THE world is full of dangers, but not quite as full as it sometimes seems. Last week pregnant women, who live or work with smokers, may have been alarmed to read a story that linked passive smoking with genetic defects in unborn children. Researchers led by Dr Barry Finette, of the University of Vermont in Burlington, analysed blood samples taken from babies at birth for mutations in a gene called HPRT. They reported in Nature Medicine that they found some mutations in the babies of mothers who were not smokers, but who had been exposed to smoke from others during their pregnancies.
On the face of it, this is an alarming finding. But is it a plausible one? A search of the scientific literature by Steven Milloy, who runs a junk science home page, found reasons for treating the study with scepticism.
The same four authors had already published a much larger study involving 63 babies, rather than 24, in which they found no such changes. This study compared the babies of smokers, non-smokers and those exposed to only passive smoke. It found no statistically significant difference in HPRT mutations between the groups. The new study, the team says, is a more detailed examination of the earlier data in which they looked not at the total number of mutations, but at the pattern of mutations. They conclude that although the babies of mothers exposed to passive smoke carry no greater number of HPRT mutations, the ones they do carry are more serious. These mutations are of the type found in leukaemias.
The result would be more persuasive if the team had found the same changes in the babies of smokers, where they should be much more frequent than in passive smokers. But there were too few such samples containing mutations for proper comparison.
If what the study found is true, then we would expect to see a higher level of cancers in the children of smokers. Yet a whole series of epidemiological studies have failed to show this.
Smoking during pregnancy is unwise but is there any evidence to justify the fears of passive smoking created by the Vermont study? Steven Milloy thinks not, I agree.
This kind of study, taken on its own, gives science a bad name.
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