Exploring the Relationship Between Anxiety and Insistence on Sameness in Autism Spectrum Disorders

Background: Elevated anxiety symptoms are one of the most common forms of psychopathology to co-occur with autism spectrum disorders (ASD).  Evidence exists to suggest a shared genetic risk between ASD and anxiety disorders, however it is unclear whether this explains the high rates of co-occurrence or suggests that anxiety is an intrinsic feature of ASD, possibly as a result of restricted, compulsive behaviors. Of note, rates of overlap in anxiety and Insistence on Sameness (IS) have not yet been documented and replicated in large ASD samples. 

Objectives: The purpose of this study was to explore the association between anxiety and ASD symptoms, particularly the degree to which the relationship is explained by IS behaviors and/or cognitive ability. 

Methods: The sample included 1429 individuals aged 5:8 to 18:0 years who participated in the Simons Simplex Collection (SSC), a genetic consortium study of ASD. Child Behavior Checklist Anxiety Problems T-scores and Autism Diagnostic Interview-Revised “Insistence on Sameness” item raw totals were treated as both categorical and continuous measures of anxiety and IS respectively. Chronological age, verbal IQ, and a variety of ASD phenotype-related and other behavioral variables were assessed for potential association with anxiety and IS. 

Results: Anxiety and IS continuous variables were minimally though significantly associated with each other and with chronological age and verbal IQ. Neither anxiety nor IS was associated with other core autism diagnostic scores. Anxiety was associated with a variety of other psychiatric and behavioral symptoms in ASD, including irritability, attention problems, and aggression, while IS was not. 

Conclusions: Anxiety and Insistence on Sameness appear to function as distinct constructs, each with a wide range of expression in children with ASD across age and IQ levels. Thus, both variables could be of use in ASD behavioral research or in dimensional approaches to genetic exploration. Unlike IS, however, anxiety is related to non-ASD-specific behavioral symptoms.