

That is now changing. On September 7th, Yuri Dubrova, a geneticist at the University of Leicester, in England, presented a study of radiation-induced mutation in human germ cells (sperm and eggs) to a scientific meeting called “Children with Leukaemia”, which was held in London. He and his colleagues have been looking for mutations in the germ cells of those who live in areas contaminated by fallout from the nuclear accident at Chernobyl in 1986.

They have done this by examining parts of the human genome that contain repetitive sequences of DNA, and comparing corresponding regions in exposed and unexposed people from rural areas of Ukraine and Belarus. These repetitive sequences are easy to quantify, and mutation rates in different places can thus be calculated. The upshot is that men (though not women) exposed to fallout had a 1.6-fold increase in the mutation rate of DNA in their germ cells.

Dr Dubrova has also worked with the unfortunate denizens of Semey, as Semipalatinsk was renamed after the break-up of the Soviet Union. Overground atomic testing was halted in 1965, so he was able to find families in Semey with varying levels of exposure to radiation. He can now show that as the radiation dose decreased, so did the mutation-rate in the germ cells. This kind of “dose-response curve” is the sort of thing that turns toxicologists weak at the knees, because it shows a quantitative relationship between the putative cause and the effect.

Until Dr Dubrova's work, studies on human germ-line radiation-damage had drawn a blank. The children of people who lived in Hiroshima and Nagasaki when they were bombed, those of Chernobyl clean-up workers, and those born to cancer patients who had been treated with radiotherapy had all failed to show a higher incidence of inherited mutation. And work that did show an increase in such malformations (in children in the Chernobyl region) was inconclusive because there was a similar increase in malformations in uncontaminated areas.

Of course, the crucial question is not whether germ cells are susceptible to mutation, but whether such mutations are passed from parent to offspring, and whether they can then cause disease. Dr Dubrova has shown such transgenerational instability in mice, and has demonstrated that it can be transmitted at least as far as the third generation.

In normal circumstances, the mice who inherit this genetic instability have no greater risk of developing cancer than normal mice. However, if they are “challenged” with a carcinogenic substance they have a much higher incidence of cancer. There is, says Dr Dubrova, not a shred of evidence that the same is true in humans. Nevertheless, he will go so far as to speculate that transgenerational instability might be a contributing factor to the unexplained cluster of childhood leukaemia cases around the Sellafield nuclear plant in England, which was the site of an accident in 1957.