Our sample consisted of 198 African-American and 203 Hispanic subjects (Table 1). We have reported methylation levels of 329 Caucasian subjects, used in this study as a comparison group for the extent of methylation (Nielsen et al. 2009). The 401 former severe heroin addicts and control subjects of African-American and Hispanic ethnicity were drawn from consecutive volunteers (January 1995-May 2007) in genetic studies conducted by the Laboratory of the Biology of Addictive Diseases at The Rockefeller University who met the inclusion criteria defined below (same criteria for the Caucasians reported earlier). Subjects were recruited from clinical resources in New York City, and from newspaper advertisements, referrals, and posted notices. Ethnicity was based on the ethnic/cultural background of the subjects, their parents, grandparents, and great-grandparents. All subjects gave specific consent for genetic studies and signed an informed consent approved by The Rockefeller University Hospital Institutional Review Board.
