Maximizing the Value of Twin Studies in Health and Behaviour

The team dived into the classical twin design and explored recent developments in twin studies. The team read hundreds of papers to collect their material and analyzed the outcomes of recent twin studies on the concordance and discordance for major diseases and mental disorders  challenging the belief that genetic influences are deterministic.

The classical twin design is indispensable to understand how genetic and environmental factors relate to human traits and obtain an estimate of their heritability. In their review, the authors explore the heritability of new phenotypes and summarize the latest insights into twinning. They argue that stronger efforts to increase representativeness are needed to ensure that twin study results are representative of the general population and global diversity.

Jana Hirzinger, Sophie Breunig, Dmitry Kuznetsov, and Kirsten Schut, who were pursuing their Master’s degree during the COVID-19 pandemic, when the paper was written, conducted the research for the paper and were joined by PhD student Susanne Bruins and post-doctoral researchers Fiona Hagenbeek and Veronika Odintsova. This dynamic team, led by Professor Dorret Boomsma combined their insights to create a comprehensive and cutting-edge paper.

They contend that collaboration and cooperation are critical among the over 60 twin registers that exist worldwide, and suggest creating new twin registries, particularly in underrepresented populations such as African, Arab, Hispanic, and other non-European groups, as well as in advanced age groups to accelerate research into aging. Twin studies have been instrumental in understanding the influence of the environment and in determining the partial genetic control of the environment individuals experience. They point out that twin registers often have multi-generational genotype data and a wide variety of phenotypes, making them essential contributors of data to gene-finding studies, causality modelling, and longitudinal studies.

According to lead author Fiona Hagenbeek, “Our research has major implications for ongoing efforts to translate genetic risk, as assessed by polygenic scores, into clinical practice. It is often noted that the utility of polygenic scores will increase as studies become larger and many believe genetic risk prediction will eventually capture trait heritability. However, our review shows that the upper limit for prediction is set by the monozygotic (MZ) concordance rate, that is, the degree of similarity in MZ twin pairs, who share, on average, 100% of their DNA sequence. Thus, our review demonstrated the continued need for twin studies in an era defined by large-scale genomics studies."

Dmitry Kuznetsov said: “This paper covers the most recent methodological advancements in twin studies, addressing in particular the highly intriguing topics of causality, gene-environment correlation and interaction" and Jana Hirzinger added: "Being part of a review on twin studies not only allowed me a first glance into academia's publishing world but also provided me with the current state of knowledge on genetic research, a good preparation for my PhD."  The others confirmed: "As research master students, it was a great learning experience to conduct this research and work together as a team. We are very grateful for the support."

The research was conducted as part of the Research Master “Genes, Behavior and Health” at the Vrije Universiteit, Amsterdam and was supervised by Dorret Boomsma, who is a well-respected expert in the field for whom this is her fourth review paper on the value of twin studies.

She explains:  “With the enormous progress in human genetics and the advances in our field, every decade or so questions are asked about the value of twin studies. I am proud of the hard work and dedication shown by these students in conducting this research. This publication will make a significant impact in the field of human behaviour genetics.

Video
Watch this video for more information about the research.