Genetic Liability in Stroke

BACKGROUND AND PURPOSE: Few studies have assessed the overall importance of genetic factors on stroke risk, and the results have been contradictory. We used a large, population-based twin register and nationwide registries of death and hospitalization with long-term follow-up to estimate the effect of genetic factors on the risk of stroke. METHODS: Through the population-based Danish Twin Register, we identified same-sex twin pairs born in 1870 through 1952 for whom at least 1 twin was recorded under a stroke diagnosis in the Register of Causes of Death or the Danish National Discharge Register. From the day of the first stroke event in each twin pair, the live co-twins were followed up for stroke. In survival analyses, we estimated the age- and sex-adjusted effect of zygosity on the risk of stroke death or hospitalization for stroke. Concordance rates, tetrachoric correlations, and heritability were also assessed. RESULTS: Thirty-five of 351 monozygotic pairs (10%) and 34 of 639 dizygotic pairs (5%) were concordant for stroke death. The age- and sex-adjusted relative risk of stroke death in monozygotic compared with dizygotic co-twins was 2.1 (95% CI, 1.3 to 3.3). The probandwise concordance rates were 0.18 (95% CI, 0.14 to 0.22) for monozygotic and 0.10 (95% CI, 0.08 to 0.13) for dizygotic pairs. Thirty-three of 309 monozygotic pairs (11%) and 39 of 560 dizygotic pairs (7%) were concordant for stroke hospitalization or stroke death. The age- and sex-adjusted relative risk of stroke hospitalization or stroke death in monozygotic compared with dizygotic co-twins was 1.5 (95% CI, 0.9 to 2.4). The probandwise concordance rates were 0.19 (95% CI, 0.15 to 0.24) for monozygotic and 0.13 (95% CI, 0.10 to 0.16) for dizygotic pairs. The heritability estimates were 0.32 for the liability to stroke death and 0.17 for the liability to stroke hospitalization or stroke death. CONCLUSIONS: The observed increased risk of stroke death and stroke hospitalization in monozygotic compared with dizygotic co-twins suggests that genetic factors increase the risk of stroke and that the size of this effect is moderate.