The autistic phenotype in Down syndrome: differences in adaptive behaviour versus Down syndrome alone and autistic disorder alone.

The autistic phenotype in Down syndrome (DS) is marked by a characteristic pattern of stereotypies, anxiety and social withdrawal. Our aim was to study adaptive behaviour in DS with and without autistic comorbidity using the Vineland Adaptive Behaviour Scales (VABS), the Childhood Autism Rating Scales (CARS) and the DSM IV-TR criteria. We assessed 24 individuals and established three groups: Down syndrome (DS), DS and autistic disorder (DS-AD), and autistic disorder (AD). The DS and DS-AD groups showed statistically significantly similar strengths on the VABS (in receptive and domestic skills). The DS and DS-AD subjects also showed similar strengths on the CARS (in imitation and relating), differing significantly from the AD group. The profile of adaptive functioning and symptoms in DS-AD seemed to be more similar to that found in DS than to the profile emerging in AD. We suggest that the comorbidity of austistic symptoms in DS hampered the acquisition of adaptive skills more than did the presence of DS alone.