Risk factors for schizophrenia.

Over the last decade, much progress has been made towards identifying risk factors for schizophrenia. It is now thought that many genes of small effect contribute towards risk of developing schizophrenia and some of these probably confer susceptibility to environmental factors. Large population-based studies, using record linkage, have investigated environmental risk factors and found that urbanization is an important factor. Other population-based studies have followed up birth cohorts and found evidence for abnormal neurodevelopment in those who subsequently developed schizophrenia. Meta-analyses have clarified the role of obstetric and perinatal complications especially hypoxia. Low IQ has emerged as a risk factor and suggests that cognitive factors are important in the etiology of psychosis. Social risk factors are now being investigated with some evidence that discrimination and isolation are significant. The role of recreational drug use is still unclear. Finally, evidence suggests that there is a continuum of psychosis both within the disorders that present clinically, but also in the general population.