Posttraumatic stress disorder (PTSD) is a complex and severe mental disorder triggered by exposure to an extraordinarily traumatic event. Many studies have provided evidence supporting a genetic predisposition to PTSD. Human and animal studies suggest that the oxytocin-oxytocin receptor system may be an important mediators of abnormal stress responses following exposure to traumatic events, which implicates an important role of this system in the development of PTSD. This dissertation focused on the associations between the oxytocin receptor gene (OXTR， rs1042778 genotype) x trauma exposure interaction and PTSD, and aimed to systematically investigate the role of the oxytocin receptor system in the occurrence, development, transition and comorbidity of PTSD.
The studies were comprised of four sections. Section 1 contained three studies to investigate the associations between the rs1042778 genotype x trauma exposure interaction and PTSD symptoms. Study 1 aimed to examine the association between interaction and total PTSD symptoms. The results showed that the interaction was associated with total PTSD symptoms in females, but not in males. Study 2 investigated the dimensionality underlying DSM-5 PTSD symptoms, and examining the stability of PTSD symptom structure across gender. Confirmatory factor analyses revealed that the seven-factor hybrid PTSD model provided the best fit to the data for both females and males. Moreover, measurement equivalence of this model held across gender. On the basis of Study 2, Study 3 showed that the interaction was only associated with severity of the intrusion and externalizing behaviors symptoms in females.
Two studies in Section 2 intended to verify the relationships between the rs1042778 genotype x trauma exposure interaction and the trajectories of PTSD symptoms. In Study 4, PTSD symptoms were found to follow 3 trajectories in females, and 2 trajectories in males. Study 5 further revealed that the interaction could not predict the trajectories of PTSD symptoms both in females and males.
Section 3 includes two studies focused on the effect of interaction on the transition of PTSD symptom profiles. Study 6 aimed to determine the population-based profiles of posttraumatic stress disorder (PTSD) symptomatology and the longitudinal patterns of transitions across these profiles. Latent profile analyses (LPA) identified three classes at each time point. Latent transition analysis (LTA) revealed notable movement between classes over time. In Study 7, it was found that the interaction was not associated with the transition.
Finally, two studies in Section 4 were conducted with the goal to examine the relationships between the rs1042778 genotype x trauma exposure interaction and patterns of co-occurring PTSD and depression symptoms. Study 8 showed that a 3-class solution in females and a 2-class solution in males fit the data best. According to Study 9, the interaction was not associated with patterns of co-occurring PTSD and depression symptoms.
In all, the findings of this dissertation suggest that the rs1042778 genotype x trauma exposure interaction could predict total PTSD symptoms and the intrusion/externalizing behaviors symptoms in females. However, it was not associated with trajectories, transition and comorbidity of PTSD symptoms. Findings from the series of studies are pertinent for further understanding of the underlying mechnism of PTSD, and may help to identify novel biomakers and potential therapeutic targets for PTSD.