A possible alternative interpretation of our findings is suggested by a report (Zeller et al. 2010) that conducted genomewide expression analyses using RNA extracted from peripheral blood monocytes of a community-based German sample in which a genomewide association study (GWAS) had been completed. Among a total of 2745 expression quantitative trait loci (eqtl’s) that had p values less than 5.78 × 10−12, rs2236855 was found to be a cis-eqtl for two genes (p values shown): PHACTR4 (7.57 × 10−27) and ATPIF1 (2.85 × 10−12). Both are expressed in the brain and located in proximity (~300–600 kb) to OPRD1 on chromosome 1. PHACTR4 is thought to be a protein phosphatase-1 (PP-1) inhibitor (Allen PB et al. 2004). cAMP-regulated phosphoprotein (DARPP-32), mediates the action of multiple drugs of abuse (including opioids) by regulating striatal dopaminergic transmission via its actions as a inhibitor of PP-1 and protein kinase A (Svenningsson, Nairn, & Greengard 2005). DARPP-32 has been implicated in maintenance of morphine-induced CPP (Narita et al. 2010) and suggested as a putative therapeutic target for opiate addiction (Mahajan et al. 2009). ATPIF1, a
