Autism spectrum

The term "autism spectrum" is often used to describe disorders that are currently classified as pervasive developmental disorders. Pervasive developmental disorders include Autistic Disorder, Asperger's Disorder, Childhood Disintegrative Disorder, Rett's Disorder and Pervasive Development Disorder Not Otherwise Specified (PPD-NOS).^[1] These disorders are typically characterized by social deficits, communication difficulties, stereotyped or repetitive behaviors and interests, and/or cognitive delays. Although these diagnoses share some common features, individuals with these disorders are thought to be "on the spectrum" because of differences in severity across these domains.

Classification

Pervasive developmental disorders or "autism spectrum" disorders include:

1. Autistic Disorder
2. Asperger's Disorder (or Asperger syndrome)
3. Childhood Disintegrative Disorder
4. Rett's Disorder (or Rett Syndrome)
5. Pervasive Developmental Disorder Not Otherwise Specified

Autistic Disorder is characterized by delays or abnormal functioning before the age of 3 in one or more of the following domains: 1) social interaction, 2) communication, and 3) restricted, repetitive and stereotyped patterns of behavior, interests and activities.^[1] Social impairments are marked by poor use of nonverbal communication, difficulty in peer relations, lack of social-emotional reciprocity and a lack of shared enjoyment. Communication deficits may include failure to develop speech, use of stereotyped or delayed echolalia, and difficulties maintaining conversations. Social and communication impairments may also result in a lack of symbolic or imaginative play. Restricted and repetitive behaviors may include unusual preoccupations with narrow interests, inflexibility to nonfunctional routines, stereotyped and repetitive mannerisms and preoccupations with parts of objections.

Asperger's Disorder can be distinguished from Autistic Disorder by the lack of delay or deviance in early language development.^[1] Additionally, individuals with Asperger's Disorder do not have significant cognitive delays. Individuals with Asperger's Disorder typically demonstrate obsessive interest in a single topic or activity. Other symptoms include: repetitive routines or rituals, peculiarities in speech and language, inappropriate affect or social behavior, problems with non-verbal communication and clumsy or uncoordinated motor movements.^[2] As a result of these difficulties, individuals with Asperger's Disorder often have challenges interacting with their peers.

Unlike Autistic Disorder and Asperger's Disorder, Childhood Disintegrative Disorder is characterized by significant regression or loss of functioning following at least 2 years of typical development.^[1] A child who is affected with this condition may lose communication skills, nonverbal behaviors, motor functioning, or skills that have already been learned (i.e., toy play).^[3]

Rett's disorder (or Rett Syndrome) appears only in females and is characterized by multiple deficits following a period of normal functioning after birth.^[1] At onset, Rett's Disorder is characterized by deceleration of head growth, loss of purposeful hand skills, loss of social engagement and language, and poor physical coordination.

Pervasive Developmental Disorder Not Otherwise Specified(PDD-NOS) is thought as "subthreshold autism" or "atypical autism" because it is often characterized by milder symptoms of autism or symptoms in only one domain (e.g., social difficulties).^[4] An individual with PDD-NOS may demonstrate pervasive deficits in the development of reciprocal social interaction or stereotyped behaviors, but does not meet the criteria for a specific pervasive developmental disorder or other psychological disorders (e.g., Schizophrenia or Avoidant Personality Disorder).^[1]

Autism Spectrum Disorder in the DSM-V

Further information: Autism classification

Autism Spectrum Disorder (ASD) is a proposed revision to the Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5), which will be released in May 2013.^[5] This new diagnosis will encompass current diagnoses of Autistic Disorder, Asperger's Disorder, Childhood Disintegrative Disorder, and Pervasive Developmental Disorder Not Otherwise Specified. Rather than categorizing these diagnoses, the DSM-5 will adopt a dimensional approach to diagnosing disorders that fall underneath the autism spectrum umbrella. It is thought that individuals with ASDs are best represented as a single diagnostic category because they demonstrate similar types of symptoms and are better differentiated by clinical specifiers (i.e., dimensions of severity) and associated features (i.e., known genetic disorders, epilepsy and intellectual disability). An additional change to the DSM includes collapsing social and communication deficits into one domain. Thus, an individual with an ASD diagnosis will be described in terms of severity of social communication symptoms, severity of fixated or restricted behaviors or interests and associated features.

Epidemiology

Main article: Epidemiology of autism

Reviews tend to estimate a prevalence of 6 per 1,000 for autism spectrum disorders as a whole,^[6] however prevalence rates vary for each of the developmental disorders in the spectrum. Autism prevalence has been estimated at 1-2 per 1,000, Asperger syndrome at roughly 0.6 per 1,000, childhood disintegrative disorder at 0.02 per 1,000, and PDD-NOS at 3.7 per 1,000.^[6] These rates are consistent across cultures and ethnic groups, as autism is considered a universal disorder.^[7]

While rates of autism spectrum disorders are consistent across cultures, they vary greatly by gender, with boys being affected far more frequently than girls. The average male-to-female ratio for ASD's is 4.2:1,^[8] affecting 1 in 70 males, but only 1 in 315 females.^[9] Females, however, are more likely to have associated cognitive impairment. Among those with an ASD and mental retardation, the sex ratio may be closer to 2:1.^[10]

Developmental course

Although autism spectrum disorders are thought to follow two possible developmental courses, most parents report that symptom onset occurred within the first year of life.^[11] One course of development follows a gradual course of onset in which parents tend to report concerns in development over the first two years of life and diagnosis is made around 3-4 years of age. Some of the early signs of ASD's in this course include decreased looking at faces, failure to turn when name is called, failure to show interests by showing or pointing, and delayed pretend play (see Table 1).^[12] A second course of development is characterized by normal or near-normal development followed by loss of skills or regression in the first 2-3 years. Regression may occur in a variety of domains, including communication, social, cognitive, and self-help skills; however, the most common regression is loss of language.^[12] There continues to be a debate over the differential outcomes based on these two developmental courses. Some studies suggest that regression is associated with poorer outcomes and others report no differences between those with early gradual onset and those who experience a regression period.^[13] Overall, the prognosis for individuals with autism is poor with respect to academic achievement and independent living abilities, particularly for those who have not received early intervention.^[13] However, many individuals show improvements as they grow older. The two best predictors of favorable outcome in autism are non-retarded intellectual ability and the development of some communicative speech prior to 5 years of age.^[14] Overall, the literature stresses the importance of early intervention in achieving positive longitudinal outcomes.^[15]

Table 1: Early Symptoms of Autism^[13]

Social behavior	Typically develops	Behavior in children with autism compared to typically developing children
Looking at faces	Birth	Less at 12 months
Following person's gaze	6-9 months	Less at 18 months
Turning when name called	6-9 months	Less at 9 and 12 months
Showing objects to others	9-12 months	Less at 12 months
Pointing at interesting objects	9-12 months	Less at 12 months and 18 months
Pointing to request	9-12 months	Not delayed at 18 months
Symbolic play	14 months	Absent at 18 months

Comorbidity with Autism Spectrum Disorders

Autism spectrum disorders tend to be highly comorbid with other disorders. Comorbidity may increase with age and may worsen the course of youth with ASD's and make intervention/treatment more difficult.^[16] Distinguishing between ASD's and other diagnoses can be challenging because the traits of ASD's often overlap with symptoms of other disorders and the characteristics of ASD's make traditional diagnostic procedures difficult.^[17] In spite of these difficulties, comorbid disorders are readily identified and tend to fall into six categories, medical conditions, intellectual disabilities, anxiety disorders, mood disorders, behavior-related disorders, and sensory processing disorders.

Medical conditions

A variety of medical conditions commonly occur in individuals with ASD's. The most common is seizure disorder or epilepsy, which occurs in 11-39% of individuals with ASD.^[18] Typically, onset of epilepsy occurs before age five or during puberty.^[19] and is more common in females and individuals who also have comorbid mental retardation. Tic disorder is another common medical condition seen in individuals with ASD's. While only about 6.5% of individuals with an ASD have full blown Tourette syndrome, nearly 30% show some form of tics.^[20] Tuberous sclerosis, a medical condition in which non-malignant tumors grow in the brain and on other vital organs, occurs in 1-4% of individuals with ASD's.^[21] Sleep disorders are also commonly reported by parents of children with ASD's, including late sleep onset, early morning awakening, and poor sleep maintenance.^[19]

Intellectual disabilities

Intellectual disabilities are some of the most common comorbid disorders with ASD's. Recent estimates suggest that 40-69% of individuals with ASD have some degree of mental retardation,^[13] with females more likely to be in severe range of mental retardation. Learning disabilities are also highly comorbid in individuals with an ASD. Approximately 25-75% of individuals with an ASD also have some degree of learning disability,^[22] although the types of learning disability vary depending on the specific strengths and weaknesses of the individual.

Anxiety disorders

A variety of anxiety disorders tend to co-occur with autism spectrum disorders, with overall comorbidity rates of 7-84%.^[13] Specific phobia is the most common comorbid condition over the lifetime for those with ASD, with comorbidity rates of 38-63%.^[16] Common phobias for children with ASD include the fear of certain places or situations, the fear of medically related people, places, or things, and the fear of loud noises.^[23] Obsessive-compulsive disorder (OCD) occurs in 11-35% of individuals with ASD, with nearly 16-81% showing features of the disorder without a full diagnosis. While individuals with ASD exhibit rigid thinking and compulsions, similar to OCD, the repetitive behaviors displayed in ASD (i.e., flapping, spinning, repeating phrases) are distinct and serve alternate functions than the repetitive behaviors displayed in OCD (i.e., checking, cleaning, counting).^[16] Social Phobia or Social Anxiety Disorder is seen in approximately 7.4% of individuals with ASD, but is more common in higher-functioning individuals who have a desire for social interactions, but are also aware of their social deficits.^[16]

Mood disorders

Rates of comorbid depression in individuals with an ASD range from 4-58%.^[24] The presentation of depression in ASD's can depend on level of cognitive functioning, with lower functioning children displaying more behavior issues and higher functioning children displaying more traditional depressive symptoms.^[17] Depression is thought to develop and occur more in high-functioning individuals during adolescence, when they develop greater insight into their differences from others.^[13] Bipolar disorder may also be comorbid with an ASD, although it is far less common than many other disorders. Rates of comorbidity vary greatly, but tend to be around 2-8%.^[23]

Behavior-related disorders

Deficits in ASD are often linked to behavior problems, such as difficulties following directions, being cooperative, and doing things on other people's terms. These behavior problems are also characteristic of Oppositional Defiant Disorder (ODD) and Conduct Disorder (CD), but the reasons for the behaviors often differ.^[23] For this reason, comorbidity rates of ODD and CD range from 7%^[23] to 73%.^[16] Attention Deficit Hyperactivity Disorder (ADHD) has ASD comorbidity rates of 30-80%; however, current diagnostic guidelines prevent diagnosing ADHD along with ASD.^[23] Rather, ADHD-like symptoms are seen to be part of the ASD diagnosis.^[25]

Sensory processing disorders

Sensory processing disorder is also comorbid with ASD, with comorbidity rates of 42-88%.^[26] Three patterns of sensory processing difficulties are commonly seen, hyperresponsiveness (behavioral over-reactivity to sensory stimuli), hyporesponsiveness (behavioral under-reactivity to sensory stimuli), and sensory-seeking (craving or fascination with certain stimuli). These patterns of processing difficulties may be present with auditory, visual, or tactile stimuli.^[27]

Neuropsychological findings

Frontal lobe

The frontal lobe is central to many functions that are associated with autism, such as language and executive functioning. For instance, Broca's area, which is related to language production, is located in the inferior prefrontal lobe. Other important areas of the frontal lobe include: the prefrontal cortex (involved with aspects of executive functioning such as working memory, inhibition, planning, organizing, set-shifting and cognitive flexibility), the orbitofrontal cortex (involved in social cognition and theory of mind) and the inferior frontal gyrus (part of the mirror neuron system). Current research suggests that dysfunction in the frontal lobe may be associated with some of the deficits observed in individuals with ASD, including social cognition, imitation, face processing, language, attention, working memory, and problem-solving. For example, it has been found that individuals with autism have decreased concentrations of N-acetyl-asparate (NAA) and reduced glutaminergic neurons in the frontal lobe, suggesting some dysfunction in this region.^[28] Another study using fMRI found that boys with high-functioning autism had reduced activity in the pars opercularis when observing and imitating emotions.^[29] Orbitofrontal cortex deficits have also been implicated with autism, as individuals with high-functioning autism have shown decreased functioning in this area when participating in a task that involved the perception of fearful faces.^[30] Finally, individuals with ASD have shown decreased activation in the medial prefrontal cortex relative to a control group during a theory of mind task.^[31]

Mirror neuron system

The mirror neuron system (MNS) consists of a network of brain areas that have been associated with empathy processes in both animals^[32] and humans.^[33] In humans, the MNS has been identified in the inferior frontal gyrus (IFG) and the inferior parietal lobule (IPL) and is thought to be activated during imitation or observation of behaviors.^[34] It has been suggested that the MNS generates internal representations of the self and others, which facilitates an understanding of other people. Many researchers have hypothesized that the MNS is related to cognitive processes such as imitative learning, "mind-reading", and empathy; all of which are necessary for social-communication.^[35] Several studies using functional brain-imaging have found evidence of mirror neuron dysfunction in autism,^[36][37] suggesting this neural system is associated with social impairments in individuals with ASDs. Specifically, it has been found that reduced mirror neuron activity and MNS cortical thinning^[38] are highly correlated with autism severity.

Limbic system

Social skills impairments in autism have been theorized to reflect abnormal functioning in the limbic system. In animal models, it has been found that monkeys with lesions in the medial temporal lobe (e.g., the amygdala and hippocampus) demonstrate autistic-like behaviors, such as a failure to develop normal social relationships, stereotyped movements, and poor eye-contact.^[39] Notably, it was found that that the most severe autistic symptoms resulted from lesions in the amygdala and hippocampus whereas less severe forms resulted from lesions to the amygdala alone. Human autopsy studies have also found evidence for limbic system abnormalities in individuals with ASDs. These studies revealed reduced neuronal cell size and increased cell-packing density in the hippocampus and amygdala.^[40] However, MRI studies have not found any evidence for abnormalities in the hippocampus.^[41]

Evidenced-based assessment

The diverse expressions of ASD symptoms pose diagnostic challenges to clinicians. Individuals with an ASD may present at various times of development (e.g., toddler, child, or adolescent) and symptom expression may vary over the course of development.^[42] Furthermore, clinicians are required to differentiate among the different pervasive developmental disorders as well as other disorders such as mental retardation not associated with a pervasive developmental disorder, specific developmental disorders (e.g. language), and early onset schizophrenia.

Considering the unique challenges associated with diagnosing ASD, specific practice parameters for the assessment of ASD have been published by the American Academy of Neurology,^[43] the American Academy of Child and Adolescent Psychiatry,^[42] and a consensus panel with representation from various professional societies.^[44] The practice parameters outlined by these societies include an initial screening of children by general practitioners (i.e., "Level 1 screening") and for children who fail the initial screening, a comprehensive diagnostic assessment by experienced clinicians (i.e. "Level 2 evaluation"). Furthermore, it has been suggested that assessments of children with suspected ASD be evaluated within a developmental framework, include multiple informants (e.g., parents and teachers) from diverse contexts (e.g., home and school), and employ a multidisciplinary team of professionals (e.g., clinical psychologists, neuropsychologists, and psychiatrists).^[45]

After a child fails an initial screening, psychologists administer various psychological assessment tools to assess for ASD.^[45] Amongst these measurements, the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS) are considered the "gold standards" for assessing children with autism. The ADI-R is a semi-structured parent interview that probes for symptoms of autism by evaluating a child's current behavior and developmental history. The ADOS is a semistructured interactive evaluation of ASD symptoms that is used to measure social and communication abilities by eliciting a number of opportunities (or "presses") for spontaneous behaviors (e.g., eye contact) in standardized context. Various other questionnaires (e.g., The Childhood Autism Rating Scale) and tests of cognitive functioning (e.g., The Peabody Picture Vocabulary Test) are typically included in an ASD assessment battery.

Management

Main article: Autism therapies

The main goals of treatment are to lessen associated deficits and family distress, and to increase quality of life and functional independence. No single treatment is best and treatment is typically tailored to the child's needs. Intensive, sustained special education programmes and behaviour therapy early in life can help children acquire self-care, social, and job skills. Available approaches include applied behaviour analysis (ABA), developmental models, structured teaching, speech and language therapy, social skills therapy, and occupational therapy.^[46] ABA therapy has a strong research base but it maybe limited by diagnostic severity and IQ.^[47][48]

Many popular therapies including auditory integration therapy, GFCF diets, and chelation have repeatedly been shown to be ineffective and are not considered evidence-based practices.^{[citation needed]}

See also

• Autism
• Autism therapies
• Autism Speaks

References

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Further reading

• Baron IS. Autism Spectrum Disorder: complex, controversial, and confounding. Neuropsychol Rev. 2008;18(4):271–2. doi:10.1007/s11065-008-9070-1. PMID 18846426.

External links

• Autism spectrum at the Open Directory Project

• For more information about Sensory Integration please visit www.sensoryintegration.org.uk
• For a short documentary about autism see BBC Four's 1992 Video here http://www.youtube.com/thefamilarity#p/u/2/PrViCkYF-lY