We performed a hypothesis -driven case-control association study, using an “addiction-focused” SNP array (Hodgkinson et al., 2008) in African Americans (AA) that extends our original study in EA (Levran et al., 2008). The two populations were separated for analysis based on significant differences in allele frequencies and the vulnerabilities of these studies to population stratification. The cases were selected from the extreme margin of the specific phenotype range (e.g., severe heroin addicts in methadone maintenance treatment) and the controls were selected by detailed personal interview and stringent criteria.
