DOWN SYNDROME: WHO'S AT FAULT?
APRIL 6, 2019 @ 7.11 PM
The first positive test after years of trying to conceive. You’ve been waiting for this moment when you pee on a stick and see two lines – indicating that you are now pregnant. You’re filled with excitement, amazement and joy. Then there’s a part of you that is consumed with fear –eager to get a doctor or two’s opinion as to whether the fetus would be a normal baby. The possibility of getting a down syndrome baby strike you with terror even further as you realise that you are now in your 30’s.
Genetics background of down syndrome
Dr Raman Subramaniam, Consultant Obstetrician & Gynaecologist, Fetal Medicine and Gynaecology Centre (FMGC) explained that down syndrome effects younger women who are in their 20’s and early 30’s and late 30’s where the incidence are high.
“The genetic cause of down syndrome is an extra chromosome. In chromosome 21, we have 22 sets of chromosome and one pair of sex chromosome. So we have 23 pairs. But the sex chromosome, can be X or Y –XX is female while XY is male.”
In younger women, down syndrome can be caused by translocation which means part of another chromosome breaks off between chromosome 13 to 15 and comes and joins chromosome 21.
“That kind of chromosomal abnormality sometimes exist between the husband and wife. It becomes down syndrome when the sperm and egg meet.
“However, down syndrome that occurs in the older female is called regular down syndrome or non-disjunction which happens when the sperm meets the egg at fertilisation, because the egg has 46 chromosomes. The sperm has 23 chromosomes, so when the sperm enters the egg, the egg has to divide into two - 23 – 23. The defect occurs there.
“An extra chromosome is dragged into 21, so you get 22 and 24, and that joins with 23 of the male and therefore you get 47 which is down syndrome if it is in 21,” he added.
Peak of fertility
According to Raman, the peak of fertility is 22 - 26 years for a female when the quality of egg production is good. This however, deteriorates as a woman is in her late 30’s.
He indicated that the problem of conceiving a child with down syndrome is increasing in women who are in their late 30’s or 40’s due to lifestyle where women are predominantly getting married later in life and ending up pregnant at the age of 44 till 48.
“Although the chances are low, they are able to deliver a normal child as they don’t have a history of down syndrome,” he said.
Beyond the age of 48, he said that women would usually experience menopause. Although this was the case, the quality of the egg is already bad 10 years before.
“In the late 30’s and 40’s, firstly you don’t ovulate, and even if you do, the egg quality is poor. When it divides, it becomes abnormal,” he said.
Only 70 per cent of downs are born alive while 30 per cent die in the womb. It may be through miscarriage or defects such as swelling in the neck, body, fluid in the chest and defects in the heart.
Although there is no way of accessing the downs - their IQ and how good the motor power is, early detection can be done through ultrasound and DNA testing to prepare parents in advance.
In western countries, screening is available through ultrasound at 11 and 13 weeks and six days.
“When the ultrasound is done, the length of the baby and the skin at the back of the neck is measured. If the skin behind the neck appears to be thick, then it is a down syndrome. The same applies if the nose bone is missing.
“In a DNA testing, a mother’s blood would be extracted and sent to a DNA lab for a bio-chemical analysis where a mathematical modeling of the risk against the age will be done. This is 80 – 85 per cent accurate compared to an ultrasound which has only a 70 per cent accuracy rate,” he explained.
Raman advises women ideally to marry early, exercise regularly, eat good diet and maintain a healthy weight and not to marry close within the family.
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