Many of these gene identification efforts focus on adult alcohol and substance dependence. This focus is in part so that subjects will have passed through the age of onset for common addictive substance disorders and to ensure that there is no ambiguity associated with whether an unaffected individual simply has not yet manifested problems. However, some projects have focused specifically on adolescent samples. Many of these studies have come from the Colorado Center for the Genetics of Antisocial Drug Dependence (CADD), which is an ongoing multicomponent, collaborative study at the University of Colorado57 consisting of more than 5000 youths. The CADD is using several research designs and strategies in its study of the genetic basis for antisocial drug dependence in adolescents. Stallings and colleagues57 reported a genome-wide linkage study for the average number of substance dependence symptoms (a quantitative index of substance use liability) that implicated several genomic regions, including chromosomes 3q24-25 (near markers D3S1279 and D3S1614) and 9q34 (near markers D9S1826 and D9S1838). A 2008 study58 reported SNP association results from a targeted gene assay designed to test 50
