Adoption studies of schizophrenia

The observation that schizophrenia is more commonly observed among the rela tives 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 f or schizophrenia. This genetically mediated risk to relatives includes an i ncreased prevalence of both schizophrenia and a nonpsychotic syndrome analo gous to schizophrenia, but does not represent a general liability to other forms of psychopathology. Although adoption studies have convincingly demon strated an important role for genetic factors in schizophrenia, the necessi ty and specificity of such factors, their precise identity, and their inter action with environmental influences remain unknown. (C) 2000 Wiley-Liss, I nc.