Vulnerability to heavy use and development of dependence on alcohol and/or an illegal abused substance (“addiction vulnerability”) appears to be such a trait. The substantial genetic influences on addiction vulnerability are documented by data from family, adoption and twin studies [1], [2], [3], [4]. Twin studies also document shared heritable influences on vulnerability to dependence on addictive substances from different pharmacological classes, including alcohol and illegal drugs from several pharmacological classes [2], [3], [5]. Combined data from linkage and initial GWA studies [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19] suggest that much of the genetic influence on vulnerability to substance dependence is likely to be polygenic.
