Aetiological relationship between language performance and autistic-like traits in childhood:: a twin study

Background: Impairments in language and communication are core features of autism spectrum disorders (ASDs). The basis for this association is poorly understood. How early language is related to each of the triad of impairments characteristic of ASDs is also in need of clarification. Aims: This is the first study that aims to determine the extent to which shared genetic and environmental factors underlie the association between early language performance and autistic-like traits (ALTs) in middle childhood. Methods & Procedures: Data came from a population-based twin sample ( n=56087 pairs) assessed prospectively at 2, 3, 4 and 8 years. ALTs measured by the Childhood Asperger Syndrome Test ( CAST) at 8 years were investigated in relation to language assessed by the MacArthur Communicative Development Inventory (CDI) at 2, 3 and 4 years. Multivariate model fitting techniques were used to analyse the origins of this association. Outcomes & Results: Total CAST scores, as well as Social and Communication subscales, at 8 years were weakly but significantly negatively correlated with language ability at 2, 3 and 4 years. Correlations between language and restrictive and repetitive behaviours and interests (RRBI) were not significant. The phenotypic correlations between language and Social and Communication ALTs were almost entirely mediated by shared genetic influences. There were specific genetic influences on early language that were not shared with ALTs, and specific genetic influences on ALTs not shared with earlier language performance.