Genetic and environmental etiology of speech and word reading in Chinese

Abstract

PURPOSE: The present study examined the genetic and environmental etiology of the connection between speech and word reading in Chinese. METHOD: A total of 371 pairs of Chinese twins (278 pairs of monozygotic twins and 93 pairs of same-sex dizygotic twins) were tested on speech, phonological skills, semantic skills, and Chinese word reading at the mean age 7.5 years. RESULTS: Results of univariate genetic analyses showed moderate genetic influences on speech, semantic skills, and Chinese word reading, while moderate shared environmental influences on phonological skills. The genetic correlations among all the variables were significant. Results of testing several models on the link between speech and reading supported a common genetic factor underlying speech, phonological skills, semantic skills, and word reading in Chinese. CONCLUSIONS: The present findings suggest that around 50% of individual differences of speech, semantic skills, and word reading in Chinese are due to genetic factors. Individual differences of phonological skills are relatively less heritable while semantic skills are more heritable in Chinese than those in English. This may be partly due to the fact that more phonics instruction was carried out in English-speaking schools while more word compounding activities in Chinese-speaking schools. The genetic linkage between speech and Chinese word reading is both phonological and semantic in nature. A single common genetic etiology for speech, phonological skills, semantic skills, and word reading suggests that those who are good in speech, may also develop better phonological and semantic skills, and in turn facilitates the development of reading skills.