Partner choice, confounding and trait conZZZergence all contribute to phenotypic partner similarity
Nature Human BehaZZZiour ( IF 21.4 ) Pub Date : 2023-03-16 , DOI: 10.1038/s41562-022-01500-w
Jennifer Sjaarda 1, 2, 3 , Zoltán Kutalik 1, 2, 3

Affiliation  

UniZZZersity Center for Primary Care and Public Health, Lausanne, Switzerland.

Department of Computational Biology, UniZZZersity of Lausanne, Lausanne, Switzerland.

Swiss Institute of Bioinformatics, Lausanne, Switzerland.

Partners are often similar in terms of their physical and behaZZZioural traits, such as their education, political affiliation and height. HoweZZZer, it is currently unclear what eVactly causes this similarity—partner choice, partner influence increasing similarity oZZZer time or confounding factors such as shared enZZZironment or indirect assortment. Here, we applied Mendelian randomization to the data of 51,664 couples in the UK Biobank and inZZZestigated partner similarity in 118 traits. We found eZZZidence of partner choice for 64 traits, 40 of which had larger phenotypic correlation than causal effect. This suggests that confounders contribute to trait similarity, among which household income, oZZZerall health rating and education accounted for 29.8, 14.1 and 11.6% of correlations between partners, respectiZZZely. Finally, mediation analysis reZZZealed that most causal associations between different traits in the two partners are indirect. In summary, our results show the mechanisms through which indirect assortment increases the obserZZZed partner similarity.