been identified in GWAS for drug dependence may be involved either in adjusting brain “wiring” prior to drug experiences or subsequent to drug experiences, or both. Based on this analysis, and consistent with the high comorbidity of drug dependence with other psychiatric disorders, it was suggested that GWAS for a number of psychiatric conditions will identify overlapping sets of genes with pleiotropic influences (G. R. Uhl, Drgon, Johnson, Li, et al., 2008). This was confirmed for substance dependence and bipolar disorder in one analysis (Johnson, Drgon, McMahon, & Uhl, 2009) and is discussed in detail in Uhl et al. (2008). Furthermore, analysis of the genes associated with smoking cessation identified a plausible Bayesian network which could not be produced by random selection of SNPs (G. R. Uhl, et al., 2010). Analysis of genes associated with smoking initiation, nicotine dependence and smoking cessation found that these genes were enriched in particular in certain enzymatic and neuroanatomical pathways (J. Wang & Li, 2010). However, it must be noted that this was based upon both GWAS and candidate gene association studies which would be likely to bias the results towards a priori expectations (such as dopaminergic systems).
