We examined several functional DRD2 polymorphisms. rs12364283 is located in a conserved suppressor region of DRD2 and affects expression in prefrontal cortex and striatum (Zhang et al., 2007). rs2283265 and rs1076560 are two frequent intronic SNPs that alter the expression of the short and long isoforms of DRD2, and are associated with differential neural activity patterns in prefrontal cortex and striatum during working memory (Zhang et al., 2007). Notably, rs1800497 is localized within the ankyrin repeat and kinase domain containing 1 gene (ANKK1) (Neville, Johnstone & Walton, 2004). However, despite residing 10 kilobases downstream from DRD2, rs1800497 has been shown to affect DRD2 messenger RNA translation and stability, and postsynaptic DRD2 density in striatum (Ritchie & Noble, 2003). Thus, we thought that the DRD2 SNPs investigated here might evidence associations with working memory and ADHD symptoms but none were detected. Of note, we did not look for epistasis within DRD1 or DRD2, nor between DRD1 and DRD2. Epitasis undoubtedly contributes to the development of a complex genetic disorder such as ADHD as well as to intermediate phenotypes such as working
