Radiation Causes Mutations for Several Generations
Third generation of mice still show damage, study says
MONDAY, May 6, 2002 (HealthDayNews) -- Open-jawed about an unanticipated finding and puzzled about its implications for human health, researchers report a mouse study shows genetic mutations caused by radiation can continue into a third generation.
The results, appearing in the May 14 issue of the Proceedings of the National Academy of Sciences, were "totally unexpected," says Yuri E. Dubrova, head of the research team.
The finding is "a complete nightmare," says Dubrova, a reader in genetics at the University of Leicester in England. "I expected to find nothing in the grandchildren" of irradiated mice, he says, "but no, they show exactly the same increase in germ line mutation rate." Germ line cells are those involved in reproduction.
The study was actually a double-check of results found in a previous trial, in which one strain of mice was irradiated with high-energy neutrons, Dubrova says. "To our surprise, we got a high mutation rate in the offspring of males. But fission neutrons are known to be a powerful mutagen [something that causes mutations], so we asked what would happen if we do the same thing with more well-known X-rays."
So three strains of mice were exposed to both fission neutrons and X-rays, and their offspring were studied to see if they had the same mutations as occurred in the radiation-exposed generation.
"The bottom line is that first, all three strains show the same effects in the offspring of irradiated males and second, both X-rays and fission neutrons do the same thing," Dubrova says.
"The remarkable finding that radiation-induced germ-line instability persists for at least two generations raises important issues of risk evaluation in humans," the journal report says.
No human studies of the effects of radiation exposure on future generations have been done. The Radiation Effects Research Foundation, a joint Japanese-American effort looking at the effects of the atomic bombs dropped on Hiroshima and Nagasaki, reported in 1991 that a study of 76,625 babies born to survivors found "no statistically demonstrable increase in major birth defects considered in total or in any specific type among the children of atomic-bomb survivors."
However, it is possible that radiation exposure might increase the risk of cancer, Dubrova says, stressing this is pure speculation.
"If we can speculate, if children of irradiated parents are unstable [have inherited mutations], this might create a situation where they have a higher chance of getting cancer," he says.
And the concluding sentence of the journal report says "the data raise the important issue of trans-generational effects of ionizing radiation for humans, providing, for example, a plausible explanation for the apparent leukemia cluster near Sellafield nuclear plant." The plant is in England.
It is an almost unprovable speculation, says Richard B. Setlow, a senior biophysicist at the Brookhaven National Laboratory, who edited the journal paper. Proving that what happened in the laboratory mice happens in humans would require a study that might last a century, he says.
"Think of how long it would take, following generation after generation," Setlow says. "I don't know if we will ever find out if it is acceptable to extrapolate from mice to men and women."
The result of the study is "rather surprising," Setlow says, largely because "no one has thought of the possibility. When you know the answer, you say, 'Why shouldn't it happen?' But people haven't looked."
It's possible that even if the same thing happens in humans, health effects might be limited because "sometimes mutations that are deleterious don't get transmitted," Setlow says.
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The report should not raise doubts about the safety of medical radiation, because "the kind of doses you get medically do not cause mutations," Setlow says.