On April 26, 1986, an accident at the nuclear power station in Chernobyl, Ukraine, released huge amounts of radioactive material into the environment. The radiation not only affected the surrounding areas but was carried by rain clouds to places as far away as Great Britain and Sweden. In a study published today (April 22) in Science, researchers found no evidence for transgenerational genetic effects on the children of people exposed to the accident’s radiation.
In a companion paper, the same set of investigators studied the development of papillary thyroid cancer, one of the most common cancers in Chernobyl survivors, and determined that thyroid tumors develop due to radiation-induced double-stranded DNA breaks.
Much of what researchers know about how the fallout affected genetic material comes from epidemiological data, says Anna Poetsch, who studies DNA damage and repair at Dresden University of Technology in Germany and did not participate in either study. “But nobody has ever really looked into the actual genomes of those people who were exposed,” she adds. These papers are “a tour de force. They’ve used a lot of data, and they came up with surprisingly little.”
We take that as an element of reassurance that for the Fukushima population there probably is not a radiation effect in the next generation.—Stephen Chanock, National Cancer Institute
When the work started about eight years ago, National Cancer Institute geneticist Stephen Chanock and an international group of colleagues wanted to leverage whole genome sequencing to probe the genetic effects that come from environmental exposure to radiation.
They started their work just two years after an earthquake caused the Fukushima Daiichi nuclear power plant in Japan to release radioactivity—including caesium-137 and iodine-131, the same two ions released in the Chernobyl disaster—into the environment. Following this incident, Chanock says, one of the questions foremost on peoples’ minds was, how does radiation exposure affect the next generation?
To tackle that question, the researchers sequenced the genomes of 105 families: 130 people born between 1987 and 2002, and their parents, who had some level of exposure to the radiation from Chernobyl through the environment or by direct involvement in its cleanup. The team looked for de novo mutations—those that are not present in either parent, indicating that they’ve arisen for the first time in the child—and saw no effect of radiation on the number or type of these mutations. “The rates were no different than what happens normally from generation to generation,” Chanock explains.
Maybe the time after exposure is relevant, and the authors are “looking at children who survived to older ages,” says Roxana Moslehi, a genetic epidemiologist at the State University of New York at Albany who did not participate in the work. A “more extensive survey of the reproductive outcomes—such as [miscarriage], stillbirth, or low birth weight would have been helpful in deciding whether general mutations could possibly play a role at some point, in those children that will not survive to adulthood.”
Chanock acknowledges the survivorship bias in the data and explains that very few pregnancies occurred within the first year after the Chernobyl accident because men and women were largely segregated because mostly men worked on cleanup. “It’s a very important question, but it’s a much harder question to look at what the effects of the exposure in utero are,” he says.
The findings have “public health implications for places like Fukushima, where we know the major concern of the people who live there or evacuated are the transgenerational effects,” Chanock says. “The truth of the matter is their levels of exposure that are estimated are much lower than the ones that we were looking at in many of our individuals from the Chernobyl accident. We take that as an element of reassurance that for the Fukushima population there probably is not a radiation effect in the next generation.”
Thyroid cancer after Chernobyl
Previous epidemiological studies had established that incidences of papillary thyroid cancer are much higher in children who were exposed to ionizing radiation following Chernobyl than in people who weren’t exposed. For the second paper, Chanock and colleagues contacted the individuals who were part of those epidemiologic studies and sequenced tumors and normal thyroid tissue or blood from 440 people who had papillary thyroid cancer—359 of whom had iodine-131 exposures as children and 81 who were born after 1986 and thus were not exposed.
The team confirmed that radiation causes double-stranded DNA breaks—something that had been shown in animals, but not before in people. In almost 95 percent of the tumors, those breaks had caused mutations in genes related to the mitogen-activated protein kinase (MAPK) pathway, which was also already known to be important in thyroid cancer. Exposure to radiation “created the errors in a restricted number of genes that then, in the setting of the thyroid in young individuals, could take off as a cancer,” explains Chanock.
“The biggest development with this paper is that it’s a quantum leap forward in the ability to identify the underlying cause of the cancer, showing this direct linkage between radiation exposure and certain kinds of cancers,” says the University of South Carolina’s Timothy Mousseau, who studies the ecological and evolutionary effects of radioactive contamination at Chernobyl and Fukushima and did not participate in the new work. “There’s been a suggestion of increased thyroid cancers in children from Fukushima, but it’s been very controversial,” he adds. “This kind of approach will actually allow folks to determine with a greater degree of certainty as to whether or not radiation exposure is the underlying cause for the cancer.”
L.M. Morton et al., “Radiation-related genomic profile of papillary thyroid cancer after the Chernobyl accident,” Science, doi:10.1126/science.abg2538, 2021.
M. Yeager et al., “Lack of transgenerational effects of ionizing radiation exposure in cleanup workers and evacuees of the Chernobyl accident,” Science, doi:10.1126/science.abg2365, 2021.