Second, as we begin to identify the sets of genetic variants contributing to the polygenic architecture of complex behavioral outcomes—efforts that are currently being led through large GWAS collaborations such as the Psychiatric Genomics Consortium— the next step will be to characterize their underlying biology. Gene-network analyses, which permit examination of whether variants included in polygenic scores are located in functionally related genes (Wang et al., 2011) will be critical to these efforts. Relatedly, there are exciting cross-disciplinary opportunities to identify whether the genetic variants that contribute to polygenic scores are located in regulatory regions of the genome (i.e., regions that include enhancers, promoters, insulators, and silencers) using data from the ENCODE project (ENCODE Project Consortium, 2004). Initial findings from the ENCODE project indicate that many of the top variants that have emerged from GWAS of complex diseases (e.g., multiple sclerosis and ulcerative colitis) are located in potential regulatory DNA regions (ENCODE Project Consortium, 2012). Whether this is the case for common psychiatric disorders, such as the externalizing disorders examined here, remains to be seen. Moving beyond gene identification to
