COGA recruited AD probands from treatment facilities through seven participating sites, as described previously.34,35 Institutional review boards at all sites approved the study. Participants were administered the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA), a poly-diagnostic interview.36 Individuals aged <18 years were administered an adolescent SSAGA. In addition, DNA and EEG were collected. Principal components (PCs) derived from GWAS data were used to assign ancestry in the full genotyped sample and were the basis for the selection of AA families. A total of 99.5% of the AA (defined by PCs) individuals self-identify as ‘Black/African-American’ when given the following response options: ‘Native American/American Indian’, ‘Asian’, ‘Pacific Islander’, ‘African-American/Black’, ‘Caucasian/White’, and ‘Other’. Independent of their self-reported race/ethnicity, 11.1% of the sample endorsed being of ‘Hispanic or Latino descent’. The analytical sample consisted of all participants with EEG and GWAS data available, 2382 individuals from 482 families. The demographic characteristics of the full AA sample and the EEG subsample are comparable (Table 1). While 27.6% of the full AA sample met criteria for AD, rates of other co-occurring substance use and externalizing disorders (for example, cocaine dependence (CoD), ADHD) were also substantial.
