Paternal exposure not to blame

Induction of lympho-haemopoietic malignancy: impact of preconception paternal irradiation

PURPOSE

To investigate the effects of preconception paternal irradiation (PPI) from injected 239Pu on the susceptibility to induction of lympho-haemopoietic malignancy by subsequent irradiation or exposure to a chemical carcinogen.

MATERIALS AND METHODS

The male CBA/H and DBA2 mouse was injected with 0, 128 or 256 Bqg(-1) 239Pu 12 weeks before mating with the normal CBA/H and C57B1 female respectively. CBA/H offspring were exposed to 3.3 Gy gamma-rays total body irradiation: BDF1 offspring were injected with 50 mg kg(-1) methyl nitrosourea (MNU). The offspring were assayed for changes in bone marrow progenitor cell numbers and chromosome aberrations and were followed up for subsequent induction of neoplasia.

RESULTS

While the untreated mouse showed a normal distribution for cellularity, spleen colony-forming units (CFU-S) and fibroblastoid colony-forming units (CFU-F), significant numbers of PPI offspring presented levels outside the normal range. There was a tendency for them also to show increased, dose-related, levels of chromosomal aberrations. Offspring treated with irradiation or MNU developed an increased incidence of lympho-haemopoietic malignancies.

CONCLUSIONS

These studies have shown that PPI results in offspring that are more susceptible to the induction of lymphohaemopoietic malignancy on encountering a secondary carcinogenic insult. This may be linked to inherited chromosomal instability and abnormal kinetics of haemopoiesis. The experiments indicate a potential mechanism by which an increased incidence of leukaemia may be linked to PPI.

Tumour induction by methyl-nitroso-urea following preconceptional paternal contamination with plutonium-239

We have investigated the possibility that transgenerational effects from preconceptional paternal irradiation (PPI) may render offspring more vulnerable to secondary exposure to an unrelated carcinogen. 239Pu (0, 128 or 256 Bq g(-1)) was administered by intravenous injection to male mice, 12 weeks before mating with normal females. Two strains of mouse were used -- CBA/H and BDF1. Haemopoietic spleen colony-forming units (CFU-S) and fibroblastoid colony-forming units (CFU-F), a component of their regulatory microenvironment, were assayed independently in individual offspring at 6, 12 and 19 weeks of age. Bone marrow and spleen from each of these mice were grown in suspension culture for 2 or 7 days for assessment of chromosomal aberrations. Female BDF1 were injected with methyl-nitroso-urea (MNU) as a secondary carcinogen at 10 weeks of age and monitored for onset of leukaemia/lymphoma. Mean values of CFU-S and CFU-F were unaffected by preconceptional paternal plutonium-239 (PP-239Pu), although for CFU-F in particular there was an apparent increase in variation between individual animals. There was significant evidence of an increase in chromosomal aberrations with dose in bone marrow but not in spleen. By 250 days, 68% of MNU-treated control animals (no PPI) had developed thymic lymphoma (62%) or leukaemia (38%). The first case arose 89 days after MNU administration. In the groups with PPI, leukaemia/lymphoma developed from 28 days earlier, rising to 90% by 250 days. Leukaemia (65%) now predominated over lymphoma (35%). This second generation excess of leukaemia appears to be the result of PPI and may be related to inherited changes that affect the development of haemopoietic stem cells.

Investigation of lung tumour induction in C3H/HeH mice, with and without tumour promotion with urethane, following paternal X-irradiation

In series of papers Nomura has reported that parental irradiation can lead to an enhanced incidence of lung and other tumours. However, in a recent study with BALB/cJ mice, using optimum conditions as defined by Nomura, we were unable to confirm this. We have now repeated the investigation using a different inbred strain, C3H/HeH, with and without tumour promotion in the F1 by urethane, again using protocols defined by Nomura. In a series of replicate studies spanning over 2 years, males were exposed to single, acute doses of 0, 250 and 500 cGy X-rays and thereafter placed with two females each in each of two consecutive weeks. Half the offspring from each treatment group and each week of mating were given 5 mmol/kg body weight of the urethane, while the remainder remained untreated. Most of the offspring produced were killed and scored for lung tumours at 6 months of age, while the rest were examined at 12 months of age. The proportion of fertile females and litter size provided evidence of a dose-dependent mutational response to the paternal irradiation, but no trace of a radiation-enhanced lung tumour incidence was detected among the progeny, whether in the urethane or non-urethane groups at 6 or 12 months of age, and whether assessed by numbers of mice with tumours, clusters of tumours, or cluster size. As seen in the BALB/cJ study, significant differences among different replicates were found, again suggesting a cyclical or seasonal variation in tumour incidence, but the variations seen with the two strains were not the same. The need for concurrent controls for tumour work was, nevertheless, again indicated. The overall findings do not therefore accord with those of Nomura. Furthermore, they do not support the causal association between the raised incidence of childhood leukaemia and non-Hodgkins lymphoma near Sellafield and the father's recorded radiation exposure during employment in the nuclear industry, as suggested by the Gardner report.

Common and emerging infectious causes of hematological malignancies in the young

Comparative epidemiological studies have for a long time suggested a link (or links) between infectious agents and hematological malignancies in the young. Identification of Epstein-Barr virus (EBV) as the major cause of specific subtypes of Burkitt's lymphoma and Hodgkin's disease 20 and 10 years ago, respectively, and the recent involvement of human T-cell leukemia virus in non-Hodgkin's lymphomas of the T-cell lineage in young adults in Jamaica have given further credit to early presumptions that these diseases have an infectious etiology. The spectrum of possibly involved viruses: old, EBV, and new, herpesviruses 6, 7 and 8, and unknown retroviruses - as well as the list of partially or totally unresolved disease entities: Hodgkin's disease in adolescents, non-Hodgkin's lymphomas in the immunocompromised, and acute lymphocytic leukemia - is rapidly expanding. Both direct and indirect transforming effects of the above-mentioned viruses are being rapidly disclosed. However, the complex interaction between the different viruses and other causes of hematological malignancies in the young guarantees that many things remain to be discovered also in the future.

The North Cumbria Community Genetics Project

The aim of the North Cumbria Community Genetics Project is to establish a store of DNA, plasma, and viable cells from a cohort of around 8000 Cumbrian infants. To meet this objective, specimens of umbilical cord blood and tissue will be collected with maternal consent from babies born at the West Cumberland Hospital, Whitehaven over a five year period from January 1996. These samples will be used in a series of genetic and epidemiological studies investigating the interaction between genes, the environment, and health. There is little population movement in West Cumbria and so it will be possible to follow many of the babies throughout their childhood and to investigate the relationship between their genetic constitution and health outcome.

Spatial clustering of childhood leukaemia: summary results from the EUROCLUS project

The interpretation of reports of clusters of childhood leukaemia is difficult, first because little is known about the causes of the disease, and second because there is insufficient information on whether cases show a generalized tendency to cluster geographically. The EUROCLUS project is a European collaborative study whose primary objective is to determine whether the residence locations of cases at diagnosis show a general tendency towards spatial clustering. The second objective is to interpret any patterns observed and, in particular, to see if clustering can be explained in terms of either infectious agents or environmental hazards as aetiological agents. The spatial distribution of 13351 cases of childhood leukaemia diagnosed in 17 countries between 1980 and 1989 has been analysed using the Potthoff-Whittinghill method. The overall results show statistically significant evidence of clustering of total childhood leukaemia within small census areas (P=0.03) but the magnitude of the clustering is small (extra-Poisson component of variance (%) = 1.7 with 90% confidence interval 0.2-3.1). The clustering is most marked in areas that have intermediate population density (150-499 persons km[-2]). It cannot be attributed to any specific age group at diagnosis or cell type and involves spatial aggregation of cases of different ages and cell types. The results indicate that intense clusters are a rare phenomenon that merit careful investigation, although aetiological insights are more likely to come from investigation of large numbers of cases. We present a method for detecting clustering that is simple and readily available to cancer registries and similar groups.

Risk assessment of the nuclear medicine patient

Two types of risk are identified following the administration of a radiopharmaceutical to a patient: the risk to the patient, and the risk to critical groups exposed to the patient. The method for quantifying the risk to the patient is described in terms of estimating the effective dose. The main limitations in these estimates for adult and paediatric patients are uncertainties in the biokinetic data, and the assumption of a uniform distribution of activity in each organ. Effective doses from most nuclear medicine procedures will not exceed twice the annual dose from natural background radiation in the UK. Lack of human placental transfer data is now the main limitation to estimating fetal doses. The characteristics of two methods which can be used to derive the dose to critical groups exposed to nuclear medicine patients are reviewed. It is shown that studies using either method have indicated that the current recommendations in the UK for restricting the exposure of these groups and the recommendation recently proposed for restricting the exposure of pregnant members of staff are not appropriate. Revised recommendations for restricting the behaviour of patients administered iodine-131 should await the results of a current multicentre trial. The method to estimate the dose to a breast-fed infant from a mother administered a radiopharmaceutical is outlined, and the recently revised guidance for interrupting breast feeding is summarised. When a recommendation for controlling risk is to be derived from dosimetry data obtained from a number of individuals, an outstanding issue to be resolved is the value (e.g. 95% upper confidence limit) on which it should be based.

Childhood cancer and parental use of tobacco: deaths from 1953 to 1955

Parental smoking data have been abstracted from the interview records of the case-control study that first indicated that pregnancy radiographs are a cause of childhood cancer (Oxford Survey of Childhood Cancers, deaths from 1953 to 1955). Reported smoking habits for the parents of 1549 children who died from cancer were compared with similar information for the parents of 1549 healthy controls (matched pairs analysis). There was a statistically significant positive trend between paternal daily consumption of tobacco and the risk of childhood cancer (P< 0.001). This association could not be explained by maternal smoking, social class, paternal or maternal age at the birth of the survey child, sibship position or obstetric radiography. About 15% of all childhood cancers in this series could be attributable to paternal smoking.

The sex ratio of children in relation to paternal preconceptional radiation dose: a study in Cumbria, northern England

STUDY OBJECTIVE

To investigate whether the occupational exposure to external ionising radiation of men employed at the Sellafield nuclear installation, West Cumbria, affects the sex of the children they subsequently father.

DESIGN

A retrospective cohort study using logistic regression to analyse the sex ratio, in particular in relation to paternal preconceptional irradiation.

SETTING AND PARTICIPANTS

The 260,060 singleton births between 1950 and 1989 to mothers resident in Cumbria, north west England.

RESULTS

The sex ratio among children of men employed at any time at Sellafield was 1.094 (95% CI: 1.060, 1.128), significantly higher than that among other Cumbrian children, 1.055 (95% CI: 1.046, 1.063). There was an increased sex ratio of 1.396 (95% CI: 1.127, 1.729) in the 345 children whose fathers were estimated from annual dose summaries to have received more than 10 mSv of external radiation in the 90 days preceding conception, but no significant linear trend between sex ratio and 90 day paternal preconceptional dose was found. There was no significant association between sex ratio and the external dose accumulated before the 90 day period preceding conception.

CONCLUSIONS

Men employed at Sellafield fathered a greater proportion of boys than would be expected for a Cumbrian population, which may be partly explained by their younger age distribution. A greater effect was observed in the fathers with recorded doses exceeding 10 mSv in the 90 days before conception. While this may reflect a true statistical association, it is also possible that it may be a chance finding due to imprecision in the dose estimates and consequent misclassification.

The measurement of radioactivity in people living near the Dounreay Nuclear Establishment, caithness, scotland

In 1986, a statistically significant excess of leukaemia was reported in young people living near the Dounreay Nuclear Establishment in northern Scotland. The committee on Medical Aspects of Radiation in the Environment (COMARF) confirmed this finding and concluded that, based on conventional dose and risk estimates, the radioactive discharges from the plant could not be held responsible. However, COMARF, recognizing the uncertainties involved in the dose and risk calculations, recommended that levels of radioactivity should be measured in the general population living near the plant. Alpha-emitting contamination has been measured by urinary 239Pu analysis and 241Am in-vivo skull measurements in 66 subjects associated with the Dounreay area and in 42 subjects living remote from reprocessing plants. Whole-body counting was employed to check for gamma ray-emitting contamination. Urinary 90Sr and chromosome abnormality analyses were also carried out on subsets of the study group. No significant inter-group differences for measurements of contamination were demonstrated for groups of leukaemia cases, siblings, parents, matched local controls and controls living remote from reprocessing plants. The findings suggest that it is unlikely that the observed increased incidence in leukaemia is due to the single factor of personal radioactive contamination from the Dounreay Nuclear Establishment.

Infant leukaemia after in utero exposure to radiation from Chernobyl

There has been no documented increase in childhood leukaemia following the Chernobyl accident. However, different forms of childhood leukaemia may not be equally susceptible to radiation carcinogenesis. Infant leukaemia is a distinct form associated with a specific genetic abnormality. Outside the former Soviet Union, contamination resulting from the Chernobyl accident has been highest in Greece and Austria and high also in the Scandinavian countries. All childhood leukaemia cases diagnosed throughout Greece since 1 January 1980 have been recorded. Here we report that infants exposed in utero to ionizing radiation from the Chernobyl accident had 2.6 times the incidence of leukaemia compared to unexposed children (95% confidence interval, 1.4 to 5.1; P approximately 0.003), and those born to mothers residing in regions with high radioactive fallout were at higher risk of developing infant leukaemia. No significant difference in leukaemia incidence was found among children aged 12 to 47 months. Preconceptional irradiation had no demonstrable effect on leukaemia risk at any of the studied age groups.

Fertility, reproductive outcomes, and health of offspring, of patients treated for Hodgkin's disease: an investigation including chromosome examinations

Reproductive outcomes and health of offspring were investigated in 340 patients with Hodgkin's disease first treated at Mount Vernon Hospital, Middlesex, England, at ages under 40 (females) or 45 (males) during 1970-91. Information on offspring was obtained from case-notes and postal questionnaires to the patients. Eleven men and 16 women who had conceived any children after treatment were then interviewed. There was no excess of stillbirths, low birthweight or cogenital malformations, and no cancers have occurred in the 49 offspring after treatment. There was a significant excess of twins, compared with national expectations, in offspring of female patients (RR = 8.52, P = 0.025). Aggregation of series from the literature also showed an excess of twins. Chromosomes from cultures of peripheral lymphocytes from 45 children born to 25 patients (11 men and 14 women) after treatment were examined for numerical abnormalities and for structural abnormalities at the 550 or greater band level of resolution. All were normal except in one child with Down's syndrome (47, XY, +21), for whom we found the origin of the trisomy was from the parent without Hodgkin's disease. The chromosome constitution was also abnormal in one miscarriage (69, XXY; originating from the parent without Hodgkin's disease) and one termination (45, X; for with the parental origin could not be determined) after treatment. The study adds to previous questionnaire data and for the first time provides data also from chromosome analysis, that offspring of patients treated in adulthood for Hodgkin's disease are not at greatly raised risk of genotoxic or other adverse outcomes as a consequence of their parent's treatment. The numbers of offspring assessed in the literature remains small, however, and surveillance of larger numbers of subjects is needed to enable reliable treatment-specific analyses.

The U.S.-Japan Cooperative Cancer Research Program: some highlights of seminars, interdisciplinary program area, 1981-1996

Thirty-one seminars have been held in the 16 years since 1981. A principal interest from the beginning was the genetics of cancer, well before this subject became widely popular. This interest arose in part because of marked binational differences in type-specific cancer rates, such as the very low rates among Japanese for Hodgkin's disease in the young, testicular cancer, Ewing's sarcoma, superficial spreading melanoma, chronic lymphocytic leukemia, and Wilms' tumor (half the U.S. frequency). Three seminars were devoted to the seeming reciprocal relationship between B-cell lymphoma (low in Japan) and certain autoimmune diseases (high in Japan), which is perhaps similar in origin to the male/female differences in the rates for these diseases. A seminar on Li-Fraumeni syndrome led to the recognition of cases among Japanese pedigrees brought to the meeting, and generated a study of its occurrence in Japanese families with adrenocortical carcinoma in a child. Another seminar revealed a marked clustering of rare cancers in Werner's (premature aging) syndrome in Japan, and led to a binational study and analysis of case-reports worldwide. Three seminars on pathology heightened appreciation of the importance of subclassifying cancer by subsite and subtype for racial and other comparisons. Four seminars on biostatistics in cancer research generated a substantial exchange of specialists and trainees in this field.

Leukaemia and non-Hodgkin's lymphoma in young persons resident in small areas of West Cumbria in relation to paternal preconceptional irradiation

The results of a previous study suggested that an association between childhood leukaemia and the radiation dose received occupationally by a father before the conception of his child might provide the explanation for the marked excess of childhood leukaemia and non-Hodgkin's lymphoma in the village of Seascale, West Cumbria. The present study identifies other small areas (electoral wards) in West Cumbria where excess cases of leukaemia and non-Hodgkin's lymphoma in young people have occurred and determines whether a recorded dose of radiation was received occupationally by the father before the conception of each of the affected individuals. Forty-one cases of leukaemia and non-Hodgkin's lymphoma were diagnosed during 1968-85 in young people under 25 years of age resident in the 49 electoral wards lying within the boundary of West Cumbria and the adjacent ward of Broughton. Raised incidence rate ratios (two-sided P<0.01) were found for acute lymphoblastic leukaemia among those aged 0-14 years (concentrated among those aged 0-4 years) in Seascale ward and among those aged 0-24 years (also concentrated among those aged 0-4 years) in Egremont North ward, for acute myeloid leukaemia among those aged 0-14 years in Sandwith ward, for all leukaemias among those aged 0-14 years in Broughton ward (South Lakeland) and for non-Hodgkin's lymphoma among those aged 0-14 years in Seascale ward. For West Cumbria as a whole, incidence rates were not usual. Apart from Seascale, for none of these electoral wards has a father of an affected child been linked definitely to an occupational dose of radiation recorded before the conception of the child. Particularly striking are the excesses of acute lymphoblastic leukaemia cases among young children living in the wards of Seascale and Egremont North, situated 11 km apart. The cases in Egremont North are not associated with recorded doses of radiation received occupationally by fathers before the conception of the affected children, even though the total numbers of children associated with such doses born in Seascale and Egremont North wards are similar. This finding is further evidence against a causal role for paternal preconceptional radiation exposure in the cases of childhood leukaemia in Seascale.

Health of children born to medical radiographers

OBJECTIVES

To develop a reliable method for collecting information on reproductive outcome in an occupational setting; and to investigate the health of children born to medical radiographers.

METHODS

The study population comprised 6730 members of the College of Radiographers who were, at the time of survey; aged between 30 and 64 years, on the current membership file of the College, and were resident in Britain.

RESULTS

The postal method developed proved to be reliable, with around 87% of questionnaires being returned. The observed frequencies of reproductive events were broadly in line with findings from other studies: of the 9208 pregnancies reported, 83% were livebirths, 12% were miscarriages (gestational age < 20 weeks), 1% were stillbirths (gestational age > or = 20 weeks), and 1% were other rarer spontaneous adverse events (ectopic pregnancy, blighted ovum, and hydatidiform mole). There was little difference between men and women in the frequency of adverse reproductive events reported, with the exception that male radiographers reported fewer medical terminations, the proportions being 3.1% and 1.4% for women and men respectively. Among children, the overall risks of major congenital malformation (RR 1.0, 95%CI 0.9-1.2), chromosomal anomaly (RR 1.4, 95%CI 0.8-2.3), and cancer (RR 1.2 95%CI 0.7-2.0) were as expected based on general population rates. Borderline excesses of chromosomal anomalies other than Down's syndrome in the children of female radiographers (RR 3.9, 95%CI 1.3-9.0, based on five observations), and cancer in the children of male radiographers (RR 2.7, 95%CI 0.9-6.5, based on five observations) were noted. The numbers on which these risks are based are small and the findings should be interpreted cautiously.

CONCLUSIONS

The postal methods developed for obtaining information about reproductive events and child health proved to be reliable in men, as well as in women. Overall, the findings for medical radiographers are reassuring. Dose-response relations could not, however, be examined as long term dose records of radiographers are not routinely kept in an accessible form.

Hazards of ionising radiation: 100 years of observations on man

In November 1895, when Conrad Röntgen serendipitously discovered X-rays, epidemiology was effectively limited to the study of infectious disease. What little epidemiological work was done in other fields was done as part of clinical medicine or under the heading of geographical pathology. The risks from exposure to X-rays and subsequently from other types of ionising radiation were consequently discovered by qualitative association or animal experiment. They did not begin to be quantified in humans until half a century later, when epidemiology emerged as a scientific discipline capable of quantifying risks of non-infectious disease and the scientific world was alerted to the need for assessing the effects of the radiation to which large populations might be exposed by the use of nuclear energy in peace and war.

Investigation of disease risks in small areas

The investigation of disease risks in small areas is complicated by many issues including data quality, the retrospective nature of the statistical testing, the problems of boundary definitions in time and space around a putative disease cluster, and the lack of generally accepted definitions of the key terminology. Routine data systems have revolutionised the initial investigation of disease risks near sources of environmental pollution, although problems of data analysis and interpretation remain. This is especially true of unmeasured socioeconomic confounding, which could generate apparent positive results near a pollution source.

The power of focused tests to detect disease clustering

Statistical tests have been proposed for determining whether incident cases of adverse health effects are 'clustered' together. Several procedures, termed 'focused', specifically analyse disease surveillance data around pre-specified putative sources of environmental hazard. Little has been done to compare the performance of various proposed methods on actual models of clustering. Analytic power functions are derived for three tests of focused clustering. These functions are based on the probabilistic structure of the clustering tests and do not require simulation. The three tests are compared with respect to statistical power on hypothetical data where monotone multiplicative increases in disease risk near a putative hazard define disease clusters of varying intensity.

Childhood cancer and paternal exposure to ionizing radiation: a second report from the Oxford Survey of Childhood Cancers

Paternal occupational data already collected as part of the Oxford Survey of Childhood Cancers have been reviewed. Information on paternal occupation was available for 14,869 children dying from cancer in England, Wales, and Scotland in the period 1953-81 and for an equal number of matched controls. The importance of fathers working, at any time before or after conception of the survey child, in any of the following occupations was assessed: radiologists (clinical), surgeons and anesthetists, veterinary surgeons, dental surgeons, nuclear industry workers, industrial radiographers. There was no indication that preconception employment in any of these occupations was more important than postconception employment with regard to the risks of all childhood cancers or all childhood leukemias. Findings were consistent with neither paternal preconception exposure to external ionizing radiation nor exposure to unsealed sources of radionuclides being an important risk factor for childhood leukemia or for the overall grouping of all childhood cancers.

Spatial statistical methods in environmental epidemiology: a critique

Despite recent advances in the available statistical methods for geographical analysis, there are many constraints to their application in environmental epidemiology. These include problems of data availability and quality, especially the lack in most situations of environmental exposure measurements. Methods for disease 'cluster' investigation, point source exposures, small-area disease mapping and ecological correlation studies are critically reviewed, with the emphasis on practical applications and epidemiological interpretation. It is shown that, unless dealing with rare diseases, high specificity exposures and high relative risks, cluster investigation is unlikely to be fruitful, and is often complicated by the post hoc nature of such studies. However, it is recognized that in these circumstances proper assessment of the available data is often required as part of the public health response. Newly available methods, particularly in Bayesian statistics, offer an appropriate framework for geographical analysis and disease mapping. Again, it is uncertain whether they will give important clues as to aetiology, although they do give valuable description. Perhaps the most satisfactory approach is to test a priori hypotheses using a geographical database, although problems of interpretation remain.

Cancer in the offspring of survivors of childhood leukaemia and non-Hodgkin lymphomas

Understanding the extent to which childhood leukaemia and non-Hodgkin lymphomas are heritable is important to the survivors of these diseases, their families and clinicians who provide genetic counselling. Such understanding is also relevant to the possibility raised by Gardner et al. (1990, Br. Med. J., 300, 423-429) that paternal preconception irradiation may be an aetiological factor in these diseases. No malignant neoplasm was diagnosed among 382 offspring of survivors of childhood leukaemia and non-Hodgkin lymphoma followed up for a median period of 5.8 years, the largest available cohort of such offspring. These data indicate that it is unlikely that the risk of a malignant neoplasm occurring in the offspring exceeds eight times that expected in the general population. Similarly, the risk of leukaemia and non-Hodgkin lymphoma among offspring is unlikely to exceed 21 times that expected. The proportion of survivors of childhood leukaemia and non-Hodgkin lymphoma with the heritable form of these diseases is unlikely to exceed 5%, assuming an autosomal dominant pattern of transmission, with penetrance of at least 70% and that all heritable cases develop by age 15 years. The best (i.e. at present most likely) estimates of these risks are of course much lower. There was no evidence of an excess of congenital abnormalities among the offspring and the sex ratio was similar to that expected from the general population.

Investigation of lung tumour induction in BALB/cJ mice following paternal X-irradiation

Evidence of an enhanced incidence of lung tumours (benign adenomas and adenocarcinomas) was sought in the BALB/cJ mouse following paternal germ cell X-irradiation. In a series of replicate studies spanning approximately 1 year, males were exposed to single, acute X-ray doses of 0, 250 and 500 cGy. In each of the 2 consecutive weeks immediately thereafter they were placed with two females to generate progeny that were derived from irradiated post-meiotic cells (spermatozoa to late spermatids). These animals were then examined at 8 or 12 months for lung tumours. While the proportion of fertile females and mean litter size was affected by the radiation, showing a dose-dependent, dominant lethal response, and while cases of mutant offspring were detected, the paternal radiation did not affect lung tumour incidence in the offspring. The incidence did not vary significantly between germ cell stages irradiated (week of mating), sex of offspring, or radiation dose. However, significant differences between lung tumour incidence (mostly representing benign adenomas) were found between different replicates, these being high at the start of the study, declining and then rising to yet higher levels at its close. The finding that lung tumour incidence in BALB/cJ mice is not affected by paternal germ cell irradiation does not accord with Nomura's reports using other strains of mice. This, in turn, weakens biological support for a causal association between the raised incidence of childhood leukaemia and non-Hodgkin lymphoma near Sellafield and the father's recorded radiation exposure during employment by the nuclear industry.

Testicular toxicity of the transferrin binding radionuclide 114mIn in adult and neonatal rats

Adult (70 d) and neonatal (7 d) male rats were dosed (i.p.) with 37 MBq/kg (1 mCi/kg; approximately 1 microgram elemental indium/kg) 114mIn, a transferrin-binding radionuclide. In adults, approximately 0.25% of the injected activity localised within the testis by 48 h postinjection and remained constant for up to 63 d. In neonates, 0.06% of the activity was in the testis by 48 h, and this declined such that by 63 d only 0.03% remained. At 63 d, treated rats had reduced sperm head counts and abnormal testicular histology that was more marked in animals dosed as adults than as neonates. In vitro, uptake of 114mIn into seminiferous tubules isolated from 7-, 20-, or 70-d-old rats was compared with that of 125I. Both radionuclides were readily accumulated by the tubules. Whilst 114In uptake into 20- and 70-d tubules was inhibited by excess transferrin, uptake into 7-d tubules was unchanged. 125I uptake was not affected by excess transferrin. These data support the contention that some radionuclides may cross the blood-testis barrier by utilisation of the physiologic iron-transferrin pathway, which may lead to greater testicular damage in adult compared to neonatal animals.

Leukaemia and Sellafield: is there a heritable link?

The demonstration of a statistical association between paternal preconceptional irradiation and childhood leukaemia appeared to provide a satisfactory explanation for the excess of cases in the village of Seascale, close to the Sellafield nuclear installation, and became the basis of two legal claims for compensation. In the ensuing scientific debate the biological plausibility of a causal interpretation of this association focused on the heritability of leukaemia and a comparison of the genetic risks implied by this finding with current information on the induction of genetic damage by irradiation. After a wide ranging review of the mechanistic issues it is concluded that there is no genetic basis for a causal relationship and this, together with recent appraisals of epidemiological studies, suggests that the association between childhood leukaemia and paternal preconceptional irradiation exposure is most likely to be a chance finding.

Childhood leukaemia and non-Hodgkin's lymphoma near large rural construction sites, with a comparison with Sellafield nuclear site

OBJECTIVE

To determine whether population mixing produced by large, non-nuclear construction projects in rural areas is associated with an increase in childhood leukaemia and non-Hodgkin's lymphoma.

DESIGN

A study of the incidence of leukaemia and non-Hodgkin's lymphoma among children living near large construction projects in Britain since 1945, situated more than 20 km from a population centre, involving a workforce of more than 1000, and built over three or more calendar years. For periods before 1962 mortality was studied.

SETTING

Areas within 10 km of relevant sites, and the highland counties of Scotland with many hydroelectric schemes.

SUBJECTS

Children aged under 15.

RESULTS

A 37% excess of leukaemia and non-Hodgkin's lymphoma at 0-14 years of age was recorded during construction and the following calendar year. The excesses were greater at times when construction workers and operating staff overlapped (72%), particularly in areas of relatively high social class. For several sites the excesses were similar to or greater than that near the nuclear site of Sellafield (67%), which is distinctive in its large workforce with many construction workers. Seascale, near Sellafield, with a ninefold increase had an unusually high proportion of residents in social class I. The only study parish of comparable social class also showed a significant excess, with a confidence interval that included the Seascale excess.

CONCLUSION

The findings support the infection hypothesis and reinforce the view that the excess of childhood leukaemia and non-Hodgkin's lymphoma near Sellafield has a similar explanation.

Detection and assessment of clusters of disease: an application to nuclear power plant facilities and childhood leukaemia in Sweden

We review some recent statistical methods for examining geographic patterns of disease incidence for the presence of clusters. General methods search for clusters throughout the study area and then assess the statistical significance of any clusters detected. Focused methods check for elevated incidence rates close to prespecified locations of putative sources of hazard. We apply the methods to leukaemia incidence data for children aged 0-15 years in Sweden (1980-1990), particularly in reference to locations of nuclear power facilities. Unlike some other studies, notably in the United Kingdom, we do not find any significant clusters.

Lessons learned from epidemiologic studies of environmental exposure and genetic disease

The induction of germ cell mutations with ionizing radiation and chemicals has been clearly demonstrated in experimental animal test systems. Less is known about the effects of environmental and other exposures on human germ cells. Epidemiologic studies of atomic bomb and childhood cancer survivors and their offspring have generally not indicated an excess risk for a variety of adverse reproductive outcomes and childhood diseases, including those due to germ cell mutations. Other epidemiologic studies, including the investigation of cancer among the offspring of fathers employed at the Sellafield nuclear facility in Great Britain and studies of paternal occupation and birth defects, have found associations. This paper reviews these studies and the methodologic problems inherent in the epidemiologic approach to evaluating environmentally induced germ cell mutagenesis in humans. Epidemiologic studies incorporating newly developed techniques for the detection of mutations and abnormalities in sperm may provide the sensitivity needed to determine precisely the magnitude of risk.

Population genetics of induced mutations

The contribution of induced mutations to the burden of genetic disease in the context of population genetics is considered. A clear distinction is made between the effects of genetic disease and mutational events. Much of the existing burden of genetic disease is a consequence of mutations that occurred in the past. The problem of distinguishing between spontaneous and induced mutations is discussed. Molecular genetics techniques are blurring the definitions of these terms. Classical population genetics shows that the frequency of affected individuals will reach an equilibrium depending on the mutation rate and the selective pressure against affected individuals. Increasing the mutation rate or reducing the selective pressures would result in a new equilibrium with an increase in the frequency in subsequent generations of affected individuals with dominant and X-linked mutant alleles. The increase in the number of recessive mutant alleles would be much slower and take many generations to reach the new equilibrium level. One assumption behind such equilibria is random mating. Changes in human demography with a rapid increase in population size, the breakup of small, relatively inbred subpopulations, and relaxed selective pressures will lead to a new equilibrium for recessive genes at probably higher frequencies. These factors will be the major contributors to increasing the burden of recessive genetic disease by increasing the total numbers of cases. The proportion of the population with a genetic disease will also continue to grow as a greater proportion of the population survives to late middle age and succumbs to diseases associated with old age, such as cancer, circulatory disease, dementias, and diabetes, each of which is likely to have a genetic component.(ABSTRACT TRUNCATED AT 250 WORDS)