Other association studies of drug and alcohol addiction have used a similar DNA pooling approach. With a 1,494 variant chip, the Uhl group identified several variants that were associated with drug abuse vulnerability (Uhl et al., 2001). They extended their study with pools of African- and European-American cohorts using the 10K GeneChip and found 38 “nominally reproducibly positive” variants associated with non-specific substance abuse (Liu et al., 2005). Then, using the 100K GeneChip Set, they identified 51 “clustered positive” regions associated with alcohol dependence in European-Americans (Johnson et al., 2006). Based on these studies and a study that used 500K GeneChips, 89 genes were suggested to play a role in addiction vulnerability (Liu et al., 2006). In another study that used both 100K and 500K GeneChips, 39 genes that were identified as “clustered positive” were found to be in association with methamphetamine dependence (Uhl et al., 2008). Comparisons between studies are difficult to make as different platforms and dissimilar subject phenotyping were used.
