Abstract
The goals of this research were to investigate the genetic architecture of childhood psychiatric symptoms and disentangle the genetic and environmental pathways of transmission that link parental factors to psychiatric outcomes in children and adolescents. This thesis summarises and contextualises results from a series of molecular genetic studies, including data from up to 22 population-based cohorts with information on childhood psychiatric traits from parents, teachers, and self-report. A genome-wide association study of childhood internalising symptoms revealed substantial genetic correlations with adult internalising disorders (such as depression and anxiety) and other childhood-onset psychiatric traits (such as aggression, attention-deficit hyperactivity disorder (ADHD) and autism), indicating that genetic effects could partially explain the persistence of internalising symptoms over the lifespan and the co-occurrence of psychiatric traits in childhood. To synthesise current knowledge about the impact of parental characteristics on children’s mental health, a systematic review of genetically informed studies was conducted, which showed that parental factors were linked to children’s psychiatric outcomes through both genetic and environmental pathways. However, the size and direction of environmental effects was often unclear. Using novel family-based genetic designs, we investigated the impact of parental contributions by estimating the extent to which individual differences in children’s psychiatric outcomes were explained by genetic nurture; an effect of parental genotype that is mediated through the environment via genetically-influenced parental traits. While no strong evidence of genetic nurture was found, our results provide the first indication that genetically-indexed parental effects could explain a small proportion of variance in childhood depressive and ADHD symptoms. This calls for more studies in larger samples to make robust estimations and identify mediating factors that account for potential genetic nurture effects. One potential mediating factor is parental wellbeing, which has been linked to offspring mental health in previous research. Using polygenic scores to index genetic liability to wellbeing, we observed that associations between parental wellbeing and children’s internalising, externalising and ADHD-related symptoms were at least partly explained by overlapping genetic factors, while no clear evidence of genetic nurture effects was found. The results highlight the importance of genetically informative designs, as not accounting for the role of genes could lead to spurious or inflated associations between parental factors and children’s psychiatric outcomes. The thesis is concluded with a general discussion which highlights its clinical and research implications and provides directions for future research.
Original language | English |
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Qualification | PhD |
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Award date | 5 Jul 2022 |
Publication status | Published - 5 Jul 2022 |