Differences in ontogeny, premorbid personality, and severity of schizophrenia in twins.

Abstract

Clinical observations show that in each pair of twins, monozygotic (MZ) as well as dizygotic (DZ), differences are found in the manifestation of schizophrenic symptoms, bounded on the one hand by manifest schizophrenia and, on the other hand, by features of a schizoid anomaly of character. Differences may be maximal, when manifest schizophrenia is combined with normal in the same pair, or minimal, when both twins have manifest schizophrenia, but with a different type of course. The degree of clinical similarity and difference between concordant and discordant MZ and DZ studied by the writers was analyzed previously [i]~ It was concluded that the levels of both positive and negative disorders characteristic of schizophrenia are subject to variations in concordant pairs of both MZ and DZ twins. The number of attacks of the disease in the past, the duration and quality of the remissions may also differ. Although these differences are small, especially in MZ, nevertheless taken together they have the result that one twin of the pair is more seriously, the other less seriously affected. Differences in the course of the disease are characteristic both of concordant DZ and of MZ, except that in MZ the range of the differences is less whereas in DZ it is greater. When differences between the twins of a pair are most marked, i.e., in twins discordant for manifest schizophrenia, fundamental differences are found between MZ and DZ. In a high proportion of monozygotic co-twins of probands, nonmanifest disorders are found that are difficult to distinguish from mild, abortive, or latent variants of schizophrenia. Only in a few cases has a combination of manifest schizophrenia and anomaly of the character of the schizoid cycle been observed in pairs of MZ. By contrast, a high proportion of dizygotic cotwins of probands are clinically healthy. Regardless of how widely different are the manifestations of the schizophrenic process for any kind of disorder of the schizophrenic spectrum in twins, the question of with what these differences are linked is an interesting one. It would appear that since MZ are genetically identical, any differences between the twins of such a pair are due to the influence of environmental factors. However, all investigations on twins so far undertaken have failed to identify environmental factors which could determine the manifestation of schizophrenia in only one member of the pair or a more severe level of manifestation of the disease in him. Investigators have merely stated that differences exist in the early development of MZ who are discordant for manifest schizophrenia. In the opinion of some, birth injuries or asphyxia have been observed more frequently in the case of the affected twin, but according to others, a smaller birth weight has been noted [2-4]. The question whether order of birth is important has been keenly debated. The view has been put forward that the second twin to be born is more at risk of developing manifest schizophrenia than his partner. Some workers have drawn attention to differences in the premorbid personality of MZ and have concluded that one twin as a rule is the psychological leader, whereas the other is subordinate to him, and that the latter has the greater chance of manifestation of schizophrenia despite identity of genetic predisposition. Relations between twins have been discussed from the psychodynamic standpoint, and the onset of schizophrenia has been linked with particular conditions of existence [5, 6]. On the whole data on interconnection between factors of the perinatal period, of early ontogeny, and features of the premorbid personality and development of the schizophrenic process in twins still remain contradictory, and there have been few investigations of this problem. The aim of this investigation was to discover the most important features of early ontogeny and of the premanifest period that coincide with a more severe course of schizophrenia