In the present study we investigated the co-morbidity of pervasive developmental disorder (PDD) in 59 Prader-Willi syndrome (PWS) individuals and in 59 non-specific mentally retarded controls, matched for IQ, gender, and age. The 'Pervasive Developmental Disorder Mentally Retardation Scale' (PDD-MRScale), a screening questionnaire based on the DSM-III-R criteria for PDD, has been applied in the PWS group and in the control group. Results of the present study revealed a striking autistic-like behavioral phenotype in the majority of the PWS individuals, particularly deficits in the quality of language and communication and of imagination and interests. This intersection with autistic symptomatology is an important addition to the behavioral phenotype in PWS persons. A first approach to delineate subtypes of autistic symptomalogy among PWS persons was performed. Nineteen percent of the PWS group did meet the full diagnostic DSM-III-R criteria for PDD in comparison with 15% in the control group. Results revealed that a higher IQ in PWS does not protect to develop genuine PDD and that uniparental disomy/imprinting mutation as genetic origin seems to be an additional risk factor for developing genuine PDD. The results of the present study suggest the importance of reconsidering the commonly recognized obsessive-compulsive like behavior in PWS persons within the broader spectrum of autism disorders.

Because of the importance of contextual sensitivity in several cognitive processes that are affected in autism spectrum disorder (ASD), such as social cognition, understanding of language, or cognitive shifting, we argue that a lack of contextual sensitivity or "context blindness" should be given more attention in a neurocognitive account of ASD. Context blindness emphasizes an aspect of the central coherence hypothesis developed by Uta Frith that has been largely overlooked in both literature and scientific research, namely, the ability to use context in sense making. In this article, we will define context blindness, describe how it can explain some of the cognitive and behavioral characteristics of ASD, and explore its relationship with the other neurocognitive theories of ASD (theory of mind, empathizing-systemizing, and executive function).

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