Evidence for genetic mediation of executive control: a study of aging male twins.

The objective of this study was to investigate the genetic and environmental influences on indexes of executive control in elderly male twins (members of the National Heart, Lung, and Blood Institute Twin Study). Multivariate genetic modeling was applied to performance on four tests: Digit Symbol Substitution, color--word interference, Trail Making B, and verbal fluency. After exclusion of individuals with a positive stroke history, data were available for 80 monozygotic and 78 dizygotic twin pairs of ages 69--80 years. Performance on all measures was adjusted for age and education. Significant genetic and environmental influences to performance on each measure of executive control were identified (range of heritability = 34%--68%). Multivariate analyses revealed that a model with a latent executive control factor most adequately fit the observed covariances on test performance, chi(2)(58, N = 316) = 69.7, p =.14. The shared executive control factor had a heritability of 79% and accounted for 10%--56% of the genetic variance in performance on each of the four tests. Of the 4 tests examined in this analysis, Digit Symbol Substitution appeared to be the marker of executive control with the largest genetic component, whereas verbal fluency stood out as displaying a pattern of genetic and environmental influences distinct from the other 3 measures.