Depressive Symptoms Among Adolescents and Young Adults : Psychometrics and the Influence of Family Environment, and Candidate Gene–environment Interactions

Sammanfattning: The overall aims of this thesis were to evaluate the psychometric properties of a questionnaire designed to evaluate parenting styles, and to study how depressive symptoms among adolescents and young adults may vary depending on the family environment and candidate gene–environment interaction (cG×E).The study sample consisted of participants (born during 1997 or 1999), and their caregivers from the Survey of Adolescent Life in Västmanland Cohort Study. This thesis included data from 2012 when the participants were 13 and 15 years old (Wave I: DNA collection), 2015 at ages 16 and 18 years (Wave II: Parenting styles, parental depression, depressive symptoms, early life stress i.e., ELS) and 2018 at ages 19 and 21 years (Wave III: Depressive symptoms).Paper I: A good model fit was obtained for the Parent as Social Context Questionnaire (PASCQ) parent and adolescent versions through psychometric evaluations. Paper II: Positive and negative parenting styles were associated with fewer or more depressive symptoms among adolescents and young adults, respectively. Parental depression×sex was associated with more depressive symptoms, preponderant among female adolescents. The findings were not significant among young adults. Paper III: A significant cG×E effect between oxytocin receptor single-nucleotide polymorphism (SNP) rs6770632 and negative parenting style on depressive symptoms among young adults was found. Paper IV: Significant cG×E effects were found for the FKBP5 SNPs rs1360780, rs4713916, rs7748266 and rs9394309 moderated by ELS and positive parenting style on depressive symptoms among young adults.These findings suggest that parenting styles may be measured with the PASCQ and that depressive symptoms among adolescents and young adults seem to vary dependent on the family environment and cG×E effects. However, the cG×E effects may be more central for some individuals depending on differences in diathesis- or sensitivity towards the family environment. The variance in depressive symptoms may therefore contain diathesis stress and differential susceptibility effects regarding the cG×E interaction. The insight gained from this thesis provides a foundation for future research and contributes to research areas such as parenting research and the understanding of biological factors behind depressive symptomology among adolescents and young adults.