Interestingly, we noticed that nine SNPs around 7p12.1–7p12.2 in the SAGE sample reached genome-wide significance level (p < 5×10−7), whereas all of them were not significant in the COGA sample (Table 3). Especially, 8 SNPs in DDC gene showed significant associations with MaxDrinks (p< 5×10−7) in the SAGE sample (Table 3). All the nine p-values based on Q statistic were significant, which indicated that there was heterogeneity for these 9 SNPs between COGA and SAGE samples (Table 3). In addition, we found two SNPs, i.e., rs11575522 and rs11575542 (Arg462Gln) at DDC, that had significant cis-acting regulatory effects on the transcript expression of DDC both in the brain and PBMC (p<0.05) (Table 5).
