The final GWAS sample consisted of the remaining SAGE study participants. The full SAGE sample included participants from COGEND, the Collaborative Study on the Genetics of Alcoholism22 and the Family Study of Cocaine Dependence.23 For our study, we excluded the COGEND participants to avoid redundancy. Because the remaining Collaborative Study on the Genetics of Alcoholism and Family Study of Cocaine Dependence participants were ascertained as part of case–control studies of addictive disorders and all were ascertained from sites in the United States, we analyzed them together as done in previous GWAS analyses.9 We henceforth refer to this sample as SAGE*. We obtained their Illumina Human1M-Duo BeadChip genotypes and phenotype data via dbGaP accession number phs000092.v1.p1. After applying our standard QC procedures (Supplementary Information), there remained 832 participants for analysis.
