Mutation Rate Doubled in Chernobyl's Children
Mutation rate doubled in Chernobyl's children
- 27 April 1996
- From New Scientist Print Edition. Subscribe and get 4 free issues.
- Rob Edwards
Stuttgart
CHILDREN whose parents were exposed to radioactive fallout in Belarus in the aftermath of the Chernobyl disaster have twice as many mutations in their DNA as British children. The discovery by scientists investigating the impact of the accident, which happened ten years ago this week, provides the first evidence that exposure to radiation can cause permanent genetic damage.
Any increase in the number of mutations passed from parents to children heightens the risk of genetic diseases, spontaneous abortions and congenital malformations. Although there is no proof so far that the explosion at Chernobyl has led to such increases, the new findings by researchers from Russia, Belarus and Britain suggest that damage to sperm and ova could result in genetic diseases passing from irradiated parents to their children and grandchildren. The study also suggests that radiation poses greater risks to human genes than previously thought.
Independent experts from the Medical Research Council regard the findings, published in this week's issue of Nature, as an important breakthrough. "If this had been said five years ago, many people would have totally disbelieved it," says Duncan Goodhead, director of the MRC's Radiation and Genome Stability Unit in Oxfordshire. "It tells you that you should be open to the possibility that there may be rearrangements in DNA that do relate to health."
Researchers from the University of Leicester, the Russian Academy of Sciences and the Belarussian Research Institute for Radiation Medicine collected blood samples from 79 families in three towns—Bykhov, Cherikov and Krasnopolye—in the Mogilev region of Belarus, one of the worst contaminated regions. In each family, both parents had continued to live in the area since the accident and had children born between February and September 1994.
The team produced DNA fingerprints from the blood samples using the forensic technique developed by Alec Jeffreys at the University of Leicester. Any fragment of DNA in a fingerprint that could not be attributed to the child's parents was defined as "mutant". In all cases, the possibility that the alleged father was not the true father was ruled out. The rate of mutation among the Belarussian children was then compared with that in 105 uncontaminated families in Britain.
"We found a statistically significant, twofold increase in mutation frequency in the offspring of irradiated parents," says the leader of the study, Yuri Dubrova, a senior research fellow from the Vavilov Institute of General Genetics at the Russian Academy of Sciences in Moscow. He also found that the number of mutations in the children correlated closely with the level of radioactive contamination to which their parents had been exposed. The implication is that radiation caused permanent mutations in the parents' germ cells, their sperm and ova, which will be passed down from generation to generation.
Studies of the survivors of the atomic bombs dropped on Hiroshima and Nagasaki more than 50 years ago have not detected any statistically significant increase in mutations in families exposed to radiation. "We believe that our study provides the first experimental evidence that germ line mutation rates in humans can be increased by ionising radiation," says Dubrova, who is a visiting research fellow at the University of Leicester.
But he stresses that this is not the same as saying that radiation causes genetic diseases. He points out that the stretches of DNA in which the mutations were counted have no known role in human health. But he agrees with Goodhead that the discovery of more mutations in one section of DNA suggests that similar damage might be found in other regions where they would damage health.
"The situation with regard to congenital deformities and illnesses is not clear," says Dubrova. He suggests that there may be a slight increase in the rate of spontaneous abortions in Belarus, although he adds that this is no more than speculation. He emphasises the difficulties of interpreting the possible health effects of the mutations he has found. "We don't know and we can't say whether or how they might affect health," he says.
In 1993 Russian researchers claimed to have measured increased rates of congenital malformations in babies and fetuses from heavily contaminated areas of Belarus. But Western scientists doubted that the increases could be attributed to radiation from Chernobyl. Instead they suspected that more malformations were being found simply because researchers were looking harder for them.
"We have to do further research," says Dubrova. He suggests that the enhanced mutation rate could have been caused by exposure to iodine-131 in the immediate aftermath of the Chernobyl accident or by longer-term exposure to caesium-137. Doses of radiation from caesium could have been "substantially underestimated", he says. "Alternatively, it is possible that low doses of chronic radiation are more effective at inducing mutations than higher doses of acute radiation."
From issue 2027 of New Scientist magazine, 27 April 1996, page Page 6