The possible functional relevance of this polymorphism prompted a number of studies, across several ethnicities, to examine its effect on the risk of developing opioid dependence. Results have been mixed, with some indication for association with opioid dependence in Indians belonging to the Kayastha and Brahmin castes of the Bengali-Hindu ethnic background, Indian, and Hong Kong Chinese samples (Deb et al., 2010; Tan et al., 2003; Kapur et al., 2007; Szeto et al., 2001) and negative results in American-Indian, African-American, European-American, European, Chinese, Malays and Han Chinese samples (Arias et al., 2006; Crowley et al., 2003; Franke et al., 2001; Glatt et al., 2007; Shi et al., 2002; Tan et al., 2003; Zhang et al., 2007). Haplotypes from two SNPs (rs510769, rs3778151) show nominally significant association with opioid dependence, but do not include the 118A>G polymorphism although they are in linkage disequilibrium with it (Levran et al., 2008). In a meta-analysis of 22 studies including 8000 subjects divided by ethnicity and substance dependence type, the 118A>G polymorphism did not appear to affect the risk for substance dependence in general (Arias
