These genetic associations with nicotine and alcohol dependence and proposed mechanisms of biologic action including neurotransmission and metabolism provide new insights to the underlying biology associated with addiction. Identifying how specific variants and genes associated with addictive behavior affect brain function will be key to understanding the development of dependence; yet numerous questions remain. For instance, will these mechanisms of action associated with genetic variation be expressed in all regions of the brain, or will the genetic effect be region specific? Will these variants have a similar influence throughout the lifespan, or will there be critical periods when these genetic variations alter risk of developing addiction? Though these biological mechanisms are proposed to lead to the altered risk for the development of addiction, they represent an initial understanding of the mechanisms of dependence, and it is likely that there will be more complex biologic functions underlying these genetic associations.
