The heritability of level and rate-of-change in cognitive functioning in Danish twins aged 70 years and older.

To investigate heritable influences on overall level and rate-of-change in cognitive ability, biometric growth models were fit to cognitive data from nearly 1000 Danish twins age 70 years and older. Twins are participants in the ongoing Longitudinal Study of Aging Danish Twins, a cohort-sequential study of twins assessed every 2 years for up to four waves. Cognitive ability was assessed by five brief cognitive tasks: a fluency measure, forward and backward digit span, and immediate and delayed list recall. Model-fitting results indicated that although the overall level of cognitive functioning was highly heritable (h(2) = .76, 95% confidence interval of .68 to .82), the rate of linear change was not (h(2) = .06, 95% confidence interval of .00 to .57). These findings suggest that the search for specific genes might reasonably focus on average level of cognitive performance, whereas specific environmental influences might account for cognitive change.