The genetic findings of the present study, along with those of Ehringer et al.[19] and Zeiger et al.[20], implicate initial sensitivity as a key variable in smoking development [40] and provide critical support for the usefulness of early-experience reports. What is needed next is the development of real-time assessments of sensitivity to nicotine based on objective measures [41] that can be refined and validated ultimately as phenotypes in successive tests of association with genetic variants.
