OBJECTIVE: The aim of the study was to investigate the type and nature
of personality disorders among biological relatives of schizophrenic
probands. METHOD: A total of 176 nonschizophrenic co-twins and other
first-degree relatives of schizophrenic probands were compared to 101
co-twins and first-degree relatives of probands with major depression.
RESULTS: Schizotypal personality disorders were more common and histrionic
personality disorders less common among the biological relatives of
schizophrenic probands than among relatives of probands with major
depression. A further exploration of the schizotypal criteria revealed that
the so-called "negative" criteria such as odd speech, inappropriate affect,
and odd behavior, as well as excessive social anxiety, were significantly
more common among the relatives of schizophrenic probands. The latter
criterion seems particularly important. The so-called "positive"
schizotypal criteria were partly, although not statistically significantly,
more common among the relatives of probands with major depression. There
were only minor differences in frequencies of the negative criteria between
monozygotic co-twins, dizygotic co-twins, and other first-degree relatives
of schizophrenic probands. CONCLUSIONS: The present study suggests that
DSM-III-R schizotypal disorder is defined by a set of criteria that partly
describe a "true" schizophrenia-related personality disorder and partly
features that are not specific for relatives of schizophrenic probands.
Furthermore, the genetic relationship between schizophrenia and "true"
schizotypal personality disorder seems weak. Excessive social anxiety may
be a marker of a possible genetic link between the disorders.