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.