Background: the genetic and environmental contributions to cognitive function in the old people have been well addressed for the Western populations using twin modelling showing moderate to high heritability. No similar study has been conducted in the world largest and rapidly ageing Chinese population living under distinct environmental condition as the Western populations.
Objective: this study aims to explore the genetic and environmental impact on normal cognitive ageing in the Chinese twins.
Design/setting: cognitive function was measured on 384 complete twin pairs with median age of 50 years for seven cognitive measurements including visuospatial, linguistic skills, naming, memory, attention, abstraction and orientation abilities. Data were analysed by fitting univariate and bivariate twin models to estimate the genetic and environmental components in the variance and co-variance of the cognitive assessments.
Results: intra-pair correlation on cognitive measurements was low to moderate in monozygotic twins (0.23–0.41, overall 0.42) and low in dizygotic twins (0.05–0.30, overall 0.31) with the former higher than the latter for each item. Estimate for heritability was moderate for overall cognitive function (0.44, 95% CI: 0.34–0.53) and low to moderate for visuospatial, naming, attention and orientation abilities ranging from 0.28 to 0.38. No genetic contribution was estimated to linguistic skill, abstraction and memory which instead were under low to moderate control by shared environmental factors accounting for 23–33% of the total variances. In contrast, all cognitive performances showed moderate to high influences by the unique environmental factors.
Conclusions: genetic factor and common family environment have a limited contribution to cognitive function in the Chinese adults. Individual unique environment is likely to play a major role in determining the levels of cognitive performance.