Autism: Comprehensive Overview

Autism is a brain development disorder that is characterized by impaired social interaction and communication, and restricted and repetitive behavior, all starting before a youngster is three years old. This set of signs distinguishes autism from milder Autism Spectrum Disorders (ASD) such as pervasive developmental disorder not otherwise specified (PDD-NOS).

Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether Autism Spectrum Disorders is explained more by multigene interactions or by rare mutations. In rare cases, autism is strongly associated with agents that cause birth defects. Other proposed causes, such as childhood vaccines, are controversial; the vaccine hypotheses lack convincing scientific evidence. Most recent reviews estimate a prevalence of one to two cases per 1,000 individuals for autism, and about six per 1,000 for Autism Spectrum Disorders, with Autism Spectrum Disorders averaging a 4.3:1 male-to-female ratio. The number of individuals known to have autism has increased dramatically since the 1980s, at least partly as a result of changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved.

Autism affects many parts of the brain; how this occurs is not understood. Moms and dads usually notice signs in the first two years of their youngster's life. Early behavioral or cognitive intervention can help kids gain self-care, social, and communication skills. There is no known cure. Few kids with autism live independently after reaching adulthood, but some become successful, and an autistic culture has developed, with some seeking a cure and others believing that autism is a condition rather than a disorder.


Autism is a brain development disorder that first appears during infancy or childhood, and generally follows a steady course without remission. Impairments result from maturation-related changes in various systems of the brain. Autism is one of the five pervasive developmental disorders (PDD), which are characterized by widespread abnormalities of social interactions and communication, and severely restricted interests and highly repetitive behavior.

Of the other four PDD forms, Aspergers 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; PDD not otherwise specified (PDD-NOS) is diagnosed when the criteria are not met for a more specific disorder. Unlike autism, Aspergers has no substantial delay in language development. The terminology of autism can be bewildering, with autism, Aspergers and PDD-NOS often called the autism spectrum disorders (ASD) or sometimes the autistic disorders, whereas autism itself is often called autistic disorder, childhood autism, or infantile autism. In this article, autism refers to the classic autistic disorder; in clinical practice, though, autism, Autism Spectrum Disorders, and PDD are often used interchangeably. Autism Spectrum Disorders, in turn, is a subset of the broader autism phenotype (BAP), which describes individuals who may not have Autism Spectrum Disorders but do have autistic-like traits, such as avoiding eye contact.

The manifestations of autism 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. Sometimes the syndrome is divided into low-, medium- and high-functioning autism (LFA, MFA, and HFA), based on IQ thresholds, 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. Although individuals with Aspergers tend to perform better cognitively than those with autism, the extent of the overlap between Aspergers, HFA, and non-syndromal autism is unclear.

Some studies have reported diagnoses of autism in kids due to a loss of language or social skills after 14 months of age, 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.

The inability to identify biologically meaningful sub-populations has hampered research into causes. It has been proposed to classify autism using genetics as well as behavior, with the name Type 1 autism denoting rare autism cases that test positive for a mutation in the gene contactin associated protein-like (CNTNAP).


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. Individual symptoms of autism occur in the general population and appear not to associate highly, without a sharp line separating pathological severity from common traits.

Social development:

Individuals with autism have social impairments and often lack the intuition about others that many individuals take for granted. Noted autistic Temple Grandin described her inability to understand the social communication of neurotypicals, or individuals with normal neural development, as leaving her feeling "like an anthropologist on Mars".

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 more likely to communicate by manipulating another person's hand. Three- to five-year-old autistic kids are less likely to exhibit social understanding, approach others spontaneously, imitate and respond to emotions, communicate non-verbally, and take turns with others. However, they do form attachments to their primary caregivers. They display moderately less attachment security than usual, although this feature disappears in kids with higher mental development or less severe Autism Spectrum Disorders. Older kids and adults with Autism Spectrum Disorders perform worse on tests of face and emotion recognition.

Contrary to common belief, autistic kids 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.

There are many anecdotal reports, but few systematic studies, of aggression and violence in individuals with Autism Spectrum Disorders. The limited data suggest that in kids with mental retardation, autism is associated with aggression, destruction of property, and tantrums. Dominick et al. interviewed the moms and dads of kids with Autism Spectrum Disorders and reported that about two-thirds of the kids had periods of severe tantrums and about one-third had a history of aggression, with tantrums significantly more common than in kids with a history of language impairment. A Swedish study found that, of individuals aged or older discharged from hospital with a diagnosis of Autism Spectrum Disorders, those who committed violent crimes were significantly more likely to have other psycho-pathological conditions such as psychosis.


About a third to a half of individuals with autism do not develop enough natural speech to meet their daily communication needs. 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 de-synchronization of vocal patterns with the caregiver. In the second and third years, autistic kids have less frequent and less diverse babbling, consonants, words, and word combinations; their gestures are less often integrated with words. Autistic kids are less likely to make requests or share experiences, and are more likely to simply repeat others' words (echolalia) or reverse pronouns. Joint attention seems to be necessary for functional speech, and deficits in joint attention seem to distinguish infants with Autism Spectrum Disorders: for example, they may look at a pointing hand instead of the pointed-at object, and they consistently fail to point at objects in order to comment on or share an experience. Autistic kids may have difficulty with imaginative play and with developing symbols into language.

In a pair of studies, high-functioning autistic kids aged – 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 individuals are often sized up initially from their basic language skills, these studies suggest that individuals speaking to autistic individuals are more likely to overestimate what their audience comprehends.

Repetitive behavior:

Autistic individuals display many forms of repetitive or restricted behavior, which the Repetitive Behavior Scale-Revised (RBS-R) categorizes as follows:
  • Compulsive behavior is intended and appears to follow rules, such as arranging objects in a certain way.
  • Restricted behavior is limited in focus, interest, or activity, such as preoccupation with a single television program.
  • Ritualistic behavior involves the performance of daily activities the same way each time, such as an unvarying menu or dressing ritual. This is closely associated with sameness and an independent validation has suggested combining the two factors.
  • Sameness is resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.
  • 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 kids with Autism Spectrum Disorders.
  • Stereotypy is apparently purposeless movement, such as hand flapping, head rolling, or body rocking.

No single repetitive behavior seems to be specific to autism, but only autism appears to have an elevated pattern of occurrence and severity of these behaviors.

Other symptoms:

Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect the individual or the family. An estimated 0.5% to 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.

Unusual responses to sensory stimuli are more common and prominent in autistic kids, although there is no good evidence that sensory symptoms differentiate autism from other developmental disorders. Differences are greater for under-responsivity (for example, walking into things) than for over-responsivity (for example, distress from loud noises) or for seeking (for example, rhythmic movements). Several studies have reported associated motor problems that include poor muscle tone, poor motor planning, and toe walking; Autism Spectrum Disorders is not associated with severe motor disturbances.

Atypical eating behavior occurs in about three-quarters of kids with Autism Spectrum Disorders, to the extent that it was formerly a diagnostic indicator. Selectivity is the most common problem, although eating rituals and food refusal also occur; this does not appear to result in malnutrition. Although some kids with autism also have gastrointestinal (GI) symptoms, there is a lack of published rigorous data to support the theory that autistic kids have more or different GI symptoms than usual; studies report conflicting results, and the relationship between GI problems and Autism Spectrum Disorders is unclear.

Sleep problems are known to be more common in kids with developmental disabilities, and there is some evidence that kids with Autism Spectrum Disorders are more likely to have even more sleep problems than those with other developmental disabilities; autistic kids may experience problems including difficulty in falling asleep, frequent nocturnal awakenings, and early morning awakenings. Dominick et al. found that about two-thirds of kids with Autism Spectrum Disorders had a history of sleep problems.

moms and dads of kids with Autism Spectrum Disorders have higher levels of stress. Siblings of kids with Autism Spectrum Disorders report greater admiration of and less conflict with the affected sibling; siblings of individuals with Autism Spectrum Disorders have greater risk of negative well-being and poorer sibling relationships as adults.


Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether Autism Spectrum Disorders is explained more by multigene interactions or by rare mutations with major effects. Early studies of twins estimated heritability explains more than 90% of the risk of autism, assuming a shared environment and no other genetic or medical syndromes. However, most of the mutations that increase autism risk have not been identified. Typically, autism cannot be traced to a Mendelian (single-gene) mutation or to a single chromosome abnormality like Angelman syndrome or fragile X syndrome, and none of the genetic syndromes associated with Autism Spectrum Disorders has been shown to selectively cause Autism Spectrum Disorders. There may be significant interactions among mutations in several genes, or between the environment and mutated genes. Numerous candidate genes have been located, with only small effects attributable to any particular gene. The large number of autistic individuals with unaffected family members may result from copy number variations—spontaneous deletions or duplications in genetic material during meiosis. Hence, a substantial fraction of autism cases may be traceable to genetic causes that are highly heritable but not inherited: that is, the mutation that causes the autism is not present in the parental genome.

All known teratogens (agents that cause birth defects) related to the risk of autism 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. Although evidence for other environmental causes is anecdotal and has not been confirmed by reliable studies, extensive searches are underway. Environmental factors that have been claimed to contribute to or exacerbate autism, or may be important in future research, include certain foods, infectious disease, heavy metals, solvents, diesel exhaust, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, vaccines, and prenatal stress. Although moms and dads may first become aware of autistic symptoms in their youngster around the time of a routine vaccination, and parental concern about vaccines has led to a decreasing uptake of childhood immunizations and an increasing likelihood of measles outbreaks, there is overwhelming scientific evidence showing no causal association between the measles-mumps-rubella vaccine and autism, and there is no scientific evidence that the vaccine preservative thiomersal helps cause autism.


Despite extensive investigation, how autism occurs is not well understood. Its mechanism can be divided into two areas: the patho-physiology of brain structures and processes associated with autism, and the neuro-psychological linkages between brain structures and behaviors. The behaviors appear to have multiple patho-physiologies.


Autism appears to result from developmental factors that affect many or all functional brain systems, and to disturb the course of brain development more than the final product. Neuro-anatomical studies and the associations with teratogens strongly suggest that autism's mechanism includes alteration of brain development soon after conception. This localized anomaly appears to start a cascade of pathological events in the brain that are significantly influenced by environmental factors. Although many major structures of the human brain have been implicated, almost all postmortem studies have been of individuals who also had mental retardation, making it difficult to draw conclusions. Brain weight and volume and head circumference tend to be greater in autistic kids. The cellular and molecular bases of pathological early overgrowth are not known, nor is it known whether the overgrown neural systems cause autism's characteristic signs. Current hypotheses include:
  • Abnormal formation of synapses and dendritic spines, for example, by modulation of the neurexin-neuroligin cell-adhesion system.
  • An excess of neurons that causes local overconnectivity in key brain regions.
  • Disturbed neuronal migration during early gestation.
  • Unbalanced excitatory-inhibitory networks.

Interactions between the immune system and the nervous system begin early during embryogenesis, and successful neuro-development depends on a balanced immune response. Several symptoms consistent with a poorly regulated immune response have been reported in autistic kids. It is possible that aberrant immune activity during critical periods of neuro-development is part of the mechanism of some forms of Autism Spectrum Disorders. As auto-antibodies have not been associated with pathology, are found in diseases other than Autism Spectrum Disorders, and are not always present in Autism Spectrum Disorders, the relationship between immune disturbances and autism remains unclear and controversial.

Several neurotransmitter abnormalities have been detected in autism, notably increased blood levels of serotonin. Whether these lead to structural or behavioral abnormalities is unclear. Some data suggest an increase in several growth hormones; other data argue for diminished growth factors. Also, some inborn errors of metabolism are associated with autism but probably account for less than 5% of cases.

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 individuals by enabling the modeling of their behavior via embodied simulation of their actions, intentions, and emotions. Several studies have tested this hypothesis by demonstrating structural abnormalities in MNS regions of individuals with Autism Spectrum Disorders, delay in the activation in the core circuit for imitation in individuals with Aspergers, and a correlation between reduced MNS activity and severity of the syndrome in kids with Autism Spectrum Disorders. However, individuals with autism also have abnormal brain activation in many circuits outside the MNS and the MNS theory does not explain the normal performance of autistic kids on imitation tasks that involve a goal or object.

In autism there is evidence for reduced functional connectivity of the default mode network, a large-scale brain network involved in social and emotional processing, with intact connectivity of the task-positive network, used in sustained attention and goal-directed thinking. The two networks are not negatively correlated in individuals with autism, suggesting an imbalance in toggling between the two networks, possibly reflecting a disturbance of self-referential thought. A brain-imaging study found a specific pattern of signals in the cingulate cortex which differs in individuals with Autism Spectrum Disorders.

The under-connectivity theory of autism hypothesizes that autism is marked by under-functioning high-level neural connections and synchronization, along with an excess of low-level processes. Evidence for this theory has been found in functional neuro-imaging studies on autistic individuals and by a brain wave study that suggested that adults with Autism Spectrum Disorders have local over-connectivity in the cortex and weak functional connections between the frontal lobe and the rest of the cortex. Other evidence suggests the under-connectivity is mainly within each hemisphere of the cortex and that autism is a disorder of the association cortex.

From studies based on event-related potentials, transient changes to the brain's electrical activity in response to stimuli, there is considerable evidence for differences in autistic individuals with respect to attention, orientation to auditory and visual stimuli, novelty detection, language and face processing, and information storage; several studies have found a preference for non-social stimuli.


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. 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. 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 kids' atypical responses to the Sally-Anne test for reasoning about others' motivations, and is mapped well from the mirror neuron system theory of autism.

The second category focuses on nonsocial or general processing. Executive dysfunction hypothesizes that autistic behavior results in part from deficits in working memory, planning, inhibition, and other forms of executive function. Tests of core executive processes such as eye movement tasks indicate improvement from late childhood to adolescence, but performance never reaches typical adult levels. A strength of the theory is predicting stereotyped behavior and narrow interests; a weakness is that executive function deficits have not been found in young autistic kids. 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 individuals. A related theory—enhanced perceptual functioning—focuses more on the superiority of locally oriented and perceptual operations in autistic individuals. These theories map well from the under-connectivity 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. A combined theory based on multiple deficits may prove to be more useful.


About half of moms and dads of kids with Autism Spectrum Disorders notice their youngster's unusual behaviors by age months, and about four-fifths notice by age months. As postponing treatment may affect long-term outcome, any of the following signs is reason to have a youngster evaluated by a specialist without delay:
  • Any loss of any language or social skills, at any age.
  • 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 (other than instances of echolalia) by 24 months.

The American Academy of Pediatrics recommends that all kids be screened for Autism Spectrum Disorders at the 18- and 24- month well-youngster doctor visits, using autism-specific formal screening tests. In contrast, the UK National Screening Committee recommends against screening for Autism Spectrum Disorders in the general population, because screening tools have not been fully validated and interventions lack sufficient evidence for effectiveness. Screening tools include the Modified Checklist for Autism in Toddlers (M-CHAT), the Early Screening of Autistic Traits Questionnaire, and the First Year Inventory; initial data on M-CHAT and its predecessor CHAT on kids aged – months suggests that it is best used in a clinical setting and that it has low sensitivity (many false-negatives) but good specificity (few false-positives). It may be more accurate to precede these tests with a broadband screener that does not distinguish Autism Spectrum Disorders from other developmental disorders. Screening tools designed for one culture's norms for behaviors like eye contact may be inappropriate for a different culture. Genetic screening for autism is generally still impractical.


Diagnosis is based on behavior, not cause or mechanism. 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. ICD- uses essentially the same definition.

Several diagnostic instruments are available. Two are commonly used in autism research: the Autism Diagnostic Interview-Revised (ADI-R) is a semi-structured parent interview, and the Autism Diagnostic Observation Schedule (ADOS) uses observation and interaction with the youngster. The Childhood Autism Rating Scale (CARS) is used widely in clinical environments to assess severity of autism based on observation of kids.

A pediatrician commonly performs a preliminary investigation by taking developmental history and physically examining the youngster. If warranted, diagnosis and evaluations are conducted with help from Autism Spectrum Disorders specialists, observing and assessing cognitive, communication, family, and other factors using standardized tools, and taking into account any associated medical conditions. A pediatric neuro-psychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions. A differential diagnosis for Autism Spectrum Disorders at this stage might also consider mental retardation, hearing impairment, and a specific language impairment such as Landau-Kleffner syndrome.

Clinical genetics evaluations are often done once Autism Spectrum Disorders is diagnosed, particularly when other symptoms already suggest a genetic cause. Although genetic technology allows clinical geneticists to link an estimated 40 % of cases to genetic causes, consensus guidelines in the U.S. and UK are limited to high-resolution chromosome and fragile X testing. A genotype-first model of diagnosis has been proposed, which would routinely assess the genome's copy number variations. As new 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. Metabolic and neuro-imaging tests are sometimes helpful, but are not routine.

Autism Spectrum Disorders can sometimes be diagnosed by age 14 months, although diagnosis becomes increasingly stable over the first three years of life: for example, a one-year-old who meets diagnostic criteria for Autism Spectrum Disorders is less likely than a three-year-old to continue to do so a few years later. 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. A 2006 U.S. study found the average age of first evaluation by a qualified professional was 48 months and of formal Autism Spectrum Disorders diagnosis was 61 months, reflecting an average 13-month delay, all far above recommendations. Although the symptoms of autism and Autism Spectrum Disorders begin early in childhood, they are sometimes missed; grown-ups may seek 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.

Under-diagnosis and over-diagnosis are problems in marginal cases, and much of the recent increase in the number of reported Autism Spectrum Disorders cases is likely due to changes in diagnostic practices. The increasing popularity of drug treatment options and the expansion of benefits have given providers incentives to diagnose Autism Spectrum Disorders, resulting in some over-diagnosis of kids with uncertain symptoms. Conversely, the cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis. 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.


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 youngster's needs. Intensive, sustained special education programs and behavior therapy early in life can help kids acquire self-care, social, and job skills, and often improve functioning and decrease symptom severity and maladaptive behaviors; claims that intervention by age two to three years is crucial are not substantiated. Available approaches include applied behavior analysis (ABA), developmental models, structured teaching, speech and language therapy, social skills therapy, and occupational therapy. Educational interventions have some effectiveness in kids: intensive ABA treatment has demonstrated effectiveness in enhancing global functioning in preschool kids and is well-established for improving intellectual performance of young kids.

Neuro-psychological reports are often poorly communicated to educators, resulting in a gap between what a report recommends and what education is provided. The limited research on the effectiveness of adult residential programs shows mixed results.

Many drugs are used to treat problems associated with Autism Spectrum Disorders. More than half of U.S. kids diagnosed with Autism Spectrum Disorders are prescribed psychoactive drugs or anti-convulsants, with the most common drug classes being antidepressants, stimulants, and anti-psychotics. Aside from anti-psychotics, there is scant reliable research about the effectiveness or safety of drug treatments for adolescents and adults with Autism Spectrum Disorders. A person with Autism Spectrum Disorders may respond atypically to drugs, the drugs can have adverse effects, and no known medication relieves autism's core symptoms of social and communication impairments.

Although many alternative therapies and interventions are available, few are supported by scientific studies. Treatment approaches have little empirical support in quality-of-life contexts, and many programs focus on success measures that lack predictive validity and real-world relevance. Scientific evidence appears to matter less to service providers than program marketing, training availability, and parent requests. Though most alternative treatments, such as melatonin, have only mild adverse effects some may place the youngster at risk. A 2008 study found that compared to their peers, autistic males have significantly thinner bones if on casein-free diets; in 2005, botched chelation therapy killed a five-year-old youngster with autism.

Treatment is expensive; indirect costs are more so. A U.S. study estimated an average cost of $3.2 million in 2003 U.S. dollars for someone born in 2000, with about 10% medical care, 30% extra education and other care, and 60% lost economic productivity. Publicly supported programs are often inadequate or inappropriate for a given youngster, and un-reimbursed out-of-pocket medical or therapy expenses are associated with likelihood of family financial problems; one 2008 U.S. study found a 14% average loss of annual income in families of kids with Autism Spectrum Disorders, and a related study found that Autism Spectrum Disorders is associated with higher probability that youngster care problems will greatly affect parental employment. After childhood, key treatment issues include residential care, job training and placement, sexuality, social skills, and estate planning.


There is no known cure. Kids recover occasionally, sometimes after intensive treatment and sometimes not; it is not known how often this happens. Most kids with autism lack social support, meaningful relationships, future employment opportunities or self-determination. Although core difficulties remain, symptoms often become less severe in later childhood. Few high-quality studies address long-term prognosis. Some adults show modest improvement in communication skills, but a few decline; no study has focused on autism after midlife. Acquiring language before age six, having an IQ above 50, and having a marketable skill all predict better outcomes; independent living is unlikely with severe autism. A 2004 British study of 68 adults who were diagnosed before 1980 as autistic kids 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 Autism Spectrum Disorders with a high level of support and very limited autonomy, and 12% needed high-level hospital care. A 2005 Swedish study of 78 adults that did not exclude low IQ found worse prognosis; for example, only 4% achieved independence. A 2008 Canadian study of 48 young adults diagnosed with Autism Spectrum Disorders as preschoolers found outcomes ranging through poor (46%), fair (32%), good (17%), and very good (4%); 56% of these young adults had been employed at some point during their lives, mostly in volunteer, sheltered or part time work. Changes in diagnostic practice and increased availability of effective early intervention make it unclear whether these findings can be generalized to recently diagnosed kids.


Most recent reviews tend to estimate a prevalence of 1–2 per 1,000 for autism and close to 6 per 1,000 for Autism Spectrum Disorders; because of inadequate data, these numbers may underestimate ASDs true prevalence. PDD-NOS cases are the vast majority of Autism Spectrum Disorders, Aspergers prevalence is about 0.3 per 1,000, and the remaining Autism Spectrum Disorders forms are much more rare. 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, though unidentified contributing environmental risk factors cannot be ruled out. It is unknown whether autism's prevalence increased during the same period; a real increase would suggest directing more attention and funding toward changing environmental factors instead of continuing to focus on genetics.

The risk of autism is associated with several prenatal and perinatal risk factors. A 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.

Autism is associated with several other conditions:
  • Epilepsy, with variations in risk of epilepsy due to age, cognitive level, and type of language disorder.
  • Genetic disorders. About 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome abnormality, or other genetic syndrome, and Autism Spectrum Disorders is associated with several genetic disorders.
  • Maleness. Males are at higher risk for autism than females. The Autism Spectrum Disorders 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.
  • Mental retardation. The fraction of autistic individuals who also meet criteria for mental retardation has been reported as anywhere from 25% to 70%, a wide variation illustrating the difficulty of assessing autistic intelligence. For Autism Spectrum Disorders other than autism, the association with mental retardation is much weaker.
  • Minor physical anomalies are significantly increased in the autistic population.
  • Preempted diagnoses. Although the DSM-IV rules out concurrent diagnosis of many other conditions along with autism, the full criteria for ADHD, Tourette syndrome, and other of these conditions are often present and these comorbid diagnoses are increasingly accepted.
  • Several metabolic defects, such as phenylketonuria, are associated with autistic symptoms.

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