These results support our expectation that multiple definitive association findings will be detected for many psychiatric disorders, often requiring large samples. We therefore organized the Psychiatric GWAS Consortium which includes almost all known GWAS studies to date for SCZ, BD, MDD, ADHD and AUT, contributed by 110 investigators at 54 institutions around the world (Table 6). The PGC has three specific aims: Within-disorder meta-analyses of all available GWAS data. These diagnoses are based on definitions that produced maximum heritability estimates in genetic-epidemiological studies. Thus, disorder-specific analyses represent our strongest hypotheses.Cross-disorder analyses, including analyses of combinations of disorders and of phenotypes observed in two or more disorders (such as depression or psychosis), based on the recommendations of an expert committee. Because data are insufficient to determine what common, cross-disorder etiologic factors might exist, alternative phenotypes should be explored. GWAS have produced surprising cross-disorder associations such as those for cancers (54)and for inflammatory bowel diseases (72), which could also exist for psychiatric disorders given the many common symptoms.Analyses of comorbidities such as alcohol,nicotine and illicit drug use disorders, which can be studied across multiple case groups.
