The goal of genetic association studies of SUD is to identify genetic markers that may have a role in the development or progression of addiction. Identifying these markers may aid in the treatment or prevention of SUD. There are two main catagories of genetic association studies. Candidate gene association studies (CGAS) test the association of previously identified markers with SUD phenotypes. Markers are selected for CGAS analysis due to demonstrated functional significance in prior animal, molecular genetic, and/or human SUD studies (Kwon & Goate, 2000; Rebbeck, Spitz, & Wu, 2004). Together, these studies can develop a strong case for the importance of a genetic variant or biological pathway in SUD etiology. In contrast, genome-wide association studies (GWAS) test for significant associations between a SUD phenotype and hundreds of thousands single nucleotide polymorphisms (SNP) throughout the entire genome without prior knowledge about gene function. Thus, GWAS can identify novel candidate genes contributing to SUD. In addition, the aggregate effect of all SNPs associated with an outcome, whether or not they reach genome-wide significance, can be modeled via a polygenetic risk score (PRS) (Dudbridge, 2013; Ferreira et al., 2009; Purcell et al., 2009).
