Genetic testing for autism and ADHD in the UK: what to expect

This guide is general information only, not advice about your child. Local pathways vary. Speak to your own doctor or your regional genetics service about your situation.

Parents often ask me whether their child should have a genetic test for autism or ADHD (attention deficit hyperactivity disorder). The answer depends on the child, not the diagnosis. This guide sets out who gets tested on the National Health Service (NHS) in England, what the results can mean, and what happens next.

Who is offered a test

NICE (the National Institute for Health and Care Excellence) says a genetic test should not be a routine part of an autism assessment. It should be considered when a child also has specific dysmorphic features (unusual physical features), congenital anomalies (differences present from birth) or a learning (intellectual) disability.¹

Since 1 April 2026, the main NHS test for these children in England is whole genome sequencing, ordered under the test code R27 (Paediatric disorders) in the National Genomic Test Directory.^2,3 It is eligible for children with at least a moderate learning disability or a moderately severe global developmental delay that is unexplained, or with congenital anomalies and/or dysmorphic features. Autism alone, and mild learning disability without other features, do not qualify.³

ADHD is not an eligibility criterion for R27. A child with ADHD alone will not usually be offered a genetic test on the NHS. The NICE ADHD guideline does not recommend genetic testing as part of assessment.⁴ If a child with ADHD also has at least a moderate learning disability, a moderately severe global developmental delay, or physical features that point to a genetic condition, those features are what make the test worth doing.

How the test is arranged

The NHS Genomic Medicine Service (GMS) runs testing through regional genomic laboratory hubs.² A paediatrician can order the test directly for a child with at least a moderate learning disability. Referral to clinical genetics is needed only when there are signs of a syndrome, such as subtle differences in facial features or unusual growth. A blood sample is usually taken from the child and, where possible, both parents. Testing the parents too helps the laboratory tell new changes from inherited ones.

The doctor who ordered the test, or the genetics team, gives the result, usually at an appointment.

The three kinds of result

A clear finding. The laboratory finds a change it classes as pathogenic or likely pathogenic: it explains, or very probably explains, the child's difficulties. This can lead to specific health checks, information about what to expect, contact with families of children with the same condition, and accurate advice about the chance of it happening again in a future pregnancy. It rarely changes autism or ADHD support itself.

A variant of uncertain significance (VUS). The laboratory finds a change but cannot yet say whether it matters. A VUS is not a diagnosis, and it should not be used to make decisions about a pregnancy. Some are reclassified later as more evidence builds up.

No finding. This does not mean the cause is not genetic. It means no explanation was found with current knowledge. Autism and ADHD are strongly heritable, but much of that inheritance comes from many common variants, each with a tiny effect, which a clinical test does not report.^5–7 Genome data are stored, so the laboratory can reanalyse them later as new genes are discovered.

Things worth knowing first

• A result can affect other family members. A parent may turn out to carry the same change, sometimes with health implications of their own.⁸
• Most children who are tested do not get a clear answer. In a 2026 Belgian trial of children and adults with developmental disorders, genome sequencing found a diagnosis in 40%.⁸
• A result does not change whether a child has autism or ADHD, or their entitlement to support.

For what a genome adds and how often it finds an answer, see what genome sequencing adds for children with developmental delay. For how much of autism and ADHD is genetic, see Autism and ADHD: is it genetic?

References

1. National Institute for Health and Care Excellence. Autism spectrum disorder in under 19s: recognition, referral and diagnosis (CG128), recommendation 1.7.1. nice.org.uk/guidance/cg128
2. NHS England. National Genomic Test Directory. england.nhs.uk
3. Leeds Teaching Hospitals / North East and Yorkshire Genomic Laboratory Hub. Important: changes to National Test Directory from April 2026. leedsth.nhs.uk; East Genomics. Rare disease directory update (April 2026). eastgenomics.nhs.uk
4. National Institute for Health and Care Excellence. Attention deficit hyperactivity disorder: diagnosis and management (NG87). nice.org.uk/guidance/ng87
5. Sandin S, Lichtenstein P, Kuja-Halkola R, et al. The heritability of autism spectrum disorder. JAMA. 2017;318(12):1182–1184. doi:10.1001/jama.2017.12141
6. Faraone SV, Larsson H. Genetics of attention deficit hyperactivity disorder. Molecular Psychiatry. 2019;24:562–575. doi:10.1038/s41380-018-0070-0
7. Grove J, Ripke S, Als TD, et al. Identification of common genetic risk variants for autism spectrum disorder. Nature Genetics. 2019;51:431–444. doi:10.1038/s41588-019-0344-8
8. Geysens M, Souche E, Baroni MC, et al. Genome Medicine. 2026;18:144. doi:10.1186/s13073-026-01771-2

Dr Odet Aszkenasy is a Consultant Community Paediatrician and the author of The Genetics of Autism: A Guide for Parents and Professionals.