Autism Spectrum Disorders are diagnosed on the basis of behaviour. This is because at this time there are no specific genetic or biological markers that accurately identify a person as being on the autism spectrum. People on the spectrum have in common three main types of difficulties. These difficulties are:
1. Impairment in social interaction
2. Impairment in communication
3. Restricted and/or repetitive patterns of behaviour, interests and activities
Autism first manifests in childhood, with age of onset for a diagnosis being under the age of 3 years. This does not necessarily mean that a person is diagnosed before turning 3 years of age, only that symptoms were present at that developmental stage.
Although not stated in the main diagnostic schedules, many clinicians use the term "Autism Spectrum Disorder" (ASD) to describe a continuum of related disorders, including autism, Asperger syndrome, and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS). The categories within the autism spectrum are related to both severity and the presence or absence of some symptoms.
Impairments in social interaction
The type of impairment in social interaction in ASD is varied. These can include marked problems with nonverbal behaviours, such as eye contact, facial expression, gestures, and body position, which are commonly used to regulate social interactions. It is often the case that people with an ASD do not develop relationships with children and adults from their peer groups at school and work. They may also feel no need to share personal experiences of achievement or enjoyment with others, and may also be unresponsive to social or emotional displays by others, especially those that are not immediately obvious.
Impairments in communication
Delay in development of spoken language (including not developing language at all) is also a symptom of ASD. It is important to understand that language delay or absence is an indicator of autism only where a person does not try an alternative strategy to communicate actively, such as through gestures or mime. For people with an ASD who are able to speak, it is often the case that they do not initiate or sustain conversations. People with autism who are able to use language will often use words and phrases that are repetitive. They can also use language in a very formal way when communicating with familiar people, or adopt a style of speech that they maintain at all times, regardless of the listener. In addition, children with an ASD tend not to engage in the types of pretend play commonly observed in children at their developmental level.
Restricted and/or repetitive patterns of behaviour, interests and activities
Some people with an ASD show an intense interest in one type of activity. In these cases, the object of interest, for example trains and train schedules, consumes an unusually large amount of time or attention. People with autism often find it difficult to be socially flexible with regard to routines and rituals. Small changes to routine may cause these people significant distress, especially if specific rituals are associated with the disturbance. Repetitive mannerisms, such as hand flapping and finger flicking can be observed in those with an ASD, especially when they are feeling anxious. Another aspect of ASD is that some people with autism are preoccupied with parts of objects rather than objects themselves. An example of this is can be seen where a child with autism persistently spins one wheel of a toy car, when other children of that age are playing with the car as a toy vehicle.
Other behaviours commonly observed in ASD
As well as the triad of symptoms outlined that are observed in ASD, many researchers and clinicians believe that other criteria are valid and important to consider when diagnosing ASD. Susan Mayes includes sensory disturbances in her diagnostic criteria, as well as fear of crowds, sleep disturbances, limited food preferences, and highly tolerance to pain while being sensitised to light touch. There is a significant body of evidence to suggest that people with ASD are more likely to demonstrate heightened response in all sensory domains, and this also is regarded as an important indicator of autism by Christopher Gillberg. It is also common to find motor clumsiness in people with ASD. Tony Attwood has suggested that these problems can affect gross motor skills, such as walking and balance, as well as fine motor skills such as handwriting and cutting with scissors. Motor problems can also affect timing and rhythm, as well as causing difficulties in imitating others as often occurs in social interaction.
Dr Larry Cashion for A4, 2002