Application of epidemiological research toward a model for the etiology of schizophrenia.

Epidemiological surveys based on transnationally standardized assessment procedures have shown a relatively uniform worldwide incidence rate for a restrictively defined schizophrenia syndrome. The age-corrected morbid risk appears to remain unchanged over longer periods of time and to be equal for both sexes--apart from the higher age of onset in females. For explaining these findings a continuous model is proposed, similar to that used for modelling neurobiological and genetical assumptions. The nuclear syndrome of the schizophrenic psychosis is understood to be the lower end of a morbidity dimension extending through broadly defined schizophrenic syndromes, spectrum disorder and patterns of unspecific disturbances to lack of symptoms. It may be assumed that a genetically determined vulnerability is underlying this morbidity dimension and that high values of vulnerability entail a specific psychopathology, the schizophrenic psychosis. It appears that at lower values of vulnerability the specificity decreases, and that with increasing influence of personality and environmental factors the variety of manifesting psychiatric disorders increases.