Downs Flashcards
What
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.
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 Testing
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.
