Genome-wide association study (GWAS) is a necessary step in the identification of risk genes for complex traits that has only recently been applied to gene mapping for substance dependence (SD) traits. We previously reported risk genes identified by GWAS for cocaine and opioid dependence.1,2 Numerous studies have been published for nicotine dependence (ND).3 Alcohol dependence (AD) is the next most studied SD trait.
