The older FTC is a population-based study of twins born in Finland before 1958. Four waves of surveys were conducted by mail in 1975, 1981, 1990, and 2011. Ethical approval was obtained from the HUS Regional Ethics Committee (ID 01/2011). Informed consent to participate was not obtained directly but was inferred from the completion of the questionnaires. All those who provided blood or saliva samples for DNA have provided written informed consent. The purpose of the study was explained to the participants, and all participants were aware that they could withdraw from the study at any time without any consequences. A full description of the older FTC has been published previously (36). The current study includes n=6,257 EUR participants with genetic data passing quality control and who were aged 18–40 in 1975.
