Independent diagnoses of adoptees and relatives as defined by DSM-III in the provincial and national samples of the Danish Adoption Study of Schizophrenia

Abstract

Background: This report describes the independent application of DSM-III criteria to the adoptees and relatives in the Provincial sample of the Danish Adoption Study of Schizophrenia of Kety and colleagues. We report these results and combine them with those reported previously for the Copenhagen sample to form the National sample.

Methods: Personal interviews and institutional record summaries of adoptees and biological and adoptive relatives were "blindly" diagnosed using DSM-III criteria. "Schizophrenia spectrum" was a priori defined as schizophrenia; schizoaffective disorder, mainly schizophrenic subtype; and schizotypal and paranoid personality disorders.

Results and conclusion: In the Provincial sample, the prevalence of "spectrum" disorders was significantly greater in biological relatives of schizophrenia spectrum vs control adoptees. The results were also consistent with the genetic transmission of individual diagnoses within the spectrum. When combined into the National sample, the results provided strong evidence for (1) the genetic transmission of DSM-III schizophrenia; (2) a genetic relationship between DSM-III schizophrenia, mainly schizophrenic schizoaffective disorder, and schizotypal personality disorder; and (3) the absence of a significant genetic relationship between the schizophrenia spectrum and either psychotic nonspectrum disorders, major depression, or anxiety disorders. We found no evidence for the familial environment transmission of schizophrenia spectrum disorders. These results are consistent with the findings reported by Kety and coworkers from their diagnostic review.