WHAT IS 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%)

Chromosomes

• 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

Meiosis

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

Translocation

• 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

Mosaic

• 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