As previously found, maternal smoking during pregnancy was a strong risk factor for smoking behavior in the offspring and it was linked with multiple indices of social disadvantage(39). The effect of maternal smoking in pregnancy on offspring’s smoking habits is likely to reflect a mixture of genetic and environmental contributors to liability. A genetic mechanism might be due to the fact that mothers who smoke during pregnancy might be more likely to carry and transmit risk alleles to their offspring. Although we could not directly test this hypothesis because DNA from mothers was unavailable, rs1051730[A] has been previously associated with inability to quit smoking in pregnancy(57). In our study, offspring of mothers smoking heavily during pregnancy were more likely to carry CHRNA3-rs1051730[A] as compared to the offspring of non-smoking mothers. This association might reflect an excess of A alleles in mothers smoking during pregnancy. Besides a gene-mediated effect, maternal smoking during pregnancy might increase the risk of smoking in the offspring via intrauterine exposure to nicotine(58). In our data, the effect of maternal smoking in pregnancy became non-significant after adjusting
