Interesting paper out in JAMA, Coffee, CYP1A2 genotype, and risk of myocardial infarction:
The association between coffee intake and risk of myocardial infarction (MI) remains controversial. Coffee is a major source of caffeine, which is metabolized by the polymorphic cytochrome P450 1A2 (CYP1A2) enzyme. Individuals who are homozygous for the CYP1A2*1A allele are "rapid" caffeine metabolizers, whereas carriers of the variant CYP1A2*1F are "slow" caffeine metabolizers....Intake of coffee was associated with an increased risk of nonfatal MI only among individuals with slow caffeine metabolism, suggesting that caffeine plays a role in this association.
Imagine when insurance companies get their hands on this sort of information, they'll give you your lowest risk lifestyle dependent on your genotypic predispositions. This sort of trait indicates the contextual response of genes and subsequent development. Genes don't "determine" anything, they are important (or not) parameters in concert with a host of other variables. Here is a popular press review of this paper.