Assessing Autism Co-Occurrence in Fragile X Syndrome: Proposing a Preliminary CARS-2 Cut-Off Score

The purpose of this study was to examine the agreement between autism classification from the Autism Diagnostic Observation Schedule (ADOS-2; as reported by Lord (Autism Diagnostic Observation Schedule, Second Edition, Western Psychological Services, 2012)) and the Childhood Autism Rating Scale, 2nd edition (CARS-2; as reported by Schopler (The childhood autism rating scale, second edition (CARS-2), Western Psychological Services, 2010) in individuals with fragile X syndrome (FXS) and to propose a preliminary optimal CARS-2 cut-off score for identifying co-occurring autism in FXS when using the ADOS-2 as gold-standard measure. Forty-three school-aged and adolescent individuals completed the ADOS-2, CARS-2, and cognitive assessments. We found a strong to very strong positive association between the CARS-2 total scores and ADOS-2 total scores for individuals with FXS, and fair agreement between the ADOS-2 and CARS-2 autism classification ratings. Using a receiver-operator characteristic curve, an optimal CARS-2 cut-off score of 24.25 was found for identifying autism in individuals with FXS. Our findings should be considered preliminary, as they represent an examination of measurement agreement rather than validation against comprehensive DSM-5 clinical diagnoses. Studies using CARS-2 in FXS should carefully evaluate the scores or consider using the CARS-2 as a continuous measure of autism traits until the results of this paper are replicated in a larger and more diverse sample.