Autism Spectrum Disorder (ASD)

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by: (1) persistent impairments in reciprocal social communication and social interaction, and (2) restricted, repetitive patterns of behaviour, interests, or activities. The manifestations and functional impact of the disorder vary greatly depending on the severity of the autistic symptoms, developmental level, and chronological age. Thus, the term spectrum is used in the diagnosis.

  • The approximate prevalence of autism spectrum disorder (ASD) is 1% in both US and non-US populations. Autism spectrum disorder is diagnosed four times more often in males than in females.
  • The prevalence of autism spectrum disorder has increased in the past few decades, rising up to prevalence rates of 1.7% (or 1 in 59 children). Reasons for this increase include expanded diagnostic criteria[1] and increased awareness. Whether these increases are due to social/cultural changes or reflects a true increase in the actual prevalence remains unclear. Autism is a highly heritable condition. Twin studies show an 80% chance of heritability, while the rate for fraternal twins is about 40%.[2] Expanding of the diagnostic criteria and conceptualization of autism as a spectrum disorder has also been thought to dilute the meaning of the diagnosis.[3]

In young children with autism spectrum disorder, lack of social and communication abilities may hamper learning, especially learning through social interaction or in settings with peers. In the home, insistence on routines and aversion to change, as well as sensory sensitivities, may interfere with eating and sleeping and make routine care (e.g. - haircuts, dental work) extremely difficult. Adaptive skills are typically below measured IQ. Extreme difficulties in planning, organization, and coping with change negatively impact academic achievement, even for students with above-average intelligence. During adulthood, these individuals may have difficulties establishing independence because of continued rigidity and difficulty with novelty. Many individuals with autism spectrum disorder, even without intellectual disability, have poor adult psychosocial functioning as indexed by measures such as independent living and gainful employment. Functional consequences in old age are unknown, but social isolation and communication problems (e.g. - reduced help-seeking) are likely to have consequences for health in older adulthood.


Adolescents and adults with autism spectrum disorder are at increased risk for anxiety and depression. Some individuals may develop catatonic-like motor behaviour (slowing and “freezing” mid-action), but are not usually to the severity of a true catatonic episode. Epilepsy is also more common,[4] and is further associated with greater intellectual disability and lower verbal ability.

What Happened to Asperger's, High Fuctioning Autism, and Other Diagnoses?

Autism spectrum disorder now encompasses other disorders previously referred to as early infantile autism, childhood autism, Kanner's autism, high-functioning autism, atypical autism, pervasive developmental disorder not otherwise specified, childhood disintegrative disorder, and Asperger's disorder.
Risk Factors

Advanced parental age, low birth weight, or fetal exposure to valproate, may increase the risk of autism spectrum disorder. Up to 15% of cases of autism spectrum disorder may be associated with a known genetic mutation (different de novo copy number variants or de novo mutations in specific genes). Risk for the majority of cases are polygenic, with possibly hundreds of genetic loci each making small contributions.

Criterion A

Persistent deficits in social communication and social interaction across multiple contexts, as manifested by all of the following, currently or by history (examples are illustrative and not exhaustive, see DSM-5 text for more examples[5]):

  1. Deficits in social-emotional reciprocity (e.g. - abnormal social approach and failure of normal back-and-forth conversation; reduced sharing of interests, emotions, or affect; failure to initiate or respond to social interactions)
  2. Deficits in nonverbal communicative behaviours used for social interaction (e.g. - poorly integrated verbal and nonverbal communication; abnormalities in eye contact and body language or deficits in understanding and use of gestures; total lack of facial expressions and nonverbal communication)
  3. Deficits in developing, maintaining, and understanding relationships, (e.g. - difficulties adjusting behaviour to suit various social contexts; difficulties in sharing imaginative play or in making friends; absence of interest in peers)

Severity Specifier

Criterion A severity is based on the severity level table below.

Criterion B

Restricted, repetitive patterns of behaviour, interests, or activities, as manifested by at least 2 of the following, currently or by history (examples are illustrative and not exhaustive; see text[6]):

  1. Stereotyped or repetitive motor movements, use of objects, or speech (e.g. - simple motor stereotypes like hand flapping or finger flicking, lining up toys or flipping objects, echolalia, idiosyncratic phrases)
  2. Insistence on sameness, inflexible adherence to routines, or ritualized patterns of verbal or nonverbal behaviour (e.g. - extreme distress at small changes, difficulties with transitions, rigid thinking patterns, insistence on rules, greeting rituals, need to take same route or eat same food every day)
  3. Highly restricted, fixated interests that are abnormal in intensity or focus (e.g. - strong attachment to or preoccupation with unusual objects, excessively circumscribed or perseverative interests)
  4. Hyper- or hyporeactivity to sensory input or unusual interest in sensory aspects of the environment (e.g. - apparent indifference to pain/temperature, adverse response to specific sounds or textures, excessive smelling or touching of objects, visual fascination with lights or movement)

Severity Specifier

Criterion B severity is based on the severity level table below.

Criterion C

Symptoms must be present in the early developmental period (but may not become fully manifest until social demands exceed limited capacities, or may be masked by learned strategies in later life).

Criterion D

Symptoms cause clinically significant impairment in social, occupational, or other important areas of current functioning.

Criterion E

These disturbances are not better explained by intellectual disability (intellectual developmental disorder) or global developmental delay. Intellectual disability and autism spectrum disorder frequently co-occur; to make co-morbid diagnoses of autism spectrum disorder and intellectual disability, social communication should be below that expected for general developmental level.

DSM-IV to DSM-5 Changes

Individuals with a well-established DSM-IV diagnosis of autistic disorder, Asperger’s disorder, or pervasive developmental disorder not otherwise specified should be given the diagnosis of autism spectrum disorder. Individuals who have marked deficits in social communication, but whose symptoms do not otherwise meet criteria for autism spectrum disorder, should be evaluated for social (pragmatic) communication disorder.

Severity Levels for Autism Spectrum Disorder

Severity (Level) Social Communication (Criterion A) Restricted, Repetitive Behaviours (Criterion B)
Requiring very substantial support (Level 3) Severe deficits in verbal and nonverbal social communication skills cause severe impairments in functioning, very limited initiation of social interactions, and minimal response to social overtures from others. For example, a person with few words of intelligible speech who rarely initiates interaction and, when he or she does, makes unusual approaches to meet needs only and responds to only very direct social approaches. Inflexibility of behaviour, extreme difficulty coping with change, or other restricted/repetitive behaviours, markedly interfere with functioning in all spheres. Great distress/difficulty changing focus or action.
Requiring substantial support (Level 2) Marked deficits in verbal and nonverbal social communication skills; social impairments apparent even with supports in place; limited initiation of social interactions; and reduced or abnormal responses to social overtures from others. For example, a person who speaks simple sentences, whose interaction is limited to narrow special interests, and who has markedly odd nonverbal communication. Inflexibility of behaviour, difficulty coping with change, or other restricted/repetitive behaviours appear frequently enough to be obvious to the casual observer and interfere with functioning in a variety of contexts. Distress and/or difficulty changing focus or action.
Requiring support (Level 1) Without supports in place, deficits in social communication cause noticeable impairments. Difficulty initiating social interactions, and clear examples of atypical or unsuccessful responses to social overtures of others. May appear to have decreased interest in social interactions. For example, a person who is able to speak in full sentences and engages in communication but whose to-and-fro conversation with others fails, and whose attempts to make friends are odd and typically unsuccessful. Inflexibility of behaviour causes significant interference with functioning in one or more contexts. Difficulty switching between activities. Problems of organization and planning hamper independence.

With or without accompanying intellectual impairment

If there is an accompanying intellectual impairment, indicate this in the diagnosis. Understanding the intellectual profile of a child or adult with autism spectrum disorder is important for interpreting diagnostic features. Separate estimates of verbal and nonverbal skill are necessary (e.g. - using untimed nonverbal tests to assess potential strengths in individuals with limited language).

With or without accompanying language impairment

If there is accompanying language impairment, the current level of verbal functioning should be recorded (e.g. - “with accompanying language impairment—no intelligible speech” or “with accompanying language impairment—phrase speech”).

Associated with a known medical or genetic condition or environmental factor

Record “autism spectrum disorder associated with (name of condition or factor).” This can be a known genetic disorder (e.g. - Rett syndrome, Fragile X syndrome, Down syndrome), a medical disorder (e.g. - epilepsy), or a history of environmental exposure (e.g. - valproic acid, fetal alcohol syndrome, low birth weight).

Associated with another neurodevelopmental, mental, or behavioural disorder

Record autism spectrum disorder associated with (name of disorder) (e.g. - autism spectrum disorder associated with tic disorder).

With catatonia

If catatonia is present, record separately as “catatonia associated with autism spectrum disorder.”

Symptoms of autism are typically recognized during the second year of life (12-24 months of age), and can be reliably diagnosed by age 14 months.[7]

  • In the first year of life, the first symptoms of autism spectrum disorder involve delayed language development, often accompanied by lack of social interest or unusual social interactions.
  • By the second year, odd and repetitive behaviors and the absence of typical play becomes more apparent. All young children have strong preferences and enjoy repetition (e.g. - eating the same foods, watching the same video multiple times), which can make distinguishing restricted and repetitive behaviors that are diagnostic of autism spectrum disorder can be difficult.[8] This can be distinguished based on the type, frequency, and intensity of the behaviour (e.g. - a child who lines up objects for hours every day and is becomes distressed if any item is moved).
  • Some children with autism spectrum disorder experience developmental plateaus or regression, with a gradual or relatively rapid deterioration in social behaviours or use of language, often in the first two years of life. This is a “red flag” for autism spectrum disorder.
  • If the loss of skills are beyond social communication (e.g. - loss of self-care, toileting, motor skills) or those occurring after the second year of life, then extensive medical investigations and a thorough differential diagnosis should be considered (including Rett Syndrome).
  • Sleep disturbances are also extremely common in children with ASD, with the prevalence of sleep disturbances estimated to be as high as 40% to 80%.[9]

Red Flags for Autism

Red flags for autism include:
  • Use of another persons's body as a tool is almost pathognomonic for autism (e.g. - child using parent's hand as a tool to achieve a task)
  • Seems to be in his/her “own world”
  • Doesn't respond to own name when called
  • Doesn’t respond to parent’s attempts to play, even if relaxed
  • Avoids or ignores other children when they approach or interact
  • No words by 16 months or no two-word phrases by 24 months
  • Any loss of previously acquired language or social skills
  • Doesn’t point to show others things he/she is interested in
  • Inconsistent or reduced use of eye contact with people outside the family
  • Rarely smiles when looking at others or does not exchange back and forth warm, joyful expressions
  • Does not spontaneously use gestures such as waving, reaching or pointing with others
  • Does not respond to gestures and facial expressions used by others
  • More interested in looking at objects than at people’s faces
  • May be content to spend extended periods of time alone
  • Doesn’t make attempts to get parent’s attention
  • Doesn’t follow/look when someone is pointing at something
  • Doesn’t bring a toy or other item to parent to show them

Factors That Rule Out Autism

Evidence of good social and communication skills in childhood rules out a autism spectrum disorder. For example, if parents report the individual had ordinary and sustained reciprocal friendships and good nonverbal communication skills throughout childhood, this would rule out a diagnosis of autism spectrum disorder.

Standardized behavioural diagnostic instruments with good psychometric properties, including caregiver interviews, questionnaires and clinician observation measures can improve the reliability of diagnosis.

  • Autism Spectrum Quotient (AQ) (Adult, Adolescent, and Child versions)
  • Quantitative Checklist for Autism in Toddlers (Q-CHAT)

Less than 1 percent of non-syndromic cases of autism are due to mutations in a single gene. The environment (ranging from chemical changes in gene expression, to the absorption of nutrients in the womb) is also thought to play a factor.[10]

    • Disruption of social interaction can be seen during the regressive phase of Rett syndrome (between 1-4 years of age). A significant proportion of affected young girls may have a symptoms that meet criteria for ASD. However, after this period, social communication skills usually improve.
    • In selective mutism, early development is not typically disturbed. The affected child usually exhibits appropriate communication skills in certain contexts and settings. Even in settings where the child is mute, social reciprocity is not impaired, and restricted or repetitive patterns of behaviour do not exist.
    • In some language disorders, there can be problems of communication with social difficulties. However, specific language disorder is not usually associated with abnormal nonverbal communication, nor with the presence of restricted, repetitive patterns of behaviour, interests, or activities.
    • When an individual shows impairment in social communication and social interactions but does not show restricted and repetitive behaviour or interests then social (pragmatic) communication disorder (SCD) is the the more likely diagnosis. However, the diagnosis of ASD supersedes the diagnosis of SCD whenever the criteria for autism spectrum disorder are met
    • Abnormalities of attention (being overly focused, easily distracted, or hyperactivity) is common in ASD. A diagnosis of ADHD should be considered when attentional difficulties or hyperactivity exceeds that typically seen in individuals of comparable mental age.
  • Intellectual disability without autism spectrum disorder
    • Intellectual disability without autism spectrum disorder can be difficult to differentiate from ASD in very young children, especially if they have not developed language or symbolic skills. Individuals with ID may also demonstrate repetitive behaviours. A diagnosis of ASD in an individual with ID is appropriate when social communication and interaction are significantly impaired relative to the developmental level of the individual's nonverbal skills (e.g. - fine motor skills, nonverbal problem solving). In contrast, the diagnosis of ID without autism spectrum disorder is appropriate when there is no apparent discrepancy between the level of social-communicative skills and other intellectual skills at their developmental level.
    • Motor stereotypies are one of the diagnostic characteristics of autism spectrum disorder, so an additional diagnosis of stereotypic movement disorder is not given when such repetitive behaviors are better explained by the presence of autism spectrum disorder. However, if stereotypies cause self-injury and become a focus of clinical attention and treatment, both diagnoses may be appropriate.
    • Schizophrenia with childhood onset usually develops after a period of normal, or near normal, development. A prodromal state has been described in which social impairment and atypical interests and beliefs occur, which could be confused with the social deficits seen in autism spectrum disorder. Hallucinations and delusions, which are defining features of schizophrenia, are not features of autism spectrum disorder. However, clinicians need to be aware that individuals with ASD may have concrete answers in their interpretation of questions regarding the symptoms of schizophrenia (e.g. - “Do you hear voices talking to you when you're by yourself?” “Yes [when I listen to my podcast]”).
  • Genome-wide microarray analysis should be ordered in all individuals diagnosed with ASD[11]
  • Testing for fragile X syndrome and sequencing of the PTEN gene for individuals with a large head circumference (three or more standard deviations above the mean)
  • Early, aggressive intervention has been shown to be effective in reducing symptoms.
  • Applied behaviour analysis (ABA) is an evidence-based treatment that uses theories of learning and operant conditioning to address core symptoms of ASD.[12]

Autism Guidelines

Guideline Location Year PDF Website
Canadian Medical Association Journal (CMAJ) Canada 2014 - Link
Canadian Paediatric Society (CPS) Canada 2019 - Link
National Institute for Health and Care Excellence (NICE) UK 2016 - Link
American Academy of Pediatrics (AAP) USA 2020 - Link
5) American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Arlington, VA.