To conclude, our study provides further evidence for a role of the rs1051730 SNP in the CHRNA5–CHRNA3–CHRNB4 gene cluster in smoking quantity and demonstrates an association with smoking cessation in pregnancy. Further studies are needed to assess the association between the SNP and smoking cessation in other situations. Our finding provides an example of how genes can influence what is perceived by many to be a purely behavioural phenotype. There are parallels between our results and those of genetic association studies which have implicated appetite-regulatory pathways in obesity (21,22). Both phenotypes are thought by many scientists, health-care professionals and policy-makers to be a matter of ‘self-control’ and have much social stigma attached. Twin and other studies have previously shown that these traits have a heritable component, but the identification of robust associations with common genetic variants may help a little to emphasize that physiology plays an important role in ‘socially unacceptable’ phenotypes.
