In summary, we report SNP-based heritabilities that are significantly greater than zero for all five disorders studied. We have used the largest psychiatric GWAS data sets currently available, and our results provide key pointers for future studies. Our results demonstrate that the dearth of significant associations from psychiatric GWAS so far, particularly for major depressive disorder, ASD and ADHD, reflects lack of power to detect common associated variants of small effect rather than the absence of such variants. Hence, as sample sizes increase, the success afforded to other complex genetic diseases50 in increasing the understanding of their etiologies is achievable for psychiatric disorders, as is already being shown for schizophrenia60. We also provide evidence of substantial sharing of the genetic risk variants tagged by SNPs between schizophrenia and bipolar disorder, bipolar disorder and major depressive disorder, schizophrenia and major depressive disorder, ADHD and major depressive disorder, and, to a lesser extent, between schizophrenia and ASD. Our results will likely contribute to the efforts now under way to base psychiatric nosology on a firmer empirical footing. Furthermore, they will encourage investigations into shared pathophysiologies across disorders, including potential clarification of common therapeutic mechanisms.
