July 1987

Twin Concordance for DSM-III SchizophreniaScrutinizing the Validity of the Definition

Author Affiliations

From the Institute of Psychiatry, London (Dr Farmer); the University of Wales, College of Medicine, Cardiff (Dr McGuffin); and the Departments of Psychology and Pediatrics, University of Virginia, Charlottesville (Dr Gottesman).

Arch Gen Psychiatry. 1987;44(7):634-641. doi:10.1001/archpsyc.1987.01800190054009

DSM-III diagnoses were applied to 26 monozygotic (MZ) and 34 dizygotic (DZ) probands and their co-twins from the Maudsley Hospital (1948 to 1965) schizophrenic series of Gottesman and Shields. DSM-III criteria for schizophrenia were found to be highly reliable and valid, and to have a broad heritability of 0.85, which is comparable with the Research Diagnostic Criteria and Feighner criteria from which they were derived. When the full range of DSM-III diagnoses were considered, both affective disorder and schizophrenia were found in genetically identical individuals. The effect of DSM-III nosology on the twin series was also explored by adding other diagnoses to that of schizophrenia and observing the effect on the MZ/DZ concordance ratio. The addition of affective disorder with mood-incongruent delusions to the schizophrenia spectrum produced the largest increase in the ratio and, by implication, a "more genetic" combination than schizophrenia alone. The maximum MZ/DZ concordance ratio (7.68) was produced by schizophrenia, plus affective disorder with moodincongruent delusions, plus schizotypal personality disorder, plus atypical psychosis. The effect of adding paranoid disorder (paranoia) and all other affective categories was a reduction in the ratio.