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Down Syndrome: A Disease of Chromosomal Abnormality

Updated on May 15, 2019
Pic: A child with Down Syndrome
Pic: A child with Down Syndrome | Source

What is Down Syndrome (DS)

Down Syndrome or DS is a genetic disorder that is caused by the presence of a whole extra chromosome or a part of a chromosome at the 21st chromosomal position. Normally, a normal human has two copies of each chromosome. But DS is caused due to the presence of three chromosomes in stead of two, at the 21st chromosomal position. For this reason, this syndrome is also known as "Trisomy 21".

DS inhibits the normal growth and development of children, that leads to delaying physical growth, mild to moderate intellectual abnormalities and abnormal facial features. An adult with DS has average IQ of only 50, which is equivalent to the IQ of a 8-9 year old normal healthy child. The men with DS can not father children, while the DS affected females have very low fertility rate.

In every 1000 childs, 1 child is born with the DS. Currently, there are about 5.4 million people with the Down Syndrome and their average life expectancy is 50-60 year.

Why Down Syndrome occurs

The Down Syndrome occurs due to the presence of an extra chromosome at the 21st chromosomal region. The parents of an affected person are genetically normal. But the probability of having a baby with DS increases dramatically from 0.1% in a 20 years old woman to 3% in the 45 years old woman. But why this phenomena occurs at this age is still unknown. It is believed that, environmental factors during the pregnancy may be responsible this abnormality.

Lack of proper separation of the chromosomes in the parents and Robertsonian translocation of chromosome or chromosomal segment(s) may be the reasons for the presence of a third copy of 21st chromosome in a individual.

In some individuals, some cells are normal, meaning that the cells have normal two copies of 21st chromosome but other cells contain the third 21st chromosome copy, this phenomena is known as "Mosaic Down Syndrome".

Pic: Down Syndrome of Trisomy 21 karyotype
Pic: Down Syndrome of Trisomy 21 karyotype | Source
Pic: Probability of DS by the age of the mother
Pic: Probability of DS by the age of the mother | Source


The presence of extra chromosome at the 21st chromosomal location causes the over expression of 310 genes present in that chromosome. Sometimes, the 22q22.1-22q22.3 banding area is responsible for DS. This area of the chromosome contains genes for amyloid, superoxide dismutase and some other important proteins. Due to any abnormality at this area, the normal functions of those genes are disturbed and this may lead to DS.


The common symptoms of DS are:

1. Mental impairement

2. Abnormal growth

3. Abnormal teeth

4.Low muscle tone

5. Flat head

6. Flexible ligaments

7. Flattened nose

8. Spots in the iris

9. Short neck

10. Shortened hand

11. Umbilical hernia

12. Slanted eyes

13. Heart problems

14. Blood and non-blood cancers in later life

15. Endocrinal and gastrointestinal problems


Amniocentesis or chorionic villus sampling can be done for the diagnosis of DS during the pregnancy time. But these methods are invasive and may lead to miscarriage. If the DS is confirmed, then the parents can have abortion if they want.

After the birth of a suspected child with DS, the chromosomal analysis of that child is the best reliable option.

Blood tests, ultrasound, electrocardiogram, heart diagnosis etc. are less invasive methods for the identification of DS.

Treatment and management

Currently, there is no permanent treatment of DS. Proper medications when needed, well family environment, work related training, education and proper care can improve the quality of life. Various cognitive developmental programs like giving the hearing aids, speech therapy, sign language etc. can also help the patient to lead a better life.

Currently research is going on in this aspect. Stem cell therapy and gene therapy are now being developed for treatment. Other methods of treatment where the research is going on are: the use of antioxidants, gamma secretase inhibition, memantine etc.

© 2019 Bishajit Sarkar


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