Logistic regression analyses in which sex and age were considered and population stratification analyses confirmed these findings. Additionally, specific haplotypes increased risk for CD in AAs and OD in EAs. In summary, as might be expected given that the brain’s opioidergic system plays a central role in reinforcement, which has important implications for addiction,36 variation Inhibitors,research,lifescience,medical in a number of functional candidate genes encoding opioidergic

proteins have been implicated in dependence on alcohol, cocaine, and opioids. Assuming independent replication of these findings, a key question to be addressed is the nature of gene-gene and gene by environment interactions to which risk of SD is attributable. Other studies have demonstrated associations with Inhibitors,research,lifescience,medical the cannabinoid receptor gene (CNR1),37-39 neurexin 1 (NRXN1),40 and a set of alcohol-metabolizing enzymes.41

A clear pattern emerges from the examination of this sampling of candidate gene associations with SD: insofar as genes with known function are concerned, there are no big surprises with respect to physiology. (This can not be said about genes without clearly delineated functional roles, such as ANKK1, Inhibitors,research,lifescience,medical which was identified, not incidentally, based on its position, rather than its function.) This highlights the limitations of the candidate gene approach, which is often inherently biased by prior knowledge about physiology. Unbiased studies have greater potential to reveal new mechanisms of addiction, and that is a key Inhibitors,research,lifescience,medical attraction of the genome -wide association study (GWAS) methodology discussed below. GWASs are an alternative to linkage

for locating genes anywhere in the genome without prior hypotheses. GWAS designs are of interest due to their potential to identify risk loci of relatively small effect, Inhibitors,research,lifescience,medical much smaller than through linkage strategies. (In fact, one controversy engendered by the widespread adoption of GWAS designs is that often risk alleles are identified that have such a small effect – typically with odds ratios less than 1.2 – that it is hard to know what to do with them once to they have been identified.) A second advantage of GWASs is that they may be based on case-control samples, which are easier to recruit than family sampling schemes, which must be deployed to prepare for linkage. Family samples are more difficult to recruit (markedly so for many kinds of SD because of the tendency of these disorders to fragment families) and can introduce certain kinds of bias. The first GWAS for a specific SD trait, excluding studies that used a pooling methodology 5-Fluoracil mouse exclusively (see ref 42), examined ND.43 This study employed a two-stage design; first pooled DNA was used to screen 2.4 million SNPs; second, >30 000 SNPs selected from the first stage were screened individually in ~1000 each cases and controls.