Comments on risk for schizophrenia.

Recent developments have significantly furthered understanding of genetic and environmental factors affecting risk for schizophrenia. Environmental effects, such as immigration, living in a city, and substance abuse have been found to be associated with later schizophrenia. Although the highest risk for schizophrenia is still having a monozygotic twin with schizophrenia (50%), the candidate genes claimed to be associated to date only yield a very small excess risk and all of these effects (environmental and genetics) increase the risk for schizophrenia by only 2-3 fold. Thus, given the low prevalence of the disorder in the general population (0.5-1%), they are not practical in predicting future illness. One possible strategy to make the currently known risk factors for schizophrenia more useful clinically is based on findings indicating that many of the genetic and environmental risks cited above are not specific for schizophrenia, but increase risk for psychopathology in general. As up to 50% of the general population will be affected during their lifetime by a condition defined in DSM IV as psychopathology, due to this much higher base rate, factors increasing risk by 2-3 fold might become clinically relevant.