A prospective population-based study from the Netherlands [Ott, A. et al. (1998) Lancet 351, 1840-1843)] confirms previous suggestions that smokers are at increased risk both of vascular dementia and of Alzheimer's disease, but reports that the increased risk of Alzheimer's does not apply to smokers who carry the E4 allele of the blood protein apolipoprotein E (for an explanation of the relationship between APOE genotype and risk of Alzheimer's, see Alzheimer's disease summary in the Information database). In other words, there appears to be an interaction between an individual's APOE genotype and the biological effects of smoking.
Comment: This work provides further support for the conclusion that there is no justification for APOE genetic testing to assess genetic risk of Alzheimer's disease. Smoking is just one of many 'environmental' factors that are likely to interact with an individual's genetic make-up in determining whether they will develop disease.