For Twins & Families

General Information about Twin Research

Classical Twin Research

In twin research, identical and fraternal twins are studied to investigate similarities in certain traits to help understand how strongly they are influenced by genetic and environmental factors. This also applies to diseases, for example. Unlike conventional approaches, where patients are compared with individuals without the corresponding disease, and genetic or environmental factors cannot be distinguished, the study of twin pairs allows for a precise determination of these influences. This offers great potential for gaining new insights into the development of diseases.

Mathematical analyses are used to determine the contribution of genetic predisposition (heritability) as well as the influence of experienced environmental factors. Twins are particularly valuable for research because identical twins share 100 % of their genes, while fraternal twins share approximately 50 %. Since they often grow up in similar social environments, researchers can better understand the contribution of genetics and environment to various traits and behaviors.

Imagine, for example, a pair of identical twins who grew up together. Several years ago, the twins moved to different regions: one now lives in a large city, while the other has moved to the countryside. Researchers can use this twin pair to investigate how environmental differences lead to differences in the body or brain, since their genetic predispositions and many aspects of their early environment are identical.

The goal of the twin method is to clarify the relationship between genetic predisposition and environment. The findings from twin studies are not only relevant for disease research but can also contribute to the design of human environments, such as architecture and urban planning.

Since the sequencing of the human genome in 2008, twin research has advanced significantly. Thanks to technological advances, researchers can now not only describe differences or similarities but also conduct comprehensive biological and direct comparisons of twin pairs. Various factors can be considered, such as environment, lifestyle, diet, and exercise, as well as changing genomes, which are influenced by biological conditions, life events, social circumstances, and individual behavior (so-called epigenetics).

On this page, you will find information on the following topics:

Twin Research in Germany

In Germany, multiple births account for 3-4% of all births, with the majority being twin births. Approximately one-third of these are identical twins, while the remainder are fraternal twins. Currently, more than 1.5 million twins live in Germany, and their number continues to rise.

Due to its checkered history, twin research in Germany is unfortunately a somewhat neglected field, although long-term and real-time studies of twins are still highly valued in many medical research areas. While twin research was established as early as the 19th century, it fell into disrepute during the Second World War. This stigma and the subsequent historical suppression of the atrocities committed in medical research during the Nazi era, coupled with ethical and data protection challenges, hampered the establishment of a national twin registry.

Currently, there are three major German twin cohorts: the biomedical cohort HealthTwiSt (Berlin), the socio-psychological cohort TwinLife (Bielefeld & Saarbrücken), and the research-oriented and sustainable twin research project TwinHealth (Tübingen).

Gertrud (Berlin) is working to establish a unified registry for Germany that consolidates, organizes, and ensures the ethical and data protection compliance of twin research.

Let's work together to make twin research in Germany a positive and forward-looking field of science!

For more information on twin research in Germany, see the publication:

Enck, P., Goebel-Stengel, M., Rieß, O., Hübener-Schmid, J., Kagan, K. O., Nieß, A. M., Tümmers, H., Wiesing, U., Zipfel, S., Stengel, A., & TwinHealth Consortium (2021). Medical Twin Research in Germany. Bundesgesundheitsblatt, 64, 1298–1306. https://doi.org/10.1007/s00103-021-03400-2

Benefits of Twin Research

Twin studies offer scientists a unique way to analyze the influence and relationship between genetic and environmental factors on individuals.

These analyses are based on a comparison of the similarity between identical and fraternal twins. We utilize the fact that identical twins share almost exactly the same genetic makeup while simultaneously experiencing different environmental influences (e.g., lifestyle, location, movement patterns, etc.). Fraternal twins share, on average, 50% of their genes. Unlike ordinary siblings, however, they—like identical twins—are likely to share a significant number of environmental factors (such as family, living environment, etc.).

Comparing identical and fraternal twins allows us to assess the influence of genes and environment on various traits (such as extroversion). If identical twins are more similar to fraternal twins in a particular trait than fraternal twins, this difference between the twin pairs suggests that genetic factors play a role in the expression of that trait. Conversely, if identical and fraternal twins differ only slightly, their similarity suggests that genetic factors likely have a lesser influence and that the cause is more likely to be found in the environmental realm.

https://www.youtube.com/watch?v=Vyye-8KGt5Q

Please note: This video is only available in German.

Twins, Behavioral Genetics, and Environment

In the field of behavioral genetics, scientists primarily investigate the extent to which a person's traits (such as personality, intelligence, attitudes, etc.) can be explained by differences in genes (hereditary factors), environmental influences, and their interaction. These traits are often referred to as phenotypes.

Genetic influences are based on a person's hereditary factors. Each of us has a genetic blueprint that influences our traits. Some traits are more strongly influenced by genes than others.

At the same time, almost all traits are also influenced by environmental factors, such as parental upbringing or the social environment. Environmental factors are events or circumstances that affect our traits. Similar to genes, environmental factors influence some traits more strongly than others.

Heritability describes how strongly the observed differences in a trait between individuals are attributable to genetic differences. Heritability estimates are often found in scientific articles. When members of a particular group differ in a trait (e.g., personality), heritability indicates what portion of these differences is attributable to genetic variations and cannot be explained by environmental influences. It is important to emphasize that heritability does not provide information about the development of an individual, but always refers to the average of the entire population.

History of Twin Research

Twin Research in the Kaiser Wilhelm Society

The present-day Max Planck Society emerged from the Kaiser Wilhelm Society (KWG), founded in 1911. During the Nazi era, twin research was conducted at the Kaiser Wilhelm Society's Institute for Anthropology, Human Heredity, and Eugenics. Both the research questions and the sometimes unethical practices were deeply intertwined with the inhumane aims of National Socialism. Both our historical connection to the KWG and the political appropriation of research during that period oblige us today to exercise absolute and utmost care and responsible action.

We are aware of this dark chapter of the past and are actively committed to ensuring that such crimes never happen again. We expressly distance ourselves from the politically motivated aims and practices of twin research under National Socialism. The unethical practices and the inhumane ideology of that time bear no relation whatsoever to the values and goals of today's German Twin Registry.

More information:

Our Values and Goals

Our Commitment to Ethical Research

Our twin registry stands for ethically sound research that prioritizes the well-being of participants. We are committed to protecting the privacy and safety of our study participants. The consent of our participants is always a prerequisite for our research and can be withdrawn at any time, even without giving reasons. Our strict data protection policy goes beyond the requirements of the GDPR to optimally protect the privacy of our participants. We are committed to transparency, respect, and integrity in all our scientific endeavors.

Our Research Goals

Through responsible research, we aim to make a positive contribution to society. Our research aims to better understand the effects of the physical environment on human mental and physical health. The twin design is ideally suited for this purpose, as it allows us to investigate the influence of the environment while maintaining genetic stability.

GERTRUD Twin Registry

The acronym GERTRUD is derived from the official name 'GERman Twin Registry Under Development'. We would like to clarify that the name was not inspired by any historical or contemporary figures. We distance ourselves from any such interpretations. Our database is a scientific institution focused on researching twin studies and their impact on society.

Contact

If you have any questions or concerns, please contact our research team at gertrud@mpib-berlin.mpg.de. We look forward to answering your questions and providing you with further information about our research.