DRD2 (11q22–q23) has been examined most thoroughly in relation to AD and disinhibitory phenotypes. The majority of human studies have focused on the TaqIA restriction fragment length polymorphism (rs1800497), which a recent metaanalysis estimated to be associated with AD at a modest odds ratio (OR) of 1.31 (Le Foll et al., 2009). Neville and colleagues (2004) found this SNP to be within the coding region of the neighboring ankyrin repeat and kinase domain containing 1 (ANKK1) gene; therefore, the most parsimonious explanation is that phenotypic associations are because of this nonsynonymous coding change in ANKK1. However, this SNP could be tagging a polymorphism in DRD2, which contains several SNPs in modest linkage disequilibrium (LD) (approximately 0.7) with rs1800497. Furthermore, Dick and colleagues (2007) found weak associations between variants in DRD2 and AD. Studies examining association with DRD2 and aspects of heroin dependence have generally been positive (Le Foll et al., 2009). The meta-analysis of Gizer and colleagues (2009) identified no association of DRD2 with ADHD.
