Autistic Spectrum Disorders

The terms autistic spectrum disorders and pervasive developmental disorders (PDD) are synonyms that serve as an umbrella for a wide range of cognitive and neurobehavioral developmental disorders. Individuals on the autistic spectrum show similar qualitative impairments in (a) verbal and nonverbal communication, (b) social interactions, and (c) stereotyped and repetitive behaviors or interest (American Psychiatric Association [APA], 1994). The fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (APA, 1994) includes five possible diagnoses under the PDD umbrella, all of which are concordant with the latest (10th) International Classification of Disease (ICD-10) (Filipek et al., 1999). The five possible autistic spectrum disorder diagnoses are autistic disorder (i.e., “classic” autism); Asperger disorder (i.e., Asperger's syndrome); childhood disintegrative disorder; Rett disorder; and pervasive developmental disorder–not otherwise specified (PDD-NOS) including atypical autism (APA, 1994).

Over the past two decades, there has been an intense focus on autistic spectrum disorders, and understanding of these disorders has improved greatly. However, almost all autistic spectrum disorders are still a mystery, and the exact cause or causes of these disorders are still unknown. While there are many theories on what causes autistic disorders, most research is focused primarily on genetic causes, with some research also looking at other factors, such as neurological, infectious, metabolic, immunologic, and environmental ones (Filipek et al., 1999).

Medical genetics strongly suggests that genetic heterogeneity is to be expected in autism since there are numerous examples of different genetic abnormalities all leading to what appears to be the same clinical picture (Rutter, Bailey, Simonoff, & Pickles, 1997).