alcohol, and substance use disorder phenotypes [123–125]. Early examples of genetic variants that demonstrate such pleiotropy, i.e., exert effects on more than one outcome, across addiction and other psychiatric diseases include: ZNF804A SNP rs1344706, the first genome-wide significant finding for schizophrenia [126] and later extended to heroin addiction [127, 128]; and the BDNF SNP rs6265 and CHRNA5 SNPs rs16969968 and rs1051730 implicated at genome-wide significance for smoking (Table 1) and extended to schizophrenia/bipolar disorder outcomes [129, 130]. As the sample sizes for addiction GWAS expand to sizes comparable with other psychiatric disease GWAS, polygenic risk scores and top loci that comprise these scores are likely to reveal even more extensive sharing. Once established, polygenic risk scores may have clinical utility for predicting individuals at highest risk for developing addiction or guiding treatment strategies.
