Status of Twin Research in Functional Psychoses

Abstract

After briefly reviewing the main findings of twin research in. functional psychoses, the author focuses the attention on neglected aspects of twin research, such as the study of co-twins of monozygotic (MZ) subjects with functional psychosis, and the study of life histories of discordantly affected twins. Through a thorough investigation of the nonpsychotic co-twins of MZ subjects, one might be able to identify vulnerability factors. By studying the life course of the twins in a pair, discovery of environmental etiological factors are possible. By including twins with both schizophrenic, manic-depressive and reactive psychotic symptomatology, one should be able to discover whether the environmental factors are of a specific kind.

Twin studies in schizophrenia with special emphasis on concordance figures

“…Furthermore, the normal co-twin may be paired not only with the moderately severe cases, but with extremely deteriorated partners. This is also in accordance with findings that show that there are no genetic factors determining the outcome of schizophrenia [Kringlen, 1986]. …”

Is the concept of schizophrenia useful from an aetiological point of view?

“…How then, can 30-40 per cent of co-twins of schizophrenic monozygotic (MZ) be clinically normal (9)? This finding is remarkable, both from a genetic and environmental point of view.…”