What is autism/autism spectrum disorder?

What is autism ?

ASD (autism spectrum disorder) is a lifelong neurodevelopmental disorder. The term autism refers to the prototypical condition described in 1943 by Leo Kanner, also known as core autism. However, it is well recognized that there is a spectrum of presentation and a broader autism phenotype with less severe and more subtle behavioural features that may only manifest after a change in environmental demand. Autism spectrum disorder has been characterized by qualitative behavioural abnormalities in communication, reciprocal social interaction together with patterns of repetitive, restricted and stereotyped interests and activities. These deficits are pervasive, persistent, usually present in early childhood and likely to lead to impairments in functioning across different settings.

There are currently two international classification systems for diagnosing ASD. In 2013 the American Psychiatric Association revised the Diagnostic Statistical Manual (DSM-5). Changes included the introduction of Autism Spectrum Disorder as a single diagnosis and the removal of the diagnostic sub groupings (autism, Asperger’s syndrome, atypical autism); combining the qualitative impairments of social communication and social interaction into one diagnostic domain and expanding the Restrictive, Repetitive Behaviours and Interests domain to include stereotyped and repetitive speech, hypo- and hyper-reactivity to sensory input and unusual sensory interests. DSM-5 recommends the use of a range of specifiers highlighting the importance of addressing the individual’s profile of strengths and needs. These include severity specifiers that may be used to describe current symptomology for each of the ASD domains with the recognition that severity may vary with time and environmental context so should not be used to determine eligibility for and provision of services. Specifiers also include whether there is intellectual disability, language impairment, other associated disorders or comorbidities e.g. medical, genetic, mental or behavioural. The current World Health Organisation
(ICD-10) criteria are based on the original triad of impairments, though ICD-11 update is expected in 2018 and likely to be similar to DSM-5.


ASD is not rare. The National Institute of Health and Clinical Excellence (NICE) states the diagnosis is queried in approximately 3% of the child population and epidemiological studies suggest prevalence rates of at least 1 in 100. Broadening of diagnostic criteria and improved case recognition are likely to have contributed to the increase in diagnostic rates reported since the 1990s. There are no high quality robust studies confirming a rise in the true prevalence. The condition is three to four times more common in boys, with a male preponderance rising in the high functioning group. NICE guidelines recognize that in clinical practice girls may be under-diagnosed. It has been suggested that high functioning females may be better at masking their difficulties through imitation and observation of social actions and better verbal skills.

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