CAMBRIDGE, U.K.--For survivors of the atomic bombs dropped on Japan at the end of World War II, the disfiguring burns and radiation-induced illnesses were all too real and agonizing. Now researchers have strong new evidence of a more insidious effect in other people blighted by nuclear weapons: unexplained DNA mutations from atomic tests in Kazakhstan in the early days of the Cold War.
As reported in Science, Yuri Dubrova and colleagues at the University of Leicester, United Kingdom, collected blood from three generations of 40 families in the Beskaragai district of Kazakhstan, a desert region hit particularly hard by four atomic surface tests between 1949 and 1956. The researchers examined the subjects' minisatellite DNA--short, repeating sequences that pepper the genome. In each subject they examined eight minisatellite DNA regions that are prone to mutations. The naturally high mutation rate in this DNA allows researchers to detect statistically significant increases in mutation rates in small populations.
When the data came back, "I couldn't believe my eyes," says Dubrova. Compared to control families in a nonirradiated part of Kazakhstan, individuals exposed to fallout had a mutation rate roughly 80% higher, and their children showed an average rise of 50%. Probing further, Dubrova's group found an apparent dose-related effect in the children--evidence that the radiation, not some other environmental factor, was inducing the mutations.
These results challenge the conventional view that radiation inflicts its punishment on DNA solely by direct corruption of nucleic acids, says Dudley Goodhead, director of the U.K. Medical Research Council's Radiation and Genome Stability Unit in Harwell. Goodhead says the rate of mutation found in Kazakhstan is "orders of magnitude too large" to be accounted for by direct damage to the germ line DNA--the DNA that gets passed from parent to child. But exactly how long-term exposure to low-dose radiation causes such a high mutation rate remains unknown.
What these germ line mutations mean for health is a mystery, says Bryn Bridges of the Medical Research Council's Cell Mutation Unit in Brighton, United Kingdom. But evidence is mounting that minisatellites affect gene transcription and hike the risk of contracting some diseases. Screening for such mutations might offer a new tool for monitoring radiation exposure, says William Morgan, director of the Radiation Oncology Research Laboratory at the University of Maryland School of Medicine in Baltimore.