Ionising radiations from nuclear establishments and childhood leukaemias--an enigma

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.

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

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

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.

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.