Downs Syndrome

Down’s Syndrome is caused by three copies of chromosome 21. It is also called trisomy 21. It gives characteristic dysmorphic features and is associated with a number of associated conditions. The extent to which the person is affected and the associated conditions they have vary between individuals.

 

Dysmorphic Features

  • Hypotonia (reduced muscle tone)
  • Brachycephaly (small head with a flat back)
  • Short neck
  • Short stature
  • Flattened face and nose
  • Prominent epicanthic folds
  • Upward sloping palpebral fissures
  • Single palmar crease

 

Epicanthic folds are folds of skin covering the medial portion of the eye and eyelid. The palpebral fissures are the gaps between the lower and upper eyelid.

 

Complications

  • Learning disability
  • Recurrent otitis media
  • Deafness. Eustachian tube abnormalities lead to glue ear and conductive hearing loss.
  • Visual problems such myopia, strabismus and cataracts
  • Hypothyroidism occurs in 10 – 20%
  • Cardiac defects affect 1 in 3, particularly ASD, VSD, patent ductus arteriosus and tetralogy of Fallot
  • Atlantoaxial instability
  • Leukaemia is more common in children with Down’s
  • Dementia is more common in adults with Down’s

 

Antenatal Screening for Down’s Syndrome

All women are offered screening for Down’s syndrome. The purpose of the screening test is to decide which women should receive more invasive tests that would give a definitive diagnosis.

It is the choice of the woman whether to go ahead with screening. The screening tests involve taking measurements from the fetus using ultrasound, combining those measurements with the mothers age and blood results and providing an indication of the risk of Downs syndrome. Older mothers have a greater risk of Down’s syndrome.

 

Combined Test

The combined test is the first line, most accurate and test of choice where possible. This test is performed between 11 and 14 weeks gestation. It involves combining results from ultrasound and maternal blood tests.

Ultrasound measures nuchal translucency, which is the thickness of the back of the neck of the fetus. Down’s syndrome is one cause of a nuchal thickness over 6mm.

Maternal blood tests:

  • Beta‑human chorionic gonadotrophin (beta-HCG). A higher result indicates a greater risk.
  • Pregnancy‑associated plasma protein‑A (PAPPA). A lower result indicates a greater risk.

 

Triple Test

The triple test is performed between 14 and 20 weeks gestation. It only involves maternal blood test results:

  • Beta-HCG. A higher result indicates greater risk.
  • Alpha-fetoprotein (AFP). A lower result indicates a greater risk.
  • Serum oestriol (female sex hormone). A lower result indicates a greater risk.

 

Quadruple Test

The quadruple test is performed between 14 and 20 weeks gestation. It is identical to the triple test but also includes maternal blood for inhibin-A. A higher inhibin-A indicates a greater risk.

 

Antenatal Testing for Downs Syndrome

The screening tests provide a risk score for the fetus having Down’s syndrome. When the risk of Down’s is greater than 1 in 150 (this result occurs in around 5% of tested women) the woman is offered amniocentesis or chorionic villus sampling. These tests involve taking a sample of the fetal cells, which then undergo karyotyping to give a definitive answer to whether the fetus is affected by Down’s or not.

  • Chorionic villus sampling (CVS) involves an ultrasound guided biopsy of the placental tissue. This is used when testing is done earlier in pregnancy (before 15 weeks).
  • Amniocentesis involves ultrasound guided aspiration of some amniotic fluid using a needle and syringe. This is later in pregnancy once there is enough amniotic fluid to make it safer to take a sample.

 

Non-Invasive Prenatal Testing

Non-invasive prenatal testing (NIPT) is a relatively new test for detecting abnormalities in the fetus during pregnancy. It involves a simple blood test from the mother. The blood will contain fragments of DNA, some of which will come from the placental tissue and represent the fetal DNA. These fragments can be analysed and detect conditions such as Down’s.

NIPT is not a definitive test, but it does give a very good indication of whether the fetus is affected. This is gradually being rolled out in the NHS as an alternative to invasive testing (CVS and amniocentesis) for women that have a higher than 1 in 150 risk of Down’s syndrome.

 

Management

Management involves supportive care from the multidisciplinary team to help them meet their needs:

  • Occupational therapy
  • Speech and language therapy
  • Physiotherapy
  • Dietician
  • Paediatrician
  • GP
  • Health visitors
  • Cardiologist for congenital heart disease
  • ENT specialist for ear problems
  • Audiologist for hearing aids
  • Optician for glasses
  • Social services for social care and benefits
  • Additional support with educational needs
  • Charities such as the Down’s Syndrome Association

TOM TIP: When asked by an examiner about the management of a complex multi system disorder such as Down’s syndrome, always start your answer with “management would involve members of the multidisciplinary team”. This allows you to list the common members, pick up most of the marks and impress your examiners without knowing any specific treatments.

 

There are some routine follow up investigations that are important for children with Down’s syndrome:

  • Regular thyroid checks (2 yearly)
  • Echocardiogram to diagnose cardiac defects
  • Regular audiometry for hearing impairment
  • Regular eye checks

 

Prognosis

Prognosis varies depending on the severity of the associate complications. The average life expectancy is 60 years.

 

Last updated January 2020