Pathways to schizophrenia: the impact of environmental factors.

Schizophrenia is an aetiologically complex disorder arising from the interaction of a range of factors acting at various stages of life. Schizophrenic individuals inherit genes that cause structural brain deviations which may be compounded by early environmental insults. As a result some pre-schizophrenic children exhibit subtle developmental delays, cognitive problems, or poor interpersonal relationships. They are susceptible to dysregulation of dopamine, the final pathway leading to the onset of a psychotic illness. Dopamine dysregulation may arise through a process of sensitization, which, in animals, can be caused by repeated administration of dopamine-releasing drugs. It is clear that the same process occurs in humans, and that some individuals are particularly sensitive to the effects of such drugs for either genetic reasons or through early environmental damage. Stress has also been shown to induce dopamine release in animal studies, and epidemiological studies have demonstrated that social stresses can precipitate schizophrenia. Thus, stresses, such as drug use and social adversity, in adolescence or early adult life may propel the neurodevelopmentally impaired individual over a threshold into frank psychosis.