The goal in this study was to identify gene variations which contribute to vulnerability to develop heroin addiction in African Americans. The most significant results that remained close to significance after correction for multiple testing were obtained for the GRIN2A haplotype. Glutamatergic neurotransmission is the major excitatory system in human brain, and genes encoding glutamate receptors are candidate genes for neuropsychiatric disorders. The action of glutamate is mediated by a few receptor families including the NMDA receptor family that is involved in multiple cognitive processes including memory and learning (Paoletti & Neyton, 2007). NMDA receptor Ca2+ permeable channels are heteromers composed of subunit GRIN1 and one or more of the 4 subunits: GRIN2A-D. Expression of the GRIN2A subunit begins around puberty, and a reduced GRIN2A expression was suggested as a risk factor for schizophrenia (Watanabe et al., 1993). Repeated 3,4 methylenedioxymethamphetamine (Ecstasy) administration in rats induces neuroadaptive changes in expressions of glutamatergic NMDA subunits, in regions of the brain regulating reward-related associative learning, cognition, and memory (Kindlundh-Hogberg et al., 2008). Grin2a (Nr2a) knockout mice exhibit retarded discrimination learning (Brigman et
