A control group, namely subjects from the Study on Addiction: Genetics and Environment (SAGE), was chosen because it was genotyped with Illumina Human 1M-single Infinium BeadChip (23). This cohort consisted of 1965 control subjects (from the larger SAGE case–control study). The consented sample included 31% males and 69% females, with mean age of 39.2 (SD 9.1), and 73% subjects self-identified as European-American (Caucasian), 26% as African-American and 1% as other (http://zork.wustl.edu/gei/study_description.htm). Both raw intensities and genotypes were available through NHGRI–dbGaP (http://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?study_id=phs000092.v1.p1). The SAGE control subjects have had exposure to alcohol (and possibly to other drugs), but did not meet the criteria for any illicit drug dependence.
