Objectives: The current study aimed to further our understanding of the overlap between ASD and anxiety by using a large population-based twin sample, gold-standard diagnostic tools for ASD and both parent and self-report measures of anxiety.
Methods: The study forms part of the Twins Early Development Study (TEDS), a longitudinal investigation of approximately 16,000 twin pairs born between 1994 and 1996. Within the Social Relationships Study, we visited 120 of these twin pairs, now aged 13-15, where one or both of the children were diagnosed or suspected of having ASD. These twins were representative of the full autism spectrum. 75 comparison families were also visited, with no history of ASD. The Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R) were used to determine the diagnostic status of each twin with suspected or diagnosed ASD and their cotwin. In addition, we obtained parent and self-report ratings of anxiety (using the Revised Child Anxiety and Depression Scale); which included measures of panic, social anxiety, obsessive compulsive symptoms (OCD), general anxiety and separation distress.
Results: Rates of parent-reported anxiety were significantly increased in individuals with ASD, compared to controls (p<0.05). This was true for all 5 subtypes of anxiety. OCD symptoms were the most frequently observed difficulties in the ASD group, followed by symptoms of panic and social anxiety. In general, cotwins of ASD probands scored at a level that was comparable to the control group. Children with ASD, control children and cotwins were very similar with regard to their self-reported levels of anxiety. The only exception was social anxiety, where children with ASD rated themselves as significantly more anxious than controls (although not cotwins). In the ASD group, symptoms of anxiety were most strongly associated with communication difficulties and also repetitive behaviours and interests.
Conclusions: Our results supported previous findings that children with ASD experience elevated levels of anxiety; particularly symptoms of OCD and panic disorder. However, this was only observable using parent-ratings, suggesting that the children themselves may find it difficult to introspect about their anxiety difficulties. Investigating the associations between anxiety and specific aspects of ASD may help to guide timing and targeting of anxiety interventions. For example, focused intervention on communication may help reduce anxiety in ASD by making interactions less stressful and increasing available coping strategies in high anxiety situations.