Modern efforts to identify the genetic risk factors for complex psychiatric and drug abuse disorders have focused mostly on genomic regions (in linkage analysis) or individual sequence variants (or associated haplotypes) in or near specific genes (in candidate gene association studies). A few studies 1–5 have examined epistatic models of disease etiology; these studies have, typically examined only two markers, loci or linked regions at a time. Recently genome-wide association studies (GWAS) for psychiatric disorders have appeared 6–9.
