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