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  • Autism Has Characteristic Behavioral Features

  • There Is a Strong Genetic Component in Autism

  • Autism Has Characteristic Neurological Abnormalities

  • There Are Distinctive Cognitive Abnormalities in Autism

    • Social Communication Is Impaired: The Mind Blindness Hypothesis

    • Other Social Mechanisms Contribute to Autism

    • People with Autism Show a Lack of Behavioral Flexibility

    • Some People with Autism Have Special Talents

  • Some Neurodevelopmental Disorders Have a Known Genetic Basis

    • Fragile X Syndrome

    • Rett Syndrome

    • Down Syndrome

    • Prader-Willi and Angelman Syndrome and Other Disorders

  • An Overall View

During the past century "mental retardation" was broadly used to label a variety of cognitive impairments that were linked to prenatal or early postnatal brain abnormalities. Some subgroups with easily identifiable physical features, such as Down syndrome, were recognized early on. In recent years syndromes that result from genetic anomalies but do not express obvious physical features, such as fragile X syndrome, have also been delineated.

Common to all of these disorders are mental impairments that persist throughout life, hampering development and learning, hence the terms "neurodevelopmental disorder" and "learning disability." Generally speaking, even if all mental functions seem to be affected, some tend to be more affected than others. This differential vulnerability gives interesting clues about the different origins and developmental time course of specific mental functions in normal development.

In this chapter we focus on autism and briefly consider Down syndrome, fragile X, and other neurodevelopmental disorders with a known genetic basis. Autism is especially interesting because it impairs brain functions that are highly sophisticated in human beings: social awareness and communication. Autism is also an exemplar of many psychiatric disorders: there is a striking range in severity of symptoms, an impressive heterogeneity of comorbid conditions, and no clear cut neuropathology. It is likely that autism will ultimately be viewed as a class of disorders each with different etiologies that include genetic and environmental factors and their interaction.

Autism Has Characteristic Behavioral Features

Autism has probably always been with us, but it was identified and labeled only in 1943 by Leo Kanner and by Hans Asperger in 1944. Where were the autistic people in the past? Rare historical documents suggest that some may have been valued as eccentrics or holy fools, but the majority were probably considered to suffer constitutional mental deficiency.

Today clinicians and researchers think of autism as a spectrum of disorders with three common diagnostic features, each showing a great deal of variability among individuals: impaired social interaction, impaired verbal and nonverbal communication, and restricted or circumscribed interests with stereotyped behaviors. The label "Asperger syndrome" is often used for individuals who exhibit the typical features of autism but have high verbal ability and no delay in language acquisition.

Autism and related disorders affect approximately 1% of the population, a far higher frequency than was previously recognized. Whether this reflects a better understanding ...

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