Lastly, as mentioned above, a consistent body of research stresses the need for more careful examination of maternal cigarette smoking during pregnancy within the context of genetic background. While prenatal smoke exposure-induced epigenetic modification is consistently found to impact physical health phenotypes, the examination of epigenetic modification as a moderator of later neurobehavioral effects is in its infancy. The same biological systems investigated in studies of genetic variation (e.g., nicotinic and dopaminergic systems, xenobiotic metabolism pathways) remain viable candidates for epigenetic influences on neurobehavioral outcomes in exposed offspring. Indeed, the co-modeling of genetic and epigenetic variation as they relate to these outcomes has the potential to bring new clarity to the field. Although epigenetic patterns change over time and with environmental exposures (and thus are not as static as genetic variation), DNA samples in existing datasets may be used to provide an informative cross-sectional view of this phenomenon, provided that there is careful attention given to the time of sample collection. Promising findings can be followed up with longitudinal studies with sequential sampling designed to assess the relative impact of
