IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort.
BACKGROUND
Non-clinical psychotic symptoms appear common in children, but it is possible that a proportion of reported symptoms result from misinterpretation. There is a well-established association between pre-morbid low IQ score and schizophrenia. Psychosis-like symptoms in children may also be a risk factor for psychotic disorder but their relationship with IQ is unclear.


OBJECTIVE
To investigate the prevalence, nature and frequency of psychosis-like symptoms in 12-year-old children and study their relationship with IQ.


METHODS
Longitudinal study using the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. A total of 6455 children completed screening questions for 12 psychotic symptoms followed by a semi-structured clinical assessment. IQ was assessed at 8 years of age using the Wechsler Intelligence Scale for Children (3rd UK edition).


RESULTS
The 6-month period prevalence for one or more symptoms was 13.7% (95% CI 12.8-14.5). After adjustment for confounding variables, there was a non-linear association between IQ score and psychosis-like symptoms, such that only those with below average IQ score had an increased risk of reporting such symptoms.


CONCLUSIONS
Non-clinical psychotic symptoms occur in a significant proportion of 12-year-olds. Symptoms are associated with low IQ and also less strongly with a high IQ score. The pattern of association with IQ differs from that observed in schizophrenia.
Horwood
Jeremy
J
Department of Social Medicine, University of Bristol, UK.
Salvi
Giovanni
G
Thomas
Kate
K
Duffy
Larisa
L
Gunnell
David
D
Hollis
Chris
C
Lewis
Glyn
G
Menezes
Paulo
P
Thompson
Andrew
A
Wolke
Dieter
D
Zammit
Stanley
S
Harrison
Glynn
G