We formed the Psychiatric Genomics Consortium (PGC) in 2007, to undertake meta-analyses of genomewide association studies (GWAS) for psychiatric disorders and, so far, the consortium has incorporated GWAS data from more than 19 countries for schizophrenia, bipolar disorder, major depressive disorder, attention deficit-hyperactivity disorder, and autism spectrum disorders. Previous research has suggested varying degrees of overlap in familial and genetic liability for pairs of these disorders. For example, some findings3,4 from family and twin studies support diagnostic boundaries between schizophrenia and bipolar disorder and bipolar disorder and major depressive disorder, but also suggest correlations in familial and genetic liabilities.3,5 Several molecular variants confer risk of both schizophrenia and bipolar disorder.6–8 Autism was once known as childhood schizophrenia and the two disorders were not clearly differentiated until the 1970s. Findings from the past few years have emphasised phenotypic and genetic overlap between autism spec trum disorders and schizophrenia,9,10 including identification of copy number variants conferring risk of both.11 Findings from family, twin, and molecular studies12–15 suggest some genetic overlap between autism spectrum disorder and attention deficit-hyperactivity disorder.
