Background
Family studies are in conflict as to whether schizophrenia and bipolar disorder have
independent genetic etiologies. Given the relatively low prevalence (approximately
1%) of these disorders, the use of quantitative endophenotypic markers of genetic
liability might provide a more sensitive strategy for evaluating their genetic overlap.
We have previously demonstrated that spatial working memory deficits increase in a
dose-dependent fashion with increasing genetic proximity to a proband among the unaffected
co-twins of schizophrenic patients. Here, we evaluated whether such deficits might
also mark genetic susceptibility to bipolar disorder.
Methods
The Wechsler Memory Scale-Revised Visual Memory Span and Digit Span subtests were
administered to 46 schizophrenic patients, 32 of their unaffected co-twins, 22 bipolar
patients, 16 of their unaffected co-twins, and 100 control twins, representing unselectively
nationwide twin samples.
Results
Schizophrenic patients and their unaffected co-twins performed significantly worse
than control subjects on the spatial working memory task, whereas only the schizophrenic
patients performed significantly below the control subjects on the verbal working
memory task. Neither bipolar patients nor their unaffected co-twins differed from
control subjects on these measures.
Conclusions
Our findings support the hypothesis that impairment in spatial working memory might
effectively reflect an expression of genetic liability to schizophrenia but less clearly
to bipolar disorder.
Key Words
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Article info
Publication history
Published online: August 22, 2005
Accepted:
May 13,
2005
Received in revised form:
April 11,
2005
Received:
August 10,
2004
Identification
Copyright
© 2005 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
