http://news.bbc.co.uk/low/english/sci/tech/newsid_1319000/1319386.stm

Tuesday, 8 May, 2001, 23:39 GMT 00:39 UK

Chernobyl children show DNA changes

By BBC News Online's environment correspondent Alex Kirby

Scientists say there is evidence that low radiation doses can cause multiple changes in human DNA, that are passed on to future generations.

They found "an unexpectedly high increase" in mutations among children born after the 1986 Chernobyl disaster.

The children were born to parents who had cleaned up the reactor, and were conceived after it exploded.

The scientists do not rule out the possibility of prolonged effects from the mutations.

The scientists, from Israel and Ukraine, report their findings in the Proceedings of the Royal Society: Biological Sciences, a UK journal.

They say that while exposure to ionizing radiation has for a long time been suspected of increasing the mutation load in humans, events like the atomic bombing of Japan "seem not to have yielded significant genetic defects."

Siblings as controls

Their study examined children born to the Chernobyl "liquidators" - members of the clean-up teams sent in after the reactor exploded who, the scientists say, "received the highest doses, presumably in some combination of acute and chronic forms".

Children born to liquidator families (now living either in Ukraine or Israel) conceived after their father's exposure to radiation (and in one case their mother's as well) were screened for the appearance of new fragments using multi-site DNA fingerprinting.

The children's siblings who had been conceived before their parents' exposure served as internal controls, in addition to external controls from families who had not been exposed.

The report says: "An unexpectedly high (sevenfold) increase in the number of new bands in individuals conceived after parental exposure compared with the level seen in controls was recorded.

"A strong tendency for the number of new bands to decrease with elapsed time between exposure and offspring conception was established for the Ukrainian families.

"These results indicate that low doses of radiation can induce multiple changes in human germline DNA." The germline is the collection of genes that parents pass on to their offspring.

The authors consider the possibility that the DNA changes they found could have been caused in the children themselves, not in their parents. But they reject it.

They write: "One may assume that the origin of the changes is somatic mutation in the children conceived after parental exposure.

Decrease over time

"But, if so, how can one explain the much lower frequency of such changes in their siblings born before exposure, who were subjected to the same environmental factors during the same or even a longer period?"

They also found several factors linked to decreasing changes: the passage of time between exposure and conception, and also the duration of the liquidators' work in the contaminated area.

The report concludes: "The small contribution of these changes to the immediate genetic risk does not exclude the possibility of prolonged effects.

"The very fact that much lower doses of radiation than previously generally believed can double the number of genomic changes needs serious attention.

"This is all the more important when a significant proportion of the human population is subjected to increased mutagenic pressure."

Richard Bramhall, of the Low Level Radiation Campaign, told BBC News Online: "We agree: these findings are important because so many people are exposed to environmental mutagens.

Internal exposure

"There are several indications in the report that the real problem is internal radiation.

"It shows a massive failure in the modelling of radiation risk by the International Commission on Radiological Protection.

"That is based on the Japanese bombs, single massive bursts of gamma radiation delivered externally.

"The ICRP studies are absolutely silent on the effects of internal radiation."

-- Swissrose (cellier3@mindspring.com), May 09, 2001