What is Down syndrome?
Each cell in our body has 46 chromosomes, which are arranged in 23 pairs. One chromosome from each pair is inherited from our father and another from our mother. Chromosomes contain genetic materials that control our body functions.
Down syndrome is the most common chromosomal abnormality in humans. Down syndrome occurs when there are three copies of Chromosome 21, instead of the normal two. It is not inherited from one generation to another generation (except in rare conditions a mother is a carrier of abnormal Chromosome 21).
What causes Down syndrome?
Down syndrome generally occurs in about 1 in 700 pregnancies. The incidence is higher in mothers who conceived beyond 35 years of age. The chance of having a child with Down syndrome is 1 in 350 at 35 years old and 1 in 100 if the mother conceived at 40 years old.
What are the features of Down syndrome?
A person with Down syndrome has a distinctive physical appearance; small and low set ears, up slanting eyes, prominent eyelid folds, thickening of the skin on the back of the neck, bigger than normal space between the big toe and second toe (sandal gap), short fingers with a little finger that curve inwards and protruding tongue.
They have some degree of learning disabilities and growth delay. The severity may vary from person to person. The average intellectual quotient (IQ) of an adult with Down syndrome is about 50. Delayed speech and motor development (floppy muscle) are also seen frequently.
Up to 30 per cent of children with Down syndrome have heart defects requiring heart surgery. They are also at risk of developing eye problems, ear and lung infections, dental caries, leukaemia, thyroid diseases and bowel problems.
How can we check for Down syndrome in pregnancy?
It can be detected during pregnancy or after delivery.
There are few screening tests that can be performed during pregnancy. Ultrasound scans at 13 weeks of pregnancy to examine the presence of nose bone and thickness of the fluid at the back of the fetal neck (Nuchal Translucency) have a 70 per cent detection rate.
Checking the mother’s blood for fetal DNA (Noninvasive Prenatal Testing, NIPT) is 99 per cent accurate in screening for Down syndrome.
Detailed ultrasound scans in the second trimester can also identify some of the features of the syndrome.
Diagnostics are confirmatory tests and have a detection rate of 99.9%.
Two commonly performed diagnostic tests are Chorionic Villus Sampling (CVS) and Amniocentesis. CVS involves a biopsy of placenta tissue. Amniocentesis, on the other hand, involves taking samples of amniotic fluid for Chromosomal study. Both tests carry about a 1 per cent risk of miscarriage.
Long term care
There is no cure for Down syndrome. Some children with Down syndrome have low thyroid hormones requiring thyroid medications. They may also have feeding problems and poor muscle tone that make them unable to hold their head up and sit and therefore require physiotherapy and extra assistance care.
Special education and proper supportive care have been shown to improve the quality of life in these children. Their average life expectancy is around 50 to 60 years.
The Kiwanis Down Syndrome Foundation has various branches around the country to provide interventional programs for children with Down syndrome. Patients who have a child with Down syndrome have a slightly increased risk of having another child with Down syndrome in their future pregnancies.
Do seek your Obstetrician for further counselling regarding available options.
This article is written by Dr Lim Wan Teng, Consultant Obstetrician & Gynaecologist, Maternal-Fetal Medicine Specialist MBBS (IMU), MObGyn (UM), Fellowship in Maternal-Fetal Medicine (Malaysia/Hong Kong) of Pantai Hospital Cheras.
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