Abstract
The relationship between genetic and environmental risk is complex and for many traits, estimates of genetic effects may be inflated by passive gene-environment correlation. This arises because biological offspring inherit both their genotypes and rearing environment from their parents. We tested for passive gene-environment correlation in adult body composition traits using the ‘natural experiment’ of childhood adoption, which removes passive gene-environment correlation within families. Specifically, we compared 6165 adoptees with propensity score matched non-adoptees in the UK Biobank. We also tested whether passive gene-environment correlation inflates the association between psychiatric genetic risk and body composition. We found no evidence for inflation of heritability or polygenic scores in non-adoptees compared to adoptees for a range of body composition traits. Furthermore, polygenic risk scores for anorexia nervosa, attention-deficit/hyperactivity disorder and schizophrenia did not differ in their influence on body composition traits in adoptees and non-adoptees. These findings suggest that passive gene-environment correlation does not inflate genetic effects for body composition, or the influence of psychiatric disorder genetic risk on body composition. Our design does not look at passive gene-environment correlation in childhood, and does not test for ‘pure’ environmental effects or the effects of active and evocative gene-environment correlations, where child genetics directly influences home environment. However, these findings suggest that genetic influences identified for body composition in this adult sample are direct, and not confounded by the family environment provided by biological relatives.
Highlights
Body composition traits are highly heritable (Schousboe et al 2004; Hanisch et al 2004; Tarnoki et al 2014)
We found estimates of Genomic-RElatednessbased restricted Maximum-Likelihood (GREML)-derived single nucleotide polymorphism (SNP)-based heritability for height, body mass index (BMI), BF%, fat mass (FM), fat-free mass (FFM) and waist-to-hip ratio (WHR) did not differ between adopted and non-adopted individuals, irrespective of matching (Fig. 2)
We found no significant differences in variance in body composition explained by common genetic variants or polygenic scores in adopted as compared to non-adopted individuals
Summary
Body composition traits are highly heritable (Schousboe et al 2004; Hanisch et al 2004; Tarnoki et al 2014). Estimates of genetic influence can be confounded by passive gene-environment correlation which refers to the association between the genotype an individual inherits from their parents and the environment in which they are raised (Kong et al 2018). This association arises because parents pass genetic factors to their offspring, and the home environment they provide. The latter is influenced by within family genetic factors (Knafo and Jaffee 2013). The contribution of genetic factors to body composition may be overestimated because of geneenvironment correlations
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