Relative Genetic and Environmental Influences on Self-Harm and Depression

Interpersonal violence affects millions of people worldwide. The WHO defines it as the "intentional use of physical force or power, threatened or actual, against another person, which either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment, or deprivation". This includes childhood maltreatment, bullying, intimate partner violence (IPV), and sexual violence. Exposure to these forms of interpersonal violence is an established risk factor for an array of negative mental health outcomes during adolescence and adulthood, including depression and self-harm (non-suicidal and suicidal).

Beyond environmental risks, these mental health outcomes are also influenced by genetic effects. Genetic influences are hypothesised not only to have direct effect but to interact with the environment (Genotype-environment interaction). Gene-environment interaction is often interpreted within the Diathesis-Stress framework whereby it is hypothesised that those who have high genetic predisposition to mental health difficulties will be more likely to develop a mental health disorder after exposure to a negative environment, compared to those with lower genetic predisposition. It can also be interpreted within the Differential Susceptibility framework, which suggests that some people have a predisposition to responding to the environment, explained partly by genetic differences, and those people will be more likely to be affected by exposures to negative as well as positive environments. In the case of mental health, it means that people with higher environmental susceptibility will be more likely to develop mental health difficulties following negative exposures, such as interpersonal violence.

In this PhD, the aetiology of self-harm and depression, and their relationship with interpersonal violence will be studied using genetically informed designs, with longitudinal data from the UK, Sri Lanka and Canada, and more specifically data from the Twins Early Development Study (TEDS), Colombo Twin and Singleton Study (COTASS), and Quebec Longitudinal Study of Child Development (QLSCD). Mental health and interpersonal violence are global issues, therefore using datasets from three different countries, including a lower-middle income country, will contribute to this research being more generalisable. Analyses will include twin modelling and linear models incorporating polygenic scores. The projects will incorporate community engagement and involvement ito ensure outcomes are relevant to the people affected by the research. Due to the student's positionality as a white European, this will be particularly relevant for the project involving the dataset from Sri Lanka, whereby meaningful community engagement will be achieved through a fieldwork visit to Sri Lanka. The aim of this visit will be to conduct an engagement activity (e.g., workshop) with stakeholders in Sri Lanka to inform this piece of research and to communicate the results to those involved in supporting individuals exposed to interpersonal violence. This will contribute to identifying the most effective way for the research to have a positive social impact in Sri Lanka.