A longitudinal analysis of word reading skills in Chinese twin children: genetic and environmental influences

Abstract

Previous research has shown that language and reading abilities of school aged children are strongly influenced by genetic factors. However, most findings were derived from cross-sectional data and conducted for alphabetic languages. This study investigated the etiology of individual differences in the development of Chinese word reading skills by using a longitudinal twin design. A total of 312 typically developing Chinese twin pairs aged from 3 to 11 years were given a task of 198 Chinese word to read. They were assessed at three different time points with one year interval. Their reading accuracy was recorded each time. A biometric latent growth curve model was fitted using the SAS Proc Mixed procedure. The results show that variation in Chinese word reading skills was explained by strong shared family influences (70%) together with minor additive genetic influences (28%) in pre- and early school years. The family influences remain strong during the late primary school years, but their relative importance declines with age. On the other hand, the impact of genetic influences gradually grows and the heritability estimate reaches over 40% by the age of 11. Despite the activation and acceleration of genetic influences, this study emphasizes the importance of literacy and education during the early school years.