Stillbirths and male irradiation

The Likelihood of Adverse Pregnancy Outcomes and Genetic Disease (Transgenerational Effects) from Exposure to Radioactive Fallout from the 1945 Trinity Atomic Bomb Test

The potential health consequences of the Trinity nuclear weapon test of 16 July 1945 at Alamogordo, New Mexico, are challenging to assess. Population data are available for mortality but not for cancer incidence for New Mexico residents for the first 25 y after the test, and the estimates of radiation dose to the nearby population are lower than the cumulative dose received from ubiquitous natural background radiation. Despite the estimates of low population exposures, it is believed by some that cancer rates in counties near the Trinity test site (located in Socorro County) are elevated compared with other locations across the state. Further, there is a concern about adverse pregnancy outcomes and genetic diseases (transgenerational or heritable effects) related to population exposure to fallout radiation. The possibility of an intergenerational effect has long been a concern of exposed populations, e.g., Japanese atomic bomb survivors, survivors of childhood and adolescent cancer, radiation workers, and environmentally exposed groups. In this paper, the likelihood of discernible transgenerational effects is discounted because (1) in all large-scale comprehensive studies of exposed populations, no heritable genetic effects have been demonstrated in children of exposed parents; (2) the distribution of estimated doses from Trinity is much lower than in other studied populations where no transgenerational effects have been observed; and (3) there is no evidence of increased cancer rates among the scientific, military, and professional participants at the Trinity test and at other nuclear weapons tests who received much higher doses than New Mexico residents living downwind of the Trinity site.

The joy and duty of a marginal teratologist

On the occasion of this anniversary of the Society for Birth Defects Research and Prevention, I accept the invitation to offer personal reflections on the earlier days of the Society and the importance of the discipline. My focus is on what few contributions I have offered, but more, on the value of having the teratologist's perspective on other aspects of my career in medical genetics and genetic epidemiology. Treating my professional life as a development biologist (of which teratologists are a breed), I recount the institutions I have been at, but more importantly, the people I have been influenced by, more often than not accomplished teratologists. The one big thought I wish to leave is the primacy and criticality of being mentored and mentoring at ALL stages of a career.

Ovarian failure and reproductive outcomes after childhood cancer treatment: results from the Childhood Cancer Survivor Study

These studies were undertaken to determine the effect, if any, of treatment for cancer diagnosed during childhood or adolescence on ovarian function and reproductive outcomes. We reviewed the frequency of acute ovarian failure, premature menopause, live birth, stillbirth, spontaneous and therapeutic abortion and birth defects in the participants in the Childhood Cancer Survivor Study (CCSS). Acute ovarian failure (AOF) occurred in 6.3% of eligible survivors. Exposure of the ovaries to high-dose radiation (especially over 10 Gy), alkylating agents and procarbazine, at older ages, were significant risk factors for AOF. Premature nonsurgical menopause (PM) occurred in 8% of participants versus 0.8% of siblings (rate ratio = 13.21; 95% CI, 3.26 to 53.51; P < .001). Risk factors for PM included attained age, exposure to increasing doses of radiation to the ovaries, increasing alkylating agent score, and a diagnosis of Hodgkin's lymphoma. One thousand two hundred twenty-seven male survivors reported they sired 2,323 pregnancies, and 1,915 female survivors reported 4,029 pregnancies. Offspring of women who received uterine radiation doses of more than 5 Gy were more likely to be small for gestational age (birthweight < 10 percentile for gestational age; 18.2% v 7.8%; odds ratio = 4.0; 95% CI, 1.6 to 9.8; P = .003). There were no differences in the proportion of offspring with simple malformations, cytogenetic syndromes, or single-gene defects. These studies demonstrated that women treated with pelvic irradiation and/or increasing alkylating agent doses were at risk for acute ovarian failure, premature menopause, and small-for-gestational-age offspring. There was no evidence for an increased risk of congenital malformations. Survivors should be generally reassured although some women have to consider their potentially shortened fertile life span in making educational and career choices.

Genetic effects of radiotherapy for childhood cancer: gonadal dose reconstruction

PURPOSE

To estimate the doses of radiation to organs of interest during treatment of childhood cancer for use in an epidemiologic study of possible heritable diseases, including birth defects, chromosomal abnormalities, cancer, stillbirth, and neonatal and premature death.

METHODS AND MATERIALS

The study population was composed of more than 25,000 patients with cancer in Denmark and the United States who were survivors of childhood cancer and subsequently had nearly 6,500 children of their own. Radiation therapy records were sought for the survivors who parented offspring who had adverse pregnancy outcomes (>300 offspring), and for a sample of all survivors in a case-cohort design. The records were imaged and centrally abstracted. Water phantom measurements were made to estimate doses for a wide range of treatments. Mathematical phantoms were used to apply measured results to estimate doses to ovaries, uterus, testes, and pituitary for patients ranging in age from newborn to 25 years. Gonadal shielding, ovarian pinning (oophoropexy), and field blocking were taken into account.

RESULTS

Testicular radiation doses ranged from <1 to 700 cGy (median, 7 cGy) and ovarian doses from <1 to >2,500 cGy (median, 13 cGy). Ten percent of the records were incomplete, but sufficient data were available for broad characterizations of gonadal dose. More than 49% of the gonadal doses were >10 cGy and 16% were >100 cGy.

CONCLUSIONS

Sufficient radiation therapy data exist as far back as 1943 to enable computation of gonadal doses administered for curative therapy for childhood cancer. The range of gonadal doses is broad, and for many cancer survivors, is high and just below the threshold for infertility. Accordingly, the epidemiologic study has >90% power to detect a 1.3-fold risk of an adverse pregnancy outcome associated with radiation exposure to the gonads. This study should provide important information on the genetic consequences of radiation exposure to humans.

Genetic effects of radiotherapy for childhood cancer

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

Sex ratio among offspring of childhood cancer survivors treated with radiotherapy

It has been postulated that paternal gonadal exposure would increase the sex ratio by inducing X-chromosomal dominant lethals but that maternal gonadal exposure would decrease the sex ratio by inducing recessive sex-linked lethals. We therefore evaluated the sex ratio (male-to-female ratio) of children born to survivors of childhood cancers in Denmark. Children with cancer were identified from the Danish Cancer Registry from 1943 to 1996 and their offspring from the Central Population Registry. Radiation treatments were determined from records within the Cancer Registry and gonadal radiation exposures were estimated based on the cancer being treated and the likely proximity of the radiation fields to the gonads. Overall, 1100 survivors of childhood cancer became the parents of 2130 children. The sex ratio for male (0.99) and female (1.00) cancer survivors was similar and did not differ significantly from the Danish population (1.06). Radiotherapy did not influence the sex ratio of the children of either male or female survivors, and there was no evidence for dose-related changes over categories of estimated dose to parental gonads. We saw no consistent association between the sex ratio and the interval between cancer diagnosis of the parent and birth of the child. This nationwide study provides no support for the hypothesis that radiation exposure to the gonads results in an inherited genetic effect that would be manifested by a change in the sex ratio of children born after exposure. It may be, however, that sex ratio alterations are not a good or even a valid indicator of possible genetic effects in humans.

Risk of stillbirth in offspring of men exposed to ionising radiation

Radiation genetic risk models are employed to predict the frequency of radiation-related stillbirths to partners of occupationally exposed male workers, using the incidence data recently reported by Parker et al from an epidemiological study of Cumbrian births. Expanding on previously developed conservative risk estimates suggests that, of the 130 observed stillbirths to partners of male radiation workers, 0.3 cases would be attributable to paternal preconceptional irradiation, in contrast to the 17.5 (95% confidence interval: 3.1 to 31.9) cases predicted by Parker et al from their preferred dose-response model. The incompatibility of the results reported by Parker et al with those from other investigations, both epidemiological and experimental, and the inability of the study to consider a number of factors which might affect stillbirth rates, particularly those relating to the mother, make it difficult to accept that paternal irradiation received occupationally could have contributed to a detectable increase in stillbirths.