Center for Research in Clinical Psychology, University of Oslo, 0315 Oslo 3, Norway
It is well known that dysphoric clinical conditions rarely manifest themselves as purely depressive or anxious entities. More common is a changing mixture of depressive and anxiety symptoms. The question then arises: Is the mixed anxiety-depressive disorder a phenotypic variant of anxiety or depressive disorders or is it a separate disorder in itself? A way to answer this question is to apply family-genetic methods and look for a genetic connection. Another way is to see whether the same or different environmental factors are involved in the development of the pure and the mixed conditions. In this article I will do both. The data presented in this article stem from a nationwide study of twins treated by all the Norwegian psychiatric institutions (1). Both partners in 299 sets of twins were personally interviewed. The case sum­maries were independently diagnosed by three judges. The agreement was high. Two of three judges agreed upon the diagnosis of anxiety neurosis in 95% of the cases and in 87% of the cases for neurotic depression. Seventy-six index twins received a diagnosis of anxiety neurosis and 74 a diagnosis of neurotic depression. However, the overlap of symptoms between the two diagnostic groups was high (Table 1). Consequently a discriminant analysis was performed, and Table 2 shows the symptoms that discriminated most strongly between anxiety neurosis and neu­rotic depression. The index twins were classified in three groups by means of the discriminant function, one pure anxiety neurosis group, one mixed anxiety-depressive group, a nd one pure neurotic depression group, each consisting of 50 index twins (2,3). The cotwins with anxiety neurosis and neurotic depression were also classified according to the discriminant function with the same cutting points and the results are presented in Table 3. Table 3 shows that the concordance for the same disorder as well as the two Wier affective disorders is much higher in cotwins of MZ index twins with pure anxiety neurosis compared to cotwins of DZ twins. On the other hand, the (more…)