A total of 3318 African Americans (AAs) were recruited for studies of the genetics of drug or alcohol dependence at five US sites: Yale University School of Medicine, the University of Connecticut Health Center, the University of Pennsylvania School of Medicine, the Medical University of South Carolina, and McLean Hospital (Harvard Medical School). The samples consisted of small nuclear families (SNFs) originally collected for linkage studies, and, mostly, unrelated individuals. All subjects were interviewed using an electronic version of the Semi-Structured Assessment for Drug Dependence and Alcoholism (SSADDA) [19] to derive diagnoses for major psychiatric traits according to DSM-IV criteria. Subjects gave written informed consent as approved by the institutional review board at each site, and certificates of confidentiality were obtained from NIDA and NIAAA.
