Subjects were recruited for linkage and association studies of the genetics of cocaine, opioid, and alcohol dependence (26,27). The participants were recruited at 5 sites: the University of Connecticut Health Center (538 ND cases and 467 comparison subjects), Yale University School of Medicine (432 ND cases and 428 comparison subjects), the Medical University of South Carolina (54 ND cases and 255 comparison subjects), the University of Pennsylvania School of Medicine (133 ND cases and 16 comparison subjects), and McLean Hospital of Harvard Medical School (52 ND cases and 17 comparison subjects). Written informed consent was obtained from all participants. The institutional review board at each of the participating sites approved the study protocol. All subjects were interviewed by trained interviewers using the Semi-Structured Assessment for Drug Dependence and Alcoholism (SSADDA) (28,29), which yields diagnoses for a variety of psychiatric and substance use disorders. The SSADDA diagnosis of ND is lifetime and based on DSM-IV. The reliability of the SSADDA for the lifetime diagnosis of ND was excellent, with interrater and test-retest reliability [κ] of 0.77 and 0.97, respectively (28). Subjects affected with major psychiatric illnesses, such as schizophrenia, schizoaffective disorder, or mental retardation, were excluded.
