Thirty-five years on from the infamous Chernobyl disaster, researchers have finally answered some of the most pressing questions regarding the long-term consequences of exposure to ionizing radiation. In a new study published in the journal Science, it is revealed that the children of those who were affected by the catastrophe display no additional DNA damage, with levels of genetic mutations that match those of the general population.
This finding will come as a huge relief to many who were exposed to the fall-out from the Fukushima incident in Japan in 2011, putting to rest any fears about the risk of genetic damage to their children.
The study authors sequenced the genomes of 130 individuals born between 1987 and 2002 to parents who were exposed to radiation following the Chernobyl Nuclear Power Plant explosion in Ukraine on April 26, 1986. At least one parent of each participant had been involved in the clean-up operation within the contaminated zone or had been evacuated from a town close to Chernobyl.
By also analyzing parents’ genomes, the researchers were able to observe the rate at which radiation-induced mutations were passed on from one generation to the next. In their write-up, the study authors explain that they were particularly interested in a type of mutation known as germline de novo mutations, which arise in the sperm and egg cells and therefore lead to genetic changes in offspring that are not present in parents.
Results indicated no increase in de novo mutations among the children of those who were exposed to radiation from the Chernobyl disaster, leading the authors to conclude that their data “does not provide support for a transgenerational effect of ionizing radiation on germline DNA in humans."
In a statement, study author Dr Stephen J. Chanock explained that "we view these results as very reassuring for people who were living in Fukushima at the time of the accident in 2011."
"The radiation doses in Japan are known to have been lower than those recorded at Chernobyl."
Meanwhile, a second study in Science sought to determine the mechanism by which exposure to ionizing radiation increases the risk of a type of cancer called papillary thyroid carcinoma (PTC). Following the blast, several thousand people who were exposed to the fall-out went on to develop these tumors, yet the link between radiation and cancer has never been fully illuminated.
Researchers analyzed thyroid tumors, normal thyroid tissue, and blood from 359 people who had been exposed to radiation from Chernobyl either as children or while in the womb, and compared these to samples taken from 81 unexposed individuals.
Genetic sequencing revealed that a large proportion of tumors in both groups were caused by mutations within a small group of genes associated with a particular signaling pathway called the mitogen-activated protein kinase (MAPK) pathway. Crucially, however, the types of mutations that occurred in these genes were found to differ according to whether or not tumors had been caused by radiation exposure.
In non-exposed individuals, PTC tended to develop as a result of point mutations – whereby a single base-pair is altered – within the MAPK genes. In contrast, radiation-induced tumors tended to be caused by gene fusions, whereby both strands of the DNA double-helix are broken and then joined back together in the wrong places.
This occurs as the energy in ionizing radiation breaks the chemical bonds that hold DNA together, increasing the likelihood of certain types of genetic mutation.
Summing up their findings, the study authors write that “our results point to DNA double-strand breaks as early carcinogenic events that subsequently enable PTC growth following environmental radiation exposure.”