Compared to candidate gene association studies, GWAS provide hypothesis-free, genome-wide view of possible genetic susceptibility factors underlying drug addiction [25-31]. When we compare the addiction susceptible genetic variants linked by candidate gene association studies and GWAS, we found that the GWA arrays included probes for three polymorphisms showing significant summary odds ratio of the addiction susceptibility (rs6265, rs1799971 and rs4680). Among these polymorphisms, only rs1799971 show some suggestive significance in methamphetamine abusers of Japanese (p-Value = 0.0465) [26]. Consistent with meta-analyses in Alzheimer disease, schizophrenia, major depressive disorder and Parkinson disease [3-6], it seems some important candidate genes have received inordinate attention in candidate-gene based association study, while the GWA studies with hypothesis-free design might not support many a prior hypothesis. On the other hand, GWAS provide more opportunities for traditional candidate-gene based association study to improve the experimental designs by avoiding potential biases from subjectively selection of candidate genes in the beginning of the study.
