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Autism
is a neurodevelopmental disorder characterized by impaired social
interaction and communication, repetitive and stereotyped patterns
of behavior, and uneven intellectual development often with mental
retardation. Symptoms begin in early childhood. The cause in most
children is unknown, although evidence supports a genetic component;
in some, autism may be caused by a medical condition. Diagnosis
is based on developmental history and observation. Treatment consists
of behavioral management and sometimes drug therapy.
Autism, a neurodevelopmental disorder, is the most common of the disorders called pervasive developmental disorders (PDDs—see Table 2: Learning and Developmental Disorders: Pervasive Developmental Disorders Spectrum ). Given the wide clinical variability of these conditions, many people also refer to PDDs as “autism spectrum disorders.” Estimates of prevalence range from 5/10,000 to 50/1000. Autism is 2 to 4 times more common in boys. In the past decade, there has been a rapid rise in the diagnosis of autism spectrum disorders, partially because of changes in diagnostic criteria.
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Table 2
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Pervasive Developmental
Disorders Spectrum
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Subtype
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Characteristics
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Asperger's syndrome
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Language and cognition generally better than in autism; socially isolated and often viewed as odd or eccentric; clumsiness; repetitive patterns of behavior, interests, and activities; atypical sensory responses (eg, exquisite sensitivity to noises, food odors or tastes, or clothing textures); pragmatic deficits (eg, extremely concrete use of language or difficulty recognizing irony or jokes)
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Autism (autistic disorder)
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Onset before age 3 yr; impaired social interaction and communication; repetitive stereotyped behavior; some degree of mental retardation in most cases; in some cases severe regression of language and sociability occurs between 18 and 24 mo
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Childhood disintegrative disorder
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After 2 yr of normal growth, a marked regression occurs in at least 2 of the following: social skills, language, bladder and bowel control, motor skills; can eventually become more severe than is typical in autism; other behaviors may mimic autism or childhood schizophrenia
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Pervasive developmental disorder not otherwise specified
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Does not meet criteria for any of other subtypes yet exhibits a wide range of cognitive and behavioral problems and impairment in social interactions; less severe than autism
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Rett syndrome
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Affects development after initial 6-mo period of normal development; deceleration of head growth; severe mental retardation; impaired social interaction; loss of speech and purposeful use of hands (results in “hand-wringing stereotypy”); seizures, autistic features, ataxia; affects almost exclusively girls (caused by mutation in MECP2 gene on Xq28)
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Etiology
Most cases of autism spectrum disorders are unrelated to diseases that affect the brain. However, some cases have occurred with congenital rubella syndrome, cytomegalic inclusion disease, phenylketonuria, and fragile X syndrome.
Strong evidence supports a genetic component. Parents of one child with a PDD have a risk 50 to 100 times greater of having a subsequent child with a PDD. The concordance rate of autism is high in monozygotic twins. Research on families has suggested several potential target gene areas, including those related to neurotransmitter receptors (GABA) and CNS structural control (HOX genes). Environmental causes (including vaccination and various diets) have been suspected but are unproven.
Abnormalities of brain structure and function probably underlie much of the pathogenesis of autism. Some children with autism have enlarged ventricles, some have hypoplasia of the cerebellar vermis, and others have abnormalities of brainstem nuclei.
Symptoms,
Signs, and Diagnosis
Autism usually manifests in the 1st yr of life and always by age 3. The disorder is characterized by atypical interaction (ie, lack of attachment, inability to cuddle or to form reciprocal relationships, avoidance of eye gaze), insistence on sameness (ie, resistance to change, rituals, intense attachment to familiar objects, repetitive acts), speech and language problems (ranging from total muteness to delayed onset of speech to markedly idiosyncratic use of language), and uneven intellectual performance. Some affected children injure themselves. About 25% of affected children experience a documented loss of previously acquired skills.
Current theory holds that a fundamental problem in autism spectrum disorders is “mind blindness,” the inability to imagine what another person might be thinking. This difficulty is thought to result in interaction abnormalities that in turn lead to abnormal language development. One of the earliest and most sensitive markers for autism is a 1-yr-old child's inability to point communicatively at objects. It is theorized that the child cannot imagine that another person would understand what was being indicated; instead, the child indicates wants only by physically touching the desired object or using the adult's hand as a tool.
Nonfocal neurologic findings include poorly coordinated gait and stereotyped motor movements. Seizures occur in 20 to 40% of these children (particularly those with an intelligence quotient [IQ] < 50).
Diagnosis is made clinically and usually requires evidence of impairment of social interaction and communication, and presence of restricted, repetitive, stereotyped behaviors or interests. Screening tests include the Social Communication Questionnaire, the M-CHAT, and others. See also the American Academy of Neurology's Practice
Parameter: Screening and Diagnosis of Autism. Formal “gold standard” diagnostic tests such as the Autism Diagnostic Observation Schedule (ADOS), based on DSM-IV criteria, are usually administered by psychologists. Children with autism are difficult to test; they usually do better on performance items than verbal items in IQ tests and may show instances of age-appropriate performance despite retardation in most areas. Nonetheless, an IQ test administered by an experienced examiner often can provide a useful predictor of outcome.
Treatment
Treatment is usually multidisciplinary, and recent studies show measurable benefits from intensive, behaviorally based approaches that encourage interaction and meaningful communication. Psychologists and educators typically focus on behavioral analysis and then match behavioral management strategies to the person's specific behavioral problems at home and at school. Speech and language therapy should begin early and use a range of media, including signing, picture exchange, and speech. Physical and occupational therapists plan and implement strategies to help affected children compensate for specific deficits in motor function and motor planning. SSRIs may improve control of ritualistic behaviors. Antipsychotics and mood stabilizers such as valproate may help control self-injurious behavior.
Last full review/revision November 2005
Content last modified January 2007
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