Down syndrome, also called trisomy 21, is caused by an extra copy of chromosome 21. It results in characteristic dysmorphic features and predisposes to various complications.
Dysmorphic Features
Dysmorphic features in Down syndrome include:
- Hypotonia (reduced muscle tone)
- Brachycephaly (short anteroposterior skull with a flat occiput)
- Short neck
- Short stature
- Flattened face and nose
- Prominent epicanthic folds (the folds of skin overlying the medial portion of the eye and eyelid)
- Upward-sloping palpebral fissures (the gaps between the lower and upper eyelid)
- Single palmar crease (a single line running across the palm compared with the usual two)
Complications
Complications of Down syndrome include:
- Learning disability
- Recurrent otitis media
- Recurrent respiratory infections
- Eustachian tube abnormalities leading to glue ear and conductive hearing loss
- Visual problems, such as myopia, strabismus and cataracts
- Hypothyroidism
- Coeliac disease
- Type 1 diabetes
- Obesity
- Obstructive sleep apnoea
- Hypogonadism and reduced fertility (particularly males)
- Congenital heart defects (e.g., atrioventricular septal defect)
- Congenital gastrointestinal anomalies (e.g., duodenal atresia and Hirschsprung disease)
- Atlantoaxial instability
- Acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML)
- Early-onset dementia (as adults)
Antenatal Screening
All women are offered optional screening for Down syndrome during pregnancy. The purpose of the screening test is to decide which women should receive more invasive tests to establish a definitive diagnosis. The risk increases with the mother’s age. Depending on gestational age, screening involves either the combined test or the quadruple test.
The combined test, performed between 11+2 and 14+1 weeks, is the first-line screening test for Down syndrome, and also screens for Patau syndrome (trisomy 13) and Edward syndrome (trisomy 18). It combines the results of:
- Blood tests
- Nuchal translucency measured by ultrasound
Nuchal translucency is the thickness of the fluid-filled space at the back of the fetal neck. A greater thickness indicates an increased risk.
Maternal blood tests performed for the combined test are:
- Beta‑human chorionic gonadotropin (beta-HCG) (a higher result indicates a greater risk)
- Pregnancy‑associated plasma protein‑A (PAPPA) (a lower result indicates a greater risk)
The quadruple test may be performed between 14+2 and 20+0 weeks if the combined test window is missed. It only screens for Down syndrome (not Patau or Edward). The quadruple test combines the results from a blood test for:
- Free beta-HCG (a higher result indicates greater risk)
- Alpha-fetoprotein (AFP) (a lower result indicates a greater risk)
- Unconjugated oestriol (female sex hormone) (a lower result indicates a greater risk)
- Inhibin-A (a higher result indicates a greater risk)
Further Antenatal Testing
The screening test provides a risk score for the fetus having Down syndrome. A score between 1 in 2 and 1 in 150 is considered to be a higher-chance result.
Non-invasive prenatal testing (NIPT) is offered to women with a higher-chance result. The mother’s blood is tested for fetal DNA fragments. NIPT is not definitive, but it gives a good idea of whether the fetus is affected.
Diagnostic tests can give a definitive answer by collecting and testing fetal cells. The options are:
- Chorionic villus sampling (CVS), involving an ultrasound-guided biopsy of the placental tissue (before 15 weeks)
- Amniocentesis, involving ultrasound-guided aspiration of amniotic fluid (after 15 weeks)
Management
Management involves supportive care from the multidisciplinary team to help them meet their needs:
- Occupational therapy
- Speech and language therapy
- Physiotherapy
- Dietician
- Paediatrics
- General practice
- Health visitors
- Cardiology (congenital heart disease)
- ENT (ear problems)
- Audiology (hearing aids)
- Optician (glasses)
- Social services (social care and benefits)
- Additional support with educational needs
- Charities (e.g., Downs Syndrome Association)
TOM TIP: When asked by an examiner about the management of a complex multi-system disorder such as Down syndrome, start your answer with “management will involve the multidisciplinary team”. This allows you to list the team members, pick up marks, and impress your examiners without knowing specific treatments.
Routine testing is required for all patients with Down syndrome:
- Regular thyroid function and coeliac tests
- Echocardiogram to diagnose cardiac defects
- Regular audiometry for hearing impairment
- Regular eye checks
Prognosis
Prognosis varies depending on the severity of the associated complications. Average life expectancy is around 60 years and increasing.
Last updated December 2025
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