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Jouni J.K. Jaakkola,^1,2,3 Per Nafstad,² and Per Magnus²

¹Environmental Health Program, The Nordic School of Public Health, Göteborg, Sweden
²Section of Epidemiology, Department of Population Health Sciences, National Institute of Public Health, Oslo, Norway
³Environmental Epidemiology Unit, Department of Public Health, University of Helsinki, Helsinki, Finland

Abstract

We hypothesized that the joint effect of genetic propensity to asthma and exposure to environmental tobacco smoke on the risk of childhood asthma is greater than expected on the basis of their independent effects. We performed a population-based 4-year cohort study of 2,531 children born in Oslo, Norway. We collected information on the child's health and environmental exposures at birth and when the child was 6, 12, 18, and 24 months and 4 years of age. The outcomes of interest were bronchial obstruction during the first 2 years and asthma at the age of 4 years. Parental atopy was defined as a history of maternal or paternal asthma or hay fever. Exposure to environmental tobacco smoke was defined on the basis of questionnaire information on household smokers at birth. In logistic regression analysis adjusting for confounding, parental atopy alone increased the risk of bronchial obstruction [odds ratio 1.62 ; 95% confidence interval (CI) 1.10-2.40] and asthma (1.66 ; 95% CI, 1.08-2.54) . In children without parental atopy, there was little effect of exposure to environmental tobacco smoke on bronchial obstruction (1.29 ; 95% CI, 0.88-1.89) and asthma (0.84 ; 95% CI, 0.53-1.34) . The presence of parental atopy and exposure had a substantial effect both on bronchial obstruction (2.88 ; 95% CI, 1.91-4.32) and asthma (2.68 ; 95% CI, 1.70-4.22) . The results are consistent with the hypothesized joint effect of parental atopy and exposure to environmental tobacco smoke. This phenomenon--denoted as effect modification of environmental exposure by genetic constitution, or gene by environment interaction--suggests that some genetic markers could indicate susceptibility to environmental factors. Key words: asthma, atopy, gene by environment interaction, tobacco smoke. Environ Health Perspect 109:579-582 (2001) . [Online 22 May 2001]

http://ehpnet1.niehs.nih.gov/docs/2001/109p579-582jaakkola/ abstract.html

Address correspondence to J.J.K. Jaakkola, Environmental Health Program, The Nordic School of Public Health, P.O. Box 12133, SE-402 42 Göteborg, SWEDEN. Telephone: +46-31-693980. Fax: +46-31-691777. E-mail: jouni.jaakkola@nhv.se

This research was supported by grants from the Norwegian Research Council.

Received 13 December 2000 ; accepted 10 January 2001.