The point of the third aim is specific to psychiatry. Throughout the history of psychiatry, diagnoses have been made based on signs and symptoms accrued in conversations between physician and patient. Although test-retest reliability is generally acceptable, these are fundamentally descriptive syndromes and their validity is unknown. Moreover, there is considerable overlap between disorders. For example, people with autism often have ADHD. Cases with schizophrenia frequently have symptoms highly similar to those with BIP and major depressive disorder. Indeed, major depressive disorder and BIP are alike in that both include major depressive episodes whereas BIP additionally has manic episodes. Given that clinically-derived definitions of illness may not have “carved nature at the joint” with respect to the fundamental genetic architecture (Kendell and Brockington 1980; Kendell 1989), This aim attempts to identify convincing genetic associations that are common to two or more of ADHD, autism, bipolar disorder, major depressive disorder, and schizophrenia. This work could provide critical insight into how these disorders are similar and different.
