Autism Spectrum Disorders
Elizabeth B. Caronna
I. Description of the problem. Autism is a heterogeneous neurodevelopmental disorder. It is defined clinically by characteristic behavioral impairments in
Reciprocal social interactions
Verbal and nonverbal communication
Range and nature of activities or interests
The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) uses the umbrella term pervasive developmental disorders (PDDs) to include several disorders, which appear to have different etiologies, including autistic disorder, Rett syndrome, childhood disintegrative disorder, Asperger syndrome, and pervasive developmental disorder-not otherwise specified (PDD-NOS). Recently, there has been increasing use of the term autism spectrum disorder (ASD) as a diagnosis for individuals who show less severe impairment than individuals who meet DSM criteria for autistic disorder. The autism spectrum includes PDD-NOS, atypical autism, high-functioning autism, and Asperger syndrome. This shift in nomenclature reflects the broader conceptualization of the disorder to include more individuals with milder symptoms. It is likely that this change will be reflected in the upcoming version of the DSM. (In this chapter, the term ASD is used to denote autistic disorder, PDD-NOS, and Asperger syndrome. Rett syndrome and childhood disintegrative disorder will not be discussed in detail here. Asperger syndrome is addressed in greater detail in another chapter.)
A. Epidemiology. The prevalence of ASD is hotly debated. As recently as the 1980s, prevalence estimates were in the range of 0.5-1/1000. More recent estimates have suggested a prevalence of ASD in the United States (including autistic disorder, PDD-NOS, and Asperger syndrome) as high as 9/1000. The dramatic increase in rate of diagnosed cases may be attributed to several different factors, including changes in diagnostic criteria and the broader definition of ASD, variation in case finding methods and diagnostic substitution, increased public and professional awareness of the disorders leading to earlier diagnosis and treatment, and a possible true increase in the prevalence.
Rates of ASD are significantly higher in males than in females (approximately four to five times as common in males). It is likely that there is no difference in actual prevalence of ASD based on race, ethnic background, or socioeconomic status although cases of ASD are often misidentified or identified late in disadvantaged groups.
B. Etiology/contributing factors. Historically, autism was attributed to cold, distant parenting, widely known as the “refrigerator mother theory.” The accumulation of evidence that the disorder had a neurological basis (frequency of associated seizures, obvious genetic links, and pathological abnormalities in the brain) made psychodynamic theories of etiology untenable. In the majority of cases, the etiology of ASD is idiopathic. Advanced maternal and paternal age has been found to be associated with increased rates. There are a small number of cases in which there is an underlying metabolic, infectious, or genetic disorder (such as untreated phenylketonuria, congenital cytomegalovirus or rubella, tuberous sclerosis, fragile X syndrome, CHARGE syndrome, neurofibromatosis, or Down syndrome).
A genetic contribution to ASD is supported by high rates of recurrence of autism in families with one affected child (3%-7% or higher), 25%-35% recurrence risk if a second child has autism, and twin studies that show up to 70% concordance for autistic disorder and 90% concordance for ASD in monozygotic twins. As expected, lower concordance is seen in dizygotic twins (<3% for autistic disorder and 10%-30% for broader phenotype). ASD is assumed to be a polygenic disorder resulting from gene-environment interactions. Recent studies have focused on genome wide studies, identifying microduplications and deletions associated with autism on several autosomal chromosomes. Several studies have identified different genes coding for proteins involved in synaptic connectivity. There is a high rate (up to 10%) of fragile X syndrome in individuals with ASD. Notwithstanding
rampant speculation in the lay press and on the Internet, possible environmental triggers of the disorder in genetically predisposed individuals have not yet been identified.
II. Making the diagnosis.
A. Signs and symptoms.
1. DSM-IV-TR criteria for autistic disorder. The criteria for diagnosis of autistic disorder according to DSM-IV-TR are outlined below. The presence of impairment must be judged compared with children of the same developmental level or mental age. The DSM requires at least six criteria be met from the following three groups of symptoms.
a. Qualitative impairment of reciprocal social interactions (at least two).
Marked impairment in the use of multiple nonverbal behaviors such as eye-to-eye gaze, facial expression, body postures, and gestures to regulate social interaction
Failure to develop peer relationships appropriate to developmental level
A lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest)
Lack of social or emotional reciprocity
b. Qualitative impairments in communication (at least one).
Delay in, or total lack of, the development of spoken language (not accompanied by an attempt to compensate through alternative modes of communication such as gestures or mime)
In individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others
Stereotyped and repetitive use of language or idiosyncratic language
Lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level
c. Restricted, repetitive, and stereotyped patterns of behavior, interests, and activities (at least one).
Encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus
Apparently inflexible adherence to specific, nonfunctional routines or rituals
Stereotyped and repetitive motor mannerisms (e.g., hand or finger flapping or twisting, or complex whole body movements)
Persistent preoccupation with parts of objects
In addition, delays must be present in at least one of the core areas (social interaction, social communication, or symbolic/imaginative play) by the age of 3 years. Although some children with ASD demonstrate true regression, it appears that most have atypical features in the first year of life that may not be clinically identified at the time.
2. DSM-IV-TR: PDD-NOS. This category is used for severe and pervasive impairment in development of reciprocal social interaction associated with impairment in either verbal or nonverbal communication or with the presence of stereotyped behaviors, interests, and activities, but criteria are not met for autistic disorder. This includes atypical autism because of late age of presentation, atypical symptomatology, and/or subthreshold symptomatology.
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