wild caught birds breeding in areas varying in background radiation level by more than three orders of magnitude around Chernobyl, Ukraine. The frequency of males with aspermy increased logarithmically with radiation level. While 18.4% of males from contaminated areas had no sperm that was only the case for 3.0% of males from uncontaminated control areas. Furthermore, there were negative relationships between sperm quality as reflected by reduced sperm velocity and motility, respectively, and radiation.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that radioactive contamination around Chernobyl affects sperm production and quality. We are the first to report an interspecific difference in sperm quality in relation to radioactive contamination.

p53-Dependent suppression of genome instability in germ cells

Radiation increases mutation frequencies at tandem repeat loci. Germline mutations in γ-ray-irradiated medaka fish (Oryzias latipes) were studied, focusing on the microsatellite loci. Mismatch-repair genes suppress microsatellite mutation by directly removing altered sequences at the nucleotide level, whereas the p53 gene suppresses genetic alterations by eliminating damaged cells. The contribution of these two defense mechanisms to radiation-induced microsatellite instability was addressed. The spontaneous mutation frequency was significantly higher in msh2(-/-) males than in wild-type fish, whereas there was no difference in the frequency of radiation-induced mutations between msh2(-/-) and wild-type fish. By contrast, irradiated p53(-/-) fish exhibited markedly increased mutation frequencies, whereas their spontaneous mutation frequency was the same as that of wild-type fish. In the spermatogonia of the testis, radiation induced a high level of apoptosis both in wild-type and msh2(-/-) fish, but negligible levels in p53(-/-) fish. The results demonstrate that the msh2 and p53 genes protect genome integrity against spontaneous and radiation-induced mutation by two different pathways: direct removal of mismatches and elimination of damaged cells.

Evidence relevant to untargeted and transgenerational effects in the offspring of irradiated parents

In this article we review health effects in offspring of human populations exposed as a result of radiotherapy and some groups exposed to chemotherapy. We also assess risks in offspring of other radiation-exposed groups, in particular those of the Japanese atomic bomb survivors and occupationally and environmentally exposed groups. Experimental findings are also briefly surveyed. Animal and cellular studies tend to suggest that the irradiation of males, at least at high doses (mostly 1Gy and above), can lead to observable effects (including both genetic and epigenetic) in the somatic cells of their offspring over several generations that are not attributable to the inheritance of a simple mutation through the parental germline. However, studies of disease in the offspring of irradiated humans have not identified any effects on health. The available evidence therefore suggests that human health has not been significantly affected by transgenerational effects of radiation. It is possible that transgenerational effects are restricted to relatively short times post-exposure and in humans conception at short times after exposure is likely to be rare. Further research that may help resolve the apparent discrepancies between cellular/animal studies and studies of human health are outlined.

Non-targeted effects of ionising radiation--implications for low dose risk

Non-DNA targeted effects of ionising radiation, which include genomic instability, and a variety of bystander effects including abscopal effects and bystander mediated adaptive response, have raised concerns about the magnitude of low-dose radiation risk. Genomic instability, bystander effects and adaptive responses are powered by fundamental, but not clearly understood systems that maintain tissue homeostasis. Despite excellent research in this field by various groups, there are still gaps in our understanding of the likely mechanisms associated with non-DNA targeted effects, particularly with respect to systemic (human health) consequences at low and intermediate doses of ionising radiation. Other outstanding questions include links between the different non-targeted responses and the variations in response observed between individuals and cell lines, possibly a function of genetic background. Furthermore, it is still not known what the initial target and early interactions in cells are that give rise to non-targeted responses in neighbouring or descendant cells. This paper provides a commentary on the current state of the field as a result of the non-targeted effects of ionising radiation (NOTE) Integrated Project funded by the European Union. Here we critically examine the evidence for non-targeted effects, discuss apparently contradictory results and consider implications for low-dose radiation health effects.

Characterization of unstable microsatellites in mice: no evidence for germline mutation induction following gamma-radiation exposure

Large tandem repeat DNA loci such as expanded simple tandem repeats and minisatellites are efficient markers for detecting germline mutations; however, mutation detection using these loci can be imprecise and difficult to standardize across labs. Short-tandem repeats, such as microsatellites, offer more precise and high-throughput mutation detection, but germline mutation induction at these loci has not yet been studied in model organisms such as mice. In this study, we used microsatellite enrichment and large-scale DNA sequencing of several closely related inbred mouse lines to identify a panel of 19 polymorphic microsatellites with potentially high spontaneous mutation frequencies. We used this panel and four additional loci from other sources to quantify spontaneous mutation frequency in pedigrees of outbred Swiss-Webster mice. In addition, we also examined mutation induction in families in which sires were treated with acute doses of either 0.5 Gy or 1.0 Gy gamma-irradiation to spermatogonial stem cells. Per locus mutation frequencies ranged from 0 to 5.03 × 10(-3). Considering only the 11 loci with mutations, the mutation frequencies were: control 2.78 × 10(-3), 0.5 Gy 4.09 × 10(-3), and 1.0 Gy 1.82 × 10(-3). There were no statistically significant changes in mutation frequencies among treatment groups. Our study provides the first direct quantification of microsatellite mutation frequency in the mouse germline, but shows no evidence for mutation induction at pre-meiotic male germ cells following acute gamma-irradiation. Further work using the panel is needed to examine mutation induction at different doses of radiation, exposure durations, and stages during spermatogenesis.

Effects of parental radiation exposure on developmental instability in grasshoppers

Mutagenic and epigenetic effects of environmental stressors and their transgenerational consequences are of interest to evolutionary biologists because they can amplify natural genetic variation. We studied the effect of parental exposure to radioactive contamination on offspring development in lesser marsh grasshopper Chorthippus albomarginatus. We used a geometric morphometric approach to measure fluctuating asymmetry (FA), wing shape and wing size. We measured time to sexual maturity to check whether parental exposure to radiation influenced offspring developmental trajectory and tested effects of radiation on hatching success and parental fecundity. Wings were larger in early maturing individuals born to parents from high radiation sites compared to early maturing individuals from low radiation sites. As time to sexual maturity increased, wing size decreased but more sharply in individuals from high radiation sites. Radiation exposure did not significantly affect FA or shape in wings nor did it significantly affect hatching success and fecundity. Overall, parental radiation exposure can adversely affect offspring development and fitness depending on developmental trajectories although the cause of this effect remains unclear. We suggest more direct measures of fitness and the inclusion of replication in future studies to help further our understanding of the relationship between developmental instability, fitness and environmental stress.

Sidestream tobacco smoke is a male germ cell mutagen

Active cigarette smoking increases oxidative damage, DNA adducts, DNA strand breaks, chromosomal aberrations, and heritable mutations in sperm. However, little is known regarding the effects of second-hand smoke on the male germ line. We show here that short-term exposure to mainstream tobacco smoke or sidestream tobacco smoke (STS), the main component of second-hand smoke, induces mutations at an expanded simple tandem repeat locus (Ms6-hm) in mouse sperm. We further show that the response to STS is not linear and that, for both mainstream tobacco smoke and STS, doses that induced significant increases in expanded simple tandem repeat mutations in sperm did not increase the frequencies of micronucleated reticulocytes and erythrocytes in the bone marrow and blood of exposed mice. These data show that passive exposure to cigarette smoke can cause tandem repeat mutations in sperm under conditions that may not induce genetic damage in somatic cells. Although the relationship between noncoding tandem repeat instability and mutations in functional regions of the genome is unclear, our data suggest that paternal exposure to second-hand smoke may have reproductive consequences that go beyond the passive smoker.

Mutation rates in scots pine (Pinus sylvestris L.) from the Chernobyl exclusion zone evaluated with amplified fragment-length polymorphisms (AFLPs) and microsatellite markers

Ionizing radiation is a strong mutagenic factor and, accordingly, elevated mutation rates would be expected in plants exposed to high chronic or acute radiation after the Chernobyl accident in 1986. Somatic mutations were analyzed in pines (Pinus sylvestris L.) planted before and after the Chernobyl accident and in control material of the same origin planted in sites with natural radiation. Microsatellites (SSRs) and amplified fragment-length polymorphisms (AFLPs) were investigated. The mutation rates for microsatellites were estimated as 2.8 × 10(-4)-7.1 × 10(-4) per locus for different irradiated tree populations; no mutations were detected in the controls. In the case of AFLPs, the observed mutation rates were 3.74 × 10(-3) -3.99 × 10(-3) and 1.06 × 10(-3) per locus for contaminated and control areas, respectively. Thus a statistically highly significant three-fold increase in number of mutations was found by the use of AFLP markers, indicating that ionizing radiation causes strong DNA damage across the entire genome and that AFLPs may be the appropriate marker system for this kind of analysis.

The effect of low-dose exposure on germline microsatellite mutation rates in humans accidentally exposed to caesium-137 in Goiânia

A serious radiological accident occurred in 1987 in Goiânia, Brazil, which lead to extensive human and environmental contamination as a result of ionising radiation (IR) from caesium-137. Among the exposed were those in direct contact with caesium-137, their relatives, neighbours, liquidators and health personnel involved in the handling of the radioactive material and the clean-up of the radioactive sites. The exposed group consisted of 10 two-generation families, totalling 34 people. For each exposed family, at least one of the progenitors was directly exposed to very low doses of γ-IR. The control group consisted of 215 non-irradiated families, composed of a father, mother and child, all of them from Goiânia, Brazil. Genomic DNA was purified using 100 μl of whole blood. The amplification reactions were prepared according to PowerPlex® 16, following the manufacturer's instructions. Genetic profiles were obtained from a single polymerase chain reaction amplification. The exposed group had only one germline mutation of a paternal origin in the 'locus' D8S1179 and the observed mutation presented a gain of only one repeat unit. In the control group, 11 mutations were observed and the mutational events were distributed in five loci D16S539, D3S1358, FGA, Penta E and D21S11. The mutation rates for the exposed and control groups were 0.006 and 0.002, respectively. There was no statistically significant difference (P = 0.09) between the mutation rate of the exposed and control groups. In conclusion, the quantification of mutational events in short tandem repeats can provide a useful system for detecting induced mutations in a relatively small population.

Germline minisatellite mutations in survivors of childhood and young adult cancer treated with radiation

PURPOSE

To investigate minisatellite germline mutation rates in survivors of childhood and young adult cancer who received radiotherapy.

MATERIALS AND METHODS

DNA samples from 100 families, where one parent was a cancer survivor, were analysed for mutations at eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern hybridisation.

RESULTS

No significant difference was observed between the paternal mutation rate of 5.6% in exposed fathers with a mean preconceptional testicular dose of 1.23 Gy (56 mutations in 998 informative alleles) and that of 5.8% in unexposed fathers (17 in 295 informative alleles). Subgrouping the exposed fathers into dose groups of < 0.10 Gy, 0.10-0.99 Gy, 1.00-1.99 Gy, ≥ 2.00 Gy revealed no significant differences in paternal mutation rate in comparison with the unexposed fathers. Maternal mutation rates of 1.6% in cancer survivor mothers with a mean preconceptional ovarian dose of 0.58 Gy (five mutations in 304 informative alleles) and 2.1% in unexposed mothers (21 in 987 informative alleles) were not significantly different. There were no differences in minisatellite mutation rates associated with treatment with chemotherapeutic agents.

CONCLUSIONS

This study provides evidence that preconception radiotherapy for childhood or early adulthood cancer does not increase the germline minisatellite mutation rate.

Genetics of cattails in radioactively contaminated areas around Chornobyl

Research on populations from radioactively contaminated areas around Chornobyl has produced ambiguous results for the presence of radiation effects. More studies are needed to provide information on whether radiation exposure at Chornobyl significantly affected genetic diversity in natural populations of various taxa. Eleven and nine variable microsatellite loci were used to test for differences in genetic diversity between reference and Chornobyl populations of two cattail species (Typha angustifolia and Typha latifolia, respectively) from Ukraine. Our purpose was to determine whether radiation had a significant impact on genetic diversities of the Chornobyl Typha populations, or if their genetic composition might be better explained by species demography and/or changes in population dynamics, mainly in sexual and asexual reproduction. Populations closest to the reactor had increased genetic diversities and high number of genets, which likely were due to factors other than radiation including increased gene flow among Chornobyl populations, enhanced sexual reproduction within populations, and/or origin of the genets from seed bank. Both Typha species also demonstrated small but significant effects associated with latitude, geographical regions, and watersheds. Typha's demography in Ukraine possibly varies with these three factors, and the small difference between Chornobyl and reference populations of T. latifolia detected after partitioning the total genetic variance between them is probably due primarily to these factors. However, the positive correlations of several genetic characteristics with radionuclide concentrations suggest that radiation may have also affected genetics of Chornobyl Typha populations but much less than was expected considering massive contamination of the Chornobyl area.

A pilot study examining germline minisatellite mutations in the offspring of Danish childhood and adolescent cancer survivors treated with radiotherapy

PURPOSE

To investigate germline mutation rate at eight minisatellite loci in 24 Danish families, where one parent is the survivor of childhood or adolescent cancer treated with radiotherapy.

MATERIALS AND METHODS

Parents and offspring were profiled for eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern blotting.

RESULTS

Seven paternal mutations were observed for 130 informative alleles in 18 offspring from 11 radiation-exposed fathers (mean preconceptional dose for offspring 0.29 Gy, range<0.01-1.2 Gy), compared to six mutations for 146 informative alleles in 21 offspring from 13 unexposed fathers. No statistically significant difference between the total paternal mutation rates was observed (5.4% for exposed fathers and 4.1% for unexposed fathers). Three maternal mutations were observed for 148 informative alleles in 21 offspring from 13 radiation-exposed mothers (mean preconceptional dose for offspring 0.71 Gy, range <0.01-9.2 Gy), compared to one mutation for 130 informative alleles in 18 offspring from 11 unexposed mothers. Again, no statistically significant difference was observed between the total maternal mutation rates (2.0% for exposed mothers and 0.8% for unexposed mothers).

CONCLUSIONS

The data from this pilot study demonstrate no statistically significant increase in germline minisatellite mutation rate associated with radiotherapy for childhood and adolescent cancer.

Assessing radiation-associated mutational risk to the germline: repetitive DNA sequences as mutational targets and biomarkers

This review assesses recent data on mutational risk to the germline after radiation exposure obtained by molecular analysis of tandemly repeated DNA loci (TRDLs): minisatellites in humans and expanded simple tandem repeats in mice. Some studies, particularly those including exposure to internal emitters, indicate that TRDL mutation can be used as a marker of human radiation exposure; most human studies, however, are negative. Although mouse studies have suggested that TRDL mutation analysis may be more widely applicable in biomonitoring, there are important differences between the structure of mouse and human TRDLs. Mutational mechanisms probably differ between the two species, and so care should be taken in predicting effects in humans from mouse data. In mice and humans, TRDL mutations are largely untargeted with only limited evidence of dose dependence. Transgenerational mutation has been observed in mice but not in humans, but the mechanisms driving such mutation transmission are unknown. Some minisatellite variants are associated with human diseases and may affect gene transcription, but causal relationships have not yet been established. It is concluded that at present the TRDL mutation data do not warrant a dramatic revision of germline or cancer risk estimates for radiation.

Induced transgenerational genetic effects in rodents and humans

Delayed appearance of induced mutations has been observed in Drosophila, plants, rodents and recently in humans. The significance of this phenomenon is now recognized especially after the pioneering work of Nomura demonstrating transgenerational tumour induction in mice following treatment with urethane or ionizing radiation. A brief review of the literature on transgenerational genetic effects, namely, chromosomal aberrations and mutations, in rodents and humans is presented here.

Transgenerational effects of radiation and chemicals in mice and humans

Parental exposure of mice to radiation and chemicals causes a variety of adverse effects (e.g., tumors, congenital malformations and embryonic deaths) in the progeny and the tumor-susceptibility phenotype is transmissible beyond the first post-radiation generation. The induced rates of tumors were 100-fold higher than those known for mouse specific locus mutations. There were clear strain differences in the types of naturally-occurring and induced tumors and most of the latter were malignant. Another important finding was that germ-line exposure elicited very weak tumorigenic responses, but caused persistent hypersensitivity in the offspring for the subsequent development of cancer by the postnatal environment. Activations of oncogenes, ras, mos, abl, etc. and mutations in tumor suppressor genes such as p53 were also detected in specific tumors in cancer-prone descendants. However, the majority of tumors observed in the progeny were those commonly observed in the strains that were used and oncogene activations were rarely observed in these tumors. It can be hypothesized that genetic instability modifies tumor occurrence in a transgenerational manner, but so far no links could be established between chromosomal and molecular changes and transmissible tumor risks. Our data are consistent with the hypothesis that cumulative changes in many normal but cancer-related genes affecting immunological, biochemical and physiological functions may slightly elevate the incidence of tumors or fasten the tumor development. This hypothesis is supported by our GeneChip analyses which showed suppression and/or over-expression of many such genes in the offspring of mice exposed to radiation. In humans, a higher risk of leukemia and birth defects has been reported in the children of fathers who had been exposed to radionuclides in the nuclear reprocessing plants and to diagnostic radiation. These findings have not been supported in the children of atomic bomb survivors in Hiroshima and Nagasaki, who were exposed to higher doses of atomic radiation. However, it will be important to follow the human subjects, especially for adult type cancers and chronic diseases throughout their lives to determine whether the mouse studies can predict human responses.

Germ-line mutations at a mouse ESTR (Pc-3) locus and human microsatellite loci

We examined the use of the mouse Pc-3 ESTR (expanded simple tandem repeat) locus and 72 human microsatellite loci as potentially sensitive biomarkers for mutagenic exposures to germ cells in mice and humans respectively. In the mouse work, we treated male mice with TCDD (2, 3, 7, 8-tetrachlorodibenzo-p-dioxin; a chemical known to induce congenital anomalies in humans and mice) and, analysed the F(1) fetuses for Pc-3 mutations. Although the incidence of anomalies was higher in the TCDD group, there were no induced mutations. However, respiratory distress syndrome (RDS) was observed in 3 of 7 fetuses born to male mice which were treated with TCDD and which showed abnormal length of Pc-3 allele. In the human studies, the children of Chernobyl liquidators were examined for mutations at a total of 72 (31 autosomal, 1 X-linked and 40 Y-linked) microsatellite loci. This study was prompted by earlier findings of increases in microsatellite mutations in barn swallows and wheat in the highly contaminated areas after the Chernobyl accident. We examined 64 liquidator families (70 children) and 66 control families (70 children). However, no increases in mutation rates were found. The estimated mean dose to the liquidators was about 39 mSv and this might be one possible reason why no increases of mutations could be found.