Down Syndrome (Part 2)

In the previous article, we learned about chromosomes as tiny particles that exist in pairs inside the nuclei of cells and carry genetic material. We also learned about the types of cells (somatic and reproductive), and that human somatic cells contain (23 pairs of chromosomes) = 46 chromosomes; and a person with Down syndrome has 47 chromosomes, due to the presence of three copies of chromosome no. 21. Therefore, this syndrome is called trisomy 21 syndrome.

The presence of this extra chromosome causes an impediment in the normal growth and development of the brain, with the appearance of special physical features.

Scientists did not provide specific reasons for this change in chromosomes, but they point to several reasons that may increase the risk of developing Down syndrome in the fetus, the most important of which are:

1 – The age of the spouses at the time of pregnancy increases the risk of developing a fetus with Down syndrome (women of 35 years and over and men of 40 years and over)

2 – A previous birth of a child with Down syndrome in the family.

Down syndrome types

Do you know that there is more than one type of Down syndrome?

Scientists classify Down syndrome into three different types, varying in the degree of symptoms:

Type I: (trisomy 21)

It is the most common type of Down syndrome (about 95% of all cases of Down syndrome) as a result of the presence of 47 chromosomes instead of 46 chromosomes since the beginning of the zygote and that as previously mentioned, there are three chromosomes of chromosome number 21 not pair in each cell of the body cells.

The second type: (transitional)

This type represents about 4% of cases of Down syndrome, in this case, part of chromosome 21 is broken during cell division, and it is attached to another chromosome, often chromosome number 14. In this type, the number of chromosomes remains 46 in all cells, but features of Down syndrome appear due to the presence of an extra part of chromosome 21.

The third type: (mosaic)

In this type, the chromosomal defect is not in all body cells, as we find some cells contain 46 chromosomes (a normal number), and others contain 47 chromosomes. This type of Down syndrome constitutes only 1% of cases of Down syndrome, and it is milder Degrees of Down syndrome, but the owner of this degree still needs special medical attention and special education, to prevent complications and to let the child develops normally.

Down syndrome diagnosis

There are several tests that must be done during pregnancy to detect that f the fetus has Down syndrome. These tests include:

1-Blood tests and ultrasound at the end of the third month of pregnancy in order to detect the thickness of the fetus’s neck. It is called (the scan of the nuchal translucency (behind the neck) of the fetus, which indicates the presence of Down syndrome. This examination is not always available and in all cases.

2-A blood test called Alpha Fetoprotein test- AFP, or AFP-quad test that is made in the second trimester of pregnancy. By measuring some of the compounds in the blood of the mother (pregnant woman), it is possible to estimate the chances of the fetus developing Down syndrome, or detect other problems in the fetus.

3-A chromosomal test (karyotype test). This test is more difficult and dangerous than other tests, but it is more accurate about whether the fetus has Down syndrome or not. The karyotype examination includes: taking a sample of the placenta villi (the area where the fetus attaches to the wall of the mother’s womb) – amniocentesis / amniotic fluid that surrounds the fetus inside the mother’s womb.

4-The syndrome may be diagnosed after birth depending on the external appearance of the newborn and a physical examination. And to confirm the diagnosis, the newborn’s blood is tested, and the conclusive result appears within two to three weeks.

And now is there a cure for Down syndrome?

And what can the family and educators do with those with Down syndrome to get the best results?

This is what we will answer next time…