Carcinogenesis, Vol. 23, No. 12, 2137,
December 2002
© 2002 Oxford University Press
RESPONSE TO LETTER TO THE EDITOR |
Controls need to be selected for the type of SNP study
1 Department of Biosciences at Novum, Karolinska Institute, 141 57 Huddinge, Sweden and
2 Division of Molecular Genetic Epidemiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
Email: kari.hemminki{at}cnt.ki.se
Dear Sir,
SNP studies are conducted for two different research aims: (a) pure gene–disease associations to establish whether the gene or its variant modify disease risk; and (b) gene–environment interactions to establish whether the gene mediates an effect of a quantifiable exposure. Epidemiologists are primarily interested in gene–environment interactions and the letter of Brennan and Boffetta (1) only covers aim (b). We agree, as we did in our initial letter (2), that for studies on gene–environment interactions, controls need to be matched to cases. However, for aim (a), testing the association of an SNP with a disease, there is no need for matching as long as the controls are drawn from the same ethnic population and as long as the Hardy–Weinberg equilibrium holds for cases and controls. The latter condition can and should always be tested with the accumulated data. `A control group for convenience', such as blood donors, is preferable for type (a) studies, because, for a fixed budget, it allows a maximal sample size, as Brennan and Boffetta call for. Requiring tight matching for type (a) study is invoking the principles of Lamarckian genetics.
References
- Brennan,P. and Boffetta,P. (2002) Re: Proper controls for SNP studies? Carcinogenesis, 23.
- Hemminki,K. and Försti,A. (2002) Proper controls for SNP studies? Letter to the editor. Carcinogenesis, 23, 1405.
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