Survivors of the Chernobyl nuclear disaster have long harboured apprehension: Did their sperm and eggs become mutated as a result of radiation exposure, potentially predisposing their children to genetic diseases? “Many people believe that if you have been irradiated, you must have effects on the next generation,” says immunologist Dimitry Bazyka, director-general of Ukraine’s National Research Centre for Radiation Medicine. However, new research from Bazyka and colleagues should dispel that fear. The researchers found no evidence of a transgenerational effect in a study of more than 200 Chernobyl survivors and their children.
The study largely resolves a major uncertainty about the health consequences of the world’s worst nuclear accident, which marks its 35th anniversary on Monday. It also sends a reassuring message to evacuees from the 2011 Fukushima nuclear disaster in Japan. “There is still a lot of concern about transgenerational effects in Japan and elsewhere,” says geneticist Stephen Chanock, director of the National Cancer Institute’s Division of Cancer Epidemiology and Genetics.
The explosion and subsequent fire at Ukraine’s Chernobyl Nuclear Power Plant’s reactor No. 4 on April 26, 1986, released a plume of radioactive contamination across a large swath of Europe. The explosion killed two plant workers, and 28 firefighters died from acute radiation poisoning. For many others who have been exposed to radionuclides, the effects have been more gradual. Ionizing radiation damages DNA; radioactive iodine emitted by the destroyed reactor caused thyroid cancers in children and adolescents about 5 years after the accident. Other research has linked exposure to cancers like leukaemia and cardiovascular disease.
Concerns about germline mutations have loomed large. Parents typically pass on to their children 50 to 100 such mutations found in the DNA of their sperm and eggs. The only proven risk factor for a higher number of these so-called de novo mutations (DNMs) is a father’s age—the older he is, the more DNMs there are in his sperm. Although DNMs are not always harmful, a small number of them have been linked to autism and other developmental disorders. Animal studies have raised concerns that radiation exposure harms germ cells: Radiation-exposed mice, for example, have more DNMs than unexposed mice. However, previous research has not revealed whether radiation causes long-term damage to human germline DNA.
Chanock began working with Bazyka and others about 8 years ago to look for DNMs in radiation-exposed parents and their children. The team sought out families in which the father was involved in the dangerous cleanup of Chernobyl’s smouldering reactor ruins, or in which one or both parents had been evacuated hours after the accident from nearby settlements such as Pripyat, where power plant workers and their families lived.
The researchers had accurate dose estimates for ionising radiation. Dosimeters were worn by cleanup workers, known as liquidators, and evacuee doses were reconstructed using environmental contamination assessments and directly measuring radioactive iodine uptake by the thyroid gland. Men received doses ranging from 0 to 4 greys, while women received doses ranging from 0 to 550 milligrays. (A single exposure to five greys can be fatal.)
Chanock’s team sequenced the genomes of 105 parents and 130 children born between 1987 and 2002 in collaboration with colleagues at the Broad Institute. Even at the highest radiation doses, the researchers found that the number of DNMs was no higher than in the general population.
“The authors have done an outstanding job. “Very impressive size and very high genome coverage,” says Yuri Dubrova, a geneticist at the University of Leicester who reported elevated mutation rates in short, repetitive DNA sequences known as minisatellites in fathers living in contaminated areas near Chernobyl in the 1990s and early 2000s. Even shorter repetitive sequences, known as microsatellite DNA, have produced conflicting results. There was no evidence of a higher mutation rate in either type of DNA, according to Chanock’s team.
According to Chanock, the mouse studies may have revealed a transgenerational effect because, unlike the Chernobyl liquidators or evacuees, the mice were generally exposed to single intense bursts of radiation. Exposures that last several hours or days may allow DNA repair mechanisms to eliminate excess mutations before they pass on to children. That explanation appeals to Dubrova. “They could be right,” he admits. “We don’t know how long germ cells can ‘remember’ a mutagenic insult.”
Next, Chanock and Bazyka hope to find more liquidators’ children born soon after the accident, in 1987 and 1988, as well as any grandchildren.
The apparent lack of a transgenerational effect, according to Bazyka, offers a ray of hope in what has been a long and dark saga for Ukraine—and him. He was in Kyiv at the time of the accident, and as a medical consultant for the interior ministry, he treated police officers he referred to as “true heroes.” They were burned by beta particles in the radioactive dust while enforcing a safety perimeter around the reactor. Since then, Bazyka has kept a grim vigil for the liquidators, many of whom have died of cancer, cardiovascular disease, or cognitive decline. “At the very least, their children should be healthier than they are,” he says.
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