Assessing human germ-cell mutagenesis in the Postgenome Era: a celebration of the legacy of William Lawson (Bill) Russell

Error-corrected next generation sequencing - Promises and challenges for genotoxicity and cancer risk assessment

Error-corrected Next Generation Sequencing (ecNGS) is rapidly emerging as a valuable, highly sensitive and accurate method for detecting and characterizing mutations in any cell type, tissue or organism from which DNA can be isolated. Recent mutagenicity and carcinogenicity studies have used ecNGS to quantify drug-/chemical-induced mutations and mutational spectra associated with cancer risk. ecNGS has potential applications in genotoxicity assessment as a new readout for traditional models, for mutagenesis studies in 3D organotypic cultures, and for detecting off-target effects of gene editing tools. Additionally, early data suggest that ecNGS can measure clonal expansion of mutations as a mechanism-agnostic early marker of carcinogenic potential and can evaluate mutational load directly in human biomonitoring studies. In this review, we discuss promising applications, challenges, limitations, and key data initiatives needed to enable regulatory testing and adoption of ecNGS - including for advancing safety assessment, augmenting weight-of-evidence for mutagenicity and carcinogenicity mechanisms, identifying early biomarkers of cancer risk, and managing human health risk from chemical exposures.

Meiotic susceptibility for induction of sperm with chromosomal aberrations in patients receiving combination chemotherapy for Hodgkin lymphoma

Improvements in survival rates with gonad-sparing protocols for childhood and adolescence cancer have increased the optimism of survivors to become parents after treatment. Findings in rodents indicate that chromosomal aberrations can be induced in male germ cells by genotoxic exposures and transmitted to offspring and future generations with effects on development, fertility and health. Thus, there is a need for effective technologies to identify human sperm carrying chromosomal aberrations to assess the germ-line risks, especially for cancer survivors who have received genotoxic therapies. The time-dependent changes in the burden of sperm carrying structural chromosomal aberrations were assessed for the first time in a cancer setting, using the AM8 sperm FISH protocol which simultaneously detects abnormalities in chromosomal structure and number in sperm. Nine Hodgkin lymphoma (HL) patients provided 20 semen samples before, during, and after NOVP therapy (Novantrone, Oncovin, Velban and Prednisone) and radiation therapy that produced scattered gonadal doses from <0.05 to 0.6 Gy. Late meiosis was found to be the most sensitive to NOVP treatment for the production of sperm with chromosomal abnormalities, both in structure and number. Earlier stages of spermatogenesis were less sensitive and there was no evidence that therapy-exposed stem cells resulted in increased frequencies of sperm with abnormalities in chromosomal structure or number. This indicates that NOVP therapy may increase the risks for paternal transmission of chromosomal structural aberrations for sperm produced 32 to 45 days after a treatment with these drugs and implies that there are no excess risks for pregnancies conceived more than 6 months after this therapy. This clinical evaluation of the AM8 sperm FISH protocol indicates that it is a promising tool for assessing an individual's burden of sperm carrying chromosomal structural aberrations as well as aneuploidies after cancer therapy, with broad applications in other clinical and environmental situations that may pose aneugenic or clastogenic risks to human spermatogenesis.

A male germ cell assay and supporting somatic cells: its application for the detection of phase specificity of genotoxins in vitro

Male germ stem cells are responsible for transmission of genetic information to the next generation. Some chemicals exert a negative impact on male germ cells, either directly, or indirectly affecting them through their action on somatic cells. Ultimately, these effects might inhibit fertility, and may exhibit negative consequences on future offspring. Genotoxic anticancer agents may interact with DNA in germ cells potentially leading to a heritable germline mutation. Experimental information in support of this theory has not always been reproducible and suitable in vivo studies remain limited. Thus, alternative male germ cell tests, which are now able to detect phase specificity of such agents, might be used by regulatory agencies to help evaluate the potential risk of mutation. However, there is an urgent need for such approaches for identification of male reproductive genotoxins since this area has until recently been dependent on in vivo studies. Many factors drive alternative approaches, including the (1) commitment to the principles of the 3R's (Replacement, Reduction, and Refinement), (2) time-consuming nature and high cost of animal experiments, and (3) new opportunities presented by new molecular analytical assays. There is as yet currently no apparent appropriate model of full mammalian spermatogenesis in vitro, under the REACH initiative, where new tests introduced to assess genotoxicity and mutagenicity need to avoid unnecessary testing on animals. Accordingly, a battery of tests used in conjunction with the high throughput STAPUT gravity sedimentation was recently developed for purification of male germ cells to investigate genotoxicity for phase specificity in germ cells. This system might be valuable for the examination of phases previously only available in mammals with large-scale studies of germ cell genotoxicity in vivo. The aim of this review was to focus on this alternative approach and its applications as well as on chemicals of known in vivo phase specificities used during this test system development.

The mutagenesis moonshot: The propitious beginnings of the environmental mutagenesis and genomics society

A mutagenesis moonshot addressing the influence of the environment on our genetic wellbeing was launched just 2 months before astronauts landed on the moon. Its impetus included the discovery that X-rays (Muller HJ. [1927]: Science 64:84-87) and chemicals (Auerbach and Robson. [1946]: Nature 157:302) were germ-cell mutagens, the introduction of a growing number of untested chemicals into the environment after World War II, and an increasing awareness of the role of environmental pollution on human health. Due to mounting concern from influential scientists that germ-cell mutagens might be ubiquitous in the environment, Alexander Hollaender and colleagues founded in 1969 the Environmental Mutagen Society (EMS), now the Environmental Mutagenesis and Genomics Society (EMGS); Frits Sobels founded the European EMS in 1970. As Fred de Serres noted, such societies were necessary because protecting populations from environmental mutagens could not be addressed by existing scientific societies, and new multidisciplinary alliances were required to spearhead this movement. The nascent EMS gathered policy makers and scientists from government, industry, and academia who became advocates for laws requiring genetic toxicity testing of pesticides and drugs and helped implement those laws. They created an electronic database of the mutagenesis literature; established a peer-reviewed journal; promoted basic and applied research in DNA repair and mutagenesis; and established training programs that expanded the science worldwide. Despite these successes, one objective remains unfulfilled: identification of human germ-cell mutagens. After 50 years, the voyage continues, and a vibrant EMGS is needed to bring the mission to its intended target of protecting populations from genetic hazards. Environ. Mol. Mutagen. 61:8-24, 2020. © 2019 Wiley Periodicals, Inc.

Disentangling the roles of maternal and paternal age on birth prevalence of down syndrome and other chromosomal disorders using a Bayesian modeling approach

Background

Multiple neonatal and pediatric disorders have been linked to older paternal ages. Combining these findings with the evidence that many men are having children at much later ages generates considerable public health concern. The risk of paternal age has been difficult to estimate and interpret because children often have parents whose ages are similar and likely to be confounded. Epidemiologic studies often model the conditional effects of paternal age using regression models that typically treat maternal age as linear, curvilinear or as age-band categories. Each of these approaches has limitations. As an alternative, the current study measures age to the nearest year, and fits a Bayesian model in which each parent’s age is given a conditional autoregressive prior (CAR).

Methods

Data containing approximately 12,000,000 birth records were obtained from the United States Natality database for the years 2014 to 2016. Date were cross-tabulated for maternal ages 15–49 years and for paternal ages 15–65 years. A Bayesian logistic model was implemented using conditional autoregressive priors for both maternal and paternal ages modeled separately and jointly for both Down syndrome and chromosomal disorders other than Down syndrome.

Results

Models with maternal and paternal ages given CAR priors were judged to be better fitting than traditional models. For Down syndrome, the approach attributed a very large risk to advancing maternal age with the effect of advancing paternal age having a very small sparing effect on birth prevalence. Maternal age was also related to the birth prevalence of chromosomal disorders other than Down syndrome while paternal age was not.

Conclusions

Advancing paternal age was not associated with an increase in risk for either Down syndrome or chromosomal disorders other than Down syndrome.

Electronic supplementary material

The online version of this article (10.1186/s12874-019-0720-1) contains supplementary material, which is available to authorized users.

Discovering human germ cell mutagens with whole genome sequencing: Insights from power calculations reveal the importance of controlling for between-family variability

Mutations in germ cells pose potential genetic risks to offspring. However, de novo mutations are rare events that are spread across the genome and are difficult to detect. Thus, studies in this area have generally been under-powered, and no human germ cell mutagen has been identified. Whole Genome Sequencing (WGS) of human pedigrees has been proposed as an approach to overcome these technical and statistical challenges. WGS enables analysis of a much wider breadth of the genome than traditional approaches. Here, we performed power analyses to determine the feasibility of using WGS in human families to identify germ cell mutagens. Different statistical models were compared in the power analyses (ANOVA and multiple regression for one-child families, and mixed effect model sampling between two to four siblings per family). Assumptions were made based on parameters from the existing literature, such as the mutation-by-paternal age effect. We explored two scenarios: a constant effect due to an exposure that occurred in the past, and an accumulating effect where the exposure is continuing. Our analysis revealed the importance of modeling inter-family variability of the mutation-by-paternal age effect. Statistical power was improved by models accounting for the family-to-family variability. Our power analyses suggest that sufficient statistical power can be attained with 4-28 four-sibling families per treatment group, when the increase in mutations ranges from 40 to 10% respectively. Modeling family variability using mixed effect models provided a reduction in sample size compared to a multiple regression approach. Much larger sample sizes were required to detect an interaction effect between environmental exposures and paternal age. These findings inform study design and statistical modeling approaches to improve power and reduce sequencing costs for future studies in this area.

Counselling regarding paternal exposures: Can we do better?

BACKGROUND

MotherSafe is a free telephone-based counselling service for the general public and healthcare providers concerned about exposures during pregnancy and breastfeeding. Calls relating to paternal exposures are less common, but can cause distress to the person concerned. This review seeks to identify the key concerns and what information is available to address these concerns.

AIMS

To review calls made to MotherSafe about paternal exposures to teratogens during the 16 year period, 2000-2015, and to document any patterns or changes in calls over the period.

MATERIALS AND METHODS

A retrospective descriptive assessment of a prospectively collected database (2000-2015) was undertaken. Telephone counselling records identified the drugs of concern regarding paternal exposures. The information about paternal exposures provided in consumer and production information was also reviewed.

RESULTS

Of a total of 253 103 calls received at MotherSafe between 2000 and 2015, 1072 calls (0.4%) were regarding paternal exposures. The majority of these calls related to immunomodifiers (19%), hair loss products (11%) and antidepressant medications.

CONCLUSIONS

Paternal exposures represent a small proportion of all the counselling calls made to MotherSafe. The study highlighted the deficient and often misleading information about paternal exposures found in most consumer and product information sheets or via the internet. The study indicates the important role of Teratogen Information Services like Mothersafe in providing evidence-based information to both consumers and healthcare providers.

Assessment of genotoxic, mutagenic, and recombinogenic potential of water resources in the Paranaíba River basin of Brazil: A case study

Exposure to certain pollutants induces a series of alterations in deoxyribonucleic acid (DNA) that may result in genotoxic/mutagenic effects in exposed individuals. The present study aimed to monitor genotoxic, mutagenic, and recombinogenic potential and consequently water quality in two streams in the Paranaíba River basin in the state of Minas Gerais, Brazil, using two bioindicator fish (Rhamdia quelen and Geophagus brasiliensis). The micronucleus (MN) test and somatic recombination and mutation test (SMART) were employed to assess DNA damage. The water quality index (WQI) at the reference site control (S1) due to its proximity to the river source was compared to Córrego do Óleo (S2) with respect to chemical parameter levels of biochemical oxygen demand (BOD), dissolved-oxygen rates (DO), and total solid and fecal coliform counts. These chemical parameters were above the permitted limits at Córrego do Óleo (S2). At a third site, Córrego Liso (S3), a poor WQI was detected, attributed to the influence of domestic and industrial activities where BOD, DO, total solid, fecal coliform, total phosphorus, and turbidity rates exceeded premissible limits. The MN frequencies and the numbers of MN per cell (CMN) at sites S2 and S3 were significantly higher than those at S1 in both species. It is of interest that the increased frequency of MN was similar to the positive control cyclophosphamide only at S3, suggesting that the effects of water contaminants were most severe at this site. At sites assessed (S2 and S3), there was a significant rise in somatic mutation and recombination in the wings of Drosophila melanogaster, indicating the presence of trace elements, mainly lead (Pb) and cadmium (Cd), in the effluents in the Paranaíba River basin sites.

Risk for congenital anomalies in offspring of childhood, adolescent and young adult cancer survivors

Offspring of cancer survivors (CS) may be at risk for congenital anomalies due to the mutagenic therapies received by their parents. Our population-based cohort study aimed to investigate the risk for congenital anomalies in offspring of CS compared to offspring of their siblings. Using the Finnish Cancer Registry, Central Population Register, and Hospital Discharge Register, we identified hospital contacts due to congenital anomalies in 6,862 offspring of CS (early-onset cancer between 1953 and 2004) and 35,690 offspring of siblings. Associations between congenital anomalies and cancer were evaluated using generalized linear regression modelling. The ratio of congenital anomalies in offspring of CS (3.2%) was slightly, but non-significantly, elevated compared to that in offspring of siblings (2.7%) [prevalence ratio (PR) 1.07, 95% confidence interval (CI) 0.91-1.25]. When offspring of childhood and adolescent survivors (0-19 years at cancer diagnosis) were compared to siblings' offspring, the risk for congenital anomalies was non-significantly increased (PR 1.17, 95% CI 0.92-1.49). No such increase existed for offspring of young adult survivors (20-34 years at cancer diagnosis) (PR 1.01, 95% CI 0.83-1.23). The risks for congenital anomalies were elevated among offspring of CS diagnosed with cancer in the earlier decades (1955-1964: PR 2.77, 95% C I 1.26-6.11; and 1965-1974: PR 1.55, 95% C I 0.94-2.56). In our study, we did not detect an overall elevated risk for congenital anomalies in offspring of survivors diagnosed in young adulthood. An association between cancer exposure of the parent and congenital anomalies in the offspring appeared only for those CS who were diagnosed in the earlier decades.

Descriptive epidemiology of birth defects thought to arise by new mutation

BACKGROUND

The current study is the first to examine the association of a broad range of sociodemographic factors with conditions thought to arise most of the time by de novo mutation.

METHODS

Data were taken from 1999 to 2009 from the Texas Birth Defects Registry (TBDR), a statewide active surveillance program. We used Poisson regression to generate crude and adjusted measures of association; the latter included models with all variables and with a parsimonious subset of variables.

RESULTS

There were 1694 cases with any of the phenotypes in the panel, 1100 cases in a subpanel with ≥90% of cases thought to arise de novo, 523 with chromosomal deletion disorders, and 243 with imprinting disorders. In the most parsimonious models, there was an increasing time trend in all groups except imprinting (p ≤ 0.01). Plurality (twins, triplets, etc.) was associated with greater risk of all groups except chromosomal deletions (p ≤ 0.01). Parental age showed strong trends with all groups; paternal age was most important for the total and imprinting groups (p ≤ 0.0001), and maternal age for the others (p ≤ 0.04). De novo mutation phenotypes were more prevalent among offspring of fathers who are non-Hispanic White compared with some other race/ethnic groups.

CONCLUSION

This study suggests that birth defects arising by new mutation may be more prevalent among offspring of older parents and in plural births. The increasing time pattern and race/ethnic pattern may be related to greater use of or access to genetic tests. This approach to mutation epidemiology seems feasible for birth defects registries to consider.

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.

Protection of the gametes embryo/fetus from prenatal radiation exposure

There is no convincing evidence of germline mutation manifest as heritable disease in the offspring of humans attributable to ionizing radiation, yet radiation clearly induces mutations in microbes and somatic cells of rodents and humans. Doses to the embryo estimated to be in the range of 0.15-0.2 Gy during the pre-implantation and pre-somite stages may increase the risk of embryonic loss. However, an increased risk of congenital malformations or growth retardation has not been observed in the surviving embryos. These results are primarily derived from mammalian animal studies and are referred to as the "all-or-none phenomenon." The tissue reaction effects of ionizing radiation (previously referred to as deterministic effects) are congenital malformations, mental retardation, decreased intelligence quotient, microcephaly, neurobehavioral effects, convulsive disorders, growth retardation (height and weight), and embryonic and fetal death (miscarriage, stillbirth). All these effects are consistent with having a threshold dose below which there is no increased risk. The risk of cancer in offspring that have been exposed to diagnostic x-ray procedures while in utero has been debated for 55 y. High doses to the embryo or fetus (e.g., >0.5 Gy) increase the risk of cancer. Most pregnant women exposed to x-ray procedures and other forms of ionizing radiation today received doses to the embryo or fetus <0.1 Gy. The risk of cancer in offspring exposed in utero at exposures <0.1 Gy is controversial and has not been fully resolved. Diagnostic imaging procedures using ionizing radiation that are clinically indicated for the pregnant patient and her fetus should be performed because the clinical benefits outweigh the potential oncogenic risks.

James V. Neel and Yuri E. Dubrova: Cold War debates and the genetic effects of low-dose radiation

This article traces disagreements about the genetic effects of low-dose radiation exposure as waged by James Neel (1915-2000), a central figure in radiation studies of Japanese populations after World War II, and Yuri Dubrova (1955-), who analyzed the 1986 Chernobyl nuclear power plant accident. In a 1996 article in Nature, Dubrova reported a statistically significant increase in the minisatellite (junk) DNA mutation rate in the children of parents who received a high dose of radiation from the Chernobyl accident, contradicting studies that found no significant inherited genetic effects among offspring of Japanese A-bomb survivors. Neel's subsequent defense of his large-scale longitudinal studies of the genetic effects of ionizing radiation consolidated current scientific understandings of low-dose ionizing radiation. The article seeks to explain how the Hiroshima/Nagasaki data remain hegemonic in radiation studies, contextualizing the debate with attention to the perceived inferiority of Soviet genetic science during the Cold War.

Impact of lymphoma treatments on spermatogenesis and sperm deoxyribonucleic acid: a multicenter prospective study from the CECOS network

OBJECTIVE

To determine consequences of lymphoma treatments on sperm characteristics and sperm DNA, and to evaluate predictors of sperm recovery.

DESIGN

Multicenter prospective longitudinal study of patients analyzed before treatment and after 3, 6, 12, and 24 months.

SETTING

University hospitals.

PATIENT(S)

Seventy-five Hodgkin lymphoma and non-Hodgkin lymphoma patients and a control group of 257 fertile men.

INTERVENTION(S)

Semen analyses, and sperm DNA and chromatin assessments.

MAIN OUTCOME MEASURE(S)

Comparisons of sperm characteristics before and after treatment.

RESULT(S)

Patients already had altered sperm characteristics before lymphoma treatment, with no identified risk factor. Sperm count, total sperm count, motility, and vitality decreased after treatment, with lowest values at 3 and 6 months. Twelve months after treatment, mean sperm count recovered to pretreatment values after doxorubicin, bleomycin, vinblastine, darcarbacine (ABVD) or ABVD+radiotherapy, but not after doxorubicin, cyclophosphamide, vincristine, prednisone (CHOP) or mechlorethamine, oncovin, procarbazine, prednisone (MOPP) chemotherapies. It was noteworthy that 7% of patients remained azoospermic at 24 months. After 24 months, Kaplan-Meier estimates showed that more than 90% of patients will recover normal sperm count after ABVD or ABVD+radiotherapy vs. 61% for CHOP chemotherapies. In multivariate analyses including diagnosis and treatment protocol, only pretreatment total sperm count was related to recovery. Compared with a control group, lymphoma patients had higher sperm chromatin alterations and DNA fragmentation before any treatment. After treatment, DNA fragmentation assessed by TUNEL assay and sperm chromatin structure assay decreased from 3 and 6 months, respectively, while remaining higher than in the control group during follow-up.

CONCLUSION(S)

Lymphoma patients had altered sperm DNA and chromatin before treatment. Lymphoma treatment had damaging effects on spermatogenesis. These data on both the recovery period according to treatment modalities and the pre- and post-treatment chromatin status of sperm are useful tools for counseling patients wishing to conceive.

Impact of chemotherapy and radiotherapy for testicular germ cell tumors on spermatogenesis and sperm DNA: a multicenter prospective study from the CECOS network

OBJECTIVE

To determine the consequences of adjuvant testicular germ cell tumor treatment (TGCT) on sperm characteristics and sperm DNA, and to evaluate the predictors of sperm recovery.

DESIGN

Multicenter prospective longitudinal study of patients analyzed before treatment and after 3, 6, 12, and 24 months.

SETTING

University hospitals.

PATIENT(S)

One hundred twenty-nine volunteer TGCT patients and a control group of 257 fertile men.

INTERVENTION(S)

Routine semen analyses, sperm DNA, and chromatin assessments.

MAIN OUTCOME MEASURE(S)

Comparisons of mean sperm characteristics before and after treatment, with sperm recovery analyzed by the Kaplan-Meier method.

RESULT(S)

The quantitative and qualitative sperm characteristics decreased after treatment, with lowest values at 3 and 6 months and with variations according to treatment type. The mean total sperm count recovered to pretreatment values at 12 months after treatment after two or fewer bleomycin, etoposide, and cisplatin (BEP) cycles, but not after radiotherapy or more than two BEP cycles. Only the treatment modalities and pretreatment sperm production were related to recovery of the World Health Organization reference sperm values. An increased proportion of patients had elevated high sperm DNA stainability at 6 months after radiotherapy.

CONCLUSION(S)

Adjuvant treatments for testicular germ cell tumor have drastic effects on spermatogenesis and sperm chromatin quality. These new data on both the recovery period according to treatment modalities and the post-treatment chromatin status of sperm are useful tools for counseling patients wishing to conceive.

Parental nutrient intake and risk of retinoblastoma resulting from new germline RB1 mutation

PURPOSE

We conducted a case-control study to examine the role of parents' nutrient intake before their child's conception in the child's risk of sporadic bilateral retinoblastoma, which results from a new germline RB1 mutation.

METHODS

Parents of 206 cases from 9 North American institutions and 269 friend and relative controls participated; fathers of 182 cases and 223 controls and mothers of 202 cases and 260 controls provided useable information in telephone interviews on their diet in the year before the child's conception. We also asked parents about supplements, a significant source of nutrients in users.

RESULTS

Father's intake of dairy-associated nutrients and his use of calcium supplements were associated with decreased risk, while his intake of copper, manganese, and vitamin E was associated with increased risk. Mother's use of multivitamins close to conception was associated with lower risk as was her intake of several micronutrients found in these supplements. In analyses to elucidate the primary factor from multiple correlated factors, the most robust findings were for father's calcium intake (adjusted OR = 0.46-0.63 for 700 mg increase) and calcium supplement use (OR = 0.35-0.41) and mother's multivitamin use (ORs 0.28-0.48).

CONCLUSIONS

There are few directly relevant studies but some data indirectly support the biologic plausibility of the inverse associations with father's calcium intake and mother's use of multivitamins; however, we cannot rule out contributions of bias, confounding, or chance. Our findings provide a starting point for further investigation of diet in the etiology of retinoblastoma and new germline mutation generally.

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.

Harnessing genomics to identify environmental determinants of heritable disease

Next-generation sequencing technologies can now be used to directly measure heritable de novo DNA sequence mutations in humans. However, these techniques have not been used to examine environmental factors that induce such mutations and their associated diseases. To address this issue, a working group on environmentally induced germline mutation analysis (ENIGMA) met in October 2011 to propose the necessary foundational studies, which include sequencing of parent-offspring trios from highly exposed human populations, and controlled dose-response experiments in animals. These studies will establish background levels of variability in germline mutation rates and identify environmental agents that influence these rates and heritable disease. Guidance for the types of exposures to examine come from rodent studies that have identified agents such as cancer chemotherapeutic drugs, ionizing radiation, cigarette smoke, and air pollution as germ-cell mutagens. Research is urgently needed to establish the health consequences of parental exposures on subsequent generations.

Parental diet and risk of retinoblastoma resulting from new germline RB1 mutation

We conducted a case-control study of sporadic bilateral retinoblastoma, which results from a new germline RB1 mutation, to investigate the role of parents' diet before their child's conception. Parents of 206 cases from nine North American institutions and 269 controls participated; of these, fathers of 184 cases and 223 controls and mothers of 204 cases and 260 controls answered a food frequency questionnaire administered by phone about their diet in the year before the child's conception. Cases provided DNA for RB1 mutation testing. We assessed parents' diet by examining 19 food groups. Father's intake of dairy products and fruit was associated with decreased risk and cured meats and sweets with increased risk. Mother's intake was not associated with disease for any food group. Considering analyses adjusted for the other food groups significantly associated with disease, energy intake, and demographic characteristics as well as more fully adjusted models, the associations with father's dairy products and cured meat intake were the most robust. In the fully adjusted, matched analysis, the odds ratios per daily serving were 0.70 (95% confidence interval (CI) 0.49-1.00, P = 0.047) for dairy products and 5.05 (CI 1.46-17.51, P = 0.01) for cured meat. The pattern of associations with paternal but not maternal diet is consistent with the fact that 85% of new germline RB1 mutations occur on the father's allele. As few human data exist on the role of diet in any condition resulting from new germ-cell mutation, additional studies will be needed to replicate or refute our findings.

Preconception exposure to mutagens: medical and other exposures to radiation and chemicals

Contrary to intuition, no environmental exposure has been proved to cause human germ line mutations that manifest as heritable disease in the offspring, not among the children born to survivors of the American atomic bombs in Japan nor in survivors of cancer in childhood, adolescence, or young adulthood who receive intensive chemotherapy, radiotherapy, or both. Even the smallest of recent case series had sufficient statistical power to exclude, with the usual assumptions, an increase as small as 20 % over baseline rates. One positive epidemiologic study of a localized epidemic of Down syndrome in Hungary found an association with periconceptual exposure to a pesticide used in fish farming, trichlorfon. Current population and occupational guidelines to protect against genetic effects of ionizing radiation should continue, with the understanding they are based on extrapolations from mouse experiments and mostly on males. Presently, pre-conceptual counseling for possible germ cell mutation due to the environment can be very reassuring, at least based on, in a sense, the worst-case exposures of cancer survivors. Prudence demands further study. Future work will address the issue with total genomic sequencing and epigenomic analysis.

Whole genome sequencing for quantifying germline mutation frequency in humans and model species: cautious optimism

Factors affecting the type and frequency of germline mutations in animals are of significant interest from health and toxicology perspectives. However, studies in this field have been limited by the use of markers with low detection power or uncertain relevance to phenotype. Whole genome sequencing (WGS) is now a potential option to directly determine germline mutation type and frequency in family groups at all loci simultaneously. Medical studies have already capitalized on WGS to identify novel mutations in human families for clinical purposes, such as identifying candidate genes contributing to inherited conditions. However, WGS has not yet been used in any studies of vertebrates that aim to quantify changes in germline mutation frequency as a result of environmental factors. WGS is a promising tool for detecting mutation induction, but it is currently limited by several technical challenges. Perhaps the most pressing issue is sequencing error rates that are currently high in comparison to the intergenerational mutation frequency. Different platforms and depths of coverage currently result in a range of 10-10(3) false positives for every true mutation. In addition, the cost of WGS is still relatively high, particularly when comparing mutation frequencies among treatment groups with even moderate sample sizes. Despite these challenges, WGS offers the potential for unprecedented insight into germline mutation processes. Refinement of available tools and emergence of new technologies may be able to provide the improved accuracy and reduced costs necessary to make WGS viable in germline mutation studies in the very near future. To streamline studies, researchers may use multiple family triads per treatment group and sequence a targeted (reduced) portion of each genome with high (20-40 ×) depth of coverage. We are optimistic about the application of WGS for quantifying germline mutations, but caution researchers regarding the resource-intensive nature of the work using existing technology.

Declaring the existence of human germ-cell mutagens

After more than 80 years of searching for human germ-cell mutagens, I think that sufficient evidence already exists for a number of agents to be so considered, and definitive confirmation seems imminent due to the application of recently developed genomic techniques. In preparation for this, an assessment panel of internationally recognized experts in germ-cell biology and genomics is required to consider either the current evidence now, or impending genomic evidence later, to declare whether an agent is a human germ-cell mutagen. I propose that such a panel be organized under the aegis of the World Health Organization and constructed similarly to the working groups assembled by the International Agency for Research on Cancer for the evaluation of human carcinogens. Support from prominent national and international organizations would be important. Many regulatory agencies already have procedures in place for assessing potential human germ-cell mutagens, and the time is approaching when definitive genomic data in humans will obligate such evaluations. In my view, application of an IARC-type of assessment using available evidence leads to the conclusion that ionizing radiation, cancer chemotherapy, cigarette smoking, and air pollution are "Group 1" human germ-cell mutagens. Consideration of the potential adverse health effects to the unexposed offspring of an exposed parent will usher in an entirely new realm of environmental health assessment. I suggest that the long search for human germ-cell mutagens is about to end, and a demonstration of the much-anticipated linkage between heritable disease and environmental factors is poised to begin.

The use of next generation sequencing technology to study the effect of radiation therapy on mitochondrial DNA mutation

The human mitochondrial genome has an exclusively maternal mode of inheritance. Mitochondrial DNA (mtDNA) is particularly vulnerable to environmental insults due in part to an underdeveloped DNA repair system, limited to base excision and homologous recombination repair. Radiation exposure to the ovaries may cause mtDNA mutations in oocytes, which may in turn be transmitted to offspring. We hypothesized that the children of female cancer survivors who received radiation therapy may have an increased rate of mtDNA heteroplasmy mutations, which conceivably could increase their risk of developing cancer and other diseases. We evaluated 44 DNA blood samples from 17 Danish and 1 Finnish families (18 mothers and 26 children). All mothers had been treated for cancer as children and radiation doses to their ovaries were determined based on medical records and computational models. DNA samples were sequenced for the entire mitochondrial genome using the Illumina GAII system. Mother's age at sample collection was positively correlated with mtDNA heteroplasmy mutations. There was evidence of heteroplasmy inheritance in that 9 of the 18 families had at least one child who inherited at least one heteroplasmy site from his or her mother. No significant difference in single nucleotide polymorphisms between mother and offspring, however, was observed. Radiation therapy dose to ovaries also was not significantly associated with the heteroplasmy mutation rate among mothers and children. No evidence was found that radiotherapy for pediatric cancer is associated with the mitochondrial genome mutation rate in female cancer survivors and their children.

Congenital anomalies in the children of cancer survivors: a report from the childhood cancer survivor study

PURPOSE

Children with cancer receive mutagenic treatments, which raises concern about the potential transmissibility of germline damage to their offspring. This question has been inadequately studied to date because of a lack of detailed individual treatment exposure assessment such as gonadal radiation doses.

METHODS

Within the Childhood Cancer Survivor Study, we performed a retrospective cohort analysis of validated cases of congenital anomalies among 4,699 children of 1,128 male and 1,627 female childhood cancer survivors. We quantified chemotherapy with alkylating agents and radiotherapy doses to the testes and ovaries and related these exposures to risk of congenital anomalies using logistic regression.

RESULTS

One hundred twenty-nine children had at least one anomaly (prevalence = 2.7%). For children whose mothers were exposed to radiation or alkylating agents versus neither, the prevalence of anomalies was 3.0% versus 3.5% (P = .51); corresponding figures were 1.9% versus 1.7% (P = .79) for the children of male survivors. Neither ovarian radiation dose (mean, 1.19 Gy; odds ratio [OR] = 0.59; 95% CI, 0.20 to 1.75 for 2.50+ Gy) nor testicular radiation dose (mean, 0.48 Gy; OR = 1.01; 95% CI, 0.36 to 2.83 for 0.50+ Gy) was related to risk of congenital anomalies. Treatment with alkylating agents also was not significantly associated with anomalies in the children of male or female survivors.

CONCLUSION

Our findings offer strong evidence that the children of cancer survivors are not at significantly increased risk for congenital anomalies stemming from their parent's exposure to mutagenic cancer treatments. This information is important for counseling cancer survivors planning to have children.

Medical radiation exposure and risk of retinoblastoma resulting from new germline RB1 mutation

Although ionizing radiation induces germline mutations in animals, human studies of radiation-exposed populations have not detected an effect. We conducted a case-control study of sporadic bilateral retinoblastoma, which results from a new germline RB1 mutation, to investigate gonadal radiation exposure of parents from medical sources before their child's conception. Parents of 206 cases from nine North American institutions and 269 controls participated; fathers of 184 cases and 223 friend and relative controls and mothers of 204 cases and 260 controls provided information in telephone interviews on their medical radiation exposure. Cases provided DNA for RB1 mutation testing. Of common procedures, lower gastrointestinal (GI) series conferred the highest estimated dose to testes and ovaries. Paternal history of lower GI series was associated with increased risk of retinoblastoma in the child [matched odds ratio (OR) = 3.6, 95% confidence interval (CI) = 1.2-11.2, two-sided p = 0.02], as was estimated total testicular dose from all procedures combined (OR for highest dose=3.9, 95% CI = 1.2-14.4, p = 0.02). Maternal history of lower GI series was also associated with increased risk (OR = 7.6, 95% CI = 2.8-20.7, p < 0.001) as was the estimated total dose (OR for highest dose = 3.0, 95% CI = 1.4-7.0, p = 0.005). The RB1 mutation spectrum in cases of exposed parents did not differ from that of other cases. Some animal and human data support our findings of an association of gonadal radiation exposure in men and women with new germline RB1 mutation detectable in their children, although bias, confounding, and/or chance may also explain the results.

Hospitalizations among children of survivors of childhood and adolescent cancer: a population-based cohort study

Curative but potentially mutagenic cancer therapy might lead to untoward disorders and increased hospitalization among the offspring of childhood cancer survivors. Hospitalizations in childhood were evaluated in a population-based cohort of 1,920 offspring of 3,963 childhood cancer survivors, 6,394 offspring of 5,657 siblings and 9,594 population-based comparisons. The Danish Cancer Registry, Central Population Register and National Hospital Register were used to identify study subjects and hospitalizations. The probability for children in the offspring cohorts of being hospitalized before a given age was estimated using the Kaplan-Meier method. Hospitalization rate ratios (HRRs) were calculated using a Cox proportional hazards model with population comparisons as referent. Little differences in hospitalization histories were seen among offspring in the 3 cohorts. HRRs of overall hospitalization was 1.05 (95% CI, 0.98-1.12) for offspring of survivors and 1.01 (95% CI, 0.97-1.05) for offspring of siblings, neither of which was significantly different from that of population comparisons. No significant associations were seen for most of the main diagnostic groups of diseases including infections and perinatal disorders. A 6-fold excess risk of hospitalization for malignant tumors in survivors' offspring, however, could largely be explained by hereditary cancer syndromes, and part of the 2-fold excess hospitalization for benign tumors might similarly be explained by an underlying genetic susceptibility or by increased surveillance of children born to survivors. Assuming that hospitalization is an indicator of multifactorial genetic disease, the findings provide further reassurance that cancer therapies do not confer a high risk of such conditions in offspring born after treatments.

Assessment of heritable genetic effects using new genetic tools and sentinels in an era of personalized medicine

The challenge of estimating human health effects from damage to the germ line may be met in the genomic era. Understanding the genetic, as opposed to postconception developmental basis of birth defects is critical to their use in monitoring heritable genetic damage. The causes of common birth defects are analyzed here: mendelian genetic, multigenic, developmental, inherited, or combinational. Only a small fraction of these (noninherited, mendelian genetic) are likely to be informative relative to germ cell mutagenesis, and these won't be discernible against the general background of birth defects. Targeted genetic testing as part of personalized medicine could be integrated into a strategy for assessing germ cell alterations in populations. Thus, "sentinel mutations," as originally proposed by Mulvihill and Ceizel, need not be restricted to X-linked or dominant mutations or conditions visible at birth. Several new sentinels related to personalized medicine are proposed, based on health impact (likelihood of monitoring), frequency, and genetic target suitability (responsiveness to diverse mutational mechanisms). Candidates could include CYP genes (related to metabolism of xenobiotics) important in optimizing drug doses and avoiding adverse reactions. High frequency LDLR mutations (related to familial high cholesterol) predict myocardial infarction in approximately50% of individuals. The more common recessive genetic diseases (cystic fibrosis, phenylketonuria, and others) monitored in newborn screening programs could be informative given parental analysis. New opportunities for genetic analyses need to be coupled with epidemiological studies on environmental exposures. These could focus on adverse outcomes related to tobacco, the mostubiquitous and potent environmental mutagen.

Chemotherapy-induced late transgenerational effects in mice

To our knowledge, there is no report on long-term reproductive and developmental side effects in the offspring of mothers treated with a widely used chemotherapeutic drug such as doxorubicin (DXR), and neither is there information on transmission of any detrimental effects to several filial generations. Therefore, the purpose of the present paper was to examine the long-term effects of a single intraperitoneal injection of DXR on the reproductive and behavioral performance of adult female mice and their progeny. C57BL/6 female mice (generation zero; G0) were treated with either a single intraperitoneal injection of DXR (G0-DXR) or saline (G0-CON). Data were collected on multiple reproductive parameters and behavioral analysis for anxiety, despair and depression. In addition, the reproductive capacity and health of the subsequent six generations were evaluated. G0-DXR females developed despair-like behaviors; delivery complications; decreased primordial follicle pool; and early lost of reproductive capacity. Surprisingly, the DXR-induced effects in oocytes were transmitted transgenerationally; the most striking effects being observed in G4 and G6, constituting: increased rates of neonatal death; physical malformations; chromosomal abnormalities (particularly deletions on chromosome 10); and death of mothers due to delivery complications. None of these effects were seen in control females of the same generations. Long-term effects of DXR in female mice and their offspring can be attributed to genetic alterations or cell-killing events in oocytes or, presumably, to toxicosis in non-ovarian tissues. Results from the rodent model emphasize the need for retrospective and long-term prospective studies of survivors of cancer treatment and their offspring.

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.

Germ cell mutagens: risk assessment challenges in the 21st century

Heritable mutations may result in a wide variety of detrimental outcomes, from embryonic lethality to genetic disease in the offspring. Despite this, today's commonly used test batteries do not include assays for germ cell mutation. Current challenges include a lack of practical assays and concrete evidence for human germline mutagens, and large data gaps that often impede risk assessment. Moreover, most regulatory assessments are based on the assumption that somatic cell mutation assays also protect the germline by default, which has not been adequately confirmed. The field is also faced with new challenges aimed at dramatically reducing animal testing, and attempts to rapidly classify thousands of chemicals using high throughput in vitro assays. These approaches may not adequately capture effects that may be particular to gametes, since many aspects of the germline are unique. In light of these challenges, an urgent need exists to develop new approaches to evaluate the potential of toxicants to cause germline mutation. The application of new technologies will greatly enhance our understanding of mutation in humans exposed to environmental mutagens. However, we must be poised to collect and interpret these data, and facilitate risk translation to regulators and the public. Genetic toxicologists must also become actively involved in the development of high-throughput tools to study germline mutation. Appropriate attention to these areas will result in the development of policies that prioritize the protection of the germline and future generations from DNA sequence mutations.

Stillbirth and neonatal death in relation to radiation exposure before conception: a retrospective cohort study

BACKGROUND

The reproductive implications of mutagenic treatments given to children with cancer are not clear. By studying the risk of untoward pregnancy outcomes, we indirectly assessed the risk of transmission of germline damage to the offspring of survivors of childhood cancer who were given radiotherapy and chemotherapy.

METHODS

We did a retrospective cohort analysis, within the Childhood Cancer Survivor Study (CCSS), of the risk of stillbirth and neonatal death among the offspring of men and women who had survived childhood cancer. Patients in CCSS were younger than 21 years at initial diagnosis of an eligible cancer, were treated at 25 US institutions and one Canadian institution, and had survived for at least 5 years after diagnosis. We quantified the chemotherapy given to patients, and the preconception radiation doses to the testes, ovaries, uterus, and pituitary gland, and related these to the risk of stillbirth or neonatal death using Poisson regression analysis.

FINDINGS

Among 1148 men and 1657 women who had survived childhood cancer, there were 4946 pregnancies. Irradiation of the testes (16 [1%] of 1270; adjusted relative risk 0.8 [95% CI 0.4-1.6]; mean dose 0.53 Gy [SD 1.40]) and pituitary gland (17 [3%] of 510, 1.1 [0.5-2.4] for more than 20.00 Gy; mean dose 10.20 Gy [13.0] for women), and chemotherapy with alkylating drugs (26 [2%] of 1195 women, 0.9 [0.5-1.5]; ten [1%] of 732 men, 1.2 [0.5-2.5]) were not associated with an increased risk of stillbirth or neonatal death. Uterine and ovarian irradiation significantly increased risk of stillbirth and neonatal death at doses greater than 10.00 Gy (five [18%] of 28, 9.1 [3.4-24.6]). For girls treated before menarche, irradiation of the uterus and ovaries at doses as low as 1.00-2.49 Gy significantly increased the risk of stillbirth or neonatal death (three [4%] of 69, 4.7 [1.2-19.0]).

INTERPRETATION

Our findings do not support concern about heritable genetic changes affecting the risk of stillbirth and neonatal death in the offspring of men exposed to gonadal irradiation. However, uterine and ovarian irradiation had serious adverse effects on the offspring that were probably related to uterine damage. Careful management is warranted of pregnancies in women given high doses of pelvic irradiation before puberty.

FUNDING

Westlakes Research Institute, National Cancer Institute, and Children's Cancer Research Fund.

Comparison of germ line minisatellite mutation detection at the CEB1 locus by Southern blotting and PCR amplification

Identification of de novo minisatellite mutations in the offspring of parents exposed to mutagenic agents offers a potentially sensitive measure of germ line genetic events induced by ionizing radiation and genotoxic chemicals. Germ line minisatellite mutations (GMM) are usually detected by hybridizing Southern blots of unamplified size-fractionated genomic DNA with minisatellite probes. However, this consumes a relatively large amount of DNA, requires several steps and may lack sensitivity. We have developed a polymerase chain reaction (PCR)-based GMM assay, which we applied to the hypermutable minisatellite, CEB1. Here, we compare the sensitivity and specificity of this assay with the conventional Southern hybridization method using DNA from 10 spouse pairs, one parent of each pair being a survivor of cancer in childhood, and their 20 offspring. We report that both methods have similar specificity but that the PCR method uses 250 times less DNA, has fewer steps and is better at detecting GMM with single repeats provided that specific guidelines for allele sizing are followed. The PCR GMM method is easier to apply to families where the amount of offspring DNA sample is limited.

Hypomethylation and genome instability in the germline of exposed parents and their progeny is associated with altered miRNA expression

Recent studies suggest that transgenerational genome instability may be epigenetic in nature and mediated via altered DNA methylation and microRNAome. Here, we investigated the nature and mechanisms underlying the disruption of DNA methylation and microRNA expression status in the germline and progeny of exposed parents. We have found that paternal irradiation leads to upregulation of the miR-29 family in the exposed male germline, which causes decreased expression of de novo methyltransferase, DNA methyltransferase 3a, and profound hypomethylation of long interspersed nuclear elements 1 (LINE1) and short interspersed nuclear elements B2 (SINE B2). Epigenetic changes in the male germline further resulted in deleterious effects in the somatic thymus tissue from the progeny of exposed animals, including hypomethylation of LINE1 and SINE B2. Hypomethylation of LINE1 and SINE B2 in the thymus tissue from the progeny was associated with a significant decrease in the levels of lymphoid-specific helicase (LSH) that is crucial for the maintenance of methylation and silencing of repetitive elements. Furthermore, we noted a significant upregulation of miR-468 that targets LSH and leads to its decreased expression in thymus in the progeny of exposed parents. We suggest that miR-468-mediated suppression of LSH leads to aberrant methylation of LINE1 and SINE B2. In summary, altered microRNAome and hypomethylation of retroelements constitute deleterious effects that may significantly influence genome stability of the parental germline and consequently cause genome instability in the progeny.

Cancer in the offspring of female radiation workers: a record linkage study

This study uses record linkage between the National Registry of Childhood Tumours (NRCT) and the National Registry for Radiation Workers to re-assess our earlier finding that the offspring of women radiation workers exposed to ionising radiation before the child's conception may be at an increased risk of childhood cancer. An additional 16 964 childhood cancer patients taken from the NRCT, together with the same number of matched controls, are included. Pooled analyses, based on the new and original datasets, include 52 612 cases and their matched controls. Relative risks (RRs) for maternal employment as a radiation worker, maternal exposure or not during the relevant pregnancy and pattern of employment relative to conception and diagnosis dates were calculated.

The new data provide no evidence of an increased risk of childhood cancer associated with maternal preconception radiation work and thus do not support our earlier finding of a raised risk in the offspring of female radiation workers. Considering the pooled data, a weak association was found between maternal radiation work during pregnancy and childhood cancer in offspring although the evidence is limited by the small numbers of linked cases and controls.

Radiotherapy for childhood cancer and risk for congenital malformations in offspring: a population-based cohort study

Offspring of childhood cancer survivors may be at risk of genetic disease due to the mutagenic cancer treatments received by their parents. Congenital malformations were evaluated in a population-based cohort study of 1715 offspring of 3963 childhood cancer survivors and 6009 offspring of 5657 survivors' siblings. The Danish Central Population Register, Cancer Registry and Hospital Register were used to identify study subjects and congenital malformations. Gonadal and uterine radiation doses were characterized based on standard radiation-treatment regimens. The prevalence of congenital malformations at birth in offspring of survivors (44 cases, 2.6%) was slightly higher but not statistically different from that of offspring of siblings (140 cases, 2.3%) [prevalence proportion ratio (PPR), 1.1; 95% confidence interval, 0.8-1.5] or of the general population (observed-to-expected ratio, 1.2; 0.9-1.6). Including malformations diagnosed later in life did not change the ratios appreciably. The risk for malformations was slightly higher in the offspring of irradiated parents than in that of non-irradiated parents (PPR 1.2 vs 1.0) but was unrelated to gonadal dose. This study provides evidence that cancer therapy of children does not increase the risk for malformations in their offspring. Continued monitoring of genetic risks among their offspring, however, is warranted.

Preconception exposures to potential germ-cell mutagens

Radiation and other agents can cause germ-cell mutations in animal systems. No human germ-cell mutagen has been identified, but this does not mean that human germ-cells are not vulnerable to mutagenesis. There has been particular concern about the possible health effects on offspring following parental preconception exposure to ionizing radiation-both occupational and therapeutic. A strong association with preconception radiation exposure in the fathers of the cases was found in a case-control study of young people with leukaemia living near the Sellafield nuclear plant in the UK. Subsequent studies of workers occupationally exposed to ionizing radiation have failed to confirm these findings. No statistically significant effects have been reported from studies of possible indicators of germ-cell mutagenesis in the A-bomb survivors. Studies of offspring of cancer survivors who receive radiotherapy and mutagenic chemotherapy have found no evidence of germ-cell mutagenesis. Failure to detect human germ-cell mutagenic agents may be a consequence of inadequate study sizes or insufficiently sensitive laboratory techniques.

Transgenic lambda medaka as a new model for germ cell mutagenesis

To address the need for improved approaches to study mutations transmitted to progeny from mutagen-exposed parents, we evaluated lambda transgenic medaka, a small fish that carries the cII mutation target gene, as a new model for germ cell mutagenesis. Mutations in the cII gene in progeny derived from ethyl-nitrosourea (ENU)-exposed males were readily detected. Frequencies of mutant offspring, proportions of mosaic or whole body mutant offspring, and mutational spectra differed according to germ cell stage exposed to ENU. Postmeiotic germ cells (spermatozoa/late spermatids) generated a higher frequency of mutant offspring (11%) compared to premeiotic germ cells (3.5%). Individuals with cII mutant frequencies (MF) elevated more than threefold above the spontaneous MF (3 x 10(-5)) in the range of 10(-4) to 10(-3) were mosaic mutant offspring, whereas those with MFs approaching 1 x 10(-2) were whole body mutant offspring. Mosaic mutant offspring comprised the majority of mutant offspring derived from postmeiotic germ cells, and unexpectedly, from spermatogonial stem cells. Mutational spectra comprised of two different mutations, but at identical sites were unusual and characteristic of delayed mutations, in which fixation of a second mutation was delayed following fertilization. Delayed mutations and prevalence of mosaic mutant offspring add to growing evidence that implicates germ cells in mediating processes postfertilization that contribute to genomic instability in progeny. This model provides an efficient and sensitive approach to assess germ cell mutations, expands opportunities to increase understanding of fundamental mechanisms of mutagenesis, and provides a means for improved assessment of potential genetic health risks.