Targeted re-sequencing of genes previously found to have common variants associated with complex diseases, or of functionally related genes, may be another method by which new sources of variation can be discovered. For example, four rare genetic variants (each with ~1% allele frequency) were found through re-sequencing that together accounted for a greater proportion of the variance in the risk of type I diabetes than a single common variant located in the same gene as detected by GWA studies (30). In addition, while SNPs represent alterations at single nucleotides which may only reduce function to a modest extent, other large types of structural changes to genetic architecture, such as copy number variations (CNVs), may have larger effects on gene function and thus have a greater phenotypic impact. The 1000 Genomes Project (http://www.1000genomes.org), an international consortium with the goal of creating a complete detailed catalogue of all genetic variation (including rare SNPs, CNVs and insertions/deletions) in at least 1000 genomes from across the world, will serve as a useful reference for future studies of addictive disorders. It is notable that although
