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 the other from our mother. They contain genetic materials that control our body functions.
Down syndrome is the most common chromosomal abnormality in humans. It occurs when there are three copies of Chromosome 21, instead of the normal two.
It is not an inheritable condition passed from one generation to another (except in rare conditions where the mother is a carrier of the abnormal Chromosome 21).
Down syndrome occurs in about one in 700 pregnancies. The incidence is higher in older mothers — those who get pregnant beyond 35 years old. The chance of having a child with Down syndrome is one in 350 at age 35, and one in 100 if the mother conceives at 40.
PHYSICAL FEATURES
A person with Down syndrome has a distinctive physical appearance — small and low-set ears, up slanting of the eyes, prominent eyelid folds, thickening of the skin on the back of the neck, a bigger than normal space between the big and second toe (sandal gap), short fingers with the little finger curved inwards, and a protruding tongue.
They have some degree of learning disability and growth delay. The severity may vary from person to person. The average intellectual quotient of an adult with Down syndrome is about 50. Delays in speech and motor development (floppy muscles) are also seen frequently in these children.
Up to 30 per cent of children with Down syndrome have heart defects requiring surgery. They are also at risk of developing eye problems, ear and lung infections, dental caries, leukaemia, thyroid diseases and bowel problems.
CHECK DURING PREGNANCY
Down syndrome can be detected during pregnancy or after delivery. There are a few tests that can be performed during pregnancy.
Ultrasound scans at 13 weeks to examine the presence of the nose bone and thickness of fluid at the back of the foetal neck (nuchal translucency) have a 70 per cent detection rate for Down syndrome.
Checking the mother's blood for foetal DNA (non-invasive prenatal testing or 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 Down syndrome.
Diagnostics, meanwhile, are confirmatory tests and have a detection rate of 99.9 per cent. 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 one per cent risk of miscarriage.
LONG-TERM CARE
There is no cure for Down syndrome. Some children with the condition have low thyroid hormone, requiring thyroid medications.
They may also have feeding problems and poor muscle tone that prevents them from holding their heads up and sitting, thus requiring physiotherapy and extra assistance care.
Special education and supportive care improve the quality of life of these children. Their average life expectancy is 50 to 60 years. The Kiwanis Down Syndrome Foundation has branches around the country to provide interventional programmes for children with Down syndrome.
Patients who have a child with Down syndrome have a slightly higher risk of having another child with Down syndrome. Do speak to your obstetrician about available options.
*The writer is a specialist in obstetrics and gynaecology at Pantai Hospital Cheras.