Williams syndrome (WS) is a neurodevelopmental disorder resulting from a hemizygous microdeletion of ~25 genes on chromosome 7q11.23 (1
). Individuals with WS have distinctive medical and cognitive profile (2
). Compared to children with other types of developmental disorders, children with WS are less reserved toward strangers, more approaching, more gregarious, overly friendly, and affectionate (see review in 3
). These prosocial behaviors make it unlikely that one would suspect overlap with the autism spectrum. However, there is also evidence that children with WS experience difficulties with social interaction and social communication. Parents often report that their children with WS are often not attuned to others socially and experience difficulties establishing and maintaining friendships (4
) Significant conversational deficits (6
), poor social skills (7
), poor understanding of socially-relevant information (8
), and restricted interests (10
) have been observed. Delayed language and gestural development are described (see review in 11
Hence, many of the socio-communicative and behavioral difficulties observed are also characteristic of children with autism spectrum disorders (ASD) and may not be accounted for by developmental delay alone. Gillberg and Rasmussen (12
) state, “…it is clear from the results of these preliminary investigations that this patient group [WS] does have several problems seen in autism. Included in this catalogue are hyperacusis, social isolation, and other types of social impairment…, distractibility, inflexibility, ritualism, obsessiveness, and pragmatic deficits…, all of which can be hallmarks of the autistic syndrome” (p. 382). There have been a few reports of children diagnosed with both WS and autism (12
). Given the prevalence of WS (1 in 7,500 live births) (17
) and the recently reported prevalence of ASD placed at 1 in 150 (18
), it would be expected that some individuals with WS would also have an ASD. A recent investigation comparing the performance of young children with WS on the ADOS to participants with clinical diagnoses of autism (16
) found that although participants with WS showed a number of socio-communicative deficits, they could reliably be distinguished from participants with clinical diagnoses of autism and had considerably fewer socio-communicative deficits. Ten percent of their sample of young children with WS met DSM-IV criteria for autism.
The possibility of overlap between children with WS and children with clinical diagnoses of PDD-NOS has not examined, however. The DSM-IV category of PDD-NOS is quite heterogeneous, with more varied ways to meet the diagnostic criteria for PDD-NOS than for Autistic Disorder. Although difficulties with social reciprocity need to be present for a diagnosis of PDD-NOS, some children with PDD-NOS do not have significant deficits in communication or do not show restricted and repetitive behaviors. Additionally, the nature of the socio-communicative deficits of people with PDD-NOS can be milder than for autism. Relatedly, individuals falling within the “Active But Odd” autism subtype do not necessarily avoid social interaction or prefer solitary activity (19
). Given the reported pattern of behavioral characteristics of young children with WS, they may be more likely to show overlap with the milder diagnostic category of PDD-NOS rather than with autism, which is characterized by more severe socio-communicative deficits.
Using the Autism Diagnostic Observation Schedule (ADOS) to assess the socio-communicative behavior of young children with WS with limited language (21
), we recently found evidence of socio-communicative deficits overlapping with those typically seen in children with ASD. In the current investigation, we further examine how these difficulties compare to those of individually matched participants with autism, PDD-NOS, or developmental disabilities of other etiologies without spectrum diagnoses. Comparison to the Mixed Etiology (ME) group enables identification of the deficits of children with WS that are not explained by developmental delay alone. Comparisons to the PDD-NOS (PDD) and Autism (AUT) groups enable further exploration of the possibility that young children with WS show socio-communicative deficits that overlap with the autism spectrum.