Down Syndrome


  • A syndrome is a condition formed by a pattern of characteristics occurring together in a person.
  • Named after Dr. Langdon Down who reported the similarities characteristics in children with intellectual disability in 1866.
  • Most common identifiable cause of intellectual disability.
  • Frequency : 1 in every 660 babies born with Down Syndrome.
  • Estimated around 1000 newborns in Malaysia are affected with Down Syndrome each year.

Clinical Features

  • Flat nasal bridge
  • Eyes may have an upward and outward slant
  • Small ears and low set
  • Small and stubby hands
  • Single crease across the palm
  • Wide gap between toes
  • Low muscle tone (hypotonia)
  • Delay in achieving milestones

Common Medical Complications

  • Cardiac malformations (40%)
  • Gastrointestinal malformations (12%)
  • Auditory Deficits (50 – 70%)
  • Respiratory problems
  • Epilepsy (5%)
  • Hypothyroidism (16%)
  • Leukamia (1%)
  • Alzheimer disease

Causes of Down Syndrome

  • Caused by chromosomal abnormalities
  • Three types
  • Each type involves extra chromosome 21

          – 1. Standard trisomy (95%)
          – 2. Translocation
          – 3. Mosaic (2%)


  • Found in the nuclues of a cell
  • Composition
    – Deoxyribonucleic Acid (DNA)
  • Exist in pairs
  • One copy of each chromosome inherited from mother and the other from father.
  •   2 types of chromosomes :
     1. Autosomes
    – not involved in sex determination
    – 22 pairs in human somatic cells
    2. Sex Chromosomes
    – determines sex of baby
    – Female -XX Male – XY

Chromosome Analysis

  • To identify the number and structure of chromosomes in cell

Trisomy 21

  • Trisomy means three copies of chromosomes
  • 95% of cases involves extra copy of chromosome 21 in every cell in the body
  • Result of faulty distribution of chromosomes in either the mother’s egg or father’s sperm


  • A process of cell division to form reproductive cells- sperm & ovum
  • Non-disjunction in Meiosis I & II


  • An extra copy of chromosome 21 is attached to another chrosome
  • Either parent may be a healthy carrier of a balanced translocation
  • May occur by chance (spontaneously) in the child or may be inherited (“unbalanced”)
  • Parental chromosomes should be analysed


  • Mixture of cells with 2 copies of chromosome 21 (normal) and some cells with trisomy 21
  • Resulted from error of cell division after conception
  • Number of trisomy cell affects the severity of the characteristics presented.

Maternal Age Risk

  • Refers to the relationship between a women’s age and risk of having child with Down Syndrome
  • Women over the age of 35 is at greater risk

Prenatal Testing

  • Chorionic Villous Sampling (CVS)
    – Between 11-14 weeks of gestation
    – 1% or 1 in 100 risk of miscarriage
  • Amniocentesis
    – Bewteen 16-18 weeks of gestation
    – 0.5% or 1 in 200 risk of miscarriage

Genetic Counselling

  • Definition : A communication process which deals with the risk of developing or transmitting a genetic condition.
  • Goal : To provide accurate information and assist client to make fully informed decision.

Reasons for Genetic Counselling

  • To obtain information
    – about a genetic condition
    – about genetic testing
  • When there is family history of inherited diseases
  • Past history of infertility, pregnancy losses, still births and early infant deaths.
  • Concern about
    – the effects of drugs and infections during early pregnancy
    – pregnancy for older parents

What happens in Genetic Counselling?

  • Determine client’s needs and intentions
  • Establishment of diagnosis
  • A family tree / pedigree will be drawn for the family
  • A physical examination may be required
  • Relevant tests to clarify the diagnosis
  • Estimation of recurrence risk
  • Burden of care
  • Reproductive options
  • Communication of relevant information
  • Provision of long term support
  • Support Group
  • Rehabilitation
  • Integration into normal society
  • Regular health monitoring