In addition to the interaction effect, this study showed that the genetic variants in the chromosome 15q25 region that predict heavy smoking and nicotine dependence also predict a later age of smoking cessation in a large community-based sample. Those with the high-risk genetic variants quit later than those at low genetic risk, manifested as a two-year delay in median quit age. Recruitment for the ARIC sample began in the late 1980′s when the population utilization of nicotine replacement therapy was quite low (36, 37), so most ARIC subjects quit smoking without any pharmacologic treatment, thus representing a “natural history” of smoking cessation. The observed association between haplotype status and quitting latency was no longer significant once smoking heaviness was taken into account. This suggests that the targeted risk haplotypes confer heightened risk of heavy smoking and that this, in turn, constitutes an obstacle to successful quitting.
