Individual differences in craving for substances may be important in predicting escalation of substance use, and considerable evidence indicates that one of the major neural substrates of craving is variation in the mesolimbic dopaminergic neurotransmission pathway (Berridge & Robinson, 1998; Wise, 1987). As noted previously, variation at DRD4 has been found to result in weaker transmission of intracellular signals for those with the 7-repeat allele relative to those with the 4-repeat allele, and the resulting hypodopaminergic functioning is associated with indicators of substance use in adolescents. For example, youths carrying at least one 7-repeat allele have been found to have higher lifetime rates of alcohol use (Conner et al., 2010; Laucht, Becker, Blomeyer, & Schmidt, 2007; Ray et al., 2008; Skowronek, Laucht, Hohm, Becker, & Schmidt, 2006; Vaughn, Beaver, DeLisi, Howard, & Perron, 2009) than do similar youths without a 7-repeat allele.
