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At a glance:

  • Developmental delay is a failure to achieve developmental milestones when compared to similar-aged peers. Delay is known as ‘global’ if two or more developmental domains are affected in a child under the age of five.
  • Up to 40% of global developmental delay cases may be related to genetic factors, most commonly chromosomal anomalies and fragile X syndrome. Single-domain delay, such as gross motor delay in muscular dystrophies, may also have a genetic cause.
  • Identifying the delay and its aetiology may occasionally lead to specific treatment, but it is important to ensure that children and their families have access to the correct services and support.
  • Alert! Developmental arrest (normal initial development followed by failure to gain further skills) and developmental regression (loss of previously gained skills) are red flags that require urgent further assessment.

Example clinical scenario

A three-year-old boy is brought to see you by his parents on the advice of their health visitor, due to concerns about his development. He began to roll over at nine months and was able to sit up unaided at 18 months. He has only recently started to walk on his own at the age of three, and cannot manage stairs. His speech is limited to a few single words: mama, dada, no, ball and bye.

Identifying those at risk of a genetic condition

  • Causes of developmental delay are many and varied. They include:
    • antenatal infection;
    • parental health and behaviours, such as alcohol consumption during pregnancy;
    • structural brain anomalies;
    • complications of prematurity;
    • birth trauma or asphyxia;
    • intrauterine growth restriction;
    • perinatal hypoglycaemia; and
    • genetic anomalies.
  • Flags for an underlying genetic diagnosis include:
    • family history of developmental delay;
    • parental consanguinity; and
    • dysmorphic features (see the resources section below).
  • Most investigations in young children will be carried out by secondary care services. First-line investigations aim to exclude correctable physical causes, such as iron deficiency and hypothyroidism.
  • In general, referrals to clinical genetics services are made by paediatrics or community paediatrics services following their assessments.
  • Initial genomic testing is usually a microarray and fragile X test, but testing for other specific genetic conditions may be suggested by family history or signs found on examination.

What do you need to do?

  • Take a thorough patient history, including family history, mother’s health during pregnancy, delivery, neonatal health, milestones in other domains and any loss of milestones.
  • Examination should incorporate inspection for dysmorphic features, developmental assessment and measurement of growth parameters, including head circumference.
  • Ensure the patient’s hearing and vision have been assessed.
  • If developmental delay is suspected on examination, refer the patient to community paediatrics services for an in-depth developmental assessment and investigation.
  • If developmental arrest or regression are present, refer the case urgently to paediatrics services for investigation.
  • If you suspect child neglect or maltreatment, follow your local children’s safeguarding policies and guidelines.
  • For more information on paediatric assessment procedures for a child with developmental delay, see Child with developmental delay or intellectual disability.
  • For information about how to arrange testing in Wales, Scotland or Northern Ireland, see our dedicated Knowledge Hub resource.
  • Information about patient eligibility and test indications were correct at the time of writing. When requesting a test, please refer to the National Genomic Test Directory to confirm the right test for your patient.


For clinicians

For patients

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  • Last reviewed: 13/06/2023
  • Next review due: 13/06/2024
  • Authors: Dr Johanna Wong
  • Reviewers: Dr Steven Bunce, Dr Asma Hamad