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A RECENT study has revealed that after aperiod of heavy nuclear testing, a largenumber of babies with Down's syndrome were born in FyIde area ofLancashire in the UK. it also showed thata fire at the nearby Windscale (nowSellafield) nuclear power station in 1957 preceded a surgein cases of the disorder (British Medical Journal, Vol3 10, No 6987).
Conducted by JohnBound, former paciiatricianat the Victoria Hospital,Blackpool; Brian Francis, ofthe Centre for AppliedStatistics, Lancaster; andPeter Harvey, pathologist atthe Royal Lancaster infirmary, the study analysed 167cases of Down's syndromefrom among 12,015 totalbirths in the region between1957 and 1991.
Women were divided into 2 age groups of below and over 35 years. This was done take into the account togreater likelihood of womenover 35 giving birth to'a child with Down's syndrome. The incidence of the syndrome was compared with the statisticsgiving estimates of whole body radiation doses that an average Britonreceived each year from nuclear test fall-outs. It was found that 2 peaks of fallout,in 1958 and 1962-64, coincided with thepeak rates of Down's syndrome cases,particularly in the older age group.
I In 1958, the younger women werebarely affected, but among women over35 years, the incidence rocketed from 67to 431 cases per 10,000. And in the1962-64 radiation peak, the incidencerate for younger women doubled from 7to 14 per 10,000 cases and for olderwomen the cases per 10,000 went up to 153 from 64.
According to Bound, these studiesshow that low dose radiation is acausative factor in Down', syndrome."It seems that the total dose you've hadin your life is much more importantthan any individual dose. The greatersusceptibility of older women suggeststhat these low doses may be the strawthat broke the camel's back," says Bound.
Nuclear test fallout is not the onlysource of radiation that humans areexposed to. In fact, of the total exposureto radiation, background radiationfrom cosmic rays or other ionisingmaterials in the earth accounts for asmuch as 90 per cent.
Women in FyIde region wereexposed to increasing amounts of radiation for the purpose of medical diagnosis or treatment between 1957%01, butthis did not have much effect on theincidence rate of the syndrome.
While the blame is largely dumpedon Sellaficld, FyIde also has a similarincidence to add to the national average.Bound and colleagues suggest that themajor reactor fire at the plant in 1957could have been responsible for theexcess ground deposits of radioactivematerial during the peak of 1958.
The study noted that there wasa non-significant rise in Down'ssyndrome cases after the Chernobylincident also, as the Chernobylcloud passed over FyIde. But, saysBound, that this would have generatedonly about a quarter as much radiationin the area as the nuclear tests of the '50sand the '60s.
Down's syndrome was first diagnosed in 1866, when natural radiationcould be the only source of exposure.Though human exposure has increasedby only about 10 per cent since then, theincidence of Down's syndrome hassteadily gone up this century.