| Disorders usually first diagnosed in infancy, childhood, or adolescence. |
Autistic Disorder--
Autism is a brain development disorder characterized by impairments in social interaction and
communication, and restricted and repetitive behavior, all exhibited before a child is three years old.
These characteristics distinguish autism from milder autism spectrum disorders (ASD).
Heritability contributes a large fraction of the risk of a child's developing the disorder, although the
genetics of autism are complex, and it is generally unclear which genes are responsible.[1] In rare
cases, autism is strongly associated with agents that cause birth defects.[2] Other proposed causes,
such as the exposure of children to vaccines, are controversial and the vaccine hypotheses are
unsupported by convincing scientific evidence.[3][4] Most recent reviews estimate a prevalence of
one to two cases per 1,000 people for autism, and about six per 1,000 for ASD, with ASD averaging
a 4.3:1 male-to-female ratio. The number of people known to have autism has increased dramatically
since the 1980s, at least partly due to changes in diagnostic practice; the question of whether
prevalence has increased is unresolved.[5]
Autism affects many parts of the brain; how this occurs is poorly understood. Parents usually notice
signs in the first year or two of their child's life. Early intervention may help children gain self-care
and social skills, although few of these interventions are supported by scientific studies; there is no
cure.[6] With severe autism, independent living is unlikely; with milder autism, there are some
success stories for adults,[7] and an autistic culture has developed, with some seeking a cure and
others believing that autism is a condition rather than a disorder.[8]
Autism is a developmental disorder of the human brain that first shows signs during infancy or
childhood and follows a steady course without remission or relapse.[9] Impairments result from
maturation-related changes in various systems of the brain.[10] Autism is one of the five pervasive
developmental disorders (PDD) or autism spectrum disorders (ASD), which are characterized by
widespread abnormalities of social interactions and communication, and severely restricted interests
and highly repetitive behavior.[9]
Of the other four autism spectrum disorders, Asperger's syndrome is closest to autism in signs and
likely causes; Rett syndrome and childhood disintegrative disorder share several signs with autism,
but may have unrelated causes; pervasive developmental disorder not otherwise specified (PDD-
NOS) is diagnosed when the criteria are not met for a more specific disorder.[11] Unlike autism,
Asperger's has no substantial delay in language development.[12] The terminology of autism can be
bewildering, with autism, Asperger's and PDD-NOS sometimes called the autistic disorders,[1]
whereas autism itself is often called autistic disorder, childhood autism, or infantile autism. In this
article, autism refers to the classic autistic disorder, while other sources sometimes use autism to
refer to autistic disorders or even ASD. ASD, in turn, is a subset of the broader autism phenotype
(BAP), which describes individuals who may not have ASD but do have autistic-like traits, such as
avoiding eye contact.[13]
Autism's manifestations cover a wide spectrum, ranging from individuals with severe impairments—
who may be silent, mentally disabled, and locked into hand flapping and rocking—to less impaired
individuals who may have active but distinctly odd social approaches, narrowly focused interests, and
verbose, pedantic communication.[14] Sometimes the syndrome is divided into low-, medium- and
high-functioning autism (LFA, MFA, and HFA), based on IQ thresholds,[15] or on how much support
the individual requires in daily life; these subdivisions are not standardized and are controversial.
Autism can also be divided into syndromal and non-syndromal autism, where the former is
associated with severe or profound mental retardation or a congenital syndrome with physical
symptoms, such as tuberous sclerosis.[16] Although individuals with Asperger's tend to perform
better cognitively than those with autism, the extent of the overlap between Asperger's, HFA, and
non-syndromal autism is unclear.[17]
Some studies have reported diagnoses of autism in children due to a loss of language or social skills,
as opposed to a failure to make progress. Several terms are used for this phenomenon, including
regressive autism, setback autism, and developmental stagnation. The validity of this distinction
remains controversial; it is possible that regressive autism is a specific subtype.[18][19]
Characteristics
Autism is distinguished by a pattern of symptoms rather than one single symptom. The main
characteristics are impairments in social interaction, impairments in communication, restricted
interests and repetitive behavior. Other aspects, such as atypical eating, are also common but are
not essential for diagnosis.[20]
Social development
Autistic people have social impairments and often lack the intuition about others that many people
take for granted. Noted autistic Temple Grandin described her inability to understand the social
communication of neurotypicals as leaving her feeling "like an anthropologist on Mars".[21]
Social impairments become apparent early in childhood and continue through adulthood. Autistic
infants show less attention to social stimuli, smile and look at others less often, and respond less to
their own name. Autistic toddlers have more striking social deviance; for example, they have less eye
contact and anticipatory postures and are less likely to use another person's hand or body as a tool.
[19] Three- to five-year-old autistic children are less likely to exhibit social understanding, approach
others spontaneously, imitate and respond to emotions, communicate nonverbally, and take turns
with others. However, they do form attachments to their primary caregivers.[22] They display
moderately less attachment security than usual, although this feature disappears in children with
higher mental development or less severe ASD.[23] Older children and adults with ASD perform
worse on tests of face and emotion recognition.[24]
Contrary to common belief, autistic children do not prefer to be alone. Making and maintaining
friendships often proves to be difficult for those with autism. For them, the quality of friendships,
not the number of friends, predicts how lonely they are.[25]
There are many anecdotal reports, but few systematic studies, of aggression and violence in
individuals with ASD. The limited data suggest that in children with mental retardation, autism is
associated with aggression, destruction of property, and tantrums. Dominick et al. interviewed the
parents of 67 children with ASD and reported that about two-thirds of the children had periods of
severe tantrums and about one third had a history of aggression, with tantrums significantly more
common than in children with a history of language impairment.[26]
Communication
About a third to a half of individuals with autism do not develop enough natural speech to meet their
daily communication needs.[27] Differences in communication may be present from the first year of
life, and may include delayed onset of babbling, unusual gestures, diminished responsiveness, and
the desynchronization of vocal patterns with the caregiver. In the second and third years, autistic
children have less frequent and less diverse babbling, consonants, words, and word combinations;
their gestures are less often integrated with words. Autistic children are less likely to make requests
or share experiences, and are more likely to simply repeat others' words (echolalia)[18][28] or
reverse pronouns.[29] Autistic children may have difficulty with imaginative play and with developing
symbols into language.[18][28] They are more likely to have problems understanding pointing; for
example, they may look at a pointing hand instead of the pointed-at object.[19][28]
In a pair of studies, high-functioning autistic children aged 8–15 performed equally well, and adults
better than individually matched controls at basic language tasks involving vocabulary and spelling.
Both autistic groups performed worse than controls at complex language tasks such as figurative
language, comprehension and inference. As people are often sized up initially from their basic
language skills, these studies suggest that people speaking to autistic individuals are more likely to
overestimate what their audience comprehends.[30]
Repetitive behavior
Autistic individuals display many forms of repetitive or restricted behavior, which the Repetitive
Behavior Scale-Revised (RBS-R) categorizes as follows:
* Stereotypy is apparently purposeless movement, such as hand flapping, head rolling, body
rocking, or spinning a plate.
* Compulsive behavior is intended and appears to follow rules, such as arranging objects in a certain
way.
* Sameness is resistance to change; for example, insisting that the furniture not be moved or
refusing to be interrupted.
* Ritualistic behavior involves the performance of daily activities the same way each time, such as an
unvarying menu or dressing ritual.
* Restricted behavior is limited in focus, interest, or activity, such as preoccupation with a single
television program.
* Self-injury includes movements that injure or can injure the person, such as biting oneself.
Dominick et al. reported that self-injury at some point affected about 30% of children with ASD.[26]
No single repetitive behavior is associated with autism, but only autism appears to have an elevated
pattern of occurrence and severity of these behaviors.[31]
Other symptoms
Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect
the individual or the family.[20] As many as 10% of individuals with ASD show unusual abilities,
ranging from splinter skills such as the memorization of trivia to the extraordinarily rare talents of
prodigious autistic savants.[32]
Unusual responses to sensory stimuli are more common and prominent in autistic children, although
there is no good evidence that sensory symptoms differentiate autism from other developmental
disorders.[33] The responses may be more common in children: a pair of studies found that autistic
children had impaired tactile perception while autistic adults did not. The same two studies also found
that autistic individuals had more problems with complex memory and reasoning tasks such as
Twenty Questions; these problems were somewhat more marked among adults.[30] Several studies
have reported associated motor problems that include poor muscle tone, poor motor planning, and
toe walking; ASD is not associated with severe motor disturbances.[34]
Atypical eating behavior occurs in about three-quarters of children with ASD, to the extent that it
was formerly a diagnostic indicator. Selectivity is the most common problem, although eating rituals
and food refusal also occur;[26] this does not appear to result in malnutrition. Some children with
autism also have gastrointestinal (GI) symptoms, but there is a lack of published rigorous data to
support the theory that autistic children have more or different GI symptoms than usual.[35]
Sleep problems are known to be more common in children with developmental disabilities, and there
is some evidence that children with ASD are more likely to have even more sleep problems than
those with other developmental disabilities; autistic children may experience problems including
difficulty in falling asleep, frequent nocturnal awakenings, and early morning awakenings. Dominick et
al. found that about two-thirds of children with ASD had a history of sleep problems.[26]
Causes of autism
Although many genetic and environmental causes of autism have been proposed, its theory of
causation is still incomplete.[36] Some researchers argue this is because autism is not a single
disorder, but rather a triad of core aspects (social impairment, communication difficulties, and
repetitive behaviors) that have distinct causes but often co-occur.[37]
Genetic factors are the most significant cause for autism spectrum disorders. Early studies of twins
estimated heritability to be more than 90%; in other words, that genetics explains more than 90%
of autism cases.[1] This may be an overestimate; new twin data and models with structural genetic
variation are needed.[38] When only one identical twin is autistic, the other often has learning or
social disabilities. For adult siblings, the risk of having one or more features of the broader autism
phenotype might be as high as 30%,[39] much higher than the risk in controls.[40]
The genetics of autism is complex.[1] Linkage analysis has been inconclusive; many association
analyses have had inadequate power.[38] For each autistic individual, mutations in more than one
gene may be implicated. Mutations in different sets of genes may be involved in different autistic
individuals. There may be significant interactions among mutations in several genes, or between the
environment and mutated genes. By identifying genetic markers inherited with autism in family
studies, numerous candidate genes have been located, most of which encode proteins involved in
neural development and function.[41] However, for most of the candidate genes, the actual
mutations that increase the risk for autism have not been identified. Typically, autism cannot be
traced to a Mendelian (single-gene) mutation or to a single chromosome abnormality such as fragile
X syndrome or 22q13 deletion syndrome.[16][42]
The large number of autistic individuals with unaffected family members may result from copy
number variations (CNVs)—spontaneous alterations in the genetic material during meiosis that delete
or duplicate genetic material. Sporadic (non-inherited) cases have been examined to identify
candidate genetic loci involved in autism. Using array comparative genomic hybridization (array CGH),
a technique for detecting CNVs, one study found them in 10% of families with one affected child.[44]
Some of the altered loci had been identified in previous studies of inherited autism; many were
unique to the sporadic cases examined in this study. Hence, a substantial fraction of autism may be
highly heritable but not inherited: that is, the mutation that causes the autism is not present in the
parental genome. The fraction of autism traceable to a genetic cause may grow to 30–40% as the
resolution of array CGH improves.[43] The Autism Genome Project database contains genetic linkage
and CNV data that connect autism to genetic loci and suggest that every human chromosome may
be involved.[45]
Teratogens (agents that cause birth defects) related to the risk of autism include exposure of the
embryo to thalidomide, valproic acid, or misoprostol, or to rubella infection in the mother. These
cases are rare.[46] All known teratogens appear to act during the first eight weeks from conception,
and though this does not exclude the possibility that autism can be initiated or affected later, it is
strong evidence that autism arises very early in development.[2] Other possible contributors to
autism include gastrointestinal or immune system abnormalities, allergies, and the exposure of
children to drugs, vaccines,[4] infection, certain foods,[47] or heavy metals; the evidence for these
risk factors is anecdotal and has not been confirmed by reliable studies,[3] and extensive further
searches are underway.[46] Parents may first become aware of autistic symptoms in their child
around the time of a routine vaccination. Although there is overwhelming scientific evidence showing
no causal association between the measles-mumps-rubella vaccine and autism, and there is no
convincing evidence that the vaccine preservative thiomersal helps cause autism, parental concern
has led to a decreasing uptake of childhood immunizations and the increasing likelihood of measles
outbreaks[48] such as the measles cases in Britain during summer 2007.[49]
Mechanism
Despite extensive investigation, how autism occurs is not well understood. Its mechanism can be
divided into two areas: the pathophysiology of brain structures and processes associated with
autism, and the neuropsychological linkages between brain structures and behaviors.[10]
Pathophysiology
Autism appears to result from developmental factors that affect many or all functional brain systems,
as opposed to localized physical damage.[42] Neuroanatomical studies and the associations with
teratogens strongly suggest that autism's mechanism includes alteration of brain development soon
after conception.[2] Many major structures of the human brain have been implicated. Consistent
abnormalities have been found in the development of the cerebral cortex; and in the cerebellum and
related inferior olive, which have a significant decrease in the number of Purkinje cells. Brain weight
and volume and head circumference tend to be greater in autistic children; the effects of these are
unknown.[50] It may be due to poorly regulated growth of neurons.[10]
Interactions between the immune system and the nervous system begin early during
embryogenesis, and successful neurodevelopment depends on a balanced immune response. Several
symptoms consistent with a poorly regulated immune response have been reported in autistic
children. It is possible that aberrant immune activity during critical periods of neurodevelopment is
part of the mechanism of some forms of ASD.[51] Given the lack of data in this area, it is still hard
to draw conclusions about the role of immune factors in autism.[52]
Several neurotransmitter abnormalities have been detected in autism, notably increased blood levels
of serotonin. Whether these lead to structural or behavioral abnormalities is unclear.[10]
The mirror neuron system (MNS) theory of autism hypothesizes that distortion in the development
of the MNS interferes with imitation and leads to autism's core features of social impairment and
communication difficulties. The MNS operates when an animal performs an action or observes
another animal of the same species perform the same action. The MNS may contribute to an
individual's understanding of other people by enabling the modeling of their behavior via embodied
simulation of their actions, intentions, and emotions.[53] Several studies have tested this
hypothesis by demonstrating structural abnormalities in MNS regions of individuals with ASD, delay
in the activation in the core circuit for imitation in individuals with Asperger's, and a correlation
between reduced MNS activity and severity of the syndrome in children with ASD.[54]
The underconnectivity theory of autism hypothesizes that autism is marked by underfunctioning
high-level neural connections and synchronization, along with an excess of low-level processes.[55]
Evidence for this theory has been found in functional neuroimaging studies on autistic individuals[30]
and by a brain wave study that suggested that adults with ASD have local overconnectivity in the
cortex and weak functional connections between the frontal lobe and the rest of the cortex.[56]
Other evidence suggests the underconnectivity is mainly within each hemisphere of the cortex and
that autism is a disorder of the association cortex.[57]
Neuropsychology
Two major categories of cognitive theories have been proposed about the links between autistic
brains and behavior.
The first category focuses on deficits in social cognition. Hyper-systemizing hypothesizes that
autistic individuals can systematize—that is, they can develop internal rules of operation to handle
internal events—but are less effective at empathizing by handling events generated by other agents.
[15] It extends the extreme male brain theory, which hypothesizes that autism is an extreme case
of the male brain, defined psychometrically as individuals in whom systemizing is better than
empathizing.[58] This in turn is related to the earlier theory of mind, which hypothesizes that autistic
behavior arises from an inability to ascribe mental states to oneself and others. The theory of mind
is supported by autistic children's atypical responses to the Sally-Anne test for reasoning about
others' motivations,[59] and is mapped well from the mirror neuron system theory of autism.[54]
The second category focuses on nonsocial or general processing. Executive dysfunction
hypothesizes that autistic behavior results in part from deficits in flexibility, planning, and other
forms of executive function. A strength of the theory is predicting stereotyped behavior and narrow
interests;[60] a weakness is that executive function deficits are not found in young autistic children.
[24] Weak central coherence theory hypothesizes that a limited ability to see the big picture
underlies the central disturbance in autism. One strength of this theory is predicting special talents
and peaks in performance in autistic people.[61] A related theory—enhanced perceptual functioning—
focuses more on the superiority of locally oriented and perceptual operations in autistic individuals.
[62] The latter two theories map well from the underconnectivity theory of autism.
Neither category is satisfactory on its own; social cognition theories poorly address autism's rigid
and repetitive behaviors, while the nonsocial theories have difficulty explaining social impairment and
communication difficulties.[37] A combined theory based on multiple deficits may prove to be more
useful.[8]
Screening
Parents are usually the first to notice unusual behaviors in their child.[63] As postponing treatment
may affect long-term outcome, any of the following signs is reason to have a child evaluated by a
specialist without delay:
* No babbling by 12 months.
* No gesturing (pointing, waving goodbye, etc.) by 12 months.
* No single words by 16 months.
* No two-word spontaneous phrases (not including echolalia) by 24 months.
* Any loss of any language or social skills, at any age.[20]
The American Academy of Pediatrics recommends that all children be screened for ASD at the 9-, 18-
, and 30-month well-child doctor visits, using autism-specific formal screening tests.[64] In contrast,
the UK National Screening Committee recommends against screening for ASD in the general
population, because screening tools have not been fully validated and interventions lack sufficient
evidence for effectiveness.[65]
Genetic screening for autism is generally still impractical. As genetic tests are developed several
ethical, legal, and social issues will emerge. Commercial availability of tests may precede adequate
understanding of how to use test results, given the complexity of autism's genetics.[66]
Diagnosis
Autism is defined in the DSM-IV-TR as exhibiting at least six symptoms total, including at least two
symptoms of qualitative impairment in social interaction, at least one symptom of qualitative
impairment in communication, and at least one symptom of restricted and repetitive behavior.
Sample symptoms include lack of social or emotional reciprocity, stereotyped and repetitive use of
language or idiosyncratic language, and persistent preoccupation with parts of objects. Onset must
be prior to age three years, with delays or abnormal functioning in either social interaction, language
as used in social communication, or symbolic or imaginative play. The disturbance must not be better
accounted for by Rett syndrome or childhood disintegrative disorder.[67] ICD-10 uses essentially
the same definition.[9]
Several diagnostic instruments are available. Two are commonly used in autism research: the Autism
Diagnostic Interview-Revised (ADI-R) is a semistructured parent interview, and the Autism
Diagnostic Observation Schedule (ADOS) uses observation and interaction with the child. The
Childhood Autism Rating Scale (CARS) is used widely in clinical environments to assess severity of
autism based on observation of children.[19]
A pediatrician commonly performs a preliminary investigation by taking developmental history and
physically examining the child. If warranted, diagnosis and evaluations are conducted with help from
ASD specialists, observing and assessing cognitive, communication, family, and other factors using
standardized tools, and taking into account any associated medical conditions. A differential
diagnosis for ASD at this stage might also consider mental retardation, hearing impairment, and a
specific language disorder[68] such as Landau-Kleffner syndrome.[69] In the UK the National Autism
Plan for Children recommends at most 30 weeks from first concern to completed diagnosis and
assessment, though few cases are handled that quickly in practice.[68] ASD can sometimes be
diagnosed by age 14 months,[70] but a 2006 U.S. study found the average age of first evaluation
by a qualified professional was 48 months and of formal ASD diagnosis was 61 months, reflecting an
average 13-month delay, all far above recommendations.[71]
Underdiagnosis and overdiagnosis are problems in marginal cases, and much of the recent increase
in the number of reported ASD cases is likely due to changes in diagnostic practices. The increasing
popularity of drug treatment options and the expansion of benefits has given providers incentives to
diagnose ASD, resulting in some overdiagnosis of children with uncertain symptoms. Conversely, the
cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis.
[72] It is particularly hard to diagnose autism among the visually impaired, partly because some of
its diagnostic criteria depend on vision, and partly because autistic symptoms overlap with those of
common blindness syndromes.[73]
The symptoms of autism and ASD begin early in childhood but are occasionally missed. Adults may
seek retrospective diagnoses to help them or their friends and family understand themselves, to help
their employers make adjustments, or in some locations to claim disability living allowances or other
benefits.[74]
Autism therapies
The goal of treatment is to manage and improve symptoms and functioning. No single treatment is
best and treatment is typically tailored to the child's needs. Intensive, sustained special education
programs and behavior therapy early in life can help children acquire self-care, social, and job skills.
[75][76] Among the available approaches, applied behavior analysis (ABA) has demonstrated efficacy
in promoting social and language development and in reducing behaviors that interfere with learning
and cognitive functioning;[76] ABA focuses on teaching tasks one-on-one using the behaviorist
principles of stimulus, response and reward.[77] Several programs are based on ABA. Some focus
on discrete trial teaching; more-comprehensive ones use multiple assessment and intervention
methods individually and dynamically.[78] Cognitive therapies based on comprehensive programs in
treatment centers are a common alternative: for example, TEACCH focuses on structuring the
physical environment and using visual supports for language development tasks.[76] A 2005
California study found that early intensive behavior analytic treatment, a form of ABA, was
substantially more effective for preschool children with autism than the mixture of methods provided
in many programs,[77], but a 2007 British study found that home-based early intensive behavioral
interventions, another ABA form, was no more effective than nursery-based eclectic programs.[79]
The limited research on the effectiveness of adult residential programs shows mixed results.[80]
Medications are often used to treat problems associated with ASD. More than half of U.S. children
diagnosed with ASD are prescribed psychoactive drugs or anticonvulsants, with the most common
drug classes being antidepressants, stimulants, and antipsychotics.[81] In the United States, the
antipsychotic risperidone is approved for treating symptomatic irritability in autistic children and
adolescents.[82] Other drugs are prescribed off-label, which means they have not been approved for
treating ASD. For example, serotonin reuptake inhibitors and dopamine blockers can sometimes
reduce some symptoms.[10] However, there is scant reliable research about the effectiveness or
safety of drug treatments for adolescents and adults with ASD.[83] A person with ASD may
respond atypically to medications, the medications can have adverse side effects, and no known
medication relieves autism's core symptoms of social and communication impairments.[63]
Many other therapies and interventions are available. Few are supported by scientific studies.[6][24]
[84][85] Treatment approaches lack empirical support in quality-of-life contexts, and many programs
focus on success measures that lack predictive validity and real-world relevance.[25] Scientific
evidence appears to matter less to service providers than program marketing, training availability,
and parent requests.[86] Even if they do not help, conservative treatments such as changes in diet
are probably harmless aside from their bother and cost.[47] Dubious invasive treatments are a much
more serious matter: for example, in 2005, botched chelation therapy killed a 5-year-old autistic boy.
[48]
Treatment is expensive;[87] indirect costs are more so. A U.S. study estimated the average
additional lifetime cost due exclusively to autism to be $3.2 million in 2003 U.S. dollars for an autistic
individual born in 2000, with about 10% medical care, 30% nonmedical care such as child care and
education, and 60% the lost economic productivity of individuals and their parents.[88] A British
study estimated an average lifetime cost of ₤2.4 million in 1997–1998 British pounds.[89] Legal
rights to treatment are complex, vary with location and age, and require advocacy by caregivers.[85]
Publicly supported programs are often inadequate or inappropriate for a given child, and
unreimbursed out-of-pocket medical or therapy expenses are associated with likelihood of family
financial problems.[90] After childhood, key treatment issues include residential care, job training and
placement, sexuality, social skills, and estate planning.[85]
Prognosis
No cure is known for autism. Most children with autism lack social support, meaningful relationships,
future employment opportunities or self-determination.[25] Although core difficulties remain, the
severity of symptoms often becomes less marked in later childhood.[91] Few high-quality studies
address long-term prognosis. Some adults show modest improvement in some symptoms, but
some decline; no study has focused on autism after midlife.[92] Acquiring language before age 6,
having IQ above 50, and having a marketable skill all predict better outcomes; independent living is
unlikely with severe autism.[93] A 2004 British study of 68 adults who were diagnosed before 1980
as autistic children with IQ above 50 found that 12% achieved a high level of independence as adults,
10% had some friends and were generally in work but required some support, 19% had some
independence but were generally living at home and needed considerable support and supervision in
daily living, 46% needed specialist residential provision from facilities specializing in ASD with a high
level of support and very limited autonomy, and 12% needed high-level hospital care.[7] A 2005
Swedish study of 78 adults that did not exclude low IQ found worse prognosis; for example, only
4% achieved independence.[94] Changes in diagnostic practice and increased availability of effective
early intervention make it unclear whether these findings can be generalized to recently diagnosed
children.[5]
Epidemiology
Estimates of the prevalence of autism vary widely depending on diagnostic criteria, age of children
screened, and geographical location.[95] Most recent reviews tend to estimate a prevalence of 1–2
per 1,000 for autism and close to 6 per 1,000 for ASD;[5] PDD-NOS is the vast majority of ASD,
Asperger's is about 0.3 per 1,000 and the atypical forms childhood disintegrative disorder and Rett
syndrome are much rarer.[96] A 2006 study of nearly 57,000 British nine- and ten-year-olds
reported a prevalence of 3.89 per 1,000 for autism and 11.61 per 1,000 for ASD; these higher
figures could be associated with broadening diagnostic criteria.[97]
The risk of autism is associated with several prenatal and perinatal risk factors. A 2007 review of risk
factors found associated parental characteristics that included advanced maternal age, advanced
paternal age, and maternal place of birth outside Europe or North America, and also found
associated obstetric conditions that included low birth weight and gestation duration, and hypoxia
during childbirth.[98]
About 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome
abnormality, or other genetic syndrome,[39] and ASD is associated with several genetic disorders.
[99] Autism is associated with mental retardation: a 2001 British study of 26 autistic children found
about 30% with intelligence in the normal range (IQ above 70), 50% with mild to moderate
retardation, and about 20% with severe to profound retardation (IQ below 35). For ASD other than
autism the association is much weaker: the same study reported about 94% of 65 children with PDD-
NOS or Asperger's had normal intelligence.[100] ASD is also associated with epilepsy, with variations
in risk of epilepsy due to age, cognitive level, and type of language disorder.[101] Boys are at higher
risk for autism than girls. The ASD sex ratio averages 4.3:1 and is greatly modified by cognitive
impairment: it may be close to 2:1 with mental retardation and more than 5.5:1 without. Recent
studies have found no association with socioeconomic status, and have reported inconsistent results
about associations with race or ethnicity.[5] Phobias, depression and other psychopathological
disorders have often been described along with ASD but this has not been assessed systematically.
[102]
Autism's incidence, despite its advantages for assessing risk, is less useful in autism epidemiology,
as the disorder starts long before it is diagnosed, and the gap between initiation and diagnosis is
influenced by many factors unrelated to risk. Attention is focused mostly on whether prevalence is
increasing with time. Earlier prevalence estimates were lower, centering at about 0.5 per 1,000 for
autism during the 1960s and 1970s and about 1 per 1,000 in the 1980s, as opposed to today's 1–2
per 1,000.[5]
Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if
any, growth came from changes in autism's prevalence.
Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if
any, growth came from changes in autism's prevalence.
The number of reported cases of autism increased dramatically in the 1990s and early 2000s. This
increase is largely attributable to changes in diagnostic practices, referral patterns, availability of
services, age at diagnosis, and public awareness,[103] though as-yet-unidentified contributing
environmental risk factors cannot be ruled out.[3] A widely cited 2002 pilot study concluded that the
observed increase in autism in California cannot be explained by changes in diagnostic criteria,[104]
but a 2006 analysis found that special education data poorly measured prevalence because so many
cases were undiagnosed, and that the 1994–2003 U.S. increase was associated with declines in
other diagnostic categories, indicating that diagnostic substitution had occurred.[105] It is unknown
whether autism's prevalence increased during the same period. An increase in prevalence would
suggest directing more attention and funding toward changing environmental factors instead of
continuing to focus on genetics.[46]
* References provided upon request.
Autism is a brain development disorder characterized by impairments in social interaction and
communication, and restricted and repetitive behavior, all exhibited before a child is three years old.
These characteristics distinguish autism from milder autism spectrum disorders (ASD).
Heritability contributes a large fraction of the risk of a child's developing the disorder, although the
genetics of autism are complex, and it is generally unclear which genes are responsible.[1] In rare
cases, autism is strongly associated with agents that cause birth defects.[2] Other proposed causes,
such as the exposure of children to vaccines, are controversial and the vaccine hypotheses are
unsupported by convincing scientific evidence.[3][4] Most recent reviews estimate a prevalence of
one to two cases per 1,000 people for autism, and about six per 1,000 for ASD, with ASD averaging
a 4.3:1 male-to-female ratio. The number of people known to have autism has increased dramatically
since the 1980s, at least partly due to changes in diagnostic practice; the question of whether
prevalence has increased is unresolved.[5]
Autism affects many parts of the brain; how this occurs is poorly understood. Parents usually notice
signs in the first year or two of their child's life. Early intervention may help children gain self-care
and social skills, although few of these interventions are supported by scientific studies; there is no
cure.[6] With severe autism, independent living is unlikely; with milder autism, there are some
success stories for adults,[7] and an autistic culture has developed, with some seeking a cure and
others believing that autism is a condition rather than a disorder.[8]
Autism is a developmental disorder of the human brain that first shows signs during infancy or
childhood and follows a steady course without remission or relapse.[9] Impairments result from
maturation-related changes in various systems of the brain.[10] Autism is one of the five pervasive
developmental disorders (PDD) or autism spectrum disorders (ASD), which are characterized by
widespread abnormalities of social interactions and communication, and severely restricted interests
and highly repetitive behavior.[9]
Of the other four autism spectrum disorders, Asperger's syndrome is closest to autism in signs and
likely causes; Rett syndrome and childhood disintegrative disorder share several signs with autism,
but may have unrelated causes; pervasive developmental disorder not otherwise specified (PDD-
NOS) is diagnosed when the criteria are not met for a more specific disorder.[11] Unlike autism,
Asperger's has no substantial delay in language development.[12] The terminology of autism can be
bewildering, with autism, Asperger's and PDD-NOS sometimes called the autistic disorders,[1]
whereas autism itself is often called autistic disorder, childhood autism, or infantile autism. In this
article, autism refers to the classic autistic disorder, while other sources sometimes use autism to
refer to autistic disorders or even ASD. ASD, in turn, is a subset of the broader autism phenotype
(BAP), which describes individuals who may not have ASD but do have autistic-like traits, such as
avoiding eye contact.[13]
Autism's manifestations cover a wide spectrum, ranging from individuals with severe impairments—
who may be silent, mentally disabled, and locked into hand flapping and rocking—to less impaired
individuals who may have active but distinctly odd social approaches, narrowly focused interests, and
verbose, pedantic communication.[14] Sometimes the syndrome is divided into low-, medium- and
high-functioning autism (LFA, MFA, and HFA), based on IQ thresholds,[15] or on how much support
the individual requires in daily life; these subdivisions are not standardized and are controversial.
Autism can also be divided into syndromal and non-syndromal autism, where the former is
associated with severe or profound mental retardation or a congenital syndrome with physical
symptoms, such as tuberous sclerosis.[16] Although individuals with Asperger's tend to perform
better cognitively than those with autism, the extent of the overlap between Asperger's, HFA, and
non-syndromal autism is unclear.[17]
Some studies have reported diagnoses of autism in children due to a loss of language or social skills,
as opposed to a failure to make progress. Several terms are used for this phenomenon, including
regressive autism, setback autism, and developmental stagnation. The validity of this distinction
remains controversial; it is possible that regressive autism is a specific subtype.[18][19]
Characteristics
Autism is distinguished by a pattern of symptoms rather than one single symptom. The main
characteristics are impairments in social interaction, impairments in communication, restricted
interests and repetitive behavior. Other aspects, such as atypical eating, are also common but are
not essential for diagnosis.[20]
Social development
Autistic people have social impairments and often lack the intuition about others that many people
take for granted. Noted autistic Temple Grandin described her inability to understand the social
communication of neurotypicals as leaving her feeling "like an anthropologist on Mars".[21]
Social impairments become apparent early in childhood and continue through adulthood. Autistic
infants show less attention to social stimuli, smile and look at others less often, and respond less to
their own name. Autistic toddlers have more striking social deviance; for example, they have less eye
contact and anticipatory postures and are less likely to use another person's hand or body as a tool.
[19] Three- to five-year-old autistic children are less likely to exhibit social understanding, approach
others spontaneously, imitate and respond to emotions, communicate nonverbally, and take turns
with others. However, they do form attachments to their primary caregivers.[22] They display
moderately less attachment security than usual, although this feature disappears in children with
higher mental development or less severe ASD.[23] Older children and adults with ASD perform
worse on tests of face and emotion recognition.[24]
Contrary to common belief, autistic children do not prefer to be alone. Making and maintaining
friendships often proves to be difficult for those with autism. For them, the quality of friendships,
not the number of friends, predicts how lonely they are.[25]
There are many anecdotal reports, but few systematic studies, of aggression and violence in
individuals with ASD. The limited data suggest that in children with mental retardation, autism is
associated with aggression, destruction of property, and tantrums. Dominick et al. interviewed the
parents of 67 children with ASD and reported that about two-thirds of the children had periods of
severe tantrums and about one third had a history of aggression, with tantrums significantly more
common than in children with a history of language impairment.[26]
Communication
About a third to a half of individuals with autism do not develop enough natural speech to meet their
daily communication needs.[27] Differences in communication may be present from the first year of
life, and may include delayed onset of babbling, unusual gestures, diminished responsiveness, and
the desynchronization of vocal patterns with the caregiver. In the second and third years, autistic
children have less frequent and less diverse babbling, consonants, words, and word combinations;
their gestures are less often integrated with words. Autistic children are less likely to make requests
or share experiences, and are more likely to simply repeat others' words (echolalia)[18][28] or
reverse pronouns.[29] Autistic children may have difficulty with imaginative play and with developing
symbols into language.[18][28] They are more likely to have problems understanding pointing; for
example, they may look at a pointing hand instead of the pointed-at object.[19][28]
In a pair of studies, high-functioning autistic children aged 8–15 performed equally well, and adults
better than individually matched controls at basic language tasks involving vocabulary and spelling.
Both autistic groups performed worse than controls at complex language tasks such as figurative
language, comprehension and inference. As people are often sized up initially from their basic
language skills, these studies suggest that people speaking to autistic individuals are more likely to
overestimate what their audience comprehends.[30]
Repetitive behavior
Autistic individuals display many forms of repetitive or restricted behavior, which the Repetitive
Behavior Scale-Revised (RBS-R) categorizes as follows:
* Stereotypy is apparently purposeless movement, such as hand flapping, head rolling, body
rocking, or spinning a plate.
* Compulsive behavior is intended and appears to follow rules, such as arranging objects in a certain
way.
* Sameness is resistance to change; for example, insisting that the furniture not be moved or
refusing to be interrupted.
* Ritualistic behavior involves the performance of daily activities the same way each time, such as an
unvarying menu or dressing ritual.
* Restricted behavior is limited in focus, interest, or activity, such as preoccupation with a single
television program.
* Self-injury includes movements that injure or can injure the person, such as biting oneself.
Dominick et al. reported that self-injury at some point affected about 30% of children with ASD.[26]
No single repetitive behavior is associated with autism, but only autism appears to have an elevated
pattern of occurrence and severity of these behaviors.[31]
Other symptoms
Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect
the individual or the family.[20] As many as 10% of individuals with ASD show unusual abilities,
ranging from splinter skills such as the memorization of trivia to the extraordinarily rare talents of
prodigious autistic savants.[32]
Unusual responses to sensory stimuli are more common and prominent in autistic children, although
there is no good evidence that sensory symptoms differentiate autism from other developmental
disorders.[33] The responses may be more common in children: a pair of studies found that autistic
children had impaired tactile perception while autistic adults did not. The same two studies also found
that autistic individuals had more problems with complex memory and reasoning tasks such as
Twenty Questions; these problems were somewhat more marked among adults.[30] Several studies
have reported associated motor problems that include poor muscle tone, poor motor planning, and
toe walking; ASD is not associated with severe motor disturbances.[34]
Atypical eating behavior occurs in about three-quarters of children with ASD, to the extent that it
was formerly a diagnostic indicator. Selectivity is the most common problem, although eating rituals
and food refusal also occur;[26] this does not appear to result in malnutrition. Some children with
autism also have gastrointestinal (GI) symptoms, but there is a lack of published rigorous data to
support the theory that autistic children have more or different GI symptoms than usual.[35]
Sleep problems are known to be more common in children with developmental disabilities, and there
is some evidence that children with ASD are more likely to have even more sleep problems than
those with other developmental disabilities; autistic children may experience problems including
difficulty in falling asleep, frequent nocturnal awakenings, and early morning awakenings. Dominick et
al. found that about two-thirds of children with ASD had a history of sleep problems.[26]
Causes of autism
Although many genetic and environmental causes of autism have been proposed, its theory of
causation is still incomplete.[36] Some researchers argue this is because autism is not a single
disorder, but rather a triad of core aspects (social impairment, communication difficulties, and
repetitive behaviors) that have distinct causes but often co-occur.[37]
Genetic factors are the most significant cause for autism spectrum disorders. Early studies of twins
estimated heritability to be more than 90%; in other words, that genetics explains more than 90%
of autism cases.[1] This may be an overestimate; new twin data and models with structural genetic
variation are needed.[38] When only one identical twin is autistic, the other often has learning or
social disabilities. For adult siblings, the risk of having one or more features of the broader autism
phenotype might be as high as 30%,[39] much higher than the risk in controls.[40]
The genetics of autism is complex.[1] Linkage analysis has been inconclusive; many association
analyses have had inadequate power.[38] For each autistic individual, mutations in more than one
gene may be implicated. Mutations in different sets of genes may be involved in different autistic
individuals. There may be significant interactions among mutations in several genes, or between the
environment and mutated genes. By identifying genetic markers inherited with autism in family
studies, numerous candidate genes have been located, most of which encode proteins involved in
neural development and function.[41] However, for most of the candidate genes, the actual
mutations that increase the risk for autism have not been identified. Typically, autism cannot be
traced to a Mendelian (single-gene) mutation or to a single chromosome abnormality such as fragile
X syndrome or 22q13 deletion syndrome.[16][42]
The large number of autistic individuals with unaffected family members may result from copy
number variations (CNVs)—spontaneous alterations in the genetic material during meiosis that delete
or duplicate genetic material. Sporadic (non-inherited) cases have been examined to identify
candidate genetic loci involved in autism. Using array comparative genomic hybridization (array CGH),
a technique for detecting CNVs, one study found them in 10% of families with one affected child.[44]
Some of the altered loci had been identified in previous studies of inherited autism; many were
unique to the sporadic cases examined in this study. Hence, a substantial fraction of autism may be
highly heritable but not inherited: that is, the mutation that causes the autism is not present in the
parental genome. The fraction of autism traceable to a genetic cause may grow to 30–40% as the
resolution of array CGH improves.[43] The Autism Genome Project database contains genetic linkage
and CNV data that connect autism to genetic loci and suggest that every human chromosome may
be involved.[45]
Teratogens (agents that cause birth defects) related to the risk of autism include exposure of the
embryo to thalidomide, valproic acid, or misoprostol, or to rubella infection in the mother. These
cases are rare.[46] All known teratogens appear to act during the first eight weeks from conception,
and though this does not exclude the possibility that autism can be initiated or affected later, it is
strong evidence that autism arises very early in development.[2] Other possible contributors to
autism include gastrointestinal or immune system abnormalities, allergies, and the exposure of
children to drugs, vaccines,[4] infection, certain foods,[47] or heavy metals; the evidence for these
risk factors is anecdotal and has not been confirmed by reliable studies,[3] and extensive further
searches are underway.[46] Parents may first become aware of autistic symptoms in their child
around the time of a routine vaccination. Although there is overwhelming scientific evidence showing
no causal association between the measles-mumps-rubella vaccine and autism, and there is no
convincing evidence that the vaccine preservative thiomersal helps cause autism, parental concern
has led to a decreasing uptake of childhood immunizations and the increasing likelihood of measles
outbreaks[48] such as the measles cases in Britain during summer 2007.[49]
Mechanism
Despite extensive investigation, how autism occurs is not well understood. Its mechanism can be
divided into two areas: the pathophysiology of brain structures and processes associated with
autism, and the neuropsychological linkages between brain structures and behaviors.[10]
Pathophysiology
Autism appears to result from developmental factors that affect many or all functional brain systems,
as opposed to localized physical damage.[42] Neuroanatomical studies and the associations with
teratogens strongly suggest that autism's mechanism includes alteration of brain development soon
after conception.[2] Many major structures of the human brain have been implicated. Consistent
abnormalities have been found in the development of the cerebral cortex; and in the cerebellum and
related inferior olive, which have a significant decrease in the number of Purkinje cells. Brain weight
and volume and head circumference tend to be greater in autistic children; the effects of these are
unknown.[50] It may be due to poorly regulated growth of neurons.[10]
Interactions between the immune system and the nervous system begin early during
embryogenesis, and successful neurodevelopment depends on a balanced immune response. Several
symptoms consistent with a poorly regulated immune response have been reported in autistic
children. It is possible that aberrant immune activity during critical periods of neurodevelopment is
part of the mechanism of some forms of ASD.[51] Given the lack of data in this area, it is still hard
to draw conclusions about the role of immune factors in autism.[52]
Several neurotransmitter abnormalities have been detected in autism, notably increased blood levels
of serotonin. Whether these lead to structural or behavioral abnormalities is unclear.[10]
The mirror neuron system (MNS) theory of autism hypothesizes that distortion in the development
of the MNS interferes with imitation and leads to autism's core features of social impairment and
communication difficulties. The MNS operates when an animal performs an action or observes
another animal of the same species perform the same action. The MNS may contribute to an
individual's understanding of other people by enabling the modeling of their behavior via embodied
simulation of their actions, intentions, and emotions.[53] Several studies have tested this
hypothesis by demonstrating structural abnormalities in MNS regions of individuals with ASD, delay
in the activation in the core circuit for imitation in individuals with Asperger's, and a correlation
between reduced MNS activity and severity of the syndrome in children with ASD.[54]
The underconnectivity theory of autism hypothesizes that autism is marked by underfunctioning
high-level neural connections and synchronization, along with an excess of low-level processes.[55]
Evidence for this theory has been found in functional neuroimaging studies on autistic individuals[30]
and by a brain wave study that suggested that adults with ASD have local overconnectivity in the
cortex and weak functional connections between the frontal lobe and the rest of the cortex.[56]
Other evidence suggests the underconnectivity is mainly within each hemisphere of the cortex and
that autism is a disorder of the association cortex.[57]
Neuropsychology
Two major categories of cognitive theories have been proposed about the links between autistic
brains and behavior.
The first category focuses on deficits in social cognition. Hyper-systemizing hypothesizes that
autistic individuals can systematize—that is, they can develop internal rules of operation to handle
internal events—but are less effective at empathizing by handling events generated by other agents.
[15] It extends the extreme male brain theory, which hypothesizes that autism is an extreme case
of the male brain, defined psychometrically as individuals in whom systemizing is better than
empathizing.[58] This in turn is related to the earlier theory of mind, which hypothesizes that autistic
behavior arises from an inability to ascribe mental states to oneself and others. The theory of mind
is supported by autistic children's atypical responses to the Sally-Anne test for reasoning about
others' motivations,[59] and is mapped well from the mirror neuron system theory of autism.[54]
The second category focuses on nonsocial or general processing. Executive dysfunction
hypothesizes that autistic behavior results in part from deficits in flexibility, planning, and other
forms of executive function. A strength of the theory is predicting stereotyped behavior and narrow
interests;[60] a weakness is that executive function deficits are not found in young autistic children.
[24] Weak central coherence theory hypothesizes that a limited ability to see the big picture
underlies the central disturbance in autism. One strength of this theory is predicting special talents
and peaks in performance in autistic people.[61] A related theory—enhanced perceptual functioning—
focuses more on the superiority of locally oriented and perceptual operations in autistic individuals.
[62] The latter two theories map well from the underconnectivity theory of autism.
Neither category is satisfactory on its own; social cognition theories poorly address autism's rigid
and repetitive behaviors, while the nonsocial theories have difficulty explaining social impairment and
communication difficulties.[37] A combined theory based on multiple deficits may prove to be more
useful.[8]
Screening
Parents are usually the first to notice unusual behaviors in their child.[63] As postponing treatment
may affect long-term outcome, any of the following signs is reason to have a child evaluated by a
specialist without delay:
* No babbling by 12 months.
* No gesturing (pointing, waving goodbye, etc.) by 12 months.
* No single words by 16 months.
* No two-word spontaneous phrases (not including echolalia) by 24 months.
* Any loss of any language or social skills, at any age.[20]
The American Academy of Pediatrics recommends that all children be screened for ASD at the 9-, 18-
, and 30-month well-child doctor visits, using autism-specific formal screening tests.[64] In contrast,
the UK National Screening Committee recommends against screening for ASD in the general
population, because screening tools have not been fully validated and interventions lack sufficient
evidence for effectiveness.[65]
Genetic screening for autism is generally still impractical. As genetic tests are developed several
ethical, legal, and social issues will emerge. Commercial availability of tests may precede adequate
understanding of how to use test results, given the complexity of autism's genetics.[66]
Diagnosis
Autism is defined in the DSM-IV-TR as exhibiting at least six symptoms total, including at least two
symptoms of qualitative impairment in social interaction, at least one symptom of qualitative
impairment in communication, and at least one symptom of restricted and repetitive behavior.
Sample symptoms include lack of social or emotional reciprocity, stereotyped and repetitive use of
language or idiosyncratic language, and persistent preoccupation with parts of objects. Onset must
be prior to age three years, with delays or abnormal functioning in either social interaction, language
as used in social communication, or symbolic or imaginative play. The disturbance must not be better
accounted for by Rett syndrome or childhood disintegrative disorder.[67] ICD-10 uses essentially
the same definition.[9]
Several diagnostic instruments are available. Two are commonly used in autism research: the Autism
Diagnostic Interview-Revised (ADI-R) is a semistructured parent interview, and the Autism
Diagnostic Observation Schedule (ADOS) uses observation and interaction with the child. The
Childhood Autism Rating Scale (CARS) is used widely in clinical environments to assess severity of
autism based on observation of children.[19]
A pediatrician commonly performs a preliminary investigation by taking developmental history and
physically examining the child. If warranted, diagnosis and evaluations are conducted with help from
ASD specialists, observing and assessing cognitive, communication, family, and other factors using
standardized tools, and taking into account any associated medical conditions. A differential
diagnosis for ASD at this stage might also consider mental retardation, hearing impairment, and a
specific language disorder[68] such as Landau-Kleffner syndrome.[69] In the UK the National Autism
Plan for Children recommends at most 30 weeks from first concern to completed diagnosis and
assessment, though few cases are handled that quickly in practice.[68] ASD can sometimes be
diagnosed by age 14 months,[70] but a 2006 U.S. study found the average age of first evaluation
by a qualified professional was 48 months and of formal ASD diagnosis was 61 months, reflecting an
average 13-month delay, all far above recommendations.[71]
Underdiagnosis and overdiagnosis are problems in marginal cases, and much of the recent increase
in the number of reported ASD cases is likely due to changes in diagnostic practices. The increasing
popularity of drug treatment options and the expansion of benefits has given providers incentives to
diagnose ASD, resulting in some overdiagnosis of children with uncertain symptoms. Conversely, the
cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis.
[72] It is particularly hard to diagnose autism among the visually impaired, partly because some of
its diagnostic criteria depend on vision, and partly because autistic symptoms overlap with those of
common blindness syndromes.[73]
The symptoms of autism and ASD begin early in childhood but are occasionally missed. Adults may
seek retrospective diagnoses to help them or their friends and family understand themselves, to help
their employers make adjustments, or in some locations to claim disability living allowances or other
benefits.[74]
Autism therapies
The goal of treatment is to manage and improve symptoms and functioning. No single treatment is
best and treatment is typically tailored to the child's needs. Intensive, sustained special education
programs and behavior therapy early in life can help children acquire self-care, social, and job skills.
[75][76] Among the available approaches, applied behavior analysis (ABA) has demonstrated efficacy
in promoting social and language development and in reducing behaviors that interfere with learning
and cognitive functioning;[76] ABA focuses on teaching tasks one-on-one using the behaviorist
principles of stimulus, response and reward.[77] Several programs are based on ABA. Some focus
on discrete trial teaching; more-comprehensive ones use multiple assessment and intervention
methods individually and dynamically.[78] Cognitive therapies based on comprehensive programs in
treatment centers are a common alternative: for example, TEACCH focuses on structuring the
physical environment and using visual supports for language development tasks.[76] A 2005
California study found that early intensive behavior analytic treatment, a form of ABA, was
substantially more effective for preschool children with autism than the mixture of methods provided
in many programs,[77], but a 2007 British study found that home-based early intensive behavioral
interventions, another ABA form, was no more effective than nursery-based eclectic programs.[79]
The limited research on the effectiveness of adult residential programs shows mixed results.[80]
Medications are often used to treat problems associated with ASD. More than half of U.S. children
diagnosed with ASD are prescribed psychoactive drugs or anticonvulsants, with the most common
drug classes being antidepressants, stimulants, and antipsychotics.[81] In the United States, the
antipsychotic risperidone is approved for treating symptomatic irritability in autistic children and
adolescents.[82] Other drugs are prescribed off-label, which means they have not been approved for
treating ASD. For example, serotonin reuptake inhibitors and dopamine blockers can sometimes
reduce some symptoms.[10] However, there is scant reliable research about the effectiveness or
safety of drug treatments for adolescents and adults with ASD.[83] A person with ASD may
respond atypically to medications, the medications can have adverse side effects, and no known
medication relieves autism's core symptoms of social and communication impairments.[63]
Many other therapies and interventions are available. Few are supported by scientific studies.[6][24]
[84][85] Treatment approaches lack empirical support in quality-of-life contexts, and many programs
focus on success measures that lack predictive validity and real-world relevance.[25] Scientific
evidence appears to matter less to service providers than program marketing, training availability,
and parent requests.[86] Even if they do not help, conservative treatments such as changes in diet
are probably harmless aside from their bother and cost.[47] Dubious invasive treatments are a much
more serious matter: for example, in 2005, botched chelation therapy killed a 5-year-old autistic boy.
[48]
Treatment is expensive;[87] indirect costs are more so. A U.S. study estimated the average
additional lifetime cost due exclusively to autism to be $3.2 million in 2003 U.S. dollars for an autistic
individual born in 2000, with about 10% medical care, 30% nonmedical care such as child care and
education, and 60% the lost economic productivity of individuals and their parents.[88] A British
study estimated an average lifetime cost of ₤2.4 million in 1997–1998 British pounds.[89] Legal
rights to treatment are complex, vary with location and age, and require advocacy by caregivers.[85]
Publicly supported programs are often inadequate or inappropriate for a given child, and
unreimbursed out-of-pocket medical or therapy expenses are associated with likelihood of family
financial problems.[90] After childhood, key treatment issues include residential care, job training and
placement, sexuality, social skills, and estate planning.[85]
Prognosis
No cure is known for autism. Most children with autism lack social support, meaningful relationships,
future employment opportunities or self-determination.[25] Although core difficulties remain, the
severity of symptoms often becomes less marked in later childhood.[91] Few high-quality studies
address long-term prognosis. Some adults show modest improvement in some symptoms, but
some decline; no study has focused on autism after midlife.[92] Acquiring language before age 6,
having IQ above 50, and having a marketable skill all predict better outcomes; independent living is
unlikely with severe autism.[93] A 2004 British study of 68 adults who were diagnosed before 1980
as autistic children with IQ above 50 found that 12% achieved a high level of independence as adults,
10% had some friends and were generally in work but required some support, 19% had some
independence but were generally living at home and needed considerable support and supervision in
daily living, 46% needed specialist residential provision from facilities specializing in ASD with a high
level of support and very limited autonomy, and 12% needed high-level hospital care.[7] A 2005
Swedish study of 78 adults that did not exclude low IQ found worse prognosis; for example, only
4% achieved independence.[94] Changes in diagnostic practice and increased availability of effective
early intervention make it unclear whether these findings can be generalized to recently diagnosed
children.[5]
Epidemiology
Estimates of the prevalence of autism vary widely depending on diagnostic criteria, age of children
screened, and geographical location.[95] Most recent reviews tend to estimate a prevalence of 1–2
per 1,000 for autism and close to 6 per 1,000 for ASD;[5] PDD-NOS is the vast majority of ASD,
Asperger's is about 0.3 per 1,000 and the atypical forms childhood disintegrative disorder and Rett
syndrome are much rarer.[96] A 2006 study of nearly 57,000 British nine- and ten-year-olds
reported a prevalence of 3.89 per 1,000 for autism and 11.61 per 1,000 for ASD; these higher
figures could be associated with broadening diagnostic criteria.[97]
The risk of autism is associated with several prenatal and perinatal risk factors. A 2007 review of risk
factors found associated parental characteristics that included advanced maternal age, advanced
paternal age, and maternal place of birth outside Europe or North America, and also found
associated obstetric conditions that included low birth weight and gestation duration, and hypoxia
during childbirth.[98]
About 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome
abnormality, or other genetic syndrome,[39] and ASD is associated with several genetic disorders.
[99] Autism is associated with mental retardation: a 2001 British study of 26 autistic children found
about 30% with intelligence in the normal range (IQ above 70), 50% with mild to moderate
retardation, and about 20% with severe to profound retardation (IQ below 35). For ASD other than
autism the association is much weaker: the same study reported about 94% of 65 children with PDD-
NOS or Asperger's had normal intelligence.[100] ASD is also associated with epilepsy, with variations
in risk of epilepsy due to age, cognitive level, and type of language disorder.[101] Boys are at higher
risk for autism than girls. The ASD sex ratio averages 4.3:1 and is greatly modified by cognitive
impairment: it may be close to 2:1 with mental retardation and more than 5.5:1 without. Recent
studies have found no association with socioeconomic status, and have reported inconsistent results
about associations with race or ethnicity.[5] Phobias, depression and other psychopathological
disorders have often been described along with ASD but this has not been assessed systematically.
[102]
Autism's incidence, despite its advantages for assessing risk, is less useful in autism epidemiology,
as the disorder starts long before it is diagnosed, and the gap between initiation and diagnosis is
influenced by many factors unrelated to risk. Attention is focused mostly on whether prevalence is
increasing with time. Earlier prevalence estimates were lower, centering at about 0.5 per 1,000 for
autism during the 1960s and 1970s and about 1 per 1,000 in the 1980s, as opposed to today's 1–2
per 1,000.[5]
Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if
any, growth came from changes in autism's prevalence.
Reports of autism cases grew dramatically in the U.S. in 1996–2005. It is unknown how much, if
any, growth came from changes in autism's prevalence.
The number of reported cases of autism increased dramatically in the 1990s and early 2000s. This
increase is largely attributable to changes in diagnostic practices, referral patterns, availability of
services, age at diagnosis, and public awareness,[103] though as-yet-unidentified contributing
environmental risk factors cannot be ruled out.[3] A widely cited 2002 pilot study concluded that the
observed increase in autism in California cannot be explained by changes in diagnostic criteria,[104]
but a 2006 analysis found that special education data poorly measured prevalence because so many
cases were undiagnosed, and that the 1994–2003 U.S. increase was associated with declines in
other diagnostic categories, indicating that diagnostic substitution had occurred.[105] It is unknown
whether autism's prevalence increased during the same period. An increase in prevalence would
suggest directing more attention and funding toward changing environmental factors instead of
continuing to focus on genetics.[46]
* References provided upon request.
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