Previously, Thorgeirsson et al. (10) observed that the same variant was associated with smoking quantity in smokers, but not with smoking prevalence, implicating the variant in nicotine dependence rather than smoking initiation. Our data are consistent with this and with other studies reporting associations between SNPs in linkage disequilibrium with rs1051730 and nicotine dependence or smoking quantity (12–14). The lack of association with smoking quantity in our third trimester smokers may reflect this group being enriched with the most nicotine-dependent subjects. Two additional studies have demonstrated highly significant associations between rs1051730 and lung cancer (OR ≈ 1.3; P < 10−8) but found either weak or no evidence of association with smoking behaviour, suggesting that further work is necessary to determine whether the variant has a role in disease susceptibility independently of smoking behaviour (15,16).
