Objectives: This study aimed to investigate the aetiological overlap between autistic traits and anxiety-related behaviours within the general population using quantitative genetic techniques. In addition, it aimed to establish whether anxiety-related behaviours were most strongly associated with the social, non-social or communicative traits characteristic of ASD.
Methods: We investigated the phenotypic and genetic overlap between measures of autistic traits and anxiety-related behaviours in a population-based sample of 3827 twin pairs at age 9, using both parent and teacher ratings.
Results: Our results showed that there was a modest correlation between characteristics of ASD and anxiety within the general population (0.31 for parent data, 0.33 for teacher data). For the parent data, a modest but significant proportion of genetic influences overlapped across autistic traits and anxiety-related behaviours in the general population, but there was also evidence for genetic influences that were specific to each. With regard to particular autistic traits, communicative difficulties showed the strongest phenotypic and genetic overlap with anxiety-related behaviours. Model-fitting using the teacher data produced similar results.
Conclusions: There appears to be a moderate overlap between ASD characteristics and anxiety-related traits, mirroring findings from clinical studies. This overlap appears to be caused in part by shared genetic influences between autistic traits and anxiety-related behaviours, particularly autistic communication difficulties. This has implications for understanding the causes of the overlap between anxiety and autistic behaviours.