Correlation of Measures of Autistic and Obsessive-Compulsive Symptoms

Background: Obsessive-Compulsive symptoms are common in Autism Spectrum Disorders (ASD) (Russell et al. (2005); McDougle et al. (1995); Zandt et al (2006).  It has been suggested that the high comorbidity of ASD and OCD may be explained by the repetitive behaviours typically present in ASD.  However nobody has directly tested this hypothesis

Objectives: To correlate severity of Obsessive or compulsive symptoms and Autistic symptoms.

Methods: 40 Right-handed male subjects age 16-45 with ASD were diagnosed using both the ADI and ADOS, and we included a similar number of age matched controls.  This investigation formed part of the MRC UK AIMS Network at the Institute of Psychiatry.  Obsessionality was measured using the Obsessive-Compulsive Index - revised version (OCI-R).

Results: 54% of people with ASD scored above the cut off for OCD, as compared to 10% of controls.  Autism Quotient scores (AQ) were positively correlated with OCI-R scores overall.  However there was no correlation between repetitive or compulsive behaviours  (as measured using sub scores of the ADI and ADOS) and the OCI-R scores.

Conclusions: The prevalence of Obsessive-compulsive symptoms is much higher in subjects with an ASD than in the general population; but this is not explained by severity of autistic repetitive behaviours.  It is likely therefore that they have a separable genetic and/or biological basis.