Autism spectrum disorder

What autism is

Autism spectrum disorder is diagnosed on the basis of two core domains: persistent differences in social communication and interaction, and restricted or repetitive behaviours, interests and activities (which include sensory differences). In the current diagnostic manual (DSM-5), several older labels — autistic disorder, Asperger syndrome and PDD-NOS — were brought together into a single 'spectrum'.

Because it is a spectrum, presentation ranges widely: some autistic people have profound support needs and little or no spoken language, while others are highly verbal and independent. Diagnosis records severity and specifiers — such as whether there is accompanying intellectual disability or language impairment, or a known genetic or medical condition.

Early signs

Signs usually emerge in the first two to three years. In a minority of children, early skills are gained and then lost (regression), typically in the second year.

• Reduced eye contact and limited response to their name by 12 months
• Few communicative gestures (pointing, showing, waving) and limited joint attention (sharing interest in something with another person)
• Delayed or absent babble and first words
• Limited pretend or imaginative play
• Repetitive movements (hand-flapping, rocking, lining up objects) and intense, narrow interests
• Strong reactions to sounds, textures, lights or routines (sensory differences)
• Loss of previously acquired words or social skills (regression) in some children

Diagnosis: criteria and methods

There is no blood test for autism — diagnosis is clinical, based on the DSM-5 criteria. Care begins with developmental surveillance at routine visits and autism-specific screening at 18 and 24 months (commonly with the M-CHAT-R/F questionnaire).

When concerns are raised, a comprehensive multidisciplinary assessment combines a detailed developmental history with direct observation. The most widely used standardised tools are the ADOS-2 (a structured play-and-interaction observation, considered a gold standard), the ADI-R (a detailed caregiver interview) and the CARS-2 (a rating scale). Assessment also covers cognition, language, adaptive skills, hearing and sensory profile, and considers differential diagnoses such as developmental language disorder, social (pragmatic) communication disorder, intellectual disability and hearing loss.

Causes, genetics and genetic testing

Autism is one of the most heritable neurodevelopmental conditions (heritability around 80%). For most people it is polygenic — many common variants each adding a little — but new (de novo) variants and copy-number changes also play an important role, and a proportion of cases are 'syndromic', linked to a single condition such as Fragile X syndrome, tuberous sclerosis complex or MECP2-related disorders.

Because identifying a cause can guide health surveillance, recurrence-risk counselling and, increasingly, treatment, genetic testing is recommended. Current first-tier tests are chromosomal microarray and Fragile X testing, with exome or genome sequencing increasingly used — the diagnostic yield is higher when there is intellectual disability, dysmorphic features or a more severe presentation.

It is also worth stating plainly, because families are often worried by misinformation: vaccines do not cause autism. This has been examined in very large studies and consistently refuted.

Co-occurring conditions

• Intellectual disability or a learning profile that is uneven across abilities
• ADHD, anxiety, and mood or obsessive–compulsive difficulties
• Epilepsy (more common than in the general population)
• Gastrointestinal problems (reported in roughly a third) and feeding selectivity
• Sleep difficulties
• Motor coordination differences

Evidence-based support and treatment

There is no medicine that treats the core features of autism, and the goal of support is not to make an autistic child 'non-autistic' but to build communication, skills, wellbeing and participation while respecting the individual. The strongest evidence is for early, developmentally-based, often parent-mediated intervention — naturalistic developmental behavioural interventions (such as the Early Start Denver Model) and approaches grounded in applied behaviour analysis — together with speech and language therapy, occupational therapy and individualised educational support.

Medicines are used to help specific co-occurring problems rather than autism itself — for example for marked irritability or aggression, ADHD, anxiety, or sleep (where melatonin has good evidence). Any medicine is a decision for the treating clinician, weighing benefits against side effects.

Precision medicine

A major direction of research is identifying biologically defined subgroups so that treatment can be tailored, rather than treating 'autism' as one thing. Genetic testing can reveal syndromic causes (such as Fragile X or tuberous sclerosis) that have their own targeted management and surveillance.

One example that has drawn attention is the folate pathway: a subset of autistic children have folate-receptor-alpha autoantibodies or cerebral folate deficiency and may respond to leucovorin (folinic acid). In March 2026 the FDA approved leucovorin specifically for cerebral folate deficiency — a rare genetic disorder — but regulators have been clear that the evidence is not sufficient to approve or recommend it for autism in general. Identifying the right biomarker-defined subgroup is exactly the kind of question precision medicine aims to answer.

Diet and supplements

Many families try dietary changes and supplements. Most have limited or mixed evidence and should be discussed with a clinician and dietitian so they support — rather than replace — evidence-based care, and so nutrition and growth are protected.

Commonly considered options include gluten-free/casein-free diets (evidence is weak and restriction carries nutritional risks), omega-3 fatty acids, vitamin and B-vitamin supplements, folinic acid (see precision medicine above), probiotics and other microbiome approaches (investigational), and melatonin (which does have good evidence, specifically for sleep). High-dose or unproven supplement regimens can carry real risks and warrant caution.

Experimental and complementary therapies

Several newer therapies are studied and sometimes marketed for autism. They are investigational — promising in some early work, but not established treatments — and families are sometimes offered costly, unregulated versions.

• Transcranial magnetic stimulation (rTMS) — non-invasive brain stimulation (for example to the right temporoparietal junction, part of the 'social brain'); small studies and ongoing multicentre trials suggest it is generally safe and tolerable, but its benefit in autism is not yet established.
• Stem-cell and exosome therapies — umbilical cord blood, mesenchymal stromal cells and stem-cell-derived exosomes are being explored for their anti-inflammatory and signalling effects; safety data are emerging but efficacy in autism is not proven, and no such therapy is approved.
• Photobiomodulation (low-level laser), oxytocin, bumetanide and similar approaches have been trialled with mixed or inconclusive results.

Education and everyday support

Beyond therapy hours, the biggest difference often comes from a well-matched educational setting, clear communication supports (including augmentative and alternative communication where speech is limited), and an approach that builds on a child's strengths and interests. Support for the whole family, predictable routines and planning ahead for transitions all matter.

How an educational review can help

An autism diagnosis raises a great many questions: what the ADOS-2 or CARS-2 reports actually mean, whether genetic testing is indicated, which therapies have real evidence versus marketing, and how to weigh precision-medicine, dietary, supplement and experimental options being offered. An educational review can explain the assessments and any genetic findings in plain language, set the current plan against evidence-based guidance, and help you prioritise and ask the right questions.

It is an educational second opinion — not a diagnosis, treatment or prescription — and it does not replace the care of your child's own clinicians.