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.

遗传和环境风险之间的关系很复杂，对于许多性状，遗传效应的估计可能会因被动的基因-环境相关性而被夸大。这是因为生物后代从父母那里继承了基因型和饲养环境。我们使用儿童收养的“自然实验”测试了成人身体成分特征中的被动基因-环境相关性，该实验消除了家庭内的被动基因-环境相关性。具体来说，我们比较了英国生物银行中 6165 名被收养者的倾向得分与非收养者相匹配的情况。我们还测试了被动基因-环境相关性是否会夸大精神病遗传风险与身体成分之间的关​​联。在一系列身体成分特征方面，我们没有发现与被收养者相比，非收养者的遗传力或多基因评分膨胀的证据。此外，神经性厌食症、注意力缺陷/多动障碍和精神分裂症的多基因风险评分对被收养者和非被收养者的身体成分特征的影响没有差异。这些发现表明，被动的基因-环境相关性不会夸大身体成分的遗传效应，或精神疾病遗传风险对身体成分的影响。我们的设计不考虑儿童时期的被动基因-环境相关性，也没有测试“纯”环境影响或主动和唤起基因-环境相关性的影响，其中儿童遗传学直接影响家庭环境。然而，