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Twins offer key to genetics of smoking.

Genes may help explain why some youths who experiment with cigarettes quickly develop a lifelong addiction while others can abstain from smoking or drop the habit easily. However, few studies have gauged the magnitude of such genetic effects or isolated where they may function in initiating, maintaining, or abandoning the cigarette habit. A new study now suggests that genes exert a moderate influence on all aspects of smoking--even on how much one smokes.

From 1967 to 1969, and again from 1983 to 1985, the National Heart, Lung, and Blood Institute in Bethesda, Md., surveyed male twins--both identical and fraternal pairs--born between 1917 and 1927. The survey included questions on such heart-disease risks as smoking.

Because these men had all served in the military during World War II -- an environment in which cigarette smoking was common, even encouraged -- this proved a group "maximally exposed to smoke," notes Dorit Carmelli of SRI International in Menlo Park, Calif., who led the new study. That's important, she says, because people must have the opportunity to smoke before any genetic influence can appear.

That pairs of identical twins (who have nearly identical genes) proved significantly more likely than pairs of fraternal twins to share the same smoking history strongly indicates a genetic role in cigarette addiction, her team reports in the Sept. 17 NEW ENGLAND JOURNAL OF MEDICINE.

Data on smoking intensity among these 4,775 pairs of twins proved "surprising -- and encouraging from the potential for intervention," Carmelli says. Specifically, her team found no evidence that family environment affected how many cigarettes a man smoked. And genes appeared to influence intensity only at the extremes: in men smoking more than 30 or fewer than 10 cigarettes daily.

Earlier studies of Scandinavian twins reported a moderate genetic effect on smoking. But the new study "is much more sophisticated methodologically than previous research - and therefore stronger," maintains John R. Hughes of the University of Vermont in Burlington. The combined findings suggest that this effect is universal, he adds.

Also novel here are data from the same subjects at two different times. In fact, the 16 years between surveys spanned a period of growing social intolerance to smoking, notes Neal L. Benowitz of the University of California, San Francisco. Smoking prevalence nearly halved between surveys, he notes in an editorial accompanying the new report. That the second survey showed 27 percent of the men still smoked in the face of increasing pressure to quit - "reflects [their] more severe and persistent drug dependence," Benowitz says.

"It is notable," he adds, "that one of the strongest genetic effects was on light smoking." Indeed, he concludes, the new data suggest that "light and heavy smoking may be influenced by different genes."
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Title Annotation:genetic research on light and heavy smoking
Author:Raloff, Janet
Publication:Science News
Article Type:Brief Article
Date:Sep 19, 1992
Words:451
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