GRM3 and major depressive disorder: The significant associations of GRM3 polymorphisms with prefrontal activity (measured by N-acetylaspartate/creatine levels) [44], cognitive set shifting [45], memory capability in healthy volunteers [46] and the risk of schizophrenia and depression in some studies [8], [10] promoted us to further evaluate the role of GRM3 polymorphisms in heroin dependence (HD).