Despite the known functional links between glutamate and dopamine, no association study has previously examined the interaction of glutamatergic and dopaminergic variants in addiction populations. Individual SNPs related to dopamine transmission have been most frequently investigated given the critical role of dopamine in reward-related behaviors and that Reward Deficiency Syndrome is characteristic of various addiction disorders.34–36 DRD1 variants have been associated with heroin, alcohol and nicotine abuse,23–25 and our results confirm this association. Of the other dopaminergic receptors, most attention to date has focused on the dopamine D2 receptor (DRD2), which is central to reward and emotional processing, and some studies have reported an association between genetic variants of DRD2 with heroin dependence or craving.37–39 The dopamine D4 receptor has also been positively associated with heroin abuse,40–43 but studies of dopamine D3 or dopamine D5 receptor have been less fruitful.44–46 Of the two studies that have assessed HOMER1 and addiction disorders, one reported significant association with HOMER1 and cocaine dependence,27 while the other failed to find any association with alcoholism.28 To date, no investigation has examined HOMER1 and heroin dependence
