Genetic transmission of schizophrenia.

There is convincing evidence form consanguinity, twin, and especially adoption studies that schizophrenia has a genetic component. There is also evidence from studies of MZ twins for an environmental component. It is not known whether the relevant environmental factors are prenatal or postnatal, psychosocial or physical; the presence of schizophrenia in the rearing family does not seem to be etiologically significant. It is likely that schizophrenia, especially if defined by symptoms alone, is etiologically heterogeneous. Study of pedigrees with several affected individuals is a useful approach to resolving this heterogeneity. The relevant genes may not code directly for schizophrenia, but for risk factors that predispose to the illness under particular environmental conditions. Careful methodology is needed to distinguish cause from effect of studying psychosocial factors. Genetic counseling is possible on the basis of empirical risk figures, but clarification of biological risk factors and environmental preciptants will make possible a much more rational approach to counseling and prevention.