Early and late environmental risk factors for schizophrenia.

Although a high proportion of liability to schizophrenia is under genetic control, a number of environmental risk factors have been identified. The earliest of these are complications of pregnancy and birth, though whether these cause or reflect disturbed brain development is not absolutely clear. Neurodevelopmental deviance is also indicated by neurological dysfunction, social, behavioural and cognitive deficits during childhood. Immigrant status is a significant risk factor, especially prominent among the African Caribbean population in England, though the mechanism is unknown. Later environmental risk factors include adverse life events and substance abuse. An additive model of multiple genetic and environmental risk factors of small effect may be too simplistic and an interactive model where genetic predisposition is compounded by environmental effects is more in keeping with current evidence. The nature of such interactions can be explored more fully when susceptibility genes for schizophrenia are identified.