. Schizophrenia is a devastating psychiatric disorder with a median lifetime prevalence of 4.0 per 1,000 and a morbid risk of 7.2 per 1,000 2. The age at onset is typically in adolescence or early adulthood 3, with onset after the fifth decade of life and in childhood both being rare 4,5. Although the prevalence for males and females is similar 2, the course of schizophrenia is often more severe and with earlier onset for males 3,6. The standardized mortality ratio (SMR; ratio of observed deaths to expected deaths) for all-cause mortality is 2.6 for patients with schizophrenia compared to the general population 2, with excess deaths mainly from suicide during the early phase of the disorder, and later from cardiovascular complications.
Schizophrenia commonly has a chronic course albeit with fluctuating patterns, and cognitive disability. Its hallmark is psychosis, mainly characterized by positive symptoms such as hallucinations and delusions that are frequently accompanied by negative (deficit) symptoms such as reduced emotions, speech, and interest, and by disorganization symptoms such as disrupted syntax and behavior. Severe mood symptoms, up to and including manic and major depressive episodes, are present in many cases. There are no diagnostic laboratory tests for schizophrenia; instead, the diagnosis relies on clinical observation and self-report. It is then remarkable that ongoing epidemiological study over the last century using the clinical phenotype, but with variable ascertainment and assessment rules, has consistently shown the importance of genetic factors in schizophrenia.