preconceptional paternal irradiation increases offspring risk of leukemia

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LONDON, July 22 (Reuters) - British scientists said on
Wednesday that they have discovered how radiation can increase
the risk of childhood leukaemia.
	    They found that male mice exposed to high doses of radiation
had damaged sperm and produced offspring which had a greater
chance of getting the blood cancer.
	    ``There is no doubt that the group of animals that were the
product of preconceptional paternal irradiation (PPI) had a
greater susceptibility to the induction of leukaemia,'' Dr Brian
Lord, the head of the research team, told a news conference.
	    Lord, an expert on the effects of plutonium on the
development of the blood system, emphasised that the study was
done on mice and did not explain the outbreak of clusters of the
disease in children living near nuclear power plants.
	    ``But what it does show us, for the first time, is a
potential way -- a mechanism -- in which paternal irradiation
can lead to an increase in leukaemia risk for the next
generation. It shows us how DNA defects can be passed from
generation to generation,'' he added.
	    The research, published in the British Journal of Cancer,
showed that the radiation produced genetic changes in the makeup
of the cells, and some of the damage was passed on to the next
generation of mice. The risk of developing leukaemia had nearly
doubled in the PPI mice.
	    The damage in the bone marrow cells alone was not enough to
cause the leukaemia, but it increased vulnerability to the
disease. Leukaemia developed earlier and more frequently in the
cells when they were exposed to a powerful cancer-causing
chemical.
	    Scientists are not sure what causes cancer. Genes certainly
play a part and certain chemicals, substances called
carcinogens, are also involved.
	    Professor Gordon McVie, the director general of Britain's
Cancer Research Campaign charity, said the latest research
supports the double-hit hypothesis of cancer -- that two
elements or causes may be needed for the disease to develop.
	    ``These laboratory tests take us on from the debate of
paternal irradiation with the important addition that the
inherited cancer risk must be activated by a second cancer
trigger to the offspring,'' McVie said.
	    The radiation increases susceptibility to leukaemia but the
researchers said another factor, perhaps a virus or something
inherited from the mother, combines to cause the disease.
	    Scientists have been debating whether radiation causes
childhood leukaemia for many years. A controversial study in
1990 claimed that a cluster of cases in northern England
resulted from parents working at the Sellafield nuclear power
plant.
	    Other studies of atomic bomb survivors and people who have
had radiotherapy found no evidence to support the theory. Recent
British research concluded that exposure to infection that
resulted from a high mixing of the population was a likely cause
of the disease clusters.
	    ``These scientists' line of inquiry may be different but
their work is complementary and both will help us understand
more about the causes of cancer,'' McVie said.
	    The population mixing theory, he added, supports the
established fact that viruses can cause cancer, although the
particular virus has not been identified.