Autism spectrum disorder (ASD) symptom profiles of children with comorbid Down syndrome (DS) and ASD: A comparison with children with DS-only and ASD-only.

BACKGROUND: Down syndrome (DS) is associated with increased rates of autism spectrum disorder (ASD), characterized by social-communicative impairments (SOC-COM) and repetitive behaviors and interests (RBI). However, little is known about the ASD symptom presentation in children with DS + ASD.

AIMS: The current study sought to describe parent-report of SOC-COM and RBI symptoms on the Autism Diagnostic Interview -Revised (ADI-R) in children with DS (n = 22), DS + ASD (n = 11), and ASD (n = 66).

METHOD: SOC-COM and RBI scores from the ADI-R were compared across the groups whose autism status was ascertained using the Autism Diagnostic Observation Schedule.

RESULTS: Differences in SOC-COM and RBI symptom severity was observed. The general pattern of findings was ASD > DS+ASD > DS. Dissimilar ASD symptom profiles were observed across groups. In ASD, SOC-COM scores were higher than RBI scores; in DS + ASD, similar SOC-COM and RBI scores were observed. Lastly, SOC-COM impairments were highly related to verbal cognition in youth with DS + ASD but not in those with DS or ASD.

CONCLUSIONS AND IMPLICATIONS: These findings suggest that children with DS + ASD have a distinct profile of ASD symptoms that differs from peers with either disorder in isolation. Thus, care should be taken in evaluating and designing treatments for this group.