Many genetic disorders of known etiology share behavioral characteristic with the autism spectrum disorders (ASD), including language delays, social difficulties, and unusual patterns of behavior. There exist tendencies to either over- or under-pathologize these similarities, resulting in both false diagnoses and diagnostic overshadowing. Recent findings in Williams syndrome (WS), a genetic disorder often contrasted with ASDs, have demonstrated a significant overlap between these two phenotypes in young children with limited language. Using a gold-standard autism diagnostic tool, the ADOS, the present study aimed to further characterize the nature of socio-communicative behaviors in verbal children with WS, both within WS and in comparison to children with Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS) and developmental conditions of mixed etiology (ME). Results indicated that approximately one-third of the children with WS met threshold for classification on the autism spectrum. There were a number of items on which the children classified ASD and those classified non-spectrum received different scores, such as conversation difficulties, quality of social overtures including integrated eye contact and facial expressions, and play behaviors. Consistent with previous studies, children with WS who have significant socio-communicative difficulties (i.e., those classified ASD ) demonstrate a behavioral
profile similar to that seen in children with Pervasive Developmental Disorder-Not Otherwise Specified. Implications for understanding the nature of the behavioral pattern in WS, and in genetic disorders in general, will be discussed
