ABSTRACT
BACKGROUND: Previous research showed significantly elevated levels of thought disorder in the relatives of persons with schizophrenia, as well as in the persons with schizophrenia themselves. Comparisons of schizophrenic and control adoptees and their respective relatives provide a method for minimizing the confounding of genetic and environmental sources of familial resemblance and for elucidating whether the elevated levels of thought disorder in persons with schizophrenia and their relatives reflect the influence of shared genetic factors, shared environmental factors, or both. The present study provides the first such adoption-sample data on an operationally defined measure of thought disorder. METHODS: Speech samples elicited by standard interview questions from schizophrenic and control adoptees and their respective biological and adoptive relatives were tape-recorded. Verbatim transcripts of these speech samples were scored, while unaware of the personal or family diagnoses of the subjects, using the Thought Disorder Index (TDI). RESULTS: The mean TDI scores were significantly higher in schizophrenic than in control adoptees and in biological relatives of the schizophrenic adoptees than in the biological relatives of the control adoptees, whereas the respective groups of adoptive relatives did not differ significantly. The differences were most marked for the samples of biological sibs and half sibs, which were larger and more representative than the samples of parents. CONCLUSION: Results suggest that the elevated TDI scores in the relatives of persons with schizophrenia that have been found in other studies reflect the operation of genes increasing the liability for schizophrenia, rather than the rearing experiences that were shared in common with schizophrenic probands.
Subject(s)
Adoption , Family , Schizophrenia/genetics , Schizophrenic Psychology , Adolescent , Adult , Cognition Disorders/diagnosis , Cognition Disorders/epidemiology , Cognition Disorders/genetics , Data Interpretation, Statistical , Female , Genetic Predisposition to Disease , Humans , Male , Psychiatric Status Rating Scales/statistics & numerical data , Schizophrenia/diagnosis , Schizophrenia/epidemiologyABSTRACT
Speech samples were collected on 20 Danish schizophrenic adoptees, along with 26 control adoptees and their respective biological and adoptive relatives. Typewritten transcripts of these speech samples were scored using the Gottschalk-Gleser Social Alienation-Personal Disorganization (SA-PD), or "Schizophrenic', content analysis scale. Both mean scale scores and the proportion of subjects with extremely high (i.e. deviant) scores were significantly higher in schizophrenic adoptees than in either (a) subjects with no psychiatric disorder or (b) the sample with psychiatric disorders other than schizophrenia. The proportion of deviant scores was also notably high among subjects who, though not schizophrenic, had schizotypal features on the SADS-L interview. Scores were particularly high in schizophrenic adoptees who had a biological parent or sibling with schizophrenia or schizotypal features. By contrast, scores of 29 adoptive relatives of the schizophrenic probands were quite low. The present study appears to corroborate the results of previous studies done in the U.S.A. and Great Britain which suggest that high scores on the SA-PD scale tend to characterize those schizophrenics for whom genetic liability appears to be strongest.
