The exact causes of psychotic disorders like schizophrenia and bipolar disorder are not fully known. Most scientists agree that these disorders do not have a single cause, but develop over time as a result of interplay between biological factors (such as inheriting certain genes) and the kind of environment and stressors to which a person is exposed. The risk for psychotic disorders is about 1-3% in the general population, depending upon which problems are being included in population estimates.
Many studies over the past 40 years have shown that the risk for psychotic disorders such as schizophrenia and bipolar disorder is higher in people who are related to individuals with these disorders. For example, if a person has one parent or one (non-twin) sibling with schizophrenia, their risk increases to about 8-14%; if they have two parents or a twin with schizophrenia, the risk increases to about 40-50%. This means that schizophrenia and bipolar disorder can run in families, although more than half of people with these problems do not have an affected relative. We know this to be true for many common medical problems, too, such as high cholesterol, heart and vascular disease, and some cancers. However, just like in medical disorders, genetic risk does not tell the whole story-genes by themselves do not make the onset of problems or disorders inevitable. In fact, the majority of people who have a risk factor, such as genetic risk, do not get the illness. Environmental factors in childhood and adolescence can either add to the vulnerability a person carries in their genes, and thereby increase the risk of developing a psychiatric disorder, or lessen the expression of genetic or neurodevelopmental factors, and decrease the overall risk of developing schizophrenia and related disorders. For these reasons, this study is designed to understand more about the development of adolescents and young adults at some amount of genetic risk for these kinds of problems and disorders.
A second important focus of this study is to understand better the similarities and differences in the development of people at risk for schizophrenia or mood disorders with psychosis. For most of the past century, it has remained unclear as to whether or not the major categories of psychosis, schizophrenia and bipolar disorder for example, are distinct diseases with specific genetic causes, brain correlates, and cognitive profiles. This study is also intended to identify and describe the differences and similarities in cognitive and social functioning and brain structure and function of people at genetic risk for these disorders.