Subclinical psychotic experiences and cognitive functioning as a bivariate phenotype for genetic studies in the general population.
OBJECTIVE
Cognitive deficits may be vulnerability markers for the development of schizophrenia. This study examined whether cognitive deficits are related to specific dimensions of subclinical psychotic experiences and whether associations between these variables are caused by additive genetic, common environmental and/or individual-specific environmental factors.


METHODS
A general population sample of 298 female twin pairs completed the Community Assessment of Psychic Experiences and a neuropsychological test battery. Associations between subclinical positive and negative psychotic dimensions and neuropsychological factors (episodic memory and information processing speed) were examined. Univariate correlation and structural equation analyses were performed to explore the role of genetic and environmental factors in the phenotypes separately. Bivariate correlation and structural equation analyses were applied to examine the causes of association.


RESULTS
There were significant correlations between information processing speed and both the positive (r=.11; p<.05) and the negative dimension (r=.10; p<.05). For the negative dimension and for speed of processing, the data suggested a model that included genetic factors. The observed phenotypic correlation between the negative dimension and information processing speed could be solely explained in terms of additive genetic factors. Although the comparison of the correlations for MZ and DZ pairs did not give a clear indication as to the underlying causes of the association, structural equation modelling suggested that the observed phenotypic correlation between the negative dimension and information processing speed could be solely explained in terms of additive genetic factors.


CONCLUSIONS
Negative symptoms and information processing speed are associated at the subclinical level and this association appears to be influenced by genetic factors exclusively. Bivariate psychosis phenotypes may represent suitable candidates for molecular genetic studies in the general population.
Simons
C J P
CJ
Department of Psychiatry and Neuropsychology, Maastricht University, European Graduate School of Neuroscience, SEARCH, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
Jacobs
N
N
Jolles
J
J
van Os
J
J
Krabbendam
L
L
D000293:Adolescent; D000328:Adult; D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009483:Neuropsychological Tests; D010641:Phenotype; D011446:Prospective Studies; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D012720:Severity of Illness Index; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic