GWAS in 2600 individuals derived from the Study of Addiction: Genes and Environment (SAGE) dataset. Neither study had genome-wide significant results but the investigators noted that among the top SNPs in each dataset, far more showed the same direction of effect in the other dataset than would be expected by chance. Other investigators have looked for commonalities of sub-threshold SNPs across several GWAS. It is interesting that several psychiatric disorder GWAS have identified genes encoding cadherins that mediate cell-cell adhesion, are involved in intracellular signaling pathways and may alter functional connectivity [75]. For example, CDH13 has shown up at sub-threshold levels in several studies of addiction including alcohol, nicotine and methamphetamine dependence [73,75,76].
