Epidemiologic Insight from Twin-Family studies: Kimchi Eating Trial and Salt Intake Habit Studies as Examples

Abstract

Twin studies have contributed to science mainly by discriminating the roles of genes versus environments by comparing the resemblances between monozygotic twins (MZ) and dizygotic twins (DZ). MZ and DZ shares most of fetal, developmental, and educational environments whereas MZ shares 100% but DZ does only 50% of genetic constitution. Recently, twin or twin-family studies have evolved; a cotwin-control study is a modern design, in which comparisons are made between two cotwins (mainly MZ), in which, comparing with a conventional case-control study, case is selected from twins and the control is replaced by the cotwin of the case. Applications of the design include biomarker, epigenetics and microbiome studies. Clinical trial is another application, where two MZ cotwins are allocated to different intervention groups. Additionally, adding other family members to various twin study design can provide unique epidemiologic insight as well.