Costa and Co-Workers Explained:

Small De Novo CNVs as Biomarkers of Parental Exposure to Low Doses of Ionising Radiation of

Caesium-137.

Reference: Costa, E.O.A., Pinto, I.P., Gonçalves, M.W. et al. (2018) Small de novo CNVs as biomarkers of parental exposure to low doses of ionizing radiation of caesium-137, Journal Scientific Reports  8, 5914.

What were the research questions?

In 1987 in Goiania, Brazil, 249 people received varying doses of gamma radiation due to the accidental dispersion of the radioactive substance, caesium-137, into the environment. This raised the possibility that DNA mutations may form in the germ cells of exposed individuals, which in turn, could result in de novo (new) mutations in their offspring.

The researchers were interested in a type of de novo mutation called copy number variation (CNV); defined as gain or loss of a DNA segment of ≥50-1000 base-pairs. CNVs occur naturally with the frequency of occurrence varying from person to person and with exposure to environmental mutagens including ionising radiation.

The research team wanted to find out if the children of parents who received 200 mGy or less, would have CNVs that were similar or different to the children of unexposed parents. The authors also sought to demonstrate the potential of CNV germline mutations as biomarkers of parental radiation exposure.

How was the scientific problem approached?

The scientists took blood samples from parents (for whom at least one of them had received a dose of up to 200 mGy) and from their child or children. Newly arising (de novo) CNV mutations in the children were identified by comparing their DNA with that of their parents.

Blood samples were taken from the control families and so, CNV mutations for the controls were identified. Then the researchers were able to compare the two sets of CNVs in the exposed and control group of families.

What did the research involve?

The group being studied was composed of 12 families (40 people) containing at least one parent who was exposed to radiation from caesium-137. The control group was composed of 8 family trios (father, mother and child - 24 people) from Goiania with no history of medical, occupational or accidental exposure to radiation.

DNA from the blood of each participant was analysed using a technique called Chromosomal Microarray Analysis. This enables differing chromosomal variations, sizes, and genomic locations to be detected at a high resolution.

What did they find?

No statistical differences were found between the total number of CNV mutations (gains or losses) for the children of exposed parents compared to the control group. However, when considered as a proportion of the genome in terms of size of CNVs, a difference was seen. The total amount of DNA lost or gained was three times greater for the children of exposed adults than for the controls.

How did the researchers interpret their results?

The researchers have evaluated the Chromosomal Microarray Analysis technique to be a good way for detecting CNV and measured changes in the genome at a resolution as low as ~500 base pairs. They suggest that the mutation rate of de novo CNV, particularly genomic losses, to be a good biomarker of parental exposure.

The authors note that their data is consistent with the results produced by some researchers, however not all. They go onto suggest that parental exposure to doses below 0.2 Gy could prove harmful due to an increase in the de novo mutation rate in the offspring.

Who did this research?

This work was done by a team of researchers from the Pontifical Catholic University of Goias, the Goias State Human Cytogenetics and Molecular Genetics Laboratory, the Catholic University of Brasilia, the State University of Goias and the Federal University of Goias.

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