Background: Smaller observational studies have suggested familial clustering of mitral regurgitation (MR). Using a large twin cohort, the aims were to assess MR concordance rates and assess mortality in MR twins and unaffected cotwins.
Methods: Through the Danish Twin Registry, twins with an International Classification of Diseases, Eighth Revision and Tenth Revision diagnosis code of MR born 1880-1989 were identified and proband-wise concordance rates were calculated. To assess whether having a cotwin with MR affected survival, 10 matched twins without MR (n = 5,575) were selected for each MR twin (n = 562), and all-cause mortality rates were assessed.
Results: Among the 87,432 twins alive January 1, 1977, or later, 494 (0.57%) MR individuals were identified. Six MR concordant pairs were found, of which 3 were monozygotic. Proband-wise concordance rate when accounting for right censoring and competing risk of death was 0.12 (95% CI 0.04-0.32) for monozygotic twins and 0.03 (95% CI 0.01-0.09) for dizygotic twins. Mortality was significantly higher among the affected twins with MR within discordant twin pairs where both were alive at the date of MR diagnosis (sex-adjusted hazard ratio [HR] 2.57, 95% CI 1.86-3.54). Overall there was no increased mortality risk for unaffected cotwins to MR cases compared with matched controls (HR 1.02, 95% CI 0.90-1.17) except for first year of life (HR 1.92, 95% CI 1.10-3.36) and for monozygotic twins older than 65 years (HR 1.49, 95% CI 1.07-2.08).
Conclusion: Although there is a familial aggregation of MR, the absolute risk is low, even for monozygotic cotwins to affected twins. The study found increased mortality in MR twins compared with their unaffected cotwins. Overall no excess mortality was observed in the unaffected cotwins except for first year of life and for monozygotic cotwins older than 65 years.
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