MENTAL-ILLNESS IN THE BIOLOGICAL AND ADOPTIVE RELATIVES OF SCHIZOPHRENIC ADOPTEES - REPLICATION OF THE COPENHAGEN STUDY IN THE REST OF DENMARK

Background: Our previous investigation of the prevalence of mental ill ness among the biological and adoptive relatives of schizophrenic adop tees in Copenhagen, Denmark, showed a significant concentration of chr onic schizophrenia (5.6%) and what Bleuler called ''latent schizophren ia'' (14.8%) in the biological relatives of chronic schizophrenic adop tees, indicating the operation of heritable factors in the liability f or schizophrenic illness. Methods: We now report the results of a repl ication of that study in the rest of Denmark (the ''Provincial Sample' '). Results: In this sample, the corresponding prevalences were 4.7% a nd 8.2%. In the combined ''National Sample'' of adoptees with chronic schizophrenia, that disorder was found exclusively in their biological relatives and its prevalence overall was 10 times greater than that i n the biological relatives of controls. Conclusions: This study and it s confirmation of previous results in the Copenhagen Study speak for a syndrome that can be reliably recognized in which genetic factors pla y a significant etiologic role. These findings provide important and n ecessary support for the assumption often made in family studies: obse rved familial clustering in schizophrenia is an expression of shared g enetic factors.