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IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort

  • Jeremy Horwood (a1), Giovanni Salvi (a2), Kate Thomas (a1), Larisa Duffy (a1), David Gunnell (a1), Chris Hollis (a3), Glyn Lewis (a2), Paulo Menezes (a4), Andrew Thompson (a5), Dieter Wolke (a6), Stanley Zammit (a7) and Glynn Harrison (a2)...
Abstract
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.

Aims

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

Method

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.

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Copyright
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial licence (http://creativecommons.org/licenses/by-nc/4.0/), which permits noncommercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited. The written permission of Cambridge University Press must be obtained for commercial re-use or in order to create a derivative work.
Corresponding author
Correspondence: Professor Glynn Harrison, The Academic Unit of Psychiatry, Community Based Medicine, Cotham House, Cotham Hill, Bristol BS6 6JL, UK Email: G.Harrison@bristol.ac.uk
Footnotes
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Declaration of interest

None.

Funding detailed in Acknowledgements.

Footnotes
References
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IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort

  • Jeremy Horwood (a1), Giovanni Salvi (a2), Kate Thomas (a1), Larisa Duffy (a1), David Gunnell (a1), Chris Hollis (a3), Glyn Lewis (a2), Paulo Menezes (a4), Andrew Thompson (a5), Dieter Wolke (a6), Stanley Zammit (a7) and Glynn Harrison (a2)...
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