Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition defined by persistent differences in social communication and social interaction together with restricted, repetitive patterns of behaviour, interests, or activities, with onset in the early developmental period. The word 'spectrum' reflects the wide range of presentations and abilities, from individuals needing substantial support to those who are highly verbal and independent.

Definition

Autism spectrum disorder is a neurodevelopmental disorder characterised by persistent deficits in social communication and social interaction across multiple contexts, alongside restricted and repetitive patterns of behaviour, interests, or activities, present from early development and causing functional impairment.

Scope

This entry covers the core features, developmental presentation, prevalence, and conceptual framing of autism spectrum disorder in children and adolescents, and its frequent co-occurrence with other neurodevelopmental and mental-health conditions. It is a reference overview of how ASD is described and studied; it does not provide diagnostic criteria for individual children or guidance on intervention.

Core questions

• What unifies the diverse presentations grouped under the autism spectrum?
• How do social-communication differences and restricted, repetitive behaviours combine to define the condition?
• Why is autism so frequently accompanied by other neurodevelopmental and psychiatric conditions?

Key concepts

• Social communication and interaction differences
• Restricted and repetitive behaviours and interests
• Spectrum and dimensional presentation
• Early developmental onset
• Co-occurring conditions
• Sensory differences

Key theories

Theory of mind account

Proposes that difficulties in attributing mental states to oneself and others contribute to the social-communication features of autism; influential as one cognitive framework but not a complete explanation of the condition.

Mechanisms

Autism is highly heritable and polygenic, with many common and rare genetic variants converging on early brain development, synaptic function, and the organisation of neural circuits supporting social cognition and information processing. No single cause accounts for most cases; instead, diverse genetic and developmental pathways are thought to produce overlapping phenotypes. Cognitive accounts such as differences in theory of mind, executive function, and information-processing style describe aspects of the presentation without fully explaining it.

Clinical relevance

Recognising autism shapes how children are supported in health, educational, and social settings, and understanding its features helps clinicians and educators interpret behaviour in developmental terms. This entry explains how the condition is conceptualised and studied; it is not a tool for diagnosing an individual child or selecting interventions, which require specialist multidisciplinary assessment.

Epidemiology

Reported prevalence of autism has risen markedly over recent decades to around 1-2 percent of children in many surveys, attributed substantially to broadened diagnostic concepts, greater awareness, and improved ascertainment rather than a clearly established rise in incidence. Autism is diagnosed more often in boys than girls, and a meta-analysis found high rates of co-occurring mental-health conditions, including attention-deficit/hyperactivity disorder and anxiety disorders, in the autistic population.

Evidence & guidelines

Diagnostic concepts follow DSM-5-TR, which combined previously separate diagnoses into a single autism spectrum disorder, and ICD-11. Diagnosis rests on developmental history and structured clinical observation rather than a biological test. Major narrative reviews summarise the evidence base, and clinical pathways are issued by bodies such as the UK National Institute for Health and Care Excellence and the American Academy of Pediatrics; this entry summarises framing rather than reproducing those pathways.

History

Autism was first described as a distinct clinical syndrome by Leo Kanner in 1943, with Hans Asperger describing related cases around the same period. Through the late twentieth century the concept broadened into a spectrum, and DSM-5 (2013) consolidated earlier subcategories, including autistic disorder and Asperger disorder, into a single autism spectrum disorder, a framing retained in DSM-5-TR and ICD-11.

Debates

Drivers of rising prevalence

Whether the substantial increase in diagnosed autism reflects broadened criteria, awareness, and ascertainment or a true rise in occurrence remains debated, with most evidence attributing much of the change to definitional and recognition factors.

Key figures

• Simon Baron-Cohen
• Catherine Lord
• Meng-Chuan Lai

Seminal works

• lai-2014
• lord-2018

Frequently asked questions

Why is autism called a 'spectrum'?

Because the condition shares core features but varies widely in how they present and in associated abilities, language, and support needs, ranging from individuals who need substantial support to those who are highly independent.

Is there a medical test that diagnoses autism?

No. Diagnosis is based on developmental history and structured observation of social communication and behaviour by trained clinicians, not on a laboratory or imaging test.