Shared Risks Between Schizophrenia and Bipolar Disorder
In a large GWAS by the ISC that included 3,322 European schizophrenia cases and 3,587 controls,16 we analyzed more than 1 million SNPs. This 2009 Nature report implicated a major histocompatibility complex on chromosome 6p. We also estimated that common polygenic variations of small individual effects could represent at least one-third of the total variation in schizophrenia risk. These findings were replicated in concurrently published reports by other investigators.17,18
The Psychiatric Genomics Collaboration (PGC): Need for Larger Sample Sizes
The ISC analyses, although replicating some finds and identifying new risk variants, is underpowered to identify all disease-associated loci. Much larger sample sizes are necessary. In recognition of this fact, more extensive collaborative networks have been developed. The PGC is an international consortium formed in 2007 that contains samples from more than 170,000 individuals worldwide with diseases such as schizophrenia, bipolar disorder, autism, obsessive compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and major depressive disorder. The Genomic Psychiatry Cohort, described next, is an essential contributor to the PGC federation.