IQ differences between patients with first episode psychosis in London and Palermo reflect differences in patterns of cannabis use

Laura Ferraro; Robin M Murray; Marta Di Forti; Diego Quattrone; Giada Tripoli; Lucia Sideli; Daniele La Barbera; Caterina La Cascia

doi:10.1016/j.schres.2019.06.004

IQ differences between patients with first episode psychosis in London and Palermo reflect differences in patterns of cannabis use

Schizophr Res. 2019 Aug:210:81-88. doi: 10.1016/j.schres.2019.06.004. Epub 2019 Jul 2.

Authors

Laura Ferraro¹, Robin M Murray², Marta Di Forti³, Diego Quattrone⁴, Giada Tripoli⁵, Lucia Sideli⁶, Daniele La Barbera⁷, Caterina La Cascia⁸

Affiliations

¹ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy; Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK. Electronic address: laura.ferraro@unipa.it.
² Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy; Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK; South London and Maudsley NHS Mental Health Foundation Trust, UK. Electronic address: robin.murray@kcl.ac.uk.
³ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy; South London and Maudsley NHS Mental Health Foundation Trust, UK; Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London SE5 8AF, UK; National Institute for Health Research (NIHR), Mental Health Biomedical Research Centre, South London and Maudsley NHS Foundation Trust and King's College London, UK. Electronic address: marta.diforti@kcl.ac.uk.
⁴ South London and Maudsley NHS Mental Health Foundation Trust, UK; Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London SE5 8AF, UK; National Institute for Health Research (NIHR), Mental Health Biomedical Research Centre, South London and Maudsley NHS Foundation Trust and King's College London, UK. Electronic address: diego.1.quattrone@kcl.ac.uk.
⁵ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy; Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK. Electronic address: giada.tripoli@kcl.ac.uk.
⁶ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy; Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, Denmark Hill, London SE5 8AF, UK. Electronic address: lucia.sideli@unipa.it.
⁷ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy. Electronic address: daniele.labarbera@unipa.it.
⁸ Department of Biomedicine, Neuroscience and advanced Diagnostics (BiND), Psychiatry Section, University of Palermo. Via Gaetano La Loggia, 1, 90129, Palermo, Italy. Electronic address: erika.lacascia@unipa.it.

PMID: 31272907
DOI: 10.1016/j.schres.2019.06.004

Abstract

Aims: Cognitive impairment is a possible indicator of neurodevelopmental impairment, but not all psychotic patients are cognitively compromised. It has been suggested that heavy cannabis use may precipitate psychosis in those who show no such compromise. This study compares two samples of patients with first-episode psychosis and their respective non-psychotic controls, in London (UK) and Palermo (Italy), and examines whether different patterns of cannabis use are reflected in differences in IQ.

Methods: The two studies used the same inclusion/exclusion criteria and instruments. The sample comprised 249 subjects from London (106 patients and 143 controls) and 247 subjects from Palermo (120 patients and 127 controls). ANCOVA was performed with IQ as the dependent variable and city and frequency of cannabis use as predictors. This was then repeated with the case group only, by adjusting for relevant confounders.

Results: We found a greater amount of cannabis use in the London sample, compared to Palermo and patients from London had higher IQ than patients from Palermo, a difference that was more significant than that reflected between controls (F_^group*city(1, 402) = 7.6, p = 0.006). Once corrected for symptomatology and treatment, patients from London who had never used cannabis were similar to patients from Palermo regarding IQ. Thus the higher IQ of patients from London was mainly due to the subgroup of cannabis-using patients (F_{cannabis*city}(2,145) = 4.6, p = 0.011).

Conclusions: We can speculate that a greater amount of cannabis-use may have contributed by precipitating psychosis in patients with a higher IQ in London but less so in patients from Palermo.

Keywords: Cannabis; Cognition; Multicentric study; Neurodevelopment; Risk factors.

Publication types

Comparative Study
Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Case-Control Studies
Cognitive Dysfunction* / chemically induced
Cognitive Dysfunction* / epidemiology
Cross-Cultural Comparison
Female
Humans
Intelligence*
Italy / epidemiology
London / epidemiology
Male
Marijuana Use* / adverse effects
Marijuana Use* / epidemiology
Psychotic Disorders* / epidemiology
Psychotic Disorders* / etiology
Young Adult