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Down's Syndrome

Down syndrome is caused by Trisomy 21 (3 copies of chromosome 21).


Presentation

  • Hypotonia

  • Brachycephaly – small head with flat back

  • Upward sloping palpebral fissures (eye lids)

  • Single palmar crease

  • Prominent epicanthic fold (fold on upper eye lid)

  • Short neck

  • Short stature

  • Flattened face and nasal bridge

“8-year-old boy with Down Syndrome” © Vanellus Foto CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/)

Associations

  • Learning disability (LD)

  • Hearing problems

    • Recurrent otitis media, Glue ear (Otitis Media with Effusion)

    • Deafness, Eustachian tube abnormalities

  • Visual problems such as myopia (short-sightedness), strabismus, cataracts

  • Congenital Heart Disease particularly ASD, VSD, PDA, ToF

  • Hypothyroidism

  • Atlantoaxial instability

  • Leukaemia and Alzheimers Dementia more common


N.B. The APP (amyloid precursor protein) gene responsible for Alzheimers is also on chromosome 21. So trisomy 21 leads to more APP, therefore a greater risk of AD.


Screening Tests

All pregnant women are offered screening for Down syndrome to know if more definitive invasive tests are needed.


1st line test is the Combined Test. This is carried out at 11-14 weeks. It involves a:

  • Ultrasound – Measure nuchal translucency – Will be thicker (>6mm) in Down’s

  • Blood test

    • Beta-hCG – higher level indicates greater risk

    • PAPPA – lower level indicates greater risk


2nd line test is the Quadruple Test. This is carried out at 14-20 weeks, or if a nuchal translucency ultrasound can't be done. It involves just 1 blood test.

  • This is less accurate than the combined test.


Diagnostic Tests

These tests are done if the screening tests indicate a greater risk of Down's. The foetal DNA is tested in 2 main ways:

  • Chorionic Villus Sampling (CVS) – US-guided biopsy of placental tissue – Used if < 15 weeks

  • Amniocentesis – US-guided aspiration of amniotic fluid – Used if > 15 weeks once there’s enough amniotic fluid to make sampling safer

“Amniocentesis” © BruceBlaus CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/) “Chorionic villus sampling” © Filip Mares CC BY CZ 3.0 (https://creativecommons.org/licenses/by/3.0/cz/)

Non-Invasive Testing

  • Blood taken from mother, and fragments of foetal DNA are analysed

    • Not definitive but gives a very good indication of Down’s, and may be preferred to the more invasive methods of CVS and Amniocentesis

    • Even if it's +ve, an invasive test is still needed for a definitive diagnosis


N.B. Think of NI Testing as the most accurate screening tool for those who don't want any invasive tests done.


Management

  • MDT involvement

  • Regular hearing tests

  • Regular eye tests

  • Echo

  • Regular thyroid checks




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