Analysis of smoking cessation did not reveal any loci associated below the suggestive significance level, and it showed that the previously reported 10 association between rs3025343 in the DBH locus can be replicated in COPD subjects with a nominal significance threshold. DBH is a plausible candidate gene for smoking cessation since it participates in the metabolism of dopamine. This neurotransmitter is released from neurons in response to nicotine,3 and is an important mediator of addiction behaviors such as smoking. The rs3025343 SNP that we extracted showed a substantial heterogeneity in this effect, which may reflect the between-study differences in factors such as use of nicotine replacement therapy or socio-economic status. Interestingly, the best proxy SNP rs3025316 (genotyped in all cohorts) showed a more pronounced effect with somewhat smaller heterogeneity index compared to the rs3025343.
