May 2019 By

Autism Spectrum Disorder (ASD)


The approximate prevalence of autism spectrum disorder (ASD) is 1% in both US and non-US populations. It is a highly heritable condition. Twin studies show an 80 percent chance, while the corresponding rate for fraternal twins is about 40 percent.

Autism Diagnoses Are Rising

The prevalence of autism spectrum disorder has increased in the past few decades. Reasons for this include expanded diagnostic criteria[1], increased awareness, and/or a true increase in the actual incidence.

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.
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, not exhaustive; see text[2]):

  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)
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, not exhaustive; see text[3]):

  1. Stereotyped or repetitive motor movements, use of objects, or speech (e.g. - simple motor stereotypes, 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, 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).
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.

Specifiers and Severity


Specify if:

  • With or without accompanying intellectual impairment
  • With or without accompanying language impairment
  • Associated with a known medical or genetic condition or environmental factor
  • Associated with another neurodevelopmental, mental, or behavioural disorder
  • With catatonia


Level Severity Social Communication (Criterion A) Restricted, Repetitive Behaviours (Criterion B)
Level 3 Requiring very substantial support 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.
Level 2 Requiring substantial support 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.
Level 1 Requiring support 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.

Red Flags

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.[4]

Early, aggressive intervention has been shown to be effective in reducing symptoms.[5]

For Patients

For Providers