The distinction between disease prediction and disease susceptibility is important because for many common variants, a substantial number of persons who do not carry the at-risk genotype may develop disease anyway owing to environmental or other factors. Indeed, for common diseases such as hypertension or diabetes, environmental or lifestyle factors may play such a strong role relative to genetics that many individuals with the at-risk genotype will develop disease for reasons that are probably unrelated to genotype, and others with the at-risk genotype may remain healthy in the absence of other important environmental exposures (60). Identifying subgroups of individuals in whom SNP-outcome associations differ according to the presence or absence of other SNPs or environmental factors might eventually be of considerable clinical use, particularly for environmental factors that can be modified.
