Race/ethnicity is a social construct incorporating biological, sociocultural, psychological, and behavioral components, and there is no genetic definition of race.1 In contrast, genetic ancestry is a genetics concept that describes the architecture of genome variation between populations.2 All genetic variation begins locally, as a new mutation in an individual, and thus, all new mutations are ...

The population-based twin registries of Denmark, Finland, Norway and Sweden represent an extraordinary resource for scientific research. Although each register has its own history and composition, they share certain common qualities. All the Nordic countries have a long tradition of population registration, a high standard of living and health-related registers of high quality. The large size o...