[Schizophrenia: on the genetic trail]

Data from genetic epidemiology studies demonstrate the existence of hereditary factors in the genesis of schizophrenia. Most authors now think that a multigenic multifactorial model will explain the transmission of this disease. Several genes may be involved, either additively (their effects added together, each gene having its own contribution), or epistatically (expression of one gene effective only if another gene is also expressed). Other risk factors - environmental, biological, and neurodevelopmental - may also play a role. There is likely to be a threshold effect above which the sum total of these factors makes the disease clinically detectable. New study strategies have therefore sought to characterize candidate regions or genes based on various biochemical or neurodevelopmental hypotheses. This research collides, however, with the heterogeneity of symptoms as well as the diversity of the disease development. Other avenues of research therefore look towards the study of endophenotypes or 'markers of vulnerability' and towards the identification of genetically homogeneous subgroups of patients and families, among whom susceptibility genes may be detected. Current genetic studies agree about the complexity of the transmission of this disease with its heterogeneous polygenic characteristics.