April 25, 1996
Chernobyl's Grim Genetic Legacy
Sir Alec Jeffreys shared some bad news on the 10th anniversary of
the worst nuclear power accident in history. The British geneticist and
his Russian colleague, Yuri Dubrova, reported that mutation rates are
unusually high among the children of families exposed to radioactive
fallout from the Chernobyl reactor meltdown in Ukraine.
Jeffreys is one of the Institute's 22 international research
scholars in the United Kingdom. The collaborative study was the subject
of a cover story in Nature on April 25, 1996, the week that
marked the anniversary of the Chernobyl disaster.
“International research scholar Alec Jeffeys believes that radiation leaked from Chernobyl more than a decade ago may only now be manifesting its diastrous legacy.”
During the past decade, physicians and government officials in
eastern Europe have grappled with the deaths of thousands from
radiation-related illness such as thyroid cancer. They haven't known
how the fallout might affect future generations.
Attracting worldwide attention, Jeffreys' results suggest the impact
may last longer than expected. The study provides the first direct
evidence that children can inherit radiation-triggered germline
mutations from their parents. The findings are particularly troublesome
because the study population lived in Belarus, more than 100 miles
north of the doomed reactor. The families in the study probably
received far lower radiation exposure than the 116,000 people evacuated
from within 15 miles of the nuclear power plant.
"Given the relatively low dose rates in the Belarus population
sample we collected, we did not expect to see any increase in
mutations," Jeffreys said. The results indicate that the genetic
consequences of such incidents are greater and longer-lived than
previous studies suggested. Jeffreys' team started its Chernobyl study
in 1994 in collaboration with Russian researchers, including lead
author Yuri Dubrova of the Institute of General Genetics in Moscow.
"The idea was to collect blood from contemporary births to get an
overall view of parental radiation during the previous eight years,"
Jeffreys said.
Colleagues at the Institute of Radiation Medicine in Mogilev,
Belarus, collected blood samples from local maternity hospitals. The
rural Mogilev district was hit fairly hard by Chernobyl's radioactive
fallout, including iodine-131. In the years following the accident,
most Mogilev residents have eaten food grown in soil contaminated with
radioactive cesium-137. Their exposure to radiation has been low but
chronic.
The samples were brought to Jeffreys' lab in England, where they
were analyzed to produce DNA fingerprints that establish identity and
paternity. Studying each family's blood samples, the researchers used
five different systems for monitoring mutations. They asked two
questions: Does the mutation rate in Mogilev exceed natural levels?
And, if so, are these mutations due to radiation exposure?
To answer those questions, the researchers compared the Mogilev
blood samples with those of 105 non-irradiated families from England
(the control group). They found that the frequency of mutation was
twice as high in families from Mogilev than in families from England.
Among the Mogilev families, children with the higher mutation rates
lived in areas where the soil is most contaminated with radioactive
cesium-137, another indication that radiation exposure might be causing
the additional mutations.
For now, the most Jeffreys and his colleagues can conclude is that
the mutations seen in the human study will likely be passed along to
future generations because they are germline in origin. Larger
questions loom. Both scientists and the public wonder whether the high
mutation rates will translate into greater health problems for future
generations. That's a question the researchers cannot answer at this
time.
One problem is that Jeffreys and colleagues cannot draw upon past
studies with similar findings. There aren't any. Despite decades of
research, there is no evidence for increased mutation rates in the
genome of residents of Hiroshima and Nagasaki since the atomic bombs
were dropped on those cities in 1945. It is very difficult even to
compare the Japanese and Chernobyl results because the radiation
exposure of the two populations is so different. What's more, animal
studies are lacking. Few researchers have conducted large-scale studies
exposing mice to chronic, low radiation like the kind caused by
Chernobyl, Jeffreys said.
"Mutations [in the genes] that we studied are most unlikely to have
any health implications for these children or their descendants,"
Jeffreys said. "It is impossible to say whether other classes of
mutations of greater potential biological significance also will show a
corresponding increase in mutation frequency." However, Jeffreys said
it is very unlikely the mutation rate is a statistical fluke. He and
Dubrova continue their investigations.
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