study and it harbors genes for the 5-hydroxytyrptamine receptor 3 (HTR3D, HTR3E). Preclinical studies have demonstrated the important role of serotonin pathways in drug abuse liability and as such 5-HT receptors may be an important target of study (see Barr and Goldman, 2006; Johnson, 2004). Unfortunately, at this time it is not possible to know what genes may actually be contributing to the linkage peaks identified in this study or in any other studies that have uncovered areas of the genome linked to externalizing phenotypes. However, future studies employing whole genome association analyses may contribute to the identification of such genes.
