Leukaemia and non-Hodgkin's lymphoma in children of male Sellafield radiation workers

Contribution of transposable elements to transgenerational effects of chronic radioactive exposure of natural populations of Drosophila melanogaster living for a long time in the zone of the Chernobyl nuclear disaster

The accident at the Chernobyl Nuclear Power Plant (ChNPP) led to the negative impact of chronic radioactive contamination on populations of organisms associated with the transgenerational transmission of genome instability. When the destabilization of genome, different genetic damages occur, the accumulation of which leads to the formation of mutations, morphological anomalies, and mortality in the offspring. The mechanisms underlying the manifestation of transgenerational events in the offspring of irradiated parents are not well understood. In this study, for the first time, the features of the influence of transposable elements (TEs) on the long-term biological consequences of the ChNPP are considered. In this work, specimens of D. melanogaster obtained from natural populations in 2007 in the areas of the ChNPP with heterogeneous radioactive contamination were studied. The descendants from these populations were maintained in laboratory (inbred) conditions for 160 generations. A stable transgenerational transmission of dominant lethal mutations (DLMs) to the offspring of all studied populations was shown. The DLM frequencies strongly were correlated with the level of survival of offspring. The mean frequencies of recessive sex-linked lethal mutations varied at the level of spontaneous point mutations. The simultaneous presence of P, hobo and I elements indicates that the studied populations do not have a definite cytotype, their phenotypic status is unstable. The behavior of TEs in the genomes of offspring depends not only on parental exposure, but also on origin of population, distance to the ChNPP, and inbred conditions. The obtained results confirm the hypothesis that TEs are involved in transgenerational transmission and accumulation of mutations by the offspring of irradiated parents. The TEs pattern present in the Chernobyl genomes of D. melanogaster is a peculiar of epigenetic mechanism for the regulation of plasticity and adaptation of populations living for many generations under conditions of a technogenically caused radiation background.

Radioactive releases from the nuclear power sector and implications for child health

Although radioactivity is released routinely at every stage of nuclear power generation, the regulation of these releases has never taken into account those potentially most sensitive-women, especially when pregnant, and children. From uranium mining and milling, to fuel manufacture, electricity generation and radioactive waste management, children in frontline and Indigenous communities can be disproportionately harmed due to often increased sensitivity of developing systems to toxic exposures, the lack of resources and racial and class discrimination. The reasons for the greater susceptibility of women and children to harm from radiation exposure is not fully understood. Regulatory practices, particularly in the establishment of protective exposure standards, have failed to take this difference into account. Anecdotal evidence within communities around nuclear facilities suggests an association between radiation exposure and increases in birth defects, miscarriages and childhood cancers. A significant number of academic studies tend to ascribe causality to other factors related to diet and lifestyle and dismiss these health indicators as statistically insignificant. In the case of a major release of radiation due to a serious nuclear accident, children are again on the frontlines, with a noted susceptibility to thyroid cancer, which has been found in significant numbers among children exposed both by the 1986 Chornobyl nuclear accident in Ukraine and the 2011 Fukushima-Daiichi nuclear disaster in Japan. The response among authorities in Japan is to blame increased testing or to reduce testing. More independent studies are needed focused on children, especially those in vulnerable frontline and Indigenous communities. In conducting such studies, greater consideration must be applied to culturally significant traditions and habits in these communities.

Transgenerational effects of gamma radiation dose and dose rate on Drosophila flies irradiated at an early embryonal stage

Ionizing radiation (IR) kills cells mainly through induction of DNA damages and the surviving cells may suffer from mutations. Transgenerational effects of IR are well documented, but the exact mechanisms underlying them are less well understood; they include induction of mutations in germ cells and epigenetic inheritance. Previously, effects in the offspring of mice and zebrafish exposed to IR have been reported. A few studies also showed indications of transgenerational effects of radiation in humans, particularly in nuclear power workers. In the present project, short- and long-term effects of low-dose-rate (LDR; 50 and 97 mGy/h) and high-dose-rate (HDR; 23.4, 47.1 and 495 Gy/h) IR in Drosophila embryos were investigated. The embryos were irradiated at different doses and dose rates and radiosensitivity at different developmental stages was investigated. Also, the survival of larvae, pupae and adults developed from embryos irradiated at an early stage (30 min after egg laying) were studied. The larval crawling and pupation height assays were applied to investigate radiation effects on larval locomotion and pupation behavior, respectively. In parallel, the offspring from 3 Gy irradiated early-stage embryos were followed up to 12 generations and abnormal phenotypes were studied. Acute exposure of embryos at different stages of development showed that the early stage embryo is the most sensitive. The effects on larval locomotion showed no significant differences between the dose rates but a significant decrease of locomotion activity above 7 Gy was observed. The results indicate that embryos exposed to the low dose rates have shorter eclosion times. At the same cumulative dose (1 up to 7 Gy), HDR is more embryotoxic than LDR. We also found a radiation-induced depigmentation on males (A5 segment of the dorsal abdomen, A5pig^-) that can be transmitted up to 12 generations. The phenomenon does not follow the classical Mendelian laws of segregation.

Germline De Novo Mutations as a Cause of Childhood Cancer

Germline de novo mutations (DNMs) represent one of the important topics that need extensive attention from epidemiologists, geneticists, and other relevant stakeholders. Advances in next-generation sequencing technologies allowed examination of parent-offspring trios to ascertain the frequency of germline DNMs. Many epidemiological risk factors for childhood cancer are indicative of DNMs as a mechanism. The aim of this review was to give an overview of germline DNMs, their causes in general, and to discuss their relation to childhood cancer risk. In addition, we highlighted existing gaps in knowledge in many topics of germline DNMs in childhood cancer that need exploration and collaborative efforts.

Radiobiological features in offspring of natural populations of Drosophila melanogaster after Chernobyl accident

In their natural habitats, populations of organisms are faced with different levels of chronic low-intensity radiation, causing a wide range of radiobiological effects (from radiosensitivity to radioadaptive response and hormesis). In this study, specimens of Drosophila melanogaster were selected from territories of the Chernobyl nuclear power plant with different levels of radioactive contamination. The isogenic stocks derived from these specimens represent the genetic systems of current populations and make it possible to study radioresistance and its mechanisms in future generations under controlled laboratory conditions. Previous studies have shown that transgenerational radiation effects at the level of lethal mutations and survival rate are unstable and depend not only on the level of chronic low-intensity irradiation, but also on other factors. A single acute irradiation exposure of offspring whose parents inhabited a site with a higher level of chronic irradiation made it possible to reveal pronounced radioresistant features in the offspring. And the offspring whose parents were exposed to radiation levels close to the natural radiation background, on the contrary, acquired radiosensitive features. Their response to acute exposure includes a high-frequency of lethal mutations and a short lifespan. The differential response to different levels of chronic parental exposure is caused by differences in the activities of certain transposons that destabilize the genome. Our data contribute to the understanding of genetic and epigenetic mechanisms (via transposon activity) of the effect of parental radiation exposure on the health and adaptive potential of populations affected by the technogenically increased radiation background.

Disproportionate Impacts of Radiation Exposure on Women, Children, and Pregnancy: Taking Back our Narrative

Narratives surrounding ionizing radiation have often minimized radioactivity's impact on the health of human and non-human animals and the natural environment. Many Cold War research policies, practices, and interpretations drove nuclear technology forward by institutionally obscuring empirical evidence of radiation's disproportionate and low-dose harm-a legacy we still confront. Women, children, and pregnancy development are particularly sensitive to exposure from radioactivity, suffering more damage per dose than adult males, even down to small doses, making low doses a cornerstone of concern. Evidence of compounding generational damage could indicate increased sensitivity through heritable impact. This essay examines the existing empirical evidence demonstrating these sensitivities, and how research institutions and regulatory authorities have devalued them, willingly sacrificing health in the service of maintaining and expanding nuclear technology (Nadesan 2019). Radiation's disproportionate impacts should now be the research and policy focus, as society is poised to make crucial and long-lasting decisions regarding climate change mitigation and future energy sources (Brown 2019b).

Evolving paradigms for the biological response to low dose ionizing radiation; the role of epigenetics

PURPOSE

In the late 1990s, it had become clear that the long-standing paradigm for the action of radiation on living cells and organisms did not have sufficient power to explain the observed effects of low dose ionizing radiation. The purpose of this commentary is to examine the experiments that lead up to the modification of the classic paradigm consequent on these observations, their historical precedents, and the development of our understanding of the role of epigenetics in low dose radiation effects.

RESULTS AND CONCLUSIONS

We discuss how parallel advances in epigenetics from developmental biology and cancer studies, and the discovery of epigenetic modifications of chromatin, such as DNA methylation, impacted on the development of an epigenetic paradigm for low dose effects. We also assess the impact of technology development in supporting the paradigm shift. We then examine recent accumulated data on epigenetic modification in response to irradiation since that shift took place, and identify areas where bringing together data from developmental biology and cancer might answer some of the paradoxes and contradictions in this data. We predict that further paradigm shifts are imminent.

Updated investigations of cancer excesses in individuals born or resident in the vicinity of Sellafield and Dounreay

BACKGROUND

Earlier studies have shown raised risks of leukaemia and non-Hodgkin lymphoma in children, teenagers and young adults resident either at birth or diagnosis in Seascale. Some increases in cancer risk in these age groups have also been noted among those living around Dounreay. We aimed to update previous analyses relating to areas close to these nuclear installations by considering data from an additional 16 years of follow-up.

METHODS

Cross-sectional analyses compared cancer incidence rates for 1963-2006 among those aged 0-24 years at diagnosis living in geographically specified areas around either Sellafield or Dounreay with general population rates. Cancer incidence for the period 1971-2006 among the cohort of Cumbrian births between 1950 and 2006 was compared to national incidence for 1971-2006 using person-years analysis. Cancer among those born in the postcode sector closest to Dounreay was compared with that among those born in the three adjoining postcode sectors. Analyses considered both cancer overall and ICD-O-3 defined diagnostic subgroups including leukaemia, central nervous system tumours and other malignancies.

RESULTS

Apart from previously reported raised risks, no new significantly increased risks for cancer overall or any diagnostic subgroup were found among children or teenagers and young adults living around either nuclear installation. Individuals born close to the installations from 1950 to 2006 were not shown to be at any increased risk of cancer during the period 1971 to date.

CONCLUSIONS

Analysis of recent data suggests that children, teenagers and young adults currently living close to Sellafield and Dounreay are not at an increased risk of developing cancer. Equally, there is no evidence of any increased cancer risk later in life among those resident in these areas at birth.

Investigating the relationship between mortality from respiratory diseases and childhood acute lymphoblastic leukaemia in Hungary

Our aim was to investigate the ecological association between death from infectious disease of the respiratory system and the risk of acute lymphoid leukaemia (ALL) in children aged less than 7 years. Poisson regression analyses were carried out using overall data and gender-specific models. The study included 176 cases (92(52.3 %) boys and 84 (47.7 %) girls) of ALL in those aged 0-6 years in South Hungary. Eight cases were diagnosed before the age of 1 year. A significant risk of ALL disease was observed with higher levels of mortality from the chronic respiratory diseases (p = 0.035) and pneumonia (p = 0.010) among children aged 2-5 years (Odds Ratio for trend was 1.001 and 95%CI [1.000-1.002] and Odds ratio for trend was 1.013 and 95%CI [1.003-1.023], respectively). Significantly increased risk of childhood ALL was detected among children under 1 year of age residing in areas around birth with higher levels of mortality from influenza (Odds Ratio (OR) for trend was 1.05; 95%CI [1.01-1.09]; p = 0.012). This risk was also detected in girls (p < 0.001), but not in boys (p = 0.43). Our findings provide new evidence that will help to understand the different pattern of female and male childhood ALL occurrence , but further studies are needed using detailed individual medical history to clarify the role of influenza and other infectious diseases in the etiology of childhood ALL and to explain gender-specific effects.

Biomarkers of chemotherapy-induced testicular damage

Increasing numbers of men are having or wanting children after chemotherapy treatment. This can be attributed to improvements in cancer therapies that increase survival. However, a side effect of most chemotherapy drugs is disruption of spermatogenesis and a drastic reduction in sperm count and quality. Although many men eventually recover reproductive function, as indicated by normal semen analyses, there is no clinical test that can assess sperm quality at a high level of sensitivity. Sperm fluorescent in situ hybridization (i.e., FISH) and several different tests for deoxyribonucleic acid (DNA) fragmentation have been used infrequently in clinical assessment. Animal models of chemotherapy-induced testicular damage are currently being used to identify potential molecular biomarkers that may be translatable to humans-these include sperm messenger RNAs, microRNAs, histone modifications, and DNA methylation patterns. Changes in these molecular measurements are quantitative and sensitive, potentially making them important clinical biomarkers of testicular function after chemotherapy treatment.

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.

The risk of childhood leukaemia following exposure to ionising radiation--a review

Since the early years of follow-up of the Japanese atomic-bomb survivors, it has been apparent that childhood leukaemia has a particular sensitivity to induction by ionising radiation, the excess relative risk (ERR) being expressed as a temporal wave with time since exposure. This pattern has been generally confirmed by studies of children treated with radiotherapy. Case-control studies of childhood leukaemia and antenatal exposure to diagnostic x-rays, a recent large cohort study of leukaemia following CT examinations of young people, and a recent large case-control study of natural background γ-radiation and childhood leukaemia have found evidence of raised risks following low-level exposure. These findings indicate that an ERR/Sv for childhood leukaemia of ~50, which may be derived from risk models based upon the Japanese atomic-bomb survivors, is broadly applicable to low dose or low dose-rate exposure circumstances.

Prevalence of adult-onset multifactorial disease among offspring of atomic bomb survivors

The first study to examine whether parental radiation exposure leads to increased heritable risk of common adult-onset multifactorial diseases (i.e., hypertension, diabetes mellitus, hypercholesterolemia, ischemic heart disease, and stroke) was conducted among 11,951 participants in the clinical examination program out of a potential of 24,673 mail survey subjects who were offspring of survivors born from May 1946 through December 1984. Logistic regression analyses demonstrated no evidence of an association between the prevalence of multifactorial diseases in the offspring and parental radiation exposure, after adjusting for age, city, gender and various risk factors. The odds ratio (OR) for a paternal dose of 1 Gy was 0.91 [95% confidence interval (CI) 0.81-1.01, P = 0.08], and that for a maternal dose of 1 Gy was 0.98 (95% CI 0.86-1.10, P = 0.71). There was no apparent effect of parental age at exposure or of elapsed time between parental exposure and birth, but male offspring had a low odds ratio (OR = 0.76 at 1 Gy) for paternal exposure, but cautious interpretation is needed for this finding. The clinical assessment of nearly 12,000 offspring of A-bomb survivors who have reached a median age of about 50 years provided no evidence for an increased prevalence of adult-onset multifactorial diseases in relation to parental radiation exposure.

What do epidemiologists mean by 'population mixing'?

There is growing evidence that some chronic diseases are caused, or promoted, by infectious disease. 'Population mixing' has been used as a proxy for the range and dose of infectious agents circulating in a community. Given the speculation over the role of population mixing in many chronic diseases, we review the various methods used for measuring population mixing, and provide a classification of these. We recommend that authors fulfill two criteria in publications: measures are demonstrably associated with the putative risk factors for which population-mixing is acting as a proxy and fundamental characteristics of the chosen measures are clearly defined.

Trans-generational radiation-induced chromosomal instability in the female enhances the action of chemical mutagens

Genomic instability can be produced by ionising radiation, so-called radiation-induced genomic instability, and chemical mutagens. Radiation-induced genomic instability occurs in both germinal and somatic cells and also in the offspring of irradiated individuals, and it is characterised by genetic changes including chromosomal rearrangements. The majority of studies of trans-generational, radiation-induced genomic instability have been described in the male germ line, whereas the authors who have chosen the female as a model are scarce. The aim of this work is to find out the radiation-induced effects in the foetal offspring of X-ray-treated female rats and, at the same time, the possible impact of this radiation-induced genomic instability on the action of a chemical mutagen. In order to achieve both goals, the quantity and quality of chromosomal damage were analysed. In order to detect trans-generational genomic instability, a total of 4806 metaphases from foetal tissues from the foetal offspring of X-irradiated female rats (5Gy, acute dose) were analysed. The study's results showed that there is radiation-induced genomic instability: the number of aberrant metaphases and the breaks per total metaphases studied increased and were found to be statistically significant (p < or = 0.05), with regard to the control group. In order to identify how this trans-generational, radiation-induced chromosomal instability could influence the chromosomal behaviour of the offspring of irradiated rat females in front of a chemical agent (aphidicolin), a total of 2481 metaphases were studied. The observed results showed that there is an enhancement of the action of the chemical agent: chromosomal breaks per aberrant metaphases show significant differences (p < or = 0.05) in the X-ray- and aphidicolin-treated group as regards the aphidicolin-treated group. In conclusion, our findings indicate that there is trans-generational, radiation-induced chromosomal instability in the foetal cells from X-ray-treated female rats and that this RIGI enhances the chromosomal damage caused by the chemical agent aphidicolin.

Paternal occupational exposure to electro-magnetic fields as a risk factor for cancer in children and young adults: a case-control study from the North of England

BACKGROUND

Numerous studies have implied that paternal occupational exposures, in particular electromagnetic fields (EMF) and ionizing radiation, may be involved in the etiology of childhood cancers. We investigated whether an association exists between paternal occupations at birth involving such exposures and cancer risk in offspring, using data from the Northern Region Young Persons' Malignant Disease Registry (NRYPMDR).

PROCEDURE

Cases (n=4,723) were matched, on sex and year of birth, to controls from two independent sources: (i) all other patients from the NRYPMDR with a different cancer, (ii) 100 cancer-free individuals per case from the Cumbrian Births Database. An occupational exposure matrix was used to assign individuals to exposure groups.

RESULTS

There was an increased risk of leukemia among the offspring of men employed in occupations likely to be associated with EMF or radiation exposures (OR 1.31, 95% CI 1.02-1.69), particularly in males aged less than 6 years (OR 1.81, 95% 1.19-2.75). No significant association was seen in females. Increased risks were also seen for chondrosarcoma (OR 8.7, 95% CI 1.55-49.4) and renal carcinoma (OR 6.75, 95% CI 1.73-26.0). These associations were consistent between control groups and remained after adjustment for socio-economic status.

CONCLUSIONS

This large case-control study identified a significantly increased risk of leukemia among the offspring of men likely to have been occupationally exposed to EMF, with differing associations between males and females. Increased risks of chondrosarcoma and renal carcinoma were also seen, although based on smaller numbers. Further detailed investigations in this area are required to understand this association.

New germline mutations in the hypervariable minisatellite CEB1 in the parents of children with leukaemia

Gardner and co-workers advanced the hypothesis that the Seascale leukaemia cluster could have been caused by new mutations in germ cells, induced by paternal preconceptional irradiation (PPI) exposure at the Sellafield nuclear installation. Since evidence has shown that PPI can increase the de novo germline mutation rate in hypervariable minisatellite loci, we investigated the hypothesis that sporadic childhood leukaemia might be associated with an increased parental germline minisatellite mutation rate. To test this hypothesis, we compared de novo germline mutation rates in the hypervariable minisatellite locus, CEB1, in family trios (both parents and their child) of children with leukaemia (n=135) compared with unaffected control families (n=124). The majority of case and control germline mutations were paternal (94%); the mean paternal germline mutation rates of children with leukaemia (0.083) and control children (0.156) were not significantly different (odds ratio, 95% confidence interval: 0.50, 0.23–1.08; P=0.11). There were no significant differences in case and control parental allele sizes, case and control germline mutation progenitor allele sizes (2.74 vs 2.54 kb; P=0.56), case and control mutant allele sizes (2.71 vs 2.67 kb; P=0.90), mutant allele size changes (0.13 vs 0.26 kb; P=0.10), or mutational spectra. Within the limitation of the number of families available for study, we conclude that childhood leukaemia is unlikely to be associated with increased germline minisatellite instability.

AZFc somatic microdeletions and copy number polymorphism of the DAZ genes in human males exposed to natural background radiation

Ionizing radiations are known to induce tumors, chromosomal lesions and minisatellite length variations, yet no correlation has been demonstrated between radiation exposure and indels or copy number polymorphism (CNP) of the genes. We studied the impact of natural background radiation (NBR) on the human Y chromosome owing to its haploid status and clonal inheritance. We analyzed the AZFc region using the DNA from blood and semen of 100 males living near the coastal peninsula in Kerala (India), exposed to NBR along with other 50 normal fertile males. STS mapping of AZFc region showed random microdeletions without conclusive gr/gr or b1/b3 phenotypes. Using a highly specific novel Taqman assay based on sY587 sequence, we detected four copies of the DAZ genes in normal males and 4-16 in those exposed to NBR. Amongst NBR exposed males with multiples copies of the DAZ genes, 75% showed varying FISH signals for DAZ genes with cosmid 18E8 whereas 30% showed mosaicism in terms of presence/absence of the signals in 6-8% cells and unexpected number of signals in 9-12% interphase nuclei. Startlingly, all germline samples studied were found to be free from AZFc microdeletions and CNP of the DAZ genes. Since the DAZ genes are heavily implicated with the germ cell development, the cells with DAZ deletion/duplication are unlikely to survive. Alternatively, an innate mechanism may be operative to protect the germline from the effects of NBR.

Transmission lines, EMF and population mixing

Draper et al. found that the incidence of childhood leukaemia was slightly elevated for children living at distances of 200-600 m from high-voltage transmission lines. This elevation cannot be explained by EMF exposure and it is suggested that it may be due to population mixing in housing developments which followed the construction of the lines.

Male gonadal dose of ionizing radiation delivered during X-ray examinations and monthly probability of pregnancy: a population-based retrospective study

Background

Male gonadal exposure to ionizing radiation may disrupt spermatogenesis, but its influence on the fecundity of couples has been rarely studied. We aimed to characterize the influence of male gonadal dose of ionizing radiation delivered during radiodiagnostic on the monthly probability of pregnancy.

Methods

We recruited a random sample of women who retrospectively described 1110 periods of unprotected intercourse beginning between 1985 and 1999 and leading either to a live birth or to no pregnancy; their duration was censored after 13 months. The male partner answered a telephone questionnaire on radiodiagnostic examinations. We assigned a mean gonadal dose to each type of radiodiagnostic examination. We defined male dose for each period of unprotected intercourse as the sum of the gonadal doses of the X-ray examinations experienced between 18 years of age and the date of discontinuation of contraception. Time to pregnancy was analysed using a discrete Cox model with random effect allowing to estimate hazard ratios of pregnancy.

Results

After adjustment for female factors likely to influence fecundity, there was no evidence of an association between male dose and the probability of pregnancy (test of homogeneity, p = 0.55). When compared to couples with a male gonadal dose between 0.01 and 0.20 milligrays (n = 321 periods of unprotected intercourse), couples with a gonadal dose above 10 milligrays had a hazard ratio of pregnancy of 1.44 (95% confidence interval, 0.73–2.86, n = 31).

Conclusion

Our study provides no evidence of a long-term detrimental effect of male gonadal dose of ionizing radiation delivered during radiodiagnostic on the monthly probability of pregnancy during the year following discontinuation of contraceptive use. Classification errors due to the retrospective assessment of male gonadal exposure may have limited the statistical power of our study.

The offspring of irradiated parents, are they stable?

Mutation induction in directly exposed cells is currently regarded as the main component of the genetic risk of ionising radiation for humans. However, recent studies showing that exposure to ionising radiation results in elevated mutation rates detectable in the non-irradiated progeny of exposed cells challenge the existing paradigm in radiation biology. This review describes some recent data on radiation-induced genomic instability in vitro and mainly focuses on the in vivo phenomenon of transgenerational instability, where elevated mutation rates are detected in the non-exposed offspring of irradiated parents. The possible mechanisms and implications of transgenerational instability are also discussed.

Spatial analysis of childhood leukemia in a case/control study

A simple and direct analysis of the spatial distribution of childhood leukemia was performed using geographic data from a large case/control study. The data consist of cases of childhood leukemia and their corresponding birth cohort controls located in seven San Francisco Bay Area counties. Both parametric and randomization analyses show no evidence of a non-random spatial pattern of childhood leukemia among six of these counties. The data from San Francisco County, however, produce a moderately small significance probability (0.08) arising from a distance analysis and a significant p-value (0.01) arising from a frequency analysis of concordant case pairs. Although these p-values accurately reflect the probability of the observed spatial pattern occurring by chance alone, these results are based on only four cases of leukemia.

Maternal effects and cancer risk in the progeny of mice exposed to X-rays before conception

To investigate in an animal model whether preconceptual X-ray exposure leads to an altered tumor rate and spectrum in the offspring, a transgeneration carcinogenesis study was carried out. Female mice received X-ray irradiation (2 x 2 Gray) 2 weeks prior to mating with untreated males. After weaning, half of the descendants were exposed for 6 months to the immunomodulating and tumor-promoting compound cyclosporine A (CsA) by diet, the others remained untreated. The animals were maintained for their entire lifespan, terminal sacrifices were carried out after 28 months. Complete autopsy was performed, and three protocol organs (lung, liver and spleen) were examined histologically, together with any suspicious lesions in other organs. Fertility and the lifetime of the maternal mice were reduced by the X-ray irradiation, and their incidence of lung and liver tumors was increased as compared to non-irradiated mice. The descendants of all groups revealed comparable body weights and mortality rates. The incidence of hematopoietic/lymphoreticular tissue tumors increased in the female hybrids by 6 months of CsA-treatment. A higher incidence of lung and liver tumors in the sham-treated male progeny of irradiated mothers was detected, pointing to a possible germ cell-transmitted alteration initiated by the preconceptual maternal X-ray exposure.

Genetic counselling following paternal therapeutic irradiation

We discuss a patient who received adjuvant radiotherapy for stage I seminoma. He was advised to avoid conception for 6 months following treatment. However, his partner became pregnant only shortly after he completed his radiotherapy (i.e. with sperm that had been irradiated). We estimated the dose received by the remaining testis as 30 cGy. Here, we review the information available to advise patients on the risks to the fetus from paternal preconception irradiation. For the population, a doubling dose for hereditary effects of 1 Gy has recently been reaffirmed (United Nations Scientific Committee on the Effects of Atomic Radiation 2001). However, a range of animal studies suggest conception with postmeiotic sperm carries a greater risk of genetic damage than conception with sperm derived from irradiated stem cells. We have attempted to quantify the risks in this particular case. Lead shielding of the testes may reduce radiation received from the primary beam, but internal scatter still produces a risk. In male patients who are potentially fertile, the best advice remains to delay conception after radiotherapy for as long as 6 months. Our case illustrates the need to reinforce such advice.

Childhood leukaemia incidence and the population mixing hypothesis in US SEER data

We evaluated the infectious aetiology hypothesis of childhood leukaemia that rapid population influx into rural areas is associated with increased risk. Using data from the US SEER program, we found that in changes in rural county population sizes from 1980 to 1989 were associated with incidence rates for childhood acute lymphocytic leukaemia (ALL). The observed associations were strongest among children 0-4 years of age, born in the same state as diagnosis, in extremely rural counties, and when counties adjacent to nonrural counties were excluded. Similar analyses for brain and central nervous system (CNS) cancer in children, a disease less linked to this infectious hypothesis, provide evidence against methodologic bias. Similar evaluations for other decades were not meaningful due to limited sample sizes and, perhaps, increased population mobility.

Comparison of Health and Safety Executive and Cumbrian birth cohort studies of risk of leukaemia/non-Hodgkin's lymphoma in relation to paternal preconceptional irradiation

In 1993, a case-control study by the Health and Safety Executive (HSE) assessed the risk of leukaemia and non-Hodgkin's lymphoma (LNHL) among children of fathers employed at the Sellafield nuclear installation in relation to paternal preconceptional irradiation (PPI). It concluded that the statistical association between risk of LNHL and PPI was confined to children born in the village of Seascale, where the dose-response was extremely high and very significant. In contrast, in 2002, a Cumbrian birth cohort study, investigating largely the same cases, concluded that this statistical association was not significantly different among children born inside and outside Seascale and estimated the dose-response inside Seascale to be much lower. This review makes a detailed comparison of the two studies, considering their design, data and analyses. The differences between their findings are due to: (i) differences in the distribution of offspring-years which are differential with respect to dose category and Seascale birth status, (ii) a non-Seascale high-dose case included in the Cumbrian but not the HSE study, (iii) differences between analyses using categorical and continuous PPI dose and (iv) the presence of Seascale controls with PPI over 200 mSv in the Cumbrian but not the HSE study.

Radiation-induced transgenerational instability

To date, the analysis of mutation induction has provided an irrefutable evidence for an elevated germline mutation rate in the parents directly exposed to ionizing radiation and a number of chemical mutagens. However, the results of numerous publications suggest that radiation may also have an indirect effect on genome stability, which is transmitted through the germ line of irradiated parents to their offspring. This review describes the phenomenon of transgenerational instability and focuses on the data showing increased cancer incidence and elevated mutation rates in the germ line and somatic tissues of the offspring of irradiated parents. The possible mechanisms of transgenerational instability are also discussed.

Radiation-related mortality among offspring of atomic bomb survivors: a half-century of follow-up

Our objective was to examine whether parental exposure to atomic bomb radiation has led to increased cancer and/or noncancer mortality rates among the offspring. We studied 41,010 subjects born from May 1946 through December 1984 (i.e., conceived between 1 month and 38 years after the bombings) and surviving for at least 1 year. One or both parents were in Hiroshima or Nagasaki at the time of the bombings and childbirth. We analyzed mortality data from 1946 to 1999 using the Japanese family registry system by Cox regression model and examined the effects of paternal and maternal irradiation with adjustment for city, sex, year of birth and parental age at childbirth. During follow-up, 314 cancer deaths and 1,125 noncancer disease deaths occurred. The mean age of living subjects was 45.7 years. Median doses were 143 mSv for 12,722 exposed fathers and 132 mSv for 7,726 exposed mothers. Cancer and noncancer mortality rates were no higher for subjects with exposed parents (5+ mSv or unknown dose) than for reference subjects (0-4 mSv), and mortality did not increase with increasing dose. For subjects with both parents exposed, the adjusted hazard ratios were 1.16 [95% confidence interval (CI) 0.92-1.46] for noncancer and 0.96 (95% CI 0.59-1.55) for cancer. This was true of deaths occurring both before and after 20 years of age. However, because of uncertainty due to the small number of deaths and relatively young ages of subjects, we cannot rule out an increase in disease mortality at this time.

Genetic effects of radiotherapy for childhood cancer

Radiation-induced heritable diseases have not been demonstrated in humans and estimates of genetic risks for protection purposes are based on mouse experiments. The most comprehensive epidemiologic study is of the Japanese atomic bomb survivors and their children, which found little evidence for inherited defects attributable to parental radiation. Studies of workers exposed to occupational radiation or of populations exposed to environmental radiation appear too small and exposures too low to convincingly detect inherited genetic damage. In contrast, survivors of childhood cancer form the largest group of people exposed to high doses of ionizing radiation before reproduction and offer unique advantages for studying trans-generation effects. A wide range of gonadal doses are possible, several comparison groups are readily available (including siblings), and there is a strong willingness among cancer survivors to participate in health studies. Cancer patients also have detailed medical records that facilitate both the accurate estimation of gonadal doses and the assessment of potentially confounding factors, such as intercurrent illness, personal and family medical histories, lifestyle characteristics such as tobacco use, and circumstances at delivery. An international study is nearing completion of over 25,000 survivors of childhood cancer in the United States and Denmark who gave birth to or fathered over 6,000 children. Doses to gonads are being reconstructed from radiotherapy records with 46% over 100 mSv and 16% over 1,000 mSv. Adverse pregnancy outcomes being evaluated include major congenital malformations, cytogenetic abnormalities, stillbirths, miscarriages, neonatal deaths, total deaths, leukemia and childhood cancers, altered sex ratio, and birth weight. The main analyses are based on dose-response evaluations. Blood studies of trios (cancer survivor, spouse or partner and offspring) have been initiated to evaluate mechanistic evidence for the transmission of any radiation-induced genetic damage such as minisatellite mutations. Markers of cancer susceptibility such as chromosomal radiosensitivity and genotype profile will also be examined. In the United States series to date, 4,214 children were born to cancer survivors among whom 157 (3.7%) genetic diseases were reported in contrast to 95 (4.1%) reported conditions among 2,339 children born to sibling controls. In the Denmark series the comparable figures were 82 (6.1%) birth defects among 1,345 children of cancer survivors and 211 (5.0%) among 4,225 children of sibling controls. Coupled with prior studies, these preliminary findings, if sustained by ongoing dose-response analyses, provide reassurance that cancer treatments including radiotherapy do not carry much if any risk for inherited genetic disease in offspring conceived after exposure.

Non-targeted and delayed effects of exposure to ionizing radiation: II. Radiation-induced genomic instability and bystander effects in vivo, clastogenic factors and transgenerational effects

The goal of this review is to summarize the evidence for non-targeted and delayed effects of exposure to ionizing radiation in vivo. Currently, human health risks associated with radiation exposures are based primarily on the assumption that the detrimental effects of radiation occur in irradiated cells. Over the years a number of non-targeted effects of radiation exposure in vivo have been described that challenge this concept. These include radiation-induced genomic instability, bystander effects, clastogenic factors produced in plasma from irradiated individuals that can cause chromosomal damage when cultured with nonirradiated cells, and transgenerational effects of parental irradiation that can manifest in the progeny. These effects pose new challenges to evaluating the risk(s) associated with radiation exposure and understanding radiation-induced carcinogenesis.

Natural radioactivity and human mitochondrial DNA mutations

Radioactivity is known to induce tumors, chromosome lesions, and minisatellite length mutations, but its effects on the DNA sequence have not previously been studied. A coastal peninsula in Kerala (India) contains the world's highest level of natural radioactivity in a densely populated area, offering an opportunity to characterize radiation-associated DNA mutations. We sampled 248 pedigrees (988 individuals) in the high-radiation peninsula and in nearby low-radiation islands as a control population. We sequenced their mtDNA, and found that the pedigrees living in the high-radiation area have significantly (P < 0.01) increased germ-line point mutations between mothers and their offspring. In each mutation case, we confirmed maternity by autosomal profiling. Strikingly, the radioactive conditions accelerate mutations at nucleotide positions that have been evolutionary hot spots for at least 60,000 years.