Autism
Autism is a brain development disorder that impairs social interaction and communication, and causes restricted and repetitive behavior, all starting before a child is three years old. This set of signs distinguishes autism from milder autism spectrum disorders (ASD) such as Asperger syndrome.
Autism is highly heritable, although the genetics of autism are complex and it is generally unclear which genes are responsible in rare cases, autism is strongly associated with agents that cause birth defects. Other proposed causes, such as childhood vaccines, are controversial and the vaccine hypotheses lack convincing scientific evidence. 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 actual prevalence has increased is unresolved
Autism affects many parts of the brain; how this occurs is poorly understood. Parents usually notice signs in the first two years 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. With severe autism, independent living is unlikely; with milder autism, there are some success stories for adults, and an autistic culture has developed, with some seeking a cure and others believing that autism is a condition rather than a disorder

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 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
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 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 less likely to use another person's hand or body as a tool. 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. They display moderately less attachment security than usual, although this feature disappears in children with higher mental development or less severe ASD. Older children and adults with ASD perform worse on tests of face and emotion recognition.
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.
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.
Communication
About a third to a half of individuals with autism does 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 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) or reverse pronouns. Autistic children may have difficulty with imaginative play and with developing symbols into language. They are more likely to have problems understanding pointing; for example, they may look at a pointing hand instead of the pointed-at object.
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
Repetitive behavior

A young boy with autism, and the precise line of toys he made
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, or body rocking.
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. This is closely associated with sameness and an independent validation has suggested combining the two factors.
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
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.
Causes

Although many genetic and environmental causes of autism have been proposed, its theory of causation is still incomplete. 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.
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. This may be an overestimate; new twin data and models with structural genetic variation are needed. 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%, much higher than the risk in controls .
The genetics of autism is complex Genetic linkage analysis has been inconclusive; many association analyses have had inadequate power. 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. 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 single chromosome abnormalities such as fragile X syndrome or 22q13 deletion syndrome.


Deletion (1), duplication (2) and inversion (3) are all chromosome abnormalities that have been implicated in autism.
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. 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. Although the fraction of autism traceable to a genetic cause may grow to 30–40% as the resolution of array CGH improves several results in this area have been described incautiously, possibly misleading the public into thinking that a large proportion of autism is caused by CNVs and is detectable via array CGH, or that detecting CNVs is tantamount to a genetic diagnosis. 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.
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. 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. Although extensive searches are underway for other environmental causes, evidence for them is anecdotal and has not been confirmed by reliable studies. Several other pre- or post-natal environmental factors have been claimed to contribute to autism or exacerbate its symptoms, or may be important to consider in future research. They include certain foods, infectious disease, heavy ****************ls, solvents, diesel exhaust, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, and vaccines. Although parents may first become aware of autistic symptoms in their child 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 convincing evidence that the vaccine preservative thiomersal helps cause autism

Management
Autism therapies
The main goals of treatment are to lessen associated deficits and family distress, and to increase quality of life and functional independence. No single treatment is best and treatment is typically tailored to the child's needs. Intensive, sustained special education programs and behavior therapy early in life can help children acquire self-care, social, and job skills; claims that intervention by age two to three years is crucial are not substantiated. 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; ABA focuses on teaching tasks one-on-one using the behaviorist principles of stimulus, response and reward. Several programs are based on ABA. Some focus on discrete trial teaching; more-comprehensive ones use multiple assessment and intervention methods individually and dynamically. Cognitive therapies based on comprehensive programs in treatment centers are a common alternative:
Medications are often used to treat problems associated with ASD. Children diagnosed with ASD are prescribed psychoactive drugs or anticonvulsants, with the most common drug classes being antidepressants, stimulants, and antipsychotics. In the United States, the antipsychotic risperidone is approved for treating symptomatic irritability in autistic children and adolescents. Other drugs are prescribed off-label, which means they have not been approved for treating ASD. For example, some selective serotonin reuptake inhibitors and dopamine blockers can reduce some maladaptive behaviors associated with ASD. Aside from antipsychotics, there is scant reliable research about the effectiveness or safety of drug treatments for adolescents and adults with ASD. 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