Autism spectrum disorders Autism spectrum disorders

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About the author About the author

Dr Natalie Silove
Developmental Paediatrician
Senior Staff Specialist and Head
Child Development Unit
The Children’s Hospital at Westmead

Associate Professor Jacqueline Roberts
Speech Pathologist
Former Director of Services of
Autism Association NSW, Australia

Full article Download full article (.pdf 527kB)

DET websites


  • American Psychiatric Association. Diagnostic and statistical manual of mental disorders, Version 4. Washington, DC: APA, 1994.

  • Clinician’s Guide to Psychotropic Prescribing in Children and Adolescents. Child and Adolescent Mental Health Statewide Network (CAMHSNET), 2004, ch. 23, p. 262-269.

  • Dodd SM. Understanding Autism. Marrickville, NSW: Elsevier Australia, 2005.

  • TAFE Autism Awareness brochure

For more web resources, please see the full article (.pdf 527kB).

  • Bailey A, Le Couteur A, Gottesman I, et al. Autism as a strongly genetic disorder: Evidence from a British twin study. Psychol Med 1995; 25:63-77.

  • Casanova MF, Buxhoeveden DP, et al. Minicolumnar pathology in autism. Neurology 2002;58:428-432.

  • Johnson CP, Myers SM and the Council on Children with Disabilities. Identification and evaluation of children with autism spectrum disorders. Pediatrics 29:2007:2007-2361 (published online).

  • Taylor B, Miller E, Farrington C, et al. Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association. Lancet 1999; 353:2026-9

What are autism spectrum disorders?

Autism is a pervasive, developmental, neurobiological disorder characterised by core deficits in three domains known as the ‘triad of impairments’. These are:

  1. Communication (.pdf 74kB)

  2. Socialisation (.pdf 80kB)

  3. Flexibility of thought and behaviour (.pdf 69kB)

Autism is pervasive, as it affects many areas of development and all aspects of an individual’s life, developmental, because the way in which it ‘presents’ or ‘looks’ will change with age, and neurobiological, because it involves biological changes affecting the developing brain.

The signs and symptoms of autism are very varied, particularly in relation to intellectual ability and associated medical and psychiatric conditions. Descriptive terms for autism have varied over time, complicating clinical diagnosis and research.

Experts from all over the world developed diagnostic criteria from existing research and knowledge which are updated at regular intervals. There are two main diagnostic systems:

  1. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (used in Australia)

  2. The ICD–10.

Over the decades, terminology has varied. In the DSM-IV, Pervasive Developmental Disorders include:

For a diagnosis of autistic disorder, an individual must meet a specified number of the 12 criteria given in DSM-IV (see Appendix, pp. 45-46 of the full article). These criteria have to be interpreted according to the individual’s developmental/mental age. It is imperative that the diagnostician has comprehensive knowledge of normal development, a full understanding of the spread of the developmental skills of that particular individual, and characteristics of autism, in order to inform the decision about the extent to which an individual meets the criteria for autism in the DSM-IV.

By definition, individuals with Asperger’s disorder (also known as Asperger syndrome) have intellectual ability within the average range, and have typical early formal language development (single words by age two years and two-word spontaneous communicative phrases by age three years)(see Appendix, p. 46 of the full article (.pdf 527kB)). Their communication development is disordered, despite good language skills. Asperger’s disorder is not mild autism, as commonly thought. Rather, it is the functional impact that having Asperger’s disorder or Autistic disorder has on the individual that varies from mild to severe/profound at different ages, depending on the demands of the environment and the acquired skills of the individual.

This category is used when there is a severe and pervasive impairment in development in all three areas impaired in autism (social interaction, communication, and inflexible behaviour patterns), but not sufficient criteria for a diagnosis of autistic disorder or Asperger’s disorder. It may also include presentations with late age at onset, atypical presentation or with symptoms at presentation which are not causing sufficient difficulty to meet DSMIV criteria.

Rett’s disorder is included as a Pervasive Developmental Disorder because there is some potential confusion with autism – particularly in the preschool years. Otherwise the course and onset of this condition is very distinctive. In people with Rett’s disorder very early development is normal. Head growth then decelerates, usually in the first months of life and a loss of purposeful hand movements occurs. Motor involvement is quite striking and profound, intellectual disability is typical. Characteristic hand-washing stereotypies develop. Historically Rett’s was thought to only affect girls. Since the discovery of the MECP2 gene, responsible for Rett’s, variants of the syndrome have been reported in males who have mutations of MECP2, with some overlap in the symptomatology observed in girls. (See also the Rett syndrome article in this website.)

Childhood disintegrative disorder (CDD) (previously called Heller’s syndrome or dementia infantilis) is characterised by a marked regression (loss of established skills) in multiple areas of functioning following a period of at least two years of apparently normal development.

There is no one single defining test or characteristic of autism; rather it is a combination of characteristics in the triad of impairment, occurring in the one individual that indicates the presence of an autism spectrum disorder. Diagnostic criteria are ‘standardised’, so that terms and definitions are consistent throughout the world.

This important age is outside the scope of this resource, but it must be emphasised that the earlier the identification and intervention, the better the life outcomes. Therefore, it is most important to note:

Absolute indications for urgent referral for an autism-specific assessment for a preschool-aged child include:

  • No babbling, or pointing, or other gestures by 12 months

  • No sharing of interest in objects with another person

  • No single words by 16 months

  • No two-word spontaneous phrases by 24 months

  • Any loss of any language or social skills at any age.

The identification of children with autism requires developmental surveillance. Teachers have a unique opportunity to observe and monitor students over a period of time and to conduct this observation of the student in a natural setting with his or her peers. It is when differences are noted in the triad of characteristics which affect the student’s ability to socialise, communicate, interact and learn, that teachers should alert the parents, school counsellor or principal as appropriate.

A number of screening tools are available that can be of assistance in identifying students at risk for an autism spectrum disorder. These screening questionnaires are age-specific and should be used to give an indication of children requiring further investigation. They are not diagnostic and require knowledge in their use and interpretation. All of them will pick up students who do NOT have an autism spectrum disorder (false positives) and will MISS students who do have an autism spectrum disorder (false negatives). Clinical experience is the most important factor in identifying students who require further evaluation.

Prevalence of autism spectrum disorders

Autism was once considered a rare condition affecting only three to four per 10,000 children. Recent Australian figures estimate the prevalence of autism spectrum disorders in Australia to be, on average, one in 160 children. This represents 10 625 children between six and 12 years with an autism spectrum disorder in Australia, and as many as 125,000 people of all ages in Australia. Explanations for this increased prevalence include:

  • changing diagnostic criteria and broadening of the spectrum

  • differences in methodology, referral patterns, diagnostic substitution (students may have been identified with an intellectual disability), availability of services, migration, and public and professional awareness.

However, it is not possible at this stage to exclude the possibility of as yet unidentified environmental factor(s) interacting with a genetic predisposition.

Causal pathways to autism

The cause of autism is as yet unknown. It is clear from research that there is a strong genetic component with a predisposition to autism in some but not all families of children with autism. While a potential environmental factor(s) cannot be ruled in or out, a number of rigorous studies show no epidemiological evidence to support the theory of a link between measles–mumps–rubella (MMR) vaccination, or between thimerosol (mercury) in vaccines, and autism. There is also no rationale for giving separate vaccinations as opposed to the combination vaccine. The consensus is therefore to continue with currently recommended immunisation schedules.

Emerging research in the neuropsychology field gives greater understanding to the differences in executive function, Theory of Mind, central coherence, amygdala and other essential brain circuitry, although none are pathognomonic of ASD.

There is clear evidence that the autistic brain is anatomically different on both the macroscopic and microscopic level. About 20–30% of children with autism spectrum disorder will have macrocephaly (a large head) which is related to an increase in total brain volume. On a microscopic level, there are differences in brain cell size and number in particular parts of the brain.

For detailed information on medical considerations, please see the full article (.pdf 527kB).

Autism can affect boys or girls, and varying degrees of impairment in each component of the triad can occur in different individuals. As a result, children may respond better to some interventions than others, and the same child may benefit from diverse interventions at various stages of his or her development.

The mainstay of intervention should be to provide opportunity for the individual to reach his or her own potential.

There are a variety of medical, behavioural and other interventions, along with thecharacteristics of effective programs.

download icon Download: Approaches to intervention to learn more (.pdf 92kB).