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A twin study of schizoaffective‐mania, schizoaffective‐depression, and other psychotic syndromes

The nosological status of schizoaffective disorders remains controversial. Twin studies are potentially valuable for investigating relationships between schizoaffective‐mania, schizoaffective‐depression, and other psychotic syndromes, but no such study has yet been reported. We ascertained 224 probandwise twin pairs [106 monozygotic (MZ), 118 same‐sex dizygotic (DZ)], where probands had psychotic or manic symptoms, from the Maudsley Twin Register in London (1948–1993). We investigated Research Diagnostic Criteria schizoaffective‐mania, schizoaffective‐depression, schizophrenia, mania and depressive psychosis primarily using a non‐hierarchical classification, and additionally using hierarchical and data‐derived classifications, and a classification featuring broad schizophrenic and manic syndromes without separate schizoaffective syndromes. We investigated inter‐rater reliability and co‐occurrence of syndromes within twin probands and twin pairs. The schizoaffective syndromes showed only moderate inter‐rater reliability. There was general significant co‐occurrence between syndromes within twin probands and MZ pairs, and a trend for schizoaffective‐mania and mania to have the greatest co‐occurrence. Schizoaffective syndromes in MZ probands were associated with relatively high risk of a psychotic syndrome occurring in their co‐twins. The classification of broad schizophrenic and manic syndromes without separate schizoaffective syndromes showed improved inter‐rater reliability, but high genetic and environmental correlations between the two broad syndromes. The results are consistent with regarding schizoaffective‐mania as due to co‐occurring elevated liability to schizophrenia, mania, and depression; and schizoaffective‐depression as due to co‐occurring elevated liability to schizophrenia and depression, but with less elevation of liability to mania. If in due course schizoaffective syndromes show satisfactory inter‐rater reliability and some specific etiological factors they could alternatively be regarded as partly independent disorders. © 2011 Wiley Periodicals, Inc.