Autism Spectrum Disorders

(American Psychiatric Association, 2000). Autism is a Issues in Diagnosis and Defining the Phenotype disorder that usually begins in infancy, at the latest, in Over the last 20 years, the conceptualization of a specthe first three years of life. Parents often first become trum of autism-related disorders, including Childhood concerned because their child is not using words to Disintegrative Disorder, Asperger’s Disorder, and Pervacommunicate, even though he or she recites passages sive Developmental Disorder-Not Otherwise Specified from videotapes or says the alphabet. Though social (PDD-NOS), which all include qualitative deficits in social deficits may not be immediately obvious in early years, behavior and communication, has been supported by they become gradually more evident as a child becomes longitudinal, epidemiological, and family studies (see more mobile and as other children become more socially Filipek et al., 2000 for a general review). However, these sophisticated. Young children with autism often do not disorders vary in pervasiveness, severity, and onset. The seek out others when they are happy, show or point to umbrella category is termed Pervasive Developmental objects of interest, or call their parents by name. In Disorder in the most common diagnostic systems preschool years, repetitive behaviors, such as using pe(American Psychiatric Association, 2000; World Health ripheral vision to look at lines or wheels, or specific hand Organization, 1992). Rett’s syndrome has been included and finger movements, begin to develop. in the category of autism spectrum disorders within psyAutism is a heterogeneous condition; no two children chiatric systems because of the overlap in symptoms or adults with autism have exactly the same profile, in toddlers and preschool children but, because of its but difficulties fall into core domains that are reliably different course (e.g., loss of purposeful hand use) and measured and usually consistent across time, even neurological characteristics (e.g., deceleration in head though specific behaviors may change with developcircumference), is a more differentiable group than the ment. A child who may spend a great deal of time spinother syndromes and so generally studied as a distinct ning objects and watching them out of the corner of her disorder. Clear distinctions among the other disorders eye at age four, may not show this behavior at all as a within the autism spectrum, as listed on Table 1, are teenager, but may be fascinated by sunroofs or bald possible according to the degree of accompanying lanheads or World War I. A child whose primary method guage deficit or general cognitive delay (American Psyof communicating requests at age two is to lead his chiatric Association, 1994) or according to the severity mother to whatever he wants, place her hand on it, or of social or behavioral symptoms (Lord et al., 2000). use her hand to gesture toward it, may learn to ask for Asperger’s disorder involves the presence of autistic what he wants quite clearly and persistently by the time social deficits and repetitive, circumscribed interests in he is three or four, but continues to show difficulty carindividuals who are verbally fluent. It has been of interest rying out back and forth conversations and coordinating to scientists because of the contrast, as discussed eareye contact and gestures. lier, between relatively intact and often verbose qualities Because of its links to genetics and neural developof language and limited behaviors. Its prevalence is in ment and the severe abnormalities in social interaction dispute because, in controlled studies, it has been diffiby which it is defined, autism offers the opportunity for cult to reliably differentiate Asperger’s syndrome from scientists to study the neurobiological origins of social autism without mental retardation or language delay, communication skills basic to human behavior. For exexcept by neuropsychological profile (which may be tauample, even as infants, typically developing children tological). are more adept at catching the eye of other people, On the other hand, the appeal of the different categori-