Drug dependence/addiction is a complex disorder which is multi-factorial, involving both environmental and genetic influences. Studies support the view that much of the heritable influence in vulnerability to dependence on addictive substances from different pharmacological classes is shared (Karkowski, Prescott, & Kendler, 2000; Kendler, Karkowski, Neale, & Prescott, 2000; Tsuang, et al., 1998). These findings have increased interest in the particular genes that are associated with addiction relevant psychological and physiological traits that may predict risk for the development of drug abuse and addiction. The complex nature of addiction has led some investigators to question the value of genetic research on addictive disorders (Merikangas & Risch, 2003) or the value of GWAS (Agrawal & Lynskey, 2008). The last few years have seen identification of few large association findings for addiction. When viewed as a polygenic trait with substantial allelic and locus heterogeneity, however, there is substantial evidence for convergent GWAS results that suggest value from these experiments. These data have profound implications for the improved understanding and treatment of the complex disorder of addiction, and may have implications for how the genetic basis of other complex diseases might be approached overall.
