In conclusion, although an association between the A118G OPRM1 SNP and opioid dependence was not supported in the current meta-analysis, further analysis of A118G is warranted which also investigates the impact of gender as a modulator. In addition, previous case studies have reported possible association of A118G SNP with opioid dependence in other ethnic groups, such as Hispanics,2,16 African-Americans,17 and Indians.13 However, these ethnicities were not represented in enough case-control studies to be included in the present meta-analysis as a separate ethnicity modulator. Furthermore, despite having no clear evidence of a direct association to the risk of developing opioid dependence, A118G may mediate or otherwise influence pharmacological and therapeutic responses to opioids, as evidenced by altered opioid dosage requirements,35 thereby possibly indirectly leading to dependence. Thus, a deeper investigation into its functionality is needed which should also consider the complex regulation of activity of the endproduct, the mu opioid receptor. Finally, the A118G polymorphism is only one of more than 100 known SNPs in OPRM1.3 Therefore, future studies should consider other candidate albeit rarer SNPs for influencing the risk of developing opioid dependence.
