The epidemiology of the genetic liability for schizophrenia.
OBJECTIVE
The low incidence of schizophrenia prohibits large scale prevention trials, and the question arises whether such studies become more feasible by taking into account genetic factors. The aim of the paper was to inform preventive endeavours with an account of the genetic background to schizophrenia.


METHODS
The family, twin and adoptive studies of schizophrenia are reviewed and recent molecular genetic data presented.


RESULTS
Children of a parent diagnosed with schizophrenia have a ten-fold increased risk of developing the disorder. Twin and adoption studies strongly suggest the risk increase is mainly due to genetic factors. On an individual level, a positive family history is the strongest known risk factor for schizophrenia. For a prevention study, very large numbers of families have to be screened in order to reach a sufficient sample size.


CONCLUSIONS
One obvious way to increase the accuracy of predicting who is at high risk of developing schizophrenia would be to find specific mutations in the human genome. Attempts to isolate specific genes by means of linkage and association studies have been unsuccessful so far and, given the number of genes involved, it is extremely unlikely that the predictive value of individual genes will be high enough to warrant intervention. Genetic studies also suggest the genetic liability extends beyond the traditional clinical phenotypes. Prevention trials might become possible by adopting a broader approach.
Hallmayer
J
J
University of Western Australia/Graylands Hospital Centre for Clinical Research in Neuropsychiatry, Perth, Australia. joachim.hallmayer@health.wa.gov.au
D000300:Adoption; D008040:Genetic Linkage / Q000235:genetics; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D006801:Humans; D012559:Schizophrenia / Q000453:epidemiology / Q000235:genetics* / Q000517:prevention & control; D012565:Schizophrenic Psychology; D012931:Social Environment; D018433:Twin Studies as Topic