A large number of association studies of this SNP across various phenotypes were reported (for a recent review see Mague and Blendy 2010). The 118G allele has been implicated in drug addiction, stress responsivity, and in treatment responses. Several association studies of 118A>G reported negative results, and meta-analyses revealed mixed results (Arias et al. 2006; Glatt et al. 2007). The118G allele was shown to be associated with opioid dependence (OD) and other substance dependencies in several studies in diverse populations. An association was observed between the 118G allele and opioid addiction in Swedish (Bart et al. 2004), Chinese (Szeto et al. 2001), EA (Drakenberg et al. 2006), and Indian patients (Deb et al. 2010; Kapur et al. 2007; Tan et al. 2003), whereas other studies did not detect such association (Franke et al. 2001; Glatt et al. 2007; Levran et al. 2008; Levran et al. 2009; Shi et al. 2002).
