Abstract
The worldwide development of twin cohorts began after World War II. These cohorts now include around 1.5 million twins, and more than 2748 twin studies have been published between 1950 and 2012. Each year, the number of twin publications increases by another 500 to 1000. The underrepresentation of German twin studies cannot be solely explained by the abuse of medical research under National Socialism. Developing and expanding large twin cohorts is a challenge in terms of both ethics and data protection. However, twin cohorts enable long-term and real-time research on many medical issues and contribute to answer the question of predisposition or environment as possible disease triggers - even after the sequencing of the human genome.There are currently two German twin cohorts: the biomedical cohort HealthTwiSt, with around 1500 pairs of twins, and TwinLife, a sociological-psychological cohort with around 4000 pairs of twins. There are also disease-specific cohorts. The TwinHealth Consortium in the Faculty of Medicine at the University of Tübingen was established in 2016 with the aim of enabling open-ended and sustainable twin research in Tübingen to answer various scientific questions.With the help of systematic literature research and medical history, this article gives an overview of the worldwide development of twin studies and databases over the last 100 years. The example of the Tübingen TwinHealth Initiative illuminates the structure of a twin cohort and its legal, ethical, and data protection aspects.