We focus here on clinical phenotypes that co-occur with addiction and a structural brain phenotype, individual differences in frontal cortical volume. Twin studies document sizable heritable components for individual differences in the volumes of brain regions. High heritabilities are especially evident for individual differences in frontal and temporal cerebral cortical regions [15]. Volumes of these brain regions have been reported to be reduced in substance dependent individuals [16–19]. Increasing evidence from fMRI and PET studies identifies functional differences in these brain regions in studies of individuals with substance dependence and related phenotypes [20, 21]. We thus focus on this “frontal cortical volume” phenotype.
