THE GENETIC-HETEROGENEITY OF SCHIZOPHRENI A - RESULTS OF A SYSTEMATICTWIN STUDY

One reason for the inconsistent findings in schizophrenia research is the lack of diagnostic conformity In the face of modern operational '' atheoretical'' diagnostic systems, this dilemma is still present. In o rder to examine specificity and validity of diagnoses, we carried out a systematic twin study with index twins suffering from schizophrenic spectrum psychoses. We compared the diagnostic systems of DSM-III-R, w hich is based on consensus of international experts, with Leonhards' n osology developed on sophisticated clinical observation and descriptio n of psychopathological phenomena occurring during the long-term cours e of psychiatric diseases. We examined twin concordance, family histor y, and the frequency and severity of complications of pregnancy and ch ildbirth. The results suggest that the schizophrenic spectrum has to b e divided into clinically and etiologically heterogeneous subgroups. T his was much more striking when Leonhard's diagnostic criteria were us ed than with DSM-III-R diagnostic criteria. There seem to be three val id and etiologically different groups: cycloid psychoses, unsystematic schizophrenias and systematic schizophrenias as proposed by Leonhard. In cycloid psychoses genetic loading seems to be low (proband concord ance MZ 38 %, DZ 29 %), but pregnancy and birth complications may have an important role in the etiology. On the other hand, unsystematic sc hizophrenias are obviously predominantly inherited (proband concordanc e MZ 88 %, DZ 17 %) and ''environmental'' factors are not very promine nt. It is striking that MZ twins with a diagnosis of systematic schizo phrenia have not yet been found, whereas 32 % of DZ index twins (6 out of 19) were diagnosed as having systematic schizophrenia. Further, al l DZ twins with the diagnosis of systematic schizophrenia were discord ant and the affected twins had threetimes as many and as severe pregna ncy and birth complications in the history than their healthy co-twins .