Autism is a disorder of neural development characterized by impaired
social interactionAn interpersonal relationship is an association between two or more people that may range from fleeting to enduring. This association may be based on limerence, love, solidarity, regular business interactions, or some other type of social commitment. Interpersonal relationships are formed in the...
and
communicationCommunication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the
brainThe human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
by altering how nerve cells and their
synapseIn the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s connect and organize; how this occurs is not well understood. It is one of three recognized disorders in the
autism spectrumThe term "autism spectrum" is often used to describe disorders that are currently classified as pervasive developmental disorders. Pervasive developmental disorders include autism, Asperger syndrome, Childhood disintegrative disorder, Rett syndrome and Pervasive Developmental Disorder Not Otherwise...
(ASDs), the other two being
Asperger syndromeAsperger's syndrome that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development...
, which lacks delays in cognitive development and language, and Pervasive Developmental Disorder-Not Otherwise Specified (commonly abbreviated as PDD-NOS), which is diagnosed when the full set of criteria for autism or Asperger syndrome are not met.
Autism has a strong genetic basis, although the
genetics of autismThe heritability of autism is the proportion of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic...
are complex and it is unclear whether ASD is explained more by rare
mutationIn molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s, or by rare combinations of common genetic variants. In rare cases, autism is strongly associated with
agents that cause birth defectsTeratology is the study of abnormalities of physiological development. It is often thought of as the study of human birth defects, but it is much broader than that, taking in other non-birth developmental stages, including puberty; and other non-human life forms, including plants.- Etymology :The...
.
ControversiesControversies in autism encompass the disagreement over the exact nature of autism, its causes and manifestations. Autism is considered to be a neurodevelopmental condition which manifests itself in markedly abnormal social interaction, communication ability, and patterns of interests.The cause of...
surround other proposed environmental
causesMany causes of autism have been proposed, but understanding of the theory of causation of autism and the other autism spectrum disorders is incomplete. Heritability contributes about 90% of the risk of a child developing autism, but the heritability of autism is complex and typically it is...
, such as heavy metals,
pesticidePesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s or childhood
vaccineA vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
s; the vaccine hypotheses are biologically implausible and lack convincing scientific evidence. The
prevalenceIn epidemiology, the prevalence of a health-related state in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population...
of autism is about 1–2 per 1,000 people worldwide; however, the
Centers for Disease Control and PreventionThe Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...
(CDC) reports approximately 9 per 1,000 children in the United States are diagnosed with ASD. 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
regressRegressive autism occurs when a child appears to develop typically but then starts to lose speech and social skills, typically between the ages of 15 and 30 months, and is subsequently diagnosed with autism...
. Early
behavioralLOVAAS technique, which is known to the general public as Applied behavior analysis , as well as Intensive behavioral intervention , and Early intensive behavioral intervention , is a form of treatment guided by ABA and developed by Dr. Ivar Lovaas, a psychology professor at UCLA...
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 cultureSociological and cultural aspects of autism come into play with recognition of autism, approaches to its support services and therapies, and how autism affects how we define personhood. The autism rights movement is based on a belief that autism is a different way of being and not a disorder to be...
has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.
Characteristics
Autism is a highly variable neurodevelopmental disorder that first appears during infancy or childhood, and generally follows a steady course without remission. Overt symptoms gradually begin after the age of six months, become established by age two or three years, and tend to continue through adulthood, although often in more muted form. It is distinguished not by a single symptom, but by a characteristic triad of symptoms: impairments in social interaction; impairments in communication; and restricted interests and repetitive behavior. Other aspects, such as atypical eating, are also common but are not essential for diagnosis. Autism's individual symptoms occur in the general population and appear not to associate highly, without a sharp line separating pathologically severe from common traits.
Social development
Social deficits distinguish autism and the related autism spectrum disorders (ASD; see
Classification) 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 GrandinTemple Grandin is an American doctor of animal science and professor at Colorado State University, bestselling author, and consultant to the livestock industry on animal behavior...
described her inability to understand the
social communicationThe term social communication refers to using the so-called social media. However there is no standardised definition yet recognised. Generally communication requires a social nexus of at least two entities in a technical or just social relation...
of
neurotypicalNeurotypical is a term that was coined in the autistic community as a label for people who are not on the autism spectrum: specifically, neurotypical people have neurological development and states that are consistent with what most people would perceive as normal, particularly with respect to...
s, or people with normal
neural developmentNeural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
, as leaving her feeling "like an anthropologist on Mars".
Unusual social development becomes apparent early in childhood. Autistic infants show less attention to social stimuli, smile and look at others less often, and respond less to their own name. Autistic toddlers differ more strikingly from social norms; for example, they have less
eye contactEye contact is a meeting of the eyes between two individuals.In human beings, eye contact is a form of nonverbal communication and is thought to have a large influence on social behavior. Coined in the early to mid-1960s, the term has come in the West to often define the act as a meaningful and...
and turn taking, and do not have the ability to use simple movements to express themselves, such as the deficiency to point at things. 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. Most autistic children display moderately less attachment security than non-autistic children, although this difference 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.
Children with high-functioning autism suffer from more intense and frequent loneliness compared to non-autistic peers, despite the common belief that children with autism 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 feel. Functional friendships, such as those resulting in invitations to parties, may affect the quality of life more deeply.
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
tantrumA tantrum is an emotional outburst, usually associated with children or those in emotional distress, that is typically characterized by stubbornness, crying, screaming, yelling, shrieking, defiance, angry ranting, a resistance to attempts at pacification and, in some cases, violence...
s. 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. A 2008 Swedish study found that, of individuals aged 15 or older discharged from hospital with a diagnosis of ASD, those who committed violent crimes were significantly more likely to have other psychopathological conditions such as
psychosisPsychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...
.
Communication
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
babblingBabbling is a stage in child development and a state in language acquisition, during which an infant appears to be experimenting with uttering sounds of language, but not yet producing any recognizable words...
, 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 (
echolaliaEcholalia is the automatic repetition of vocalizations made by another person. It is closely related to echopraxia, the automatic repetition of movements made by another person....
) or
reverse pronounsPronoun reversal is a language abnormality common in the speech of autistic children. Children refer to themselves as "he," "she," or "you," or by their own proper names. Pronoun reversal is closely linked to echolalia. Since autistic children often use echolalic speech, they refer to themselves...
.
Joint attentionJoint attention is interactionally-achieved when one person, animal or agent alerts another to a stimulus by means of eye-gazing, finger-pointing or other verbal or non-verbal indication....
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.
Repetitive behavior
Autistic individuals display many forms of repetitive or restricted behavior, which the Repetitive Behavior Scale-Revised (RBS-R) categorizes as follows.
- Stereotypy
A stereotypy is a repetitive or ritualistic movement, posture, or utterance, found in people with mental retardation, autism spectrum disorders, tardive dyskinesia and stereotypic movement disorder. Stereotypies may be simple movements such as body rocking, or complex, such as self-caressing,...
is repetitive movement, such as hand flapping, making sounds, head rolling, or body rocking.
- Compulsive behavior
Compulsive behavior is behavior which a person does compulsively—in other words, not because they want to behave that way, but because they feel they have to do so....
is intended and appears to follow rules, such as arranging objects in stacks or lines.
- Sameness is resistance to change; for example, insisting that the furniture not be moved or refusing to be interrupted.
- Ritualistic behavior involves an unvarying pattern of daily activities, such as an unchanging menu or a 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, toy, or game.
- Self-injury includes movements that injure or can injure the person, such as eye poking, skin picking, hand biting, and head banging. A 2007 study reported that self-injury at some point affected about 30% of children with ASD.
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.
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 savantSavant syndrome , sometimes referred to as savantism, is a rare condition in which people with developmental disorders have one or more areas of expertise, ability, or brilliance that are in contrast with the individual's overall limitations...
s. Many individuals with ASD show superior skills in perception and attention, relative to the general population.
SensoryA sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
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 planningApraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements...
, and
toe walkingToe walking refers to a condition where a person walks on his or her toes without putting much weight on the heel or any other part of the foot. Toe-walking in toddlers is common. These children usually adopt a normal walking pattern as they grow older...
; 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
malnutritionMalnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
. 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 or those with
Down syndromeDown syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...
; siblings of individuals with ASD have greater risk of negative well-being and poorer sibling relationships as adults.
Classification
Autism is one of the five
pervasive developmental disorderPervasive developmental disorders is a diagnostic category refers to a group of disorders characterized by delays or impairments in communication, social behaviors, and cognitive development.Pervasive developmental disorders include Autism, Asperger's syndrome, Rett's syndrome, Childhood...
s (PDD), which are characterized by widespread abnormalities of social interactions and communication, and severely restricted interests and highly repetitive behavior. These symptoms do not imply sickness, fragility, or emotional disturbance.
Of the five PDD forms,
Asperger syndromeAsperger's syndrome that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development...
is closest to autism in signs and likely causes;
Rett syndromeRett syndrome is a neurodevelopmental disorder of the grey matter of the brain that almost exclusively affects females. The clinical features include small hands and feet and a deceleration of the rate of head growth . Repetitive hand movements, such as wringing and/or repeatedly putting hands into...
and
childhood disintegrative disorderChildhood disintegrative disorder , also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays in language, social function, and motor skills...
share several signs with autism, but may have unrelated causes;
PDD not otherwise specifiedPervasive Developmental Disorder—Not Otherwise Specified is a pervasive developmental disorder /autism spectrum disorder . PDD-NOS is one of three forms of Autism Spectrum Disorders. PDD-NOS is often referred to as atypical autism....
(PDD-NOS; also called
atypical autism) is diagnosed when the criteria are not met for a more specific disorder. Unlike with autism, people with Asperger syndrome have no substantial delay in
language developmentLanguage development is a process starting early in human life, when a person begins to acquire language by learning it as it is spoken and by mimicry. Children's language development moves from simple to complex. Infants start without language. Yet by four months of age, babies can read lips and...
. The terminology of autism can be bewildering, with autism, Asperger syndrome 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,
ASD, and
PDD are often used interchangeably. ASD, in turn, is a subset of the broader autism
phenotypeA phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
, which describes individuals who may not have ASD but do have autistic-like
traitsA trait is a distinct variant of a phenotypic character of an organism that may be inherited, environmentally determined or be a combination of the two...
, such as avoiding eye contact.
The manifestations of autism cover a wide
spectrumA spectrum in psychiatry is a range of linked conditions, such that there is "not a unitary disorder but rather a syndrome composed of subgroups". The subgroups may be linked together by clinical appearance or by shared underlying causation...
, ranging from individuals with severe impairments—who may be silent, mentally disabled, and locked into hand flapping and rocking—to high functioning individuals who may have active but distinctly odd social approaches, narrowly focused interests, and verbose, pedantic communication. Because the behavior spectrum is continuous, boundaries between diagnostic categories are necessarily somewhat arbitrary. Sometimes the syndrome is divided into low-, medium- or
high-functioning autismHigh-functioning autism is an informal term applied to autistic people who are deemed to be "higher functioning" than other autistic people, by one or more metrics. There is no consensus as to the definition. HFA is not yet a recognised diagnosis in the DSM-IV-TR or the ICD-10.The amount of...
(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
syndromalIn medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
and non-syndromal autism; the syndromal autism is associated with severe or profound
mental retardationMental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
or a congenital syndrome with physical symptoms, such as
tuberous sclerosisTuberous sclerosis or tuberous sclerosis complex is a rare multi-system genetic disease that causes non-malignant tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. A combination of symptoms may include seizures, developmental delay, behavioral...
. Although individuals with Asperger syndrome tend to perform better cognitively than those with autism, the extent of the overlap between Asperger syndrome, HFA, and non-syndromal autism is unclear.
Some studies have reported diagnoses of autism in children due to a loss of language or social skills, as opposed to a failure to make progress, typically from 15 to 30 months of age. The validity of this distinction remains controversial; it is possible that
regressive autismRegressive autism occurs when a child appears to develop typically but then starts to lose speech and social skills, typically between the ages of 15 and 30 months, and is subsequently diagnosed with autism...
is a specific subtype, or that there is a continuum of behaviors between autism with and without regression.
Research into causes has been hampered by the inability to identify biologically meaningful subpopulations and by the traditional boundaries between the disciplines of
psychiatryPsychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...
,
psychologyPsychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...
,
neurologyNeurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
and
pediatricsPediatrics or paediatrics is the branch of medicine that deals with the medical care of infants, children, and adolescents. A medical practitioner who specializes in this area is known as a pediatrician or paediatrician...
. Newer technologies such as fMRI and diffusion tensor imaging can help identify biologically relevant
phenotypeA phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
s (observable traits) that can be viewed on brain scans, to help further neurogenetic studies of autism; one example is lowered activity in the
fusiform face areaThe fusiform face area is a part of the human visual system which might be specialized for facial recognition, although there is some evidence that it also processes categorical information about other objects, particularly familiar ones.-Localization:...
of the brain, which is associated with impaired perception of people versus objects. It has been proposed to classify autism using genetics as well as behavior.
Causes
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.
Autism has a strong genetic basis, although the
genetics of autismThe heritability of autism is the proportion of autism that can be explained by genetic variation; if the heritability of a condition is high, then the condition is considered to be primarily genetic...
are complex and it is unclear whether ASD is explained more by rare
mutationIn molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s with major effects, or by rare multigene interactions of common genetic variants. Complexity arises due to interactions among multiple genes, the environment, and epigenetic factors which do not change
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
but are heritable and influence
gene expressionGene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
. Studies of twins suggest that
heritabilityThe Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
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. 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
fragile X syndromeFragile X syndrome , Martin–Bell syndrome, or Escalante's syndrome , is a genetic syndrome that is the most commonly known single-gene cause of autism and the most common inherited cause of intellectual disability...
, and none of the genetic syndromes associated with ASDs have been shown to selectively cause ASD. 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
duplicationsGene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome.The second copy of the gene is often free from selective pressure — that is, mutations of it have no...
in genetic material during
meiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
. 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.
Several lines of evidence point to
synapticIn the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
dysfunction as a cause of autism. Some rare mutations may lead to autism by disrupting some synaptic pathways, such as those involved with
cell adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins. Correct cellular adhesion is essential in maintaining multicellular structure...
. 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. All known teratogens (agents that cause birth defects) related to the risk of autism appear to act during the first eight weeks from
conceptionHuman fertilization is the union of a humanoid egg and sperm, usually occurring in the ampulla of the uterine tube. The result of this union is the production of a zygote, or fertilized egg, initiating prenatal development...
, 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 factorEnvironmental factor or ecological factor or ecofactor is any factor, abiotic or biotic, that influences living organisms.- Environmental factors inducing diseases :...
s that have been claimed to contribute to or exacerbate autism, or may be important in future research, include certain foods,
infectious diseaseInfectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
,
heavy metalsA heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...
,
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s,
diesel exhaustDiesel exhaust is the exhaust gas of a diesel engine....
, PCBs,
phthalatesPhthalates , or phthalate esters, are esters of phthalic acid and are mainly used as plasticizers . They are used primarily to soften polyvinyl chloride...
and
phenolPhenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
s used in
plasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
products,
pesticidePesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s, brominated flame retardants,
alcoholEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
,
smokingSmoking is a practice in which a substance, most commonly tobacco or cannabis, is burned and the smoke is tasted or inhaled. This is primarily practised as a route of administration for recreational drug use, as combustion releases the active substances in drugs such as nicotine and makes them...
, illicit drugs,
vaccineA vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
s, and
prenatal stressPrenatal stress is exposure of an expectant mother to distress, which can be caused by stressful life events or by environmental hardships. The resulting changes to the mother's hormonal and immune system may harm the fetus's immune function and brain development....
, although no links have been found, and some have been completely disproven.
Parents may first become aware of autistic symptoms in their child around the time of a routine vaccination. This has led to unsupported theories blaming vaccine "overload", a
vaccine preservativeThe thiomersal controversy describes claims that vaccines containing the mercury-based preservative thiomersal contribute to the development of autism and other brain development disorders...
, or the
MMR vaccineThe MMR vaccine controversy was a case of scientific misconduct which triggered a health scare. It followed the publication in 1998 of a paper in the medical journal The Lancet which presented apparent evidence that autism spectrum disorders could be caused by the MMR vaccine, an immunization...
for causing autism. The latter theory was supported by a litigation-funded study that has since been shown to have been "an elaborate fraud". 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.
Mechanism
Autism's symptoms result from maturation-related changes in various systems of the brain. How autism occurs is not well understood. Its mechanism can be divided into two areas: the
pathophysiologyPathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
of brain structures and processes associated with autism, and the neuropsychological linkages between brain structures and behaviors. The behaviors appear to have multiple pathophysiologies.
Pathophysiology
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. Neuroanatomical studies and the associations with teratogens strongly suggest that autism's mechanism includes alteration of brain development soon after conception. This anomaly appears to start a cascade of pathological events in the brain that are significantly influenced by environmental factors. 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 neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s that causes local overconnectivity in key brain regions.
- Disturbed neuronal migration during early gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
.
- Unbalanced excitatory–inhibitory networks.
- Abnormal formation of synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
s and dendritic spineA dendritic spine is a small membranous protrusion from a neuron's dendrite that typically receives input from a single synapse of an axon. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body...
s, for example, by modulation of the neurexinA neurexin is a presynaptic protein that helps to glue together neurons at the synapse. Neurexins are type I membrane proteins that can be classified into two types, α-NRXNs and β-NRXNs. The α-NRXNs are larger and have different amino-terminal extracellular sequences...
–neuroligin300px|thumb|right|alt = Colored dice with checkered background|Tertiary structure of Neuroligin 4.Neuroligin , a type I membrane protein, is a protein on the postsynaptic membrane that mediates synapse formation between neurons. Neuroligins mediate signaling across the synapse and affect the...
cell-adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins. Correct cellular adhesion is essential in maintaining multicellular structure...
system, or by poorly regulated synthesis of synaptic proteins. Disrupted synaptic development may also contribute to epilepsyEpilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, which may explain why the two conditions are associated.
Interactions between the
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
and the
nervous systemThe nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
begin early during the
embryonic stageHuman embryology is the study of human development during the first eight weeks from gametogenesis pre-conception through fertilization up to and including the 8th week after implantation of the zygote in the uterus...
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. As autoantibodies are found in conditions other than ASD, and are not always present in ASD, the relationship between immune disturbances and autism remains unclear and controversial.
The relationship of
neurochemicalA neurochemical is an organic molecule, such as serotonin, dopamine, or nerve growth factor, that participates in neural activity. The science of neurochemistry studies the functions of neurochemicals.-Prominent neurochemicals:...
s to autism is not well understood; several have been investigated, with the most evidence for the role of
serotoninSerotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
and of genetic differences in its transport. Others have pointed to a role for group I metabotropic glutamate receptors (mGluR) in the pathogenesis of one type of autism, fragile X. Some data suggest an increase in several
growth hormoneGrowth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
s; other data argue for diminished
growth factorA growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Usually it is a protein or a steroid hormone. Growth factors are important for regulating a variety of cellular processes....
s. 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 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.
In autism there is evidence for reduced functional connectivity of the
default networkThe default network is a network of brain regions that are active when the individual is not focused on the outside world and the brain is at wakeful rest. Also called the default mode network , default state network, or task-negative network , it is characterized by coherent neuronal oscillations...
, 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. A 2008 brain-imaging study found a specific pattern of signals in the
cingulate cortexThe cingulate cortex is a part of the brain situated in the medial aspect of the cortex. It includes the cortex of the cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus...
which differs in individuals with ASD.
The underconnectivity theory of autism hypothesizes that autism is marked by underfunctioning high-level neural connections and synchronization, along with an excess of low-level processes. Evidence for this theory has been found in
functional neuroimagingFunctional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions...
studies on autistic individuals and by a brainwave study that suggested that adults with ASD have local overconnectivity in the
cortexThe cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
and weak functional connections between the
frontal lobeThe frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
and the rest of the cortex. Other evidence suggests the underconnectivity is mainly within each
hemisphereA cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
of the cortex and that autism is a disorder of the association cortex.
From studies based on
event-related potentialAn event-related potential is any measured brain response that is directly the result of a thought or perception. More formally, it is any stereotyped electrophysiological response to an internal or external stimulus....
s, 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, orientiation to auditory and visual stimuli, novelty detection, language and face processing, and information storage; several studies have found a preference for nonsocial stimuli. For example,
magnetoencephalographyMagnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
studies have found evidence in autistic children of delayed responses in the brain's processing of auditory signals.
In the genetic area, relations have been found between autism and
schizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
based on duplications and deletions of chromosomes; research showed that schizophrenia and autism are significantly more common in combination with
1q21.1 deletion syndrome1q21.1 deletion syndrome or 1q21.1 microdeletion is a rare aberration of chromosome 1. , the international rare chromosome disorder group, has 48 genetically confirmed registered cases of this deletion worldwide ....
. Research on autism/schizophrenia relations for chromosome 15 (15q13.3), chromosome 16 (16p13.1) and chromosome 17 (17p12) are inconclusive.
Neuropsychology
Two major categories of cognitive theories have been proposed about the links between autistic brains and behavior.
The first category focuses on deficits in
social cognitionSocial cognition is the encoding, storage, retrieval, and processing, in the brain, of information relating to conspecifics, or members of the same species. At one time social cognition referred specifically to an approach to social psychology in which these processes were studied according to the...
. 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.
These theories are somewhat related to the earlier
theory of mindTheory of mind is the ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires and intentions that are different from one's own...
approach, which hypothesizes that autistic behavior arises from an inability to ascribe mental states to oneself and others. The theory of mind hypothesis is supported by autistic children's atypical responses to the Sally–Anne test for reasoning about others' motivations, and the mirror neuron system theory of autism described in
Pathophysiology maps well to the hypothesis. However, most studies have found no evidence of impairment in autistic individuals' ability to understand other people's basic intentions or goals; instead, data suggests that impairments are found in understanding more complex social emotions or in considering others' viewpoints.
The second category focuses on nonsocial or general processing.
Executive dysfunctionExecutive dysfunction , in psychology , is a disruption to the efficacy of the executive system. It can refer to both neurocognitive deficits and behavioural symptoms...
hypothesizes that autistic behavior results in part from deficits in
working memoryWorking memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
, planning,
inhibitionInhibition theory is based on the basic assumption that, during the performance of any mental task, which requires a minimum of mental effort, the subject actually goes through a series of alternating states of distraction and attention...
, 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; two weaknesses are that executive function is hard to measure and that executive function deficits have not been found in young autistic children.
Weak central coherence theoryThe weak central coherence theory , also called the central coherence theory , suggests that a specific perceptual-cognitive style, loosely described as a limited ability to understand context or to "see the big picture", underlies the central disturbance in autism and related autism spectrum...
hypothesizes that a limited ability to see the big picture underlies the central disturbance in autism. One strength of this theory is predicting special talents and peaks in performance in autistic people. 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 underconnectivity theory of autism.
Neither category is satisfactory on its own; social cognition theories poorly address autism's rigid and repetitive behaviors, while the nonsocial theories have difficulty explaining social impairment and communication difficulties. A combined theory based on multiple deficits may prove to be more useful.
Screening
About half of parents of children with ASD notice their child's unusual behaviors by age 18 months, and about four-fifths notice by age 24 months. According to an article in the
Journal of Autism and Developmental Disorders, failure to meet any of the following milestones
"is an absolute indication to proceed with further evaluations. Delay in referral for such testing may delay early diagnosis and treatment and affect the long-term outcome."
- No babbling
Babbling is a stage in child development and a state in language acquisition, during which an infant appears to be experimenting with uttering sounds of language, but not yet producing any recognizable words...
by 12 months.
- No gesturing
A gesture is a form of non-verbal communication in which visible bodily actions communicate particular messages, either in place of speech or together and in parallel with spoken words. Gestures include movement of the hands, face, or other parts of the body...
(pointing, waving bye-bye, etc.) by 12 months.
- No single words by 16 months.
- No two-word spontaneous (not just echolalic
Echolalia is the automatic repetition of vocalizations made by another person. It is closely related to echopraxia, the automatic repetition of movements made by another person....
) phrases by 24 months.
- Any loss of any language or social skills, at any age.
US and Japanese practice is to
screenScreening, in medicine, is a strategy used in a population to detect a disease in individuals without signs or symptoms of that disease. Unlike what generally happens in medicine, screening tests are performed on persons without any clinical sign of disease....
all children for ASD at 18 and 24 months, using autism-specific formal screening tests. In contrast, in the UK, children whose families or doctors recognize possible signs of autism are screened. It is not known which approach is more effective. 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 children aged 18–30 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 ASD from other developmental disorders. Screening tools designed for one culture's norms for behaviors like eye contact may be inappropriate for a different culture. Although genetic screening for autism is generally still impractical, it can be considered in some cases, such as children with neurological symptoms and
dysmorphic featureDysmorphic feature is a medical term referring to a difference of body structure that is suggestive of a congenital disorder, genetic syndrome, or birth defect. A dysmorphic feature can be a minor and isolated birth defect...
s.
Diagnosis
DiagnosisMedical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
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 syndromeRett syndrome is a neurodevelopmental disorder of the grey matter of the brain that almost exclusively affects females. The clinical features include small hands and feet and a deceleration of the rate of head growth . Repetitive hand movements, such as wringing and/or repeatedly putting hands into...
or
childhood disintegrative disorderChildhood disintegrative disorder , also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays in language, social function, and motor skills...
.
ICD-10The International Statistical Classification of Diseases and Related Health Problems, 10th Revision is a medical classification list for the coding of diseases, signs and symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or diseases, as maintained by the...
uses essentially the same definition.
Several diagnostic instruments are available. Two are commonly used in autism research: the
Autism Diagnostic Interview-RevisedThe Autism Diagnostic Interview-Revised is structured interview conducted with the parents of individuals who have been referred for the evaluation of possible autism or autism spectrum disorders...
(ADI-R) is a semistructured parent interview, and the Autism Diagnostic Observation Schedule (ADOS) uses observation and interaction with the child. The
Childhood Autism Rating ScaleChildhood Autism Rating Scale is a behavior rating scale intended to help diagnose autism. CARS was developed by Eric Schopler, Robert J. Reichier, and Barbara Rochen Renner...
(CARS) is used widely in clinical environments to assess severity of autism based on observation of children.
A pediatrician commonly performs a preliminary investigation by taking developmental history and physically examining the child. If warranted, diagnosis and evaluations are conducted with help from ASD specialists, observing and assessing cognitive, communication, family, and other factors using standardized tools, and taking into account any associated medical conditions. A pediatric neuropsychologist is often asked to assess behavior and cognitive skills, both to aid diagnosis and to help recommend educational interventions. A
differential diagnosisA differential diagnosis is a systematic diagnostic method used to identify the presence of an entity where multiple alternatives are possible , and may also refer to any of the included candidate alternatives A differential diagnosis (sometimes abbreviated DDx, ddx, DD, D/Dx, or ΔΔ) is a...
for ASD at this stage might also consider
mental retardationMental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
,
hearing impairment-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...
, and a
specific language impairmentSpecific language impairment is diagnosed when a child's language does not develop normally and the difficulties cannot be accounted for by generally slow development , physical abnormality of the speech apparatus, autistic disorder, acquired brain damage or hearing loss.-Overview:Specific...
such as Landau–Kleffner syndrome. The presence of autism can make it harder to diagnose coexisting psychiatric disorders such as
depressionMood disorder is the term designating a group of diagnoses in the Diagnostic and Statistical Manual of Mental Disorders classification system where a disturbance in the person's mood is hypothesized to be the main underlying feature...
.
Clinical genetics evaluations are often done once ASD 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 US and UK are limited to high-resolution chromosome and fragile X testing. A
genotypeThe genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
-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
neuroimagingNeuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
tests are sometimes helpful, but are not routine.
ASD 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 ASD 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 2009 US study found the average age of formal ASD diagnosis was 5.7 years, far above recommendations, and that 27% of children remained undiagnosed at age 8 years. Although the symptoms of autism and ASD begin early in childhood, they are sometimes missed; years later, adults 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.
Underdiagnosis and overdiagnosis are problems in marginal cases, and much of the recent increase in the number of reported ASD cases is likely due to changes in diagnostic practices. The increasing popularity of drug treatment options and the expansion of benefits has given providers incentives to diagnose ASD, resulting in some overdiagnosis of children with uncertain symptoms. Conversely, the cost of screening and diagnosis and the challenge of obtaining payment can inhibit or delay diagnosis. 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 or
blindismBlindisms are stereotyped behaviors sometimes found in visually impaired toddlers or children. Blindism behaviors range from body rocking, head swaying, eye rubbing, head banging, spinning to finger flicking...
s.
Management
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
efficacyEfficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...
. Although many
psychosocialFor a concept to be psychosocial means it relates to one's psychological development in, and interaction with, a social environment. The individual needs not be fully aware of this relationship with his or her environment. It was first commonly used by psychologist Erik Erikson in his stages of...
interventions have some positive evidence, suggesting that some form of treatment is preferable to no treatment, the methodological quality of
systematic reviewA systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine...
s 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 educationSpecial education is the education of students with special needs in a way that addresses the students' individual differences and needs. Ideally, this process involves the individually planned and systematically monitored arrangement of teaching procedures, adapted equipment and materials,...
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; claims that intervention by around age three years is crucial are not substantiated. Available approaches include
applied behavior analysisApplied behavior analysis is a science that involves using modern behavioral learning theory to modify behaviors. Behavior analysts reject the use of hypothetical constructs and focus on the observable relationship of behavior to the environment...
(ABA), developmental models,
structured teachingTreatment and education of autistic and related communication handicapped children is a service, training, and research program for individuals of all ages and skill levels with autism spectrum disorders. The TEACCH approach was developed at the University of North Carolina, originating in a...
, speech and language therapy,
social skillsA social skill is any skill facilitating interaction and communication with others. Social rules and relations are created, communicated, and changed in verbal and nonverbal ways. The process of learning such skills is called socialization...
therapy, and
occupational therapyOccupational therapy is a discipline that aims to promote health by enabling people to perform meaningful and purposeful activities. Occupational therapists work with individuals who suffer from a mentally, physically, developmentally, and/or emotionally disabling condition by utilizing treatments...
.
Educational interventions can be effective to varying degrees in most children: intensive ABA treatment has demonstrated effectiveness in enhancing global functioning in preschool children and is well-established for improving intellectual performance of young children. Neuropsychological reports are often poorly communicated to educators, resulting in a gap between what a report recommends and what education is provided. It is not known whether treatment programs for children lead to significant improvements after the children grow up, and the limited research on the effectiveness of adult residential programs shows mixed results. The appropriateness of including children with varying severity of autism spectrum disorders in the general education population is a subject of current debate among educators and researchers.
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 drugA psychoactive drug, psychopharmaceutical, or psychotropic is a chemical substance that crosses the blood–brain barrier and acts primarily upon the central nervous system where it affects brain function, resulting in changes in perception, mood, consciousness, cognition, and behavior...
s or
anticonvulsantThe anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...
s, with the most common drug classes being
antidepressantAn antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...
s,
stimulantStimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...
s, and
antipsychoticAn antipsychotic is a tranquilizing psychiatric medication primarily used to manage psychosis , particularly in schizophrenia and bipolar disorder. A first generation of antipsychotics, known as typical antipsychotics, was discovered in the 1950s...
s. 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 effectsIn medicine, an adverse effect is a harmful and undesired effect resulting from a medication or other intervention such as surgery.An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. If it results from an unsuitable or incorrect dosage or...
, and no known medication relieves autism's core symptoms of social and communication impairments. Experiments in mice have reversed or reduced some symptoms related to autism by replacing or modulating gene function, suggesting the possibility of targeting therapies to specific rare mutations known to cause autism.
Although many
alternative therapies and interventionsAlternative therapies for developmental and learning disabilities include a range of practices used in the treatment of dyslexia, ADHD, Asperger syndrome, autism, Down syndrome and other developmental and learning disabilities. Treatments include changes in diet, dietary supplements, biofeedback,...
are available, few are supported by scientific studies. Treatment approaches have little empirical support in
quality-of-lifeThe term quality of life is used to evaluate the general well-being of individuals and societies. The term is used in a wide range of contexts, including the fields of international development, healthcare, and politics. Quality of life should not be confused with the concept of standard of...
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. Some alternative treatments may place the child at risk. A 2008 study found that compared to their peers, autistic boys have significantly thinner bones if on casein-free diets; in 2005, botched
chelation therapyChelation therapy is the administration of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication—those involving lead, arsenic or mercury—the standard of care in the United States dictates the use of dimercaptosuccinic acid...
killed a five-year-old child with autism.
Treatment is expensive; indirect costs are more so. For someone born in 2000, a US study estimated an average lifetime cost of $ (
net present valueIn finance, the net present value or net present worth of a time series of cash flows, both incoming and outgoing, is defined as the sum of the present values of the individual cash flows of the same entity...
in dollars, inflation-adjusted from 2003 estimate), 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 child, and unreimbursed out-of-pocket medical or therapy expenses are associated with likelihood of family financial problems; one 2008 US study found a 14% average loss of annual income in families of children with ASD, and a related study found that ASD is associated with higher probability that child care problems will greatly affect parental employment. US states increasingly require private health insurance to cover autism services, shifting costs from publicly funded education programs to privately funded health insurance. After childhood, key treatment issues include residential care, job training and placement, sexuality, social skills, and
estate planningEstate planning is the process of anticipating and arranging for the disposal of an estate. Estate planning typically attempts to eliminate uncertainties over the administration of a probate and maximize the value of the estate by reducing taxes and other expenses...
.
Prognosis
There is no known cure. Children recover occasionally, so that they lose their diagnosis of ASD; this occurs sometimes after intensive treatment and sometimes not. It is not known how often recovery happens; reported rates in unselected samples of children with ASD have ranged from 3% to 25%. Most autistic children can acquire language by age 5 or younger, though a few have developed communication skills in later years. Most children with autism lack
social supportSocial support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...
, meaningful relationships, future employment opportunities or
self-determinationSelf-determination theory is a macro theory of human motivation and personality, concerning people's inherent growth tendencies and their innate psychological needs. It is concerned with the motivation behind the choices that people make without any external influence and interference...
. Although core difficulties tend to persist, symptoms often become less severe with age. Few high-quality studies address long-term
prognosisPrognosis is a medical term to describe the likely outcome of an illness.When applied to large statistical populations, prognostic estimates can be very accurate: for example the statement "45% of patients with severe septic shock will die within 28 days" can be made with some confidence, because...
. 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 livingIndependent living, as seen by its advocates, is a philosophy, a way of looking at disability and society, and a worldwide movement of people with disabilities working for self-determination, self-respect and equal opportunities...
is unlikely with severe autism. A 2004 British study of 68 adults who were diagnosed before 1980 as autistic children with IQ above 50 found that 12% achieved a high level of independence as adults, 10% had some friends and were generally in work but required some support, 19% had some independence but were generally living at home and needed considerable support and supervision in daily living, 46% needed specialist residential provision from facilities specializing in ASD with a high level of support and very limited autonomy, and 12% needed high-level hospital care. 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 ASD 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 children.
Epidemiology
Most recent
reviewA review is an evaluation of a publication, a product or a service, such as a movie , video game, musical composition , book ; a piece of hardware like a car, home appliance, or computer; or an event or performance, such as a live music concert, a play, musical theater show or dance show...
s tend to estimate a prevalence of 1–2 per 1,000 for autism and close to 6 per 1,000 for ASD; because of inadequate data, these numbers may underestimate ASD's true prevalence. PDD-NOS's prevalence has been estimated at 3.7 per 1,000, Asperger syndrome at roughly 0.6 per 1,000, and
childhood disintegrative disorderChildhood disintegrative disorder , also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays in language, social function, and motor skills...
at 0.02 per 1,000. 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 environmental risk factors cannot be ruled out. The available evidence does not rule out the possibility that autism's true prevalence has increased; a real increase would suggest directing more attention and funding toward changing environmental factors instead of continuing to focus on genetics.
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.
Several other conditions are common in children with autism. They include:
- Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
s. About 10–15% of autism cases have an identifiable Mendelian (single-gene) condition, chromosome abnormality, or other genetic syndrome, and ASD is associated with several genetic disorders.
- Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
. 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 ASD other than autism, the association with mental retardation is much weaker.
- Anxiety disorder
Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry at the end of the 19th century. Gelder, Mayou & Geddes explains that anxiety disorders are...
s are common among children with ASD; there are no firm data, but studies have reported prevalences ranging from 11% to 84%. Many anxiety disorders have symptoms that are better explained by ASD itself, or are hard to distinguish from ASD's symptoms.
- Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
, with variations in risk of epilepsy due to age, cognitive level, and type of language disorderLanguage disorders or language impairments are disorders that involve the processing of linguistic information. Problems that may be experienced can involve grammar , semantics , or other aspects of language...
.
- Several metabolic defects, such as phenylketonuria
Phenylketonuria is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase , rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine...
, are associated with autistic symptoms.
- Minor physical anomalies
Minor physical anomalies are relatively minor congenital physical abnormalities consisting of features such as low-seated ears, single transverse palmar crease, telecanthus, micrognathism a furrowed tongue...
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
Tourette syndrome is an inherited neuropsychiatric disorder with onset in childhood, characterized by multiple physical tics and at least one vocal tic; these tics characteristically wax and wane...
, and other of these conditions are often present and these comorbid diagnosesThere are many conditions comorbid to autism spectrum disorders, such as fragile X syndrome and epilepsy. In medicine and in psychiatry, comorbidity describes the effect of other diseases an individual patient might have other than the primary disease of interest...
are increasingly accepted.
- Sleep problems affect about two-thirds of individuals with ASD at some point in childhood. These most commonly include symptoms of insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
such as difficulty in falling asleep, frequent nocturnal awakeningsMiddle-of-the-night insomnia is insomnia characterized by difficulty returning to sleep after awakening either in the middle of the night, or too early in the morning...
, and early morning awakenings. Sleep problems are associated with difficult behaviors and family stress, and are often a focus of clinical attention over and above the primary ASD diagnosis.
History
A few examples of autistic symptoms and treatments were described long before autism was named. The
Table TalkMartin Luther's Table Talk is a collection of his sayings. It was compiled by Johannes Mathesius and published at Eisleben in 1566.Mathesius spoke enthusiastically of the privilege of eating with Luther and hearing him converse...
of
Martin LutherMartin Luther was a German priest, professor of theology and iconic figure of the Protestant Reformation. He strongly disputed the claim that freedom from God's punishment for sin could be purchased with money. He confronted indulgence salesman Johann Tetzel with his Ninety-Five Theses in 1517...
, 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 childA feral child is a human child who has lived isolated from human contact from a very young age, and has no experience of human care, loving or social behavior, and, crucially, of human language...
caught in 1798, showed several signs of autism; the medical student
Jean ItardJean Marc Gaspard Itard was a French physician born in Provence.Without a university education and working at a bank, he was forced to enter the army during the French Revolution but presented himself as a physician at that time...
treated him with a behavioral program designed to help him form social attachments and to induce speech via imitation.
The
New LatinThe term New Latin, or Neo-Latin, is used to describe the Latin language used in original works created between c. 1500 and c. 1900. Among other uses, Latin during this period was employed in scholarly and scientific publications...
word
autismus (English translation
autism) was coined by the Swiss psychiatrist
Eugen BleulerPaul Eugen Bleuler was a Swiss psychiatrist most notable for his contributions to the understanding of mental illness and for coining the term "schizophrenia."-Biography:...
in 1910 as he was defining symptoms of
schizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
. He derived it from the Greek word
autós (αὐτός, meaning
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 AspergerHans Asperger was an Austrian pediatrician, after whom Asperger syndrome was named. He wrote over 300 publications, mostly concerning autism in children.-Biography:...
of the
Vienna University HospitalThe Vienna General Hospital is the University medical center of the city of Vienna, Austria. The AKH is the largest hospital of Austria and Europe, the second largest hospital in the world, and at 85-m high is one of the tallest hospital buildings in the world...
adopted Bleuler's terminology
autistic psychopaths in a lecture in German about child psychology. Asperger was investigating an ASD now known as
Asperger syndromeAsperger's syndrome that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development...
, though for various reasons it was not widely recognized as a separate diagnosis until 1981.
Leo KannerLeo Kanner was a Jewish American psychiatrist and physician known for his work related to autism. Kanner's work formed the foundation of child and adolescent psychiatry in the U.S. and worldwide....
of the
Johns Hopkins HospitalThe Johns Hopkins Hospital is the teaching hospital and biomedical research facility of Johns Hopkins University School of Medicine, located in Baltimore, Maryland . It was founded using money from a bequest by philanthropist Johns Hopkins...
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 motherThe term refrigerator mother was coined around 1950 as a label for mothers of children diagnosed with autism or schizophrenia. These mothers were often blamed for their children's atypical behavior, which included rigid rituals, speech difficulty, and self-isolation.The "refrigerator mother" label...
s". 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 stigmaSocial stigma is the severe disapproval of or discontent with a person on the grounds of characteristics that distinguish them from other members of a society.Almost all stigma is based on a person differing from social or cultural norms...
in situations where their autistic children's behaviors are perceived negatively by others, and many
primary care physicianA primary care physician, or PCP, is a physician/medical doctor who provides both the first contact for a person with an undiagnosed health concern as well as continuing care of varied medical conditions, not limited by cause, organ system, or diagnosis....
s and medical specialists still express some beliefs consistent with outdated autism research.
The
InternetThe Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
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.
Sociological and cultural aspects of autismSociological and cultural aspects of autism come into play with recognition of autism, approaches to its support services and therapies, and how autism affects how we define personhood. The autism rights movement is based on a belief that autism is a different way of being and not a disorder to be...
have developed: some in the community seek a cure, while others believe that autism is simply another way of being.
External links