Background

Personalized treatment for psychopathologies, in particular alcoholism, is highly dependent upon our ability to identify patterns of genetic and environmental effects that influence a person's risk. Unfortunately, array-based whole genome investigations into heritable factors that explain why one person becomes dependent upon alcohol and another does not, have indicated that alcohol's genetic architecture is highly complex. That said, uncovering and interpreting the missing heritability in alcohol genetics research has become all the more important, especially since the problem may extend to our inability to model the cumulative and combinatorial relationships between common and rare genetic variants. As numerous studies begin to illustrate the dependency of alcohol pharmacotherapies on an individual's genotype, the field is further challenged to identify new ways to transcend agnostic genomewide association approaches. We discuss insights from genetic studies of alcohol related diseases, as well as issues surrounding alcohol's genetic complexity and etiological heterogeneity. Finally, we describe the need for innovative systems-based approaches (systems genetics) that can provide additional statistical power that can enhance future gene-finding strategies and help to identify heretofore-unrealized mechanisms that may provide new targets for prevention/treatments efforts. Emerging evidence from early studies suggest that systems genetics has the potential to organize our neurological, pharmacological, and genetic understanding of alcohol dependence into a biologically plausible framework that represents how perturbations across evolutionarily robust biological systems determine susceptibility to alcohol dependence.

Smokers (≥10 cigarettes per day, N=331) of European ancestry taking part in a double-blind placebo-controlled randomized trial of 12 weeks of treatment with bupropion along with counseling for smoking cessation were genotyped for a variable number of tandem repeats polymorphism in exon III of the dopamine D4 receptor gene. Generalized estimating equations predicting point-prevalence abstinence at end of treatment and 2, 6 and 12 months after the end of treatment indicated that bupropion (vs placebo) predicted increased odds of abstinence. The main effect of Genotype was not significant. A Genotype × Treatment interaction (P=0.005) showed that bupropion predicted increased odds of abstinence in long-allele carriers (odds ratios (OR)=1.31, P<0.0001), whereas bupropion was not associated with abstinence among short-allele homozygotes (OR=1.06, P=0.23). The Genotype × Treatment interaction remained when controlling for demographic and clinical covariates (P=0.01) and in analyses predicting continuous abstinence (P's≤0.054). Bupropion may be more efficacious for smokers who carry the long allele, which is relevant to personalized pharmacogenetic treatment approaches.