Using quantitative genetics to explore risk factors and outcomes associated with obsessive-compulsive disorder and body dysmorphic disorder in youth

Student thesis: Doctoral ThesisDoctor of Philosophy


Obsessive-compulsive disorder (OCD) often has its onset in youth. The disorder can have a devasting impact on functioning across multiple domains, and is associated with a range of negative outcomes. OCD is known to arise as a result of genetic, environmental and cognitive influences, yet the specific risk factors remain poorly understood. Identifying environmental and cognitive risk factors is of particular clinical interest, since they may be modifiable and highlight opportunities for intervention. However, given that many environmental and cognitive factors are known to be under genetic influence, it is essential that research in this field accounts for potential genetic confounding. The primary aim of this thesis was to examine putative risk factors and outcomes associated with OCD in youth, using genetically-informative methods to control for genetic confounding. A secondary aim was to test the extent to which certain key findings extend to body dysmorphic disorder (BDD), a closely related phenotype. Studies 1 and 2 used longitudinal data collected in the Genesis 12-19(G1219) study of twins and siblings. Study 1 tested whether punitive parenting and stressful life events predicted the development of obsessive-compulsive symptoms(OCS) during adolescence. Results showed that stressful life events, but not maternal or paternal punitive parenting were prospectively associated with change in OCS between age 15 and 17 years. The prospective association between stressful life events and OCS was explained by both genetic and non-shared environmental factors, in roughly equal proportions. Study 2 examined the relationship of a specific cognitive bias, namely anxiety sensitivity, with OCS during a two-year period during adolescence. Evidence was found for a reciprocal relationship, whereby anxiety sensitivity and OCS mutually influence each other over time. The reciprocal links between OCS and anxiety sensitivity were largely mediated by non-shared environmental experiences, as opposed to common genetic vulnerability.Studies 3 and 4 utilised data from the Child and Adolescent Twin Study in Sweden (CATSS). Study 3 investigated an important clinical outcome associated with OCS, namely suicidality (encompassing suicidal ideation and suicide attempts).Results demonstrated that OCS were significantly associated with concurrent reports of suicidality at ages 18 and 24, even when controlling for coexisting symptoms of depression and anxiety. Taboo obsessions (e.g. sexual and aggressive thoughts) prospectively predicted change in suicidality between age 18 and 24. Genetic factors accounted for much of the concurrent and longitudinal covariance between OCS and suicidality, but with substantial non-shared environmental influences. Study 4 examined the extent to which the findings of study 3 also apply to BDD symptoms. BDD symptoms were strongly associated with concurrent reports of suicidality at ages 18 and 24, independent of depressive and anxiety symptoms. The majority of the association at both ages was accounted for by common genetic vulnerability, but with significant non-shared environmental influences.In summary, this thesis provides important insights into factors influencing the development of OCS, as well as mechanisms underpinning the association of OCS and BDD symptoms with suicidality. Moreover, this thesis highlights the importance of using genetically-informative approaches to understanding risk and outcomes associated with OCD and BDD.
Date of Award1 Feb 2021
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorThalia Eley (Supervisor) & Fruhling Rijsdijk (Supervisor)

Cite this