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American Journal of Epidemiology Vol. 144, No. 3: 207-213
Copyright © 1996 by The Johns Hopkins University School of Hygiene and Public Health


other

Nontraditional Epidemiologic Approaches in the Analysis of Gene Environment Interaction: Case-Control Studies with No Controls!

Muin J. Khoury1, and W. Dana Flanders2

1Birth Defects and Genetic Diseases Branch, Division of Birth Defects and Developmental Disabilities, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA
2Department of Epidemiology, Emory University School of Public Health, Atlanta, GA

Reprint requests to Dr. Muin J. Khoury, Birth Defects and Genetic Diseases Branch, CDC, 4770 Buford Hwy., (Mail stop F45), Atlanta, GA 30341–3724.

Although case-control studies are suitable for assessing gene-environment interactions, choosing appropriate control subjects is a valid concern in these studies. The authors review three nontraditional study designs that do not include a control group: 1) the case-only study, 2) the case-parental control study, and 3) the affected relative-pair method. In case-only studies, one can examine the association between an exposure and a genotype among case subjects only. Odds ratios are interpreted as a synergy index on a multiplicative scale, with independence assumed between the exposure and the genotype. In case-parental control studies, one can compare the genotypic distribution of case subjects with the expected distribution based on parental genotypes when there is no association between genotype and disease; the effect of a genotype can be stratified according to case subjects' exposure status. In affected relative-pair studies, the distribution of alleles identical by descent between pairs of affected relatives is compared with the expected distribution based on the absence of genetic linkage between the locus and the disease; the analysis can be stratified according to exposure status. Some or all of these methods have certain limitations, including linkage disequilibrium, confounding, assumptions of Mendelian transmission, an inability to measure exposure effects directly, and the use of a multiplicative scale to test for interaction. Nevertheless, they provide important tools to assess gene-environment interaction in disease etiology. Am J Epidemiol 1996; 144: 207–13.

case-control studies; environment; genes


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