The sample was drawn from a cohort of pairs of adult siblings who were cocaine-dependent and recruited to participate in genetic linkage studies of cocaine (Gelernter et al., 2005) or opioid dependence (Gelernter et al., 2006). Probands and siblings were recruited at the University of Connecticut Health Center (Farmington, CT); Yale University School of Medicine (APT Foundation; New Haven, CT); Harvard Medical School (McLean Hospital; Belmont, MA); and the Medical University of South Carolina (Charleston, SC). Informed consent was obtained as approved by each institutional review board and subjects were paid for their participation. A certificate of confidentiality was obtained from the National Institute on Drug Abuse. For the present analysis, probands with cocaine dependence were selected if they had at least one sibling with cocaine dependence. Participants with a clinical diagnosis of schizophrenia or schizoaffective disorder were excluded (Gelernter et al., 2005; Gelernter et al., 2006). A total of 449 proband/sibling pairs were identified. If probands had more than one cocaine dependent full sibling, the sibling closest in age to the proband was selected for the analysis.
