Genetic and environmental etiology of speech and word reading in Chinese

The present study examined the genetic and environmental etiology of the connection between speech and word reading in Chinese. 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 discrimination and production, phonological skills, semantic skills, and Chinese word reading at the mean age 7.4 years. 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 word reading supported a common genetic factor underlying speech, phonological skills, semantic skills, and word reading in Chinese. The present findings suggest that around 50% to 60% of individual differences of speech, semantic skills, and word reading in Chinese are due to genetic factors. Individual differences of phonological skills appear to be relatively less heritable than those in English. This may be partly due to the fact that the Chinese script does not map directly on any segmental phonological information. A single common genetic etiology for speech, phonological skills, semantic skills, and word reading suggests that development of these skills is highly connected.