Association and Function of Opioid Receptor Gene Variants to Substance Dependence

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DESCRIPTION (provided by applicant): This K99/ROO application seeks support for additional research training which will enable the applicant to become an independent investigator in neuropsychiatric genetics. The training goal will be achieved through a project aimed to identify substance (drug and/or alcohol) dependence (SD)-associated variants in three opioid receptor genes (OPRM1, OPRD1 and OPRK1) and interpret the mechanism of the association. In the mentored phase (year 2007-2009), I will use population- and family-based approaches to study the possible association between opioid receptor gene (OPR) variants and SD in both European Americans (EAs) and African Americans (AAs). Tightly-spaced single nucleotide polymorphisms (SNPs) spanning OPRs will be genotyped and the association between OPR variants and SD will be analyzed by appropriate statistical programs including structured association analysis. Moreover, gene regions of interest will be screened for new variants, which will be further analyzed for their association with SD. In the independent phase (year 2009-2012), I will focus on functional study of those OPR variants which are found to be associated with SD. For coding region variants, functional study will be conducted by receptor binding assay (to see if OPR variants alter receptor affinity) and Western Blotting (to see if OPR variants modulate receptor protein levels). For non-coding region variants, functional study will be performed by four different approaches: (1) real-time quantitative PCR, which examines whether OPR variants result in increased or decreased gene expression (or mRNA) levels; (2) allelic expression imbalance (AEI) assay, which is an alternative approach to examine whether the two alleles of a variant lead to different expression (or mRNA) levels; (3) Electrophoretic mobility shift assay (EMSA), which examines whether OPR variants are located in transcription factor (TF) binding sites and if they change the binding of a TF to its DNA sequence; (4) luciferase reporter gene assay, which examines whether OPR variants regulate gene expression. These four approaches are complementary. The proposed study will improve our understanding about the influence of OPR variants on SD in EAs and AAs. This work will lay the groundwork for a future R01 project aimed to establish a genetic model for prediction of SD with a set of OPR markers, and to investigate the contribution of OPR variants to the outcome of drug or alcohol dependence treatment or to the racial difference in outcomes of treatment. The applicant is mentored by Dr. Joel Gelernter (primary) and Dr. Jeffrey Gruen (co-mentor), who are both excellent supervisors with substantial experience in genetic studies of complex disorders and who have both mentored numerous previous trainees.