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Title: The cooccurrence, shared genetic aetiology and causal associations between tobacco use and psychotic experiences
Author: Barkhuizen, Wikus
Awarding Body: Birkbeck, University of London
Current Institution: Birkbeck (University of London)
Date of Award: 2020
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Psychotic experiences (PE) are traits in the general population that resemble psychotic symptoms. PE are associated with an increased risk of psychiatric disorders and those affected by these traits or disorders are more likely to smoke tobacco. However, studies on adolescent smoking behaviours and PE have not considered PE dimensionally, adequately accounted for confounding, or included negative symptom traits. Longitudinal studies suggest that smoking may precede PE, but findings are inconclusive. This thesis presents evidence on the phenotypic and genetic associations between PE and smoking behaviours, with an emphasis on adolescent development. Chapter 2 provides a systematic review of the literature on the association between PE and smoking behaviour. In Chapter 3, regression analyses are conducted on the association between the regularity of tobacco use and domains of PE during adolescence accounting for several confounding factors. Chapter 4 presents the first twin study to explore the degree to which PE share genetic and environmental influences with smoking in a large adolescent sample. Chapter 5 investigates the degree to which adolescent and adult PE, schizophrenia, major depression and bipolar disorder are influenced by overlapping common genetic variants using genome-wide association summary statistics. Chapter 6 investigates genetic associations between smoking behaviours and psychiatric disorders and PE accounting for the genetic influences on covariates. It also investigates causal associations between smoking initiation and PE and psychiatric disorders using Mendelian randomization. This thesis concludes with a discussion of the main findings, broader themes, limitations and conclusions. Evidence from this thesis supports phenotypic and genetic associations between smoking and PE during adolescence. This thesis provides novel insights into the aetiology of PE over the lifespan and the underlying reasons why PE cooccur with smoking behaviour. It strengthens the evidence base for a specific biological link between smoking and psychiatric illness.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available