Autism [aw-tiz-uhm] is a neurological disorder characterized by a profound withdrawal from contact with people, repetitive behavior, and fear of change in the environment. The emotional disorder affects the brain’s ability to receive and process information.

People who have autism find it difficult to act in a way that other people think is ‘normal,’ and they find it difficult to talk to other people, to look at other people, and often do not like being touched by other people. A person who has autism seems to be turned inwards. They may talk only to themselves, rock themselves backwards and forwards, and laugh at their own thoughts. They do not like any type of change and may find it very difficult to learn a new behavior like using a toilet or going to school.

Autism is caused by the way that the brain develops (both prenatally and until age 3), and is called a ‘spectrum disorder’ because some people who have autism are only mildly affected. These people may go to regular schools and workplaces, and have partners and families. Mild autism is called Asperger Syndrome or ‘High functioning Autism.’ Pervasive developmental disorder, not otherwise specified (PDD-NOS) is diagnosed when the full set of criteria for autism or Asperger syndrome are not met. Autism is heritable: parents with an Autistic Spectrum Disorder (ASD) often have children with Asperger Syndrome or with more severe Autism. A small portion of those with autism are extraordinarily gifted or talented; they are said to have ‘savant syndrome.’ They are often very good at just one thing in particular, like mathematics, playing the piano, or remembering football scores.

A normal baby without autism will usually look at people talking, look at other people’s faces, smile, and be interested in other people. Autistic babies, though, may like objects more than faces and other people. They may look for a second at a face, but quickly turn. They may not smile, or may just smile at what they are interested in. Autistic children often like to be by themselves. They might not be interested in making friends. They also might not react normally to hugging and other signs of love by their parents. This does not mean that they do not love their parents, they just do not know how to express it. They may also not see other people’s feelings; for example, they might not see much difference between whether a parent is smiling or being sad. They may laugh and cry at the wrong times. An autistic child might not try to talk, point, or otherwise try to get a message across by 1 year of age. Some do not understand their language at all. Some autistic people do not speak. Many are not good at talking with other people.

Some autistic people spend a lot of time doing the same thing over and over again; some might spend a lot of time spinning in circles, chewing their toes, or putting things in order. An autistic person might spend a huge amount of time putting toys in lines or patterns and may get angry if someone bumps something out of place. Some do not want any change, and will do exactly the same things every day without change—such as what they eat, when they eat, getting dressed, brushing their teeth, or going to school—and may even get upset if any change takes place to this. They may also be interested in strange things and may spend all of their time learning about their interest.

Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood. Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether ASD is explained more by rare mutations, or by rare combinations of common genetic variants. In rare cases, autism is strongly associated with agents that cause birth defects. Controversies surround other proposed environmental causes, such as heavy metals, pesticides, or childhood vaccines; the vaccine hypotheses are biologically implausible and lack convincing scientific evidence. The prevalence of autism is about 1–2 per 1,000 people worldwide, and the Centers for Disease Control and Prevention (CDC) report 11 per 1,000 children in the United States are diagnosed with ASD as of 2008.

The number of people diagnosed with autism has increased dramatically since the 1980s, partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved. Parents usually notice signs in the first two years of their child’s life. The signs usually develop gradually, but some autistic children first develop more normally and then regress. Early behavioral or cognitive intervention can help autistic children gain self-care, social, and communication skills. Although there is no known cure, there have been reported cases of children who recovered. Not many children with autism live independently after reaching adulthood, though some become successful. An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.

Social deficits distinguish autism and the related autism spectrum disorders from other developmental disorders. People with autism 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 (people with normal neural development) as leaving her feeling ‘like an anthropologist on Mars.’ Communication failures can lead to intense frustration. 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. A 2007 study interviewed 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 non-autistic children with language impairments.

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 vocal patterns that are not synchronized 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) or reverse pronouns. Joint attention (the shared focus of two individuals on an object) seems to be necessary for functional speech, and deficits in joint attention seem to distinguish infants with ASD: 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 children may have difficulty with imaginative play and with developing symbols into language. In a pair of studies, high-functioning autistic children aged 8–15 performed equally well as, 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.

Autistic individuals display many forms of repetitive or restricted behavior: Stereotypy (repetitive movement, such as hand flapping, head rolling, or body rocking); Compulsive behavior (appears to follow rules, such as arranging objects in stacks or lines); Sameness (resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted); Ritualistic behavior (an unvarying pattern of daily activities, such as an unchanging menu or a dressing ritual); Restricted behavior (limited focus, interest, or activity, such as preoccupation with a single television program, toy, or game); and Self-injury (movements that injure or can injure the person, such as eye poking, skin picking, hand biting, and head banging). No single repetitive or self-injurious behavior seems to be specific to autism, but only autism appears to have an elevated pattern of occurrence and severity of these behaviors.

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. Many individuals with ASD show superior skills in perception and attention, relative to the general population. Sensory abnormalities are found in over 90% of those with autism, and are considered core features by some, 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 sensation seeking (for example, rhythmic movements). An estimated 60%–80% of autistic people have motor signs that include poor muscle tone, poor motor planning, and toe walking; deficits in motor coordination are pervasive across ASD and are greater in autism proper.

Unusual 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; this does not appear to result in malnutrition. Although some children with autism also have gastrointestinal (GI) symptoms, there is a lack of published rigorous data to support the theory that autistic children have more or different GI symptoms than usual; studies report conflicting results, and the relationship between GI problems and ASD is unclear. Parents of children with ASD have higher levels of stress. Siblings of children with ASD report greater admiration of and less conflict with the affected sibling than siblings of unaffected children and were similar to siblings of children with Down syndrome in these aspects of the sibling relationship. However, they reported lower levels of closeness and intimacy than siblings of children with Down syndrome; siblings of individuals with ASD have greater risk of negative well-being and poorer sibling relationships as adults.

It has long been presumed that there is a common cause at the genetic, cognitive, and neural levels for autism’s characteristic triad of symptoms. However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur. Unlike many other brain disorders, such as Parkinson’s, autism does not have a clear unifying mechanism at either the molecular, cellular, or systems level; it is not known whether autism is a few disorders caused by mutations converging on a few common molecular pathways, or is (like intellectual disability) a large set of disorders with diverse mechanisms. Autism appears to result from developmental factors that affect many or all functional brain systems, and to disturb the timing of brain development more than the final product.

Just after birth, the brains of autistic children tend to grow faster than usual, followed by normal or relatively slower growth in childhood. It is not known whether early overgrowth occurs in all autistic children. It seems to be most prominent in brain areas underlying the development of higher cognitive specialization. Hypotheses for the cellular and molecular bases of pathological early overgrowth include the following: An excess of neurons that causes local overconnectivity in key brain regions; Disturbed neuronal migration during early gestation; Unbalanced excitatory–inhibitory networks; and Abnormal formation of synapses and dendritic spines (disrupted synaptic development may also contribute to epilepsy, which may explain why the two conditions are associated).

Interactions between the immune system and the nervous system begin early during the embryonic stage of life, and successful neurodevelopment depends on a balanced immune response. Aberrant immune activity during critical periods of neurodevelopment is possibly part of the mechanism of some forms of ASD. Although some abnormalities in the immune system have been found in specific subgroups of autistic individuals, it is not known whether these abnormalities are relevant to or secondary to autism’s disease processes.

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 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. 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 syndrome, and a correlation between reduced MNS activity and severity of the syndrome in children with ASD. 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 children on imitation tasks that involve a goal or object.

ASD-related patterns of low function and aberrant activation in the brain differ depending on whether the brain is doing social or nonsocial tasks.[94] In autism there is evidence for reduced functional connectivity of the default 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. In people with autism the two networks are not negatively correlated in time, suggesting an imbalance in toggling between the two networks, possibly reflecting a disturbance of self-referential thought.

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. The empathizing–systemizing theory postulates that autistic individuals can systemize—that is, they can develop internal rules of operation to handle events inside the brain—but are less effective at empathizing by handling events generated by other agents. An extension, the extreme male brain theory, hypothesizes that autism is an extreme case of the male brain, defined psychometrically as individuals in whom systemizing is better than empathizing; this extension is controversial, as many studies contradict the idea that baby boys and girls respond differently to people and objects. The second category focuses on nonsocial or general processing: the executive functions such as working memory, planning, inhibition. In his review, Kenworthy states that ‘the claim of executive dysfunction as a causal factor in autism is controversial,’ however, ‘it is clear that executive dysfunction plays a role in the social and cognitive deficits observed in individuals with autism.’

The main goals when treating children with autism are to lessen associated deficits and family distress, and to increase quality of life and functional independence. No single treatment is best and treatment is typically tailored to the child’s needs. Families and the educational system are the main resources for treatment. Studies of interventions have methodological problems that prevent definitive conclusions about efficacy. Although many psychosocial interventions have some positive evidence, suggesting that some form of treatment is preferable to no treatment, the methodological quality of systematic reviews of these studies has generally been poor, their clinical results are mostly tentative, and there is little evidence for the relative effectiveness of treatment options. Intensive, sustained special education programs and behavior therapy early in life can help children acquire self-care, social, and job skills, and often improve functioning and decrease symptom severity and maladaptive behaviors. Available approaches include applied behavior analysis (ABA), developmental models, structured teaching, speech and language therapy, social skills therapy, and occupational therapy.

Many medications are used to treat ASD symptoms that interfere with integrating a child into home or school when behavioral treatment fails. More than half of US children diagnosed with ASD are prescribed psychoactive drugs or anticonvulsants, with the most common drug classes being antidepressants, stimulants, and antipsychotics. However, no known medication relieves autism’s core symptoms of social and communication impairments.

Boys are at higher risk for ASD than girls. The 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. Although the evidence does not implicate any single pregnancy-related risk factor as a cause of autism, the risk of autism is associated with advanced age in either parent, and with diabetes, bleeding, and use of psychiatric drugs in the mother during pregnancy. The risk is greater with older fathers than with older mothers; two potential explanations are the known increase in mutation burden in older sperm, and the hypothesis that men marry later if they carry genetic liability and show some signs of autism. Most professionals believe that race, ethnicity, and socioeconomic background do not affect the occurrence of autism.

A few examples of autistic symptoms and treatments were described long before autism was named. The Table Talk of Martin Luther, compiled by his notetaker, Mathesius, contains the story of a 12-year-old boy who may have been severely autistic. Luther reportedly thought the boy was a soulless mass of flesh possessed by the devil, and suggested that he be suffocated, although a later critic has cast doubt on the veracity of this report. The earliest well-documented case of autism is that of Hugh Blair of Borgue, as detailed in a 1747 court case in which his brother successfully petitioned to annul Blair’s marriage to gain Blair’s inheritance. The Wild Boy of Aveyron, a feral child caught in 1798, showed several signs of autism; the medical student Jean Itard treated him with a behavioral program designed to help him form social attachments and to induce speech via imitation.

The New Latin word ‘autismus’ was coined by the Swiss psychiatrist Eugen Bleuler in 1910 as he was defining symptoms of schizophrenia. He derived it from the Greek word ‘autós’ (‘self’), and used it to mean morbid self-admiration, referring to ‘autistic withdrawal of the patient to his fantasies, against which any influence from outside becomes an intolerable disturbance.’ The word autism first took its modern sense in 1938 when Hans Asperger of the Vienna University Hospital adopted Bleuler’s terminology autistic psychopaths in a lecture in German about child psychology. Asperger was investigating an ASD now known as Asperger syndrome, though for various reasons it was not widely recognized as a separate diagnosis until 1981. Leo Kanner of the Johns Hopkins Hospital first used autism in its modern sense in English when he introduced the label early infantile autism in a 1943 report of 11 children with striking behavioral similarities. Almost all the characteristics described in Kanner’s first paper on the subject, notably ‘autistic aloneness’ and ‘insistence on sameness,’ are still regarded as typical of the autistic spectrum of disorders. It is not known whether Kanner derived the term independently of Asperger.

Kanner’s reuse of autism led to decades of confused terminology like infantile schizophrenia, and child psychiatry’s focus on maternal deprivation led to misconceptions of autism as an infant’s response to ‘refrigerator mothers’ (cold, uncaring parents). Starting in the late 1960s autism was established as a separate syndrome by demonstrating that it is lifelong, distinguishing it from mental retardation and schizophrenia and from other developmental disorders, and demonstrating the benefits of involving parents in active programs of therapy. As late as the mid-1970s there was little evidence of a genetic role in autism; now it is thought to be one of the most heritable of all psychiatric conditions. Although the rise of parent organizations and the destigmatization of childhood ASD have deeply affected how we view ASD, parents continue to feel social stigma in situations where their autistic children’s behaviors are perceived negatively by others, and many primary care physicians and medical specialists still express some beliefs consistent with outdated autism research. The Internet has helped autistic individuals bypass nonverbal cues and emotional sharing that they find so hard to deal with, and has given them a way to form online communities and work remotely.

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