Radiation damages Chernobyl children.

Survivors of the fiery meltdown of Reactor 4 in Chernobyl a decade ago won't welcome the news that radiation has altered the genetic legacy they have passed on to their children. But that is precisely what a team of Russian and British scientists has concluded in a report that began to draw critical fire from other researchers even before it appeared in the April 25 Nature. The study, published on the eve of the 10th anniversary of the nuclear disaster in the former Soviet Union, suggests that parents exposed to radiation acquired measurable mutations in their germ cells. Those cells-sperm and eggs-contain the genetic building blocks of future generations. Before Chernobyl exposed some 5 million people to radioactive fallout, survivors of the U.S. bombings of the Japanese cities of Hiroshima and Nagasaki formed the only large populations exposed to significant amounts of radiation. After World War II, the United States and Japan set up a joint research effort in Hiroshima to study those populations. Forty years later, no scientist from either nation has produced evidence of genetic problems in survivors' children.

The Hiroshima findings come largely from studies of birth defects and major chromosomal damage, however. Researchers have only recently begun using the techniques of molecular biology to examine genes.

Now, Yuri E. Dubrova of the University of Leicester in England and his colleagues claim they have found "the first scientific evidence that germline mutation rates in humans can be increased by ionizing radiation." Other researchers, such as James Neel of the University of Michigan in Ann Arbor, a 40-year veteran of the Hiroshima research, are not so sure. "I am very doubtful that the findings of these investigations are due to the fallout of the Chernobyl disaster," Neel says.

Dubrova's team compared specific gene segments isolated from the blood of people in 79 families that live in heavily contaminated Belarus with those from members of 105 unexposed families in the United Kingdom. All children in both groups were born 8 years after the meltdown.

The researchers studied gene segments known as minisatellite loci, repeating patterns of roughly 5 to 45 bases, the units that make up DNA. No one knows the genetic purpose, if any, of mini-satellites, but their variation from person to person enables scientists to use them as the basis of so-called genetic fingerprinting.

Because a child's DNA represents a combination of germline DNA from both parents, any sequence in the child that does not appear in either parent must result from a germline mutation. Dubrova's team therefore looked for minisatellite sequences in children's DNA that did not appear in either parent's DNA.

They found twice the number of mutations in children of exposed Belarus parents as in U.K. children. "We are 99 percent sure these are real germline mutations and they have been passed from parent to child," Dubrova says. Neel objects that the "doses of radiation given in their paper are very low, so their report implies a genetic sensitivity far beyond that observed in experiments with fruit flies and mice and our own observations in Japan." He adds that controls should have come from Belarus, not the United Kingdom. Dubrova counters that finding uncontaminated people in Belarus would be next to impossible.

Radiation effects also show up in wildlife in the region, according to a separate report in Nature. Biologist Robert J. Baker of Texas Tech University in Lubbock says he found mutation rates in two species of mice that were "probably thousands of times greater" than normal.