The Study of Addiction: Genetics and Environment (SAGE) was used as an independent replication sample to evaluate the SNPs showing the greatest evidence of association in the COGA sample. This is a case-control sample derived from three large, complementary studies: COGA, the Family Study of Cocaine Dependence and the Collaborative Genetics Study of Nicotine Dependence (Bierut et al., 2010). The 129 individuals who overlapped between the 118 pedigrees and SAGE were removed from the replication dataset. The remaining SAGE samples included 2,647 individuals of European American descent. AD and individual criteria were obtained from SSAGA data. Imputed dosage data were obtained using the same method as described above. Plink was used in all analyses, employing age at interview and gender as covariates.
