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Other aspects, such as atypical eating, are also common but are not essential for diagnosis.[SEP]Individual symptoms of autism occur in the general population and appear not to associate highly, without a sharp line separating pathologically severe from common traits.
Individual symptoms of autism occur in the general population and appear not to associate highly, without a sharp line separating pathologically severe from common traits.[SEP]Social development Social deficits distinguish autism and the related autism spectrum disorders (ASD; see Classification) from other developmental disorders.
Social development Social deficits distinguish autism and the related autism spectrum disorders (ASD; see Classification) from other developmental disorders.[SEP]Autistic people have social impairments and often lack the intuition about others that many people take for granted.
Autistic people have social impairments and often lack the intuition about others that many people take for granted.[SEP]Noted autistic Temple Grandin described her inability to understand the social communication of neurotypicals, or people with typical neural development, as leaving her feeling "like an anthropologist on Mars".
Noted autistic Temple Grandin described her inability to understand the social communication of neurotypicals, or people with typical neural development, as leaving her feeling "like an anthropologist on Mars".[SEP]Unusual social development becomes apparent early in childhood.
Unusual social development becomes apparent early in childhood.[SEP]Autistic infants show less attention to social stimuli, smile and look at others less often, and respond less to their own name.
Autistic infants show less attention to social stimuli, smile and look at others less often, and respond less to their own name.[SEP]Autistic toddlers differ more strikingly from social norms; for example, they have less eye contact and turn-taking, and do not have the ability to use simple movements to express themselves, such as pointing at things.
Autistic toddlers differ more strikingly from social norms; for example, they have less eye contact and turn-taking, and do not have the ability to use simple movements to express themselves, such as pointing at things.[SEP]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.
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.[SEP]However, they do form attachments to their primary caregivers.
However, they do form attachments to their primary caregivers.[SEP]Most autistic children display moderately less attachment security than neurotypical children, although this difference disappears in children with higher mental development or less pronounced autistic traits.
Most autistic children display moderately less attachment security than neurotypical children, although this difference disappears in children with higher mental development or less pronounced autistic traits.[SEP]Older children and adults with ASD perform worse on tests of face and emotion recognition although this may be partly due to a lower ability to define a person's own emotions.
Older children and adults with ASD perform worse on tests of face and emotion recognition although this may be partly due to a lower ability to define a person's own emotions.[SEP]Children with high-functioning autism have more intense and frequent loneliness compared to non-autistic peers, despite the common belief that autistic children prefer to be alone.
Children with high-functioning autism have more intense and frequent loneliness compared to non-autistic peers, despite the common belief that autistic children prefer to be alone.[SEP]Making and maintaining friendships often proves to be difficult for autistic people.
Making and maintaining friendships often proves to be difficult for autistic people.[SEP]For them, the quality of friendships, not the number of friends, predicts how lonely they feel.
For them, the quality of friendships, not the number of friends, predicts how lonely they feel.[SEP]Functional friendships, such as those resulting in invitations to parties, may affect the quality of life more deeply.
Functional friendships, such as those resulting in invitations to parties, may affect the quality of life more deeply.[SEP]There are many anecdotal reports, but few systematic studies, of aggression and violence in individuals with ASD.
There are many anecdotal reports, but few systematic studies, of aggression and violence in individuals with ASD.[SEP]The limited data suggest that, in children with intellectual disability, autism is associated with aggression, destruction of property, and meltdowns.
The limited data suggest that, in children with intellectual disability, autism is associated with aggression, destruction of property, and meltdowns.[SEP]Communication About one third to half of autistic people do not develop enough natural speech to meet their daily communication needs.
Communication About one third to half of autistic people do not develop enough natural speech to meet their daily communication needs.[SEP]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.
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.[SEP]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.
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.[SEP]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 are less likely to make requests or share experiences, and are more likely to simply repeat others' words (echolalia) or reverse pronouns.[SEP]Joint attention seems to be necessary for functional speech, and deficits in joint attention seem to distinguish infants with ASD.
Joint attention seems to be necessary for functional speech, and deficits in joint attention seem to distinguish infants with ASD.[SEP]For example, they may look at a pointing hand instead of the object to which the hand is pointing, and they consistently fail to point at objects in order to comment on or share an experience.
For example, they may look at a pointing hand instead of the object to which the hand is pointing, and they consistently fail to point at objects in order to comment on or share an experience.[SEP]Autistic children may have difficulty with imaginative play and with developing symbols into language.
Autistic children may have difficulty with imaginative play and with developing symbols into language.[SEP]In a pair of studies, high-functioning autistic children aged 8–15 performed equally well as, and as adults better than, individually matched controls at basic language tasks involving vocabulary and spelling.
In a pair of studies, high-functioning autistic children aged 8–15 performed equally well as, and as adults better than, individually matched controls at basic language tasks involving vocabulary and spelling.[SEP]Both autistic groups performed worse than controls at complex language tasks such as figurative language, comprehension, and inference.
Both autistic groups performed worse than controls at complex language tasks such as figurative language, comprehension, and inference.[SEP]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.
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.[SEP]Autistic individuals can display many forms of repetitive or restricted behavior, which the Repetitive Behavior Scale-Revised (RBS-R) categorizes as follows.
Autistic individuals can display many forms of repetitive or restricted behavior, which the Repetitive Behavior Scale-Revised (RBS-R) categorizes as follows.[SEP]Stereotyped behaviors: Repetitive movements, such as hand flapping, head rolling, or body rocking.
Stereotyped behaviors: Repetitive movements, such as hand flapping, head rolling, or body rocking.[SEP]Compulsive behaviors: Time-consuming behaviors intended to reduce the anxiety that an individual feels compelled to perform repeatedly or according to rigid rules, such as placing objects in a specific order, checking things, or handwashing.
Compulsive behaviors: Time-consuming behaviors intended to reduce the anxiety that an individual feels compelled to perform repeatedly or according to rigid rules, such as placing objects in a specific order, checking things, or handwashing.[SEP]Sameness: Resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.
Sameness: Resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.[SEP]Ritualistic behavior: Unvarying pattern of daily activities, such as an unchanging menu or a dressing ritual.
Ritualistic behavior: Unvarying pattern of daily activities, such as an unchanging menu or a dressing ritual.[SEP]This is closely associated with sameness and an independent validation has suggested combining the two factors.
This is closely associated with sameness and an independent validation has suggested combining the two factors.[SEP]Restricted interests: Interests or fixations that are abnormal in theme or intensity of focus, such as preoccupation with a single television program, toy, or game.
Restricted interests: Interests or fixations that are abnormal in theme or intensity of focus, such as preoccupation with a single television program, toy, or game.[SEP]Self-injury: Behaviors such as eye-poking, skin-picking, hand-biting and head-banging.
Self-injury: Behaviors such as eye-poking, skin-picking, hand-biting and head-banging.[SEP]No single repetitive or self-injurious behavior seems to be specific to autism, but autism appears to have an elevated pattern of occurrence and severity of these behaviors.
No single repetitive or self-injurious behavior seems to be specific to autism, but autism appears to have an elevated pattern of occurrence and severity of these behaviors.[SEP]Other symptoms Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect the individual or the family.
Other symptoms Autistic individuals may have symptoms that are independent of the diagnosis, but that can affect the individual or the family.[SEP]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.
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.[SEP]Many individuals with ASD show superior skills in perception and attention, relative to the general population.
Many individuals with ASD show superior skills in perception and attention, relative to the general population.[SEP]Sensory abnormalities are found in over 90% of autistic people, and are considered core features by some, although there is no good evidence that sensory symptoms differentiate autism from other developmental disorders.
Sensory abnormalities are found in over 90% of autistic people, and are considered core features by some, although there is no good evidence that sensory symptoms differentiate autism from other developmental disorders.[SEP]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).
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).[SEP]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.
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.[SEP]Unusual eating behavior occurs in about three-quarters of children with ASD, to the extent that it was formerly a diagnostic indicator.
Unusual eating behavior occurs in about three-quarters of children with ASD, to the extent that it was formerly a diagnostic indicator.[SEP]Selectivity is the most common problem, although eating rituals and food refusal also occur.
Selectivity is the most common problem, although eating rituals and food refusal also occur.[SEP]There is tentative evidence that gender dysphoria occurs more frequently in autistic people (see Autism and LGBT identities).
There is tentative evidence that gender dysphoria occurs more frequently in autistic people (see Autism and LGBT identities).[SEP]As well as that, a 2021 anonymized online survey of 16-90 year-olds revealed that autistic males are more likely to be bisexual, while autistic females are more likely to be homosexual.
As well as that, a 2021 anonymized online survey of 16-90 year-olds revealed that autistic males are more likely to be bisexual, while autistic females are more likely to be homosexual.[SEP]Gastrointestinal problems are one of the most commonly co-occurring medical conditions in autistic people.
Gastrointestinal problems are one of the most commonly co-occurring medical conditions in autistic people.[SEP]These are linked to greater social impairment, irritability, behavior and sleep problems, language impairments and mood changes.
These are linked to greater social impairment, irritability, behavior and sleep problems, language impairments and mood changes.[SEP]Parents of children with ASD have higher levels of stress.
Parents of children with ASD have higher levels of stress.[SEP]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.
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.[SEP]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.
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.[SEP]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.
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.[SEP]However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur.
However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur.[SEP]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 with major effects, or by rare multigene interactions of common genetic variants.
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 with major effects, or by rare multigene interactions of common genetic variants.[SEP]Complexity arises due to interactions among multiple genes, the environment, and epigenetic factors which do not change DNA sequencing but are heritable and influence gene expression.
Complexity arises due to interactions among multiple genes, the environment, and epigenetic factors which do not change DNA sequencing but are heritable and influence gene expression.[SEP]Many genes have been associated with autism through sequencing the genomes of affected individuals and their parents.
Many genes have been associated with autism through sequencing the genomes of affected individuals and their parents.[SEP]Studies of twins suggest that heritability is 0.7 for autism and as high as 0.9 for ASD, and siblings of those with autism are about 25 times more likely to be autistic than the general population.
Studies of twins suggest that heritability is 0.7 for autism and as high as 0.9 for ASD, and siblings of those with autism are about 25 times more likely to be autistic than the general population.[SEP]However, most of the mutations that increase autism risk have not been identified.
However, most of the mutations that increase autism risk have not been identified.[SEP]Typically, autism cannot be traced to a Mendelian (single-gene) mutation or to a single chromosome abnormality, and none of the genetic syndromes associated with ASDs have been shown to selectively cause ASD.
Typically, autism cannot be traced to a Mendelian (single-gene) mutation or to a single chromosome abnormality, and none of the genetic syndromes associated with ASDs have been shown to selectively cause ASD.[SEP]Numerous candidate genes have been located, with only small effects attributable to any particular gene.
Numerous candidate genes have been located, with only small effects attributable to any particular gene.[SEP]Most loci individually explain less than 1% of cases of autism.
Most loci individually explain less than 1% of cases of autism.[SEP]The large number of autistic individuals with unaffected family members may result from spontaneous structural variation—such as deletions, duplications or inversions in genetic material during meiosis.
The large number of autistic individuals with unaffected family members may result from spontaneous structural variation—such as deletions, duplications or inversions in genetic material during meiosis.[SEP]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.
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.[SEP]Autism may be underdiagnosed in women and girls due to an assumption that it is primarily a male condition, but genetic phenomena such as imprinting and X linkage have the ability to raise the frequency and severity of conditions in males, and theories have been put forward for a genetic reason why males are diagnosed more often, such as the imprinted brain hypothesis and the extreme male brain theory.
Autism may be underdiagnosed in women and girls due to an assumption that it is primarily a male condition, but genetic phenomena such as imprinting and X linkage have the ability to raise the frequency and severity of conditions in males, and theories have been put forward for a genetic reason why males are diagnosed more often, such as the imprinted brain hypothesis and the extreme male brain theory.[SEP]Maternal nutrition and inflammation during preconception and pregnancy influences fetal neurodevelopment.
Maternal nutrition and inflammation during preconception and pregnancy influences fetal neurodevelopment.[SEP]Intrauterine growth restriction is associated with ASD, in both term and preterm infants.
Intrauterine growth restriction is associated with ASD, in both term and preterm infants.[SEP]Maternal inflammatory and autoimmune diseases may damage fetal tissues, aggravating a genetic problem or damaging the nervous system.
Maternal inflammatory and autoimmune diseases may damage fetal tissues, aggravating a genetic problem or damaging the nervous system.[SEP]Exposure to air pollution during pregnancy, especially heavy metals and particulates, may increase the risk of autism.
Exposure to air pollution during pregnancy, especially heavy metals and particulates, may increase the risk of autism.[SEP]Environmental factors that have been claimed without evidence to contribute to or exacerbate autism include certain foods, infectious diseases, solvents, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, vaccines, and prenatal stress.
Environmental factors that have been claimed without evidence to contribute to or exacerbate autism include certain foods, infectious diseases, solvents, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, vaccines, and prenatal stress.[SEP]Some, such as the MMR vaccine, have been completely disproven.
Some, such as the MMR vaccine, have been completely disproven.[SEP]Parents may first become aware of autistic symptoms in their child around the time of a routine vaccination.
Parents may first become aware of autistic symptoms in their child around the time of a routine vaccination.[SEP]This has led to unsupported theories blaming vaccine "overload", a vaccine preservative, or the MMR vaccine for causing autism.
This has led to unsupported theories blaming vaccine "overload", a vaccine preservative, or the MMR vaccine for causing autism.[SEP]The latter theory was supported by a litigation-funded study that has since been shown to have been "an elaborate fraud".
The latter theory was supported by a litigation-funded study that has since been shown to have been "an elaborate fraud".[SEP]Although these theories lack convincing scientific evidence and are biologically implausible, parental concern about a potential vaccine link with autism has led to lower rates of childhood immunizations, outbreaks of previously controlled childhood diseases in some countries, and the preventable deaths of several children.
Although these theories lack convincing scientific evidence and are biologically implausible, parental concern about a potential vaccine link with autism has led to lower rates of childhood immunizations, outbreaks of previously controlled childhood diseases in some countries, and the preventable deaths of several children.[SEP]Autism's symptoms result from maturation-related changes in various systems of the brain.
Autism's symptoms result from maturation-related changes in various systems of the brain.[SEP]How autism occurs is not well understood.
How autism occurs is not well understood.[SEP]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.
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.[SEP]The behaviors appear to have multiple pathophysiologies.
The behaviors appear to have multiple pathophysiologies.[SEP]There is evidence that gut–brain axis abnormalities may be involved.
There is evidence that gut–brain axis abnormalities may be involved.[SEP]A 2015 review proposed that immune dysregulation, gastrointestinal inflammation, malfunction of the autonomic nervous system, gut flora alterations, and food metabolites may cause brain neuroinflammation and dysfunction.
A 2015 review proposed that immune dysregulation, gastrointestinal inflammation, malfunction of the autonomic nervous system, gut flora alterations, and food metabolites may cause brain neuroinflammation and dysfunction.[SEP]A 2016 review concludes that enteric nervous system abnormalities might play a role in neurological disorders such as autism.
A 2016 review concludes that enteric nervous system abnormalities might play a role in neurological disorders such as autism.[SEP]Neural connections and the immune system are a pathway that may allow diseases originated in the intestine to spread to the brain.
Neural connections and the immune system are a pathway that may allow diseases originated in the intestine to spread to the brain.[SEP]Several lines of evidence point to synaptic dysfunction as a cause of autism.
Several lines of evidence point to synaptic dysfunction as a cause of autism.[SEP]Some rare mutations may lead to autism by disrupting some synaptic pathways, such as those involved with cell adhesion.
Some rare mutations may lead to autism by disrupting some synaptic pathways, such as those involved with cell adhesion.[SEP]Gene replacement studies in mice suggest that autistic symptoms are closely related to later developmental steps that depend on activity in synapses and on activity-dependent changes.
Gene replacement studies in mice suggest that autistic symptoms are closely related to later developmental steps that depend on activity in synapses and on activity-dependent changes.[SEP]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, there is strong evidence that autism arises very early in development.
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, there is strong evidence that autism arises very early in development.[SEP]Diagnosis Diagnosis is based on behavior, not cause or mechanism.
Diagnosis Diagnosis is based on behavior, not cause or mechanism.[SEP]Under the DSM-5, autism is characterized by persistent deficits in social communication and interaction across multiple contexts, as well as restricted, repetitive patterns of behavior, interests, or activities.
Under the DSM-5, autism is characterized by persistent deficits in social communication and interaction across multiple contexts, as well as restricted, repetitive patterns of behavior, interests, or activities.[SEP]These deficits are present in early childhood, typically before age three, and lead to clinically significant functional impairment.
These deficits are present in early childhood, typically before age three, and lead to clinically significant functional impairment.[SEP]Sample symptoms include lack of social or emotional reciprocity, stereotyped and repetitive use of language or idiosyncratic language, and persistent preoccupation with unusual objects.
Sample symptoms include lack of social or emotional reciprocity, stereotyped and repetitive use of language or idiosyncratic language, and persistent preoccupation with unusual objects.[SEP]The disturbance must not be better accounted for by Rett syndrome, intellectual disability or global developmental delay.
The disturbance must not be better accounted for by Rett syndrome, intellectual disability or global developmental delay.[SEP]ICD-10 uses essentially the same definition.
ICD-10 uses essentially the same definition.[SEP]Several diagnostic instruments are available.
Several diagnostic instruments are available.[SEP]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.
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.[SEP]The Childhood Autism Rating Scale (CARS) is used widely in clinical environments to assess severity of autism based on observation of children.
The Childhood Autism Rating Scale (CARS) is used widely in clinical environments to assess severity of autism based on observation of children.[SEP]The Diagnostic interview for social and communication disorders (DISCO) may also be used.
The Diagnostic interview for social and communication disorders (DISCO) may also be used.[SEP]A pediatrician commonly performs a preliminary investigation by taking developmental history and physically examining the child.
A pediatrician commonly performs a preliminary investigation by taking developmental history and physically examining the child.[SEP]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.
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.[SEP]A pediatric neuropsychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions.
A pediatric neuropsychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions.[SEP]A differential diagnosis for ASD at this stage might also consider intellectual disability, hearing impairment, and a specific language impairment such as Landau–Kleffner syndrome.