Socioeconomic status (SES) and mental disorders run in families—representing intergenerational persistence of advantages and disadvantages. Through three original research studies, this thesis investigates intergenerational patterns of socioeconomic status and mental disorders in Norway using genetically informed designs.
First, in paper 1, I explore the coarse-grained etiology of the “big four” SES indicators —education, income, occupation, and wealth. By triangulating four advanced genetic methods, I demonstrate common and unique genetic and environmental sources of variance in parent SES. The substantial common variation across the “big four” is linked to genetic and shared environmental influences, while the considerable unique variance is explained by non-shared environment variation. Second, in paper 2, I assess the risk of mental disorders in young people given their parents’ SES—wealth in particular. In multivariable models including the “big four,” parental wealth is the strongest predictor of most mental disorder diagnoses in children, adolescents, and young adults. Significant associations between parent wealth and risk of mental disorders in young people persist after controlling for sibling-shared genetic and environmental factors. Third, in paper 3, I investigate the effects of children’s genetic differences on parents’ economic outcomes from 3 years before birth to 15 years after birth. By controlling for parent genetic factors, child genetic effects were identified using two methods. We found no conclusive evidence of child genetic effects on parent income, wealth, and government transfers.
Three broad causal models can explain SES and mental disorder outcome correlations between parents (X) and their children (Y): A) third factors causing correlated observations (X←Z→Y), B) parent factors causing child outcomes (X→Y), and C) child factors causing parent outcomes (X←Y). Paper 1 provides evidence of model A, showing how common genetic and environmental factors explain large shares of the variance between the “big four” SES indicators. Paper 2 provides evidence of both model A and B, indicating that both shared genetic and environmental factors and parental wealth influence mental disorder risk in their children. Paper 3 provides inconclusive evidence of model C child genetic effects on their parents’ economic outcomes.
This thesis argues that genetically informed designs are valuable for dissecting at least three important conceptual angles with regard to intergenerational patterns of SES and mental disorders: (i) genetic architecture as the focus—estimating the relative magnitude genetic contributions to phenotypes, and genetic correlations between phenotypes (paper 1); (ii) genetics as a confounder—estimating social effects while accounting for genetic similarity in families (papers 2 and 3), (iii) genetics as a proxy for a social effect—estimating socially-mediated genetic influences on another person’s phenotype (paper 3).