Relatively few of the controls for the studies of substance dependence report any significant use of illegal addictive substances. The genes identified herein thus could influence vulnerabilities to a number of features important for eventually developing dependence including: a) initiation of use, b) persistence of this use, c) failure of attempts at quitting, d) transition from persistent use to dependence, or other steps, in ways that are not completely unraveled by simple comparisons of dependent vs control samples.
