Adoption studies of schizophrenia

The observation that schizophrenia is more commonly observed among the relatives of individuals with schizophrenia than in the general population does not indicate the mechanism that produces such familiality occurs. Adoption designs permit evaluation of the role of genetic factors in schizophrenia independently of the influence of family environments. Results from studies of adoptees with schizophrenia and their biological and adoptive relatives indicate that genetic factors play a highly significant role in the risk for schizophrenia. This genetically mediated risk to relatives includes an increased prevalence of both schizophrenia and a nonpsychotic syndrome analogous to schizophrenia, but does not represent a general liability to other forms of psychopathology. Although adoption studies have convincingly demonstrated an important role for genetic factors in schizophrenia, the necessity and specificity of such factors, their precise identity, and their interaction with environmental influences remain unknown.