Our strongest genetic association with a drug response factor was between rs3784943 and factor F1 (Figure 2). This SNP is in the 8th intron of CDH13, which is highly expressed in multiple brain regions [50]. CDH13 has been implicated in drug-abuse related phenotypes by multiple studies from the same group that aggregate evidence at the gene level; specifically, methamphetamine dependence [52], alcohol dependence [53], [54], nicotine dependence [55], [56], successful smoking cessation [57], polysubstance dependence [58], addiction vulnerability [59], and comorbid depression and alcohol dependence [60]. In addition, a meta-analysis of cigarettes smoked per day also identified multiple SNPs in CDH13 [61]. CDH13 has also been implicated in attention deficit hyperactivity disorder (ADHD) at multiple SNPs [62], including rs11646411 [63] and rs6565113 [64]. A meta-analysis of several GWAS for ADHD identified rs8045006 [65]. Finally, a meta-analysis of linkage scans for ADHD identified a genomic region containing CDH13 (16q21–16q24) [66]. Based on these results, a candidate gene study of CDH13 and ADHD was performed that found a gene-wide significant association at one SNP (rs11150556) [67]. In addition, CDH13 has also been
