genome, accounting for 7% of the variance in disorder liability (Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014). A similar story has been found for other complex, highly heritable traits such as height, where no significant variant associations were detected with 5,000 genomes, but an analysis of 250,000 individuals was able to identify over 400 significant loci and account for up to 29% of the trait variance (Wood et al., 2014). Parallel analyses for multiple disorders indicate there is a “breakthrough point” of sample size after which discovery rates increase exponentially, although this threshold differs across phenotypes (O’Donovan, 2015). Disorders with lower heritability, stronger environmental contributions, and/or greater heterogeneity require larger samples sizes for gene identification. For example, for major depression, a disorder with a heritability of ~35% (Kendler et al., 2003) a recent meta-analysis found one genome-wide significant association in a sample of 70,000 participants (Direk et al., 2016). Other substance use and psychiatric conditions with modest heritability and as-of-yet smaller sample sizes, such as Post-Traumatic Stress Disorder and Alcohol Dependence, have not yet attained the success achieved for Schizophrenia. However, efforts are underway to increase the number of available cases for analysis, with the expectation that once
