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By Dr. Samuel Obaseki GPST2 2012 Background Down s Syndrome Is the most common and well studied chromosomal autosomal disorder and a major cause of intellectual ... – PowerPoint PPT presentation

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Title: Down

Downs Syndrome Screening
  • By Dr. Samuel Obaseki
  • GPST2 2012

Background Downs Syndrome
  • Is the most common and well studied chromosomal
    autosomal disorder and a major cause of
    intellectual and physical disability with an
    incidence of about 1 in 700 births.
  • Mostly caused by trisomy of chromosome 21,
    leading to structural and functional defects in
    people born with the condition.
  • There is decreased prenatal, and postnatal
    viability and reduced life expectancy due to
    associated physical and health problems.

Genetics/etiology of Downs Syndrome
  • Trisomy 21, 94 of cases. Occurs following
    nondysjunction during meiosis in one of the
    parents. Though this can occur with either
    parents advancing age, there is a stronger
    correlation with the maternal age.
  • Chromosomal translocation, 3.3. When genetic
    material from chromosome 21 attaches to another
    chromosome (14, 21 or 22). Could be de novo (75)
    or transmitted from the parents (25).
  • Mosacism, 2.4. Mostly from a trisomy zygote
    (after fertilization) that loses one chromosome
    leading to a mixture of trisomy 21 and normal
    karyotype autosomal cells. This results in a
    variety of phenotypes from near normal to
    classical trisomy 21 phenotype.

Genetics/epidermiology of Downs Syndrome
  • Overall frequency 1 in 700 births
  • A baby with downs syndrome may be born to a
    mother at any age, but the risk increases with
    maternal age.
  • Chances of having a baby with downs syndrome is
  • 1 in 1600 lt 20 years
  • 1 in 1500 at 20 years
  • 1 in 900 at 30 years
  • 1 in 270 at 35 years
  • 1 in 100 at 40 years
  • 1 in 50 if mum gt 45 years
  • A female patient with trisomy 21 has a 1 in 2
    chance of having a child with downs syndrome
    while male sufferers are usually infertile (those
    with mosacism being an exception).

Clinical features of Downs syndrome
  • The physical and mental effects of Downs
    syndrome are profound.
  • General appearance - Short extremities and
    height, slanted eyes, medial epicanthic folds,
    flat nasal bridge, protruding tongue, single
    simian crease etc
  • CNS - moderate to severe mental retardation,
    seizure disorders, and hypotonia in neonates.
  • Psychiatric Usually very cheerful and gentle.
    ADHD, ASD, OCD, depression, early dementia.
  • Eyes - Brushfield spots (speckled iris),
    refractive errors, strabismus.
  • Facial features Brachycephaly, large sutures
    with delayed closure, microcephaly, small ears
    with overfolded helix, flat facies,
    hypertelorism, anodontia, chronic otitis media
    and hearing loss,
  • Broad sort neck with antlantoaxial instability
    and possible cord compression.
  • CVS Congenital defects like endocardial cushion
    defect, VSD, secundum ASD, TOF, PDA.
  • GUT Duodenal atresia/stenosis, Hirschsprungs,
  • Hypothyroidism, leukaemia, Impaired cellular

UK screening criteria (Wilson Jungner)
  • The condition
  • The condition should be an important health
  • The epidemiology and natural history of the
    condition, including development from latent to
    declared disease, should be adequately understood
    and there should be a detectable risk factor,
    disease marker, latent period or early
    symptomatic stage.
  • All the cost-effective primary prevention
    interventions should have been implemented as far
    as practicable.
  • If the carriers of a mutation are identified as a
    result of screening, the natural history of
    people with this status should be understood,
    including the psychological implications.
  • The test
  • There should be a simple, safe, precise and
    validated screening test.
  • The distribution of test values in the target
    population should be known and a suitable cut-off
    level defined and agreed.
  • The test should be acceptable to the population.
  • There should be an agreed policy on the further
    diagnostic investigation of individuals with a
    positive test result and on the choices available
    to those individuals.
  • If the test is for mutations the criteria used to
    select the subset of mutations to be covered by
    screening, if all possible mutations are not
    being tested, should be clearly set out.
  • The treatment
  • There should be an effective treatment or
    intervention for patients identified through
    early detection, with evidence of early treatment
    leading to better outcomes than late treatment.
    There should be agreed evidence-based policies
    covering which individuals should be offered
    treatment and the appropriate treatment to be
  • Clinical management of the condition and patient
    outcomes should be optimised in all healthcare
    providers prior to participation in a screening

Downs Syndrome Screening
  • Is co-ordinated in the UK by the UK National
    Screening Committee which provides advice
    through its antenatal and newborn screening
  • NHS Fetal Anomaly Screening Programme Screening
    tests are offered to ALL pregnant women. Those at
    increased risk are then offered diagnostic tests.
  • NHS Newborn and Infant Physical Examination
    (NIPE) Programme Examination of all infants
    within 72 hours of birth and around 6 8 weeks
    of life.

Downs syndrome screening - Antenatal
  • Screening tests Offered to all women
  • Combined screening test - from 10 weeks 0 days
    to 14 weeks 1 day. Maternal serum levels of
    beta hCG and Pregnancy Associated Plasma Protein
    - A (PAPP-A) Nuchal Transluscency (NT) scan
    done between 11weeks 2 days and 14weeks 1
  • Quadruple test from 14 weeks 2 days to 20
    weeks 0 days. Maternal serum beta hCG,
    alphafetoprotein (AFP), inhibin A, and
    unconjugated oestriol (uE3).
  • Diagnostic tests Offered to those with a risk
    between 1 in 2 and 1 in 150
  • Chorionic Villus Sampling (CVS). Ultrasound
    guided transabdominal or transcervical
    aspiration of placenta from 110 weeks to
    126weeks (up to 136weeks for transabdominal)
  • Amniocentesis. Ultrasound guided transabdominal
    aspiration of amniotic sac fluid for
    cytogenetics, from 150 weeks.

Downs syndrome screening - Newborn
  • As part of the Baby check, the phenotypic
    features of Downs syndrome may be recognized and
    a diagnosis made at the Newborn Physical
    Examination or at the 6 8 week Infant Physical
    Examination. Note that those with mosacism may be
    quite difficult to recognize by just the physical
  • Chromosomal analysis may be offered in
    suspected/recognized cases of Downs syndrome.
    Presence of chromosomal translocation will
    suggest a much increased chance of recurrence if
    inherited from either parent.
  • All neonates with Downs syndrome should be
    screened for congenital heart disease.

Downs Syndrome screening
  • About a quarter of babies born with Downs
    syndrome are not detected by the screening tests.
  • Results of diagnostic tests eg CVS and
    amniocentesis may take between 3 and 18 days.
  • 1 in every 30 women screened will be offered a
    diagnostic test.
  • Foetal loss with CVS and amniocentesis is
    approximately 1 2. Other complications include
    preterm labour, bleeding and infection etc.
  • In 2 of diagnostic tests, sample may be deemed
  • With multiple gestation pregnancies, there is a
    higher incidence of false positive screening
    tests and complications following diagnostic

Downs syndrome screening
  • For affected pregnancies, offer the parents
    support and specialized counselling services.
  • Parents may be signposted to
  • Antenatal Results and Choices (ARC)
  • Contact a family (CAFAMILY)
  • Downs Syndrome Association
  • Downs Syndrome Medical Interest Group
  • NHS Fetal Anomaly Screening Programme

Downs syndrome screening
  • References
  • RCOG guidelines for Amniocentesis and CVS