Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder defined by persistent difficulties in social communication and social interaction together with restricted, repetitive patterns of behaviour, interests, or activities, with onset in the early developmental period. The term spectrum reflects wide variation in presentation, language ability, and intellectual functioning across affected individuals.

Definition

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

Scope

The entry covers ASD as a clinical and neurodevelopmental entity: its two core symptom domains, the concept of a spectrum with dimensional severity, its early onset, strong genetic contribution, and frequent co-occurring conditions. It is a reference description and does not provide diagnostic thresholds for use in practice or any treatment guidance.

Core questions

• What are the two core symptom domains that define autism spectrum disorder?
• What does the spectrum concept capture about variation between individuals?
• How early can features of autism be reliably recognized?
• How do co-occurring conditions shape the overall clinical picture?

Key concepts

• Social communication and interaction deficits
• Restricted, repetitive behaviours and interests
• Spectrum and dimensional severity
• Early developmental onset
• Heterogeneity of language and intellectual ability
• High heritability and genetic heterogeneity
• Co-occurring conditions (e.g., intellectual disability, ADHD, epilepsy)

Mechanisms

Autism is strongly heritable, with heritability estimates frequently exceeding 80 percent, and its genetic architecture is highly heterogeneous, involving common variants of small effect, rare de novo and inherited variants, and copy-number variants, often converging on genes important for synaptic function and neural development. No single cause accounts for most cases, and there is no biological diagnostic test; identification rests on developmental history and observation of behaviour. These accounts describe group-level biology and do not constitute individual diagnostic tools.

Clinical relevance

Recognizing the core features of autism, difficulties in reciprocal social communication and the presence of restricted, repetitive behaviours, helps clinicians, educators, and families understand a child's developmental profile and support needs. This entry describes the condition for reference and is not a basis for individual diagnosis or for any specific intervention decision.

Epidemiology

Estimated prevalence of autism spectrum disorder has risen over recent decades, with contemporary surveillance commonly reporting figures on the order of 1 to 2 percent of children, a change attributed substantially to broadened diagnostic criteria, increased awareness, and improved case ascertainment rather than to a single biological cause. Autism is diagnosed more often in boys than girls, and co-occurring intellectual disability, ADHD, anxiety, and epilepsy are common.

Evidence & guidelines

DSM-5-TR consolidated previously separate pervasive developmental disorders into a single autism spectrum disorder with two symptom domains and severity levels, and ICD-11 (category 6A02) adopts a comparable definition. Professional guidance, such as the American Academy of Pediatrics clinical report, frames identification and evaluation, while major reviews in The Lancet synthesize the genetic, neurobiological, and epidemiological evidence. Diagnosis is clinical and developmental.

History

Autism was first described as a distinct syndrome by Leo Kanner in 1943, and Hans Asperger reported a related profile shortly afterward. Through the later twentieth century the concept broadened into a family of pervasive developmental disorders, and DSM-5 (2013) merged these into a single dimensional autism spectrum disorder, reflecting evidence that the earlier subtypes could not be reliably distinguished.

Debates

What explains the rise in prevalence?

The marked increase in recorded autism prevalence is widely attributed to broadened diagnostic criteria, greater awareness, and better ascertainment, with debate continuing over how much, if any, reflects a true change in incidence.

Key figures

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

Seminal works

• lord-2018
• lai-2014

Frequently asked questions

Why is autism described as a spectrum?

Because the same two core features, social communication difficulties and restricted, repetitive behaviours, occur with very different severity and are accompanied by widely varying language and intellectual abilities, so presentations range broadly across individuals.

Does vaccination cause autism?

No. The claim of a vaccine link arose from a discredited and retracted study, and large epidemiological investigations have found no association between vaccination and autism.