The dopamine D2 receptor (DRD2) has been studied in relation to a variety of psychiatric traits, including schizophrenia (Allen et al. 2008), smoking cessation (David and Munafò 2008) and impulsivity (Eisenberg et al. 2007; Rodriguez-Jimenez et al. 2006). In particular, the historically named Taq1A SNP (also known as rs1800497) has been widely studied. Historical nomenclature describes the A1 (T) and the A2 alleles (C). This polymorphism was initially described as being located in DRD2, but is now recognized to be located in a neighboring gene, ANNK1 (Neville et al. 2004). However, this polymorphism appears to influence the expression of the DRD2 gene and thereby alter DRD2 function. In a study of DRD2 polymorphisms and gene expression in postmortem human brain tissues, rs1800497 was not associated with DRD2 expression, but the G allele of another SNP in DRD2, rs12364283, was found to be associated with enhanced expression (Zhang et al. 2007).
