Cohort profile and representativeness of participants in the Danish monozygotic twin study on migraine

The Danish Monozygotic Twin Study on Migraine is a population-based twin study established in 2023-2024. The cohort was created to lay the foundation for innovative studies of the role of environmental, genetic, and epigenetic factors and their complex interactions in the pathogenesis of migraine. The aim of this paper is to describe data collection, content, characteristics of participants and to assess the representativeness of the cohort by comparing participants to non-responders. Danish monozygotic twins born between 1967 and 2000 were invited to participate. Self-reported questionnaires were sent out to 9,036 possible participants. The questionnaires assessed migraine and migraine subtypes, life satisfaction, resilience, stress, childhood trauma and the relationship of the participant to their family. Through linkage to the nationwide Danish registries the cohort contains individual level information on education, income, patient data from hospitals, prescription medication and childbirth. The Danish registries also enable longitudinal data collection on health outcomes. Individuals who responded to the migraine questionnaire were defined as participants. The cohort consists of 3,893 individuals, including 1,822 complete twin pairs, 1,173 individuals with migraine and 280 migraine discordant twin pairs. 123 participants were included in a substudy with a migraine diagnostic interview and collection of blood samples for both genetic and epigenetic studies. Comparison between participants and non-responders showed a higher participation rate among women. For both genders participants were older, had a higher level of education and a higher level of income compared to non-responders. Sociodemographic differences in participation should be considered to avoid biased estimates in future studies based on the cohort.