Background.—Studies of twins who are separated from each other early in life and are reared in different environments offer the opportunity to resolve variation in liability to disease.
Objective.—To evaluate the importance of genetic and environmental influences in migraine; in particular, addressing the role of the shared rearing environment.
Methods.—A population-based cohort of twins, including a subsample of 314 pairs reared apart and 364 matched control pairs reared together, was drawn from the Swedish Twin Registry. Data on lifetime migraine was collected via self-administered questionnaires mailed to twins aged 42 to 81 years. Quantitative genetic models and regression models were used to analyze sources of twin similarity.
Results.—We found nonsignificant shared rearing environmental influences on migraine for men (17%) and no rearing effects at all for women. The heritability of migraine was estimated at 38% (95% confidence interval, 0 to 73) for men and 48% (95% confidence interval, 27 to 65) for women. Among monozygotic twins reared apart, those separated at 3 years of age or earlier were more similar for lifetime migraine than those separated later, and this was especially true for women.
Conclusion.—In agreement with previous twin data, family resistance in migraine is mainly due to genetic factors, whereas environmental influences make family members different, not similar.