What Causes Down Syndrome

In a normal human cell, there are 23 pairs of chromosomes, a total of 46 chromosomes. One pair of 23 chromosome comes from the father and the other pair from the mother. The egg cells from mother and sperm cells from father undergo division and each cell ends up with 23 chromosomes each. When the egg and sperm unite during fertilization, it leads to formation of a fetus with a complete set of 46 chromosomes. The genetic information related to the progeny is stored in genes that is present within the nucleus of the human cell. These genes contain codes that translate into all the inherited traits of the child. These groups of codes are called chromosomes in humans. If anything goes wrong during chromosomal division, it leads to an error in the code. This error is translated and expressed as an abnormality in the progeny. One such code error leads to development of Down syndrome in unborn babies. Let us go into the details of what causes Down syndrome in detail in the following article.

Causes of Down Syndrome during Pregnancy
Let us first understand what is Down syndrome. Down syndrome is a chromosomal disorder that occurs due to an error during cell division. This error causes impairment in cognitive ability as well as physical growth of the child. The causes of Down syndrome during pregnancy are attributed to maternal age. It is seen that Down syndrome is common in women who are over 44 years of age. There are many other causes of Down syndrome during pregnancy apart from maternal age. Let us go into the details of Down syndrome that will help us understand the causes better.

What Causes Down Syndrome in Unborn Babies
As explained above, the baby inherits 23 chromosomes from the father and 23 from the mother. In case of Down syndrome an error occurs during cell division. During cell division either the egg or sperm cell keeps both copies of chromosome number 21. So, during fertilization, the unborn baby ends up with 3 copies of the chromosome #21. This genetic disorder is called 'trisomy 21' or Down syndrome. Each and every cell in the body of the unborn child has an extra copy of the chromosome 21.

There are basically three causes of Down syndrome during pregnancy. These 2 abnormalities occur due to the extra genetic material from chromosome 21. Three genetic variations can occur during Down syndrome. This results in either trisomy 21, Mosaic Down syndrome or translocation Down syndrome. Let us see these three causes of Down syndrome in detail.

Trisomy 21
It has been found more than 90% of the cases of Down syndrome in unborn babies is due to trisomy 21. There are three copies of chromosome 21 instead of the normal 2 copies of this chromosome. This happens due to abnormal cell division during development of the egg or sperm cell.

Mosaic Down Syndrome
The mosaic Down syndrome is a rare form of Down syndrome where a few cells end up with an extra copy of chromosome 21. This causes a mosaic pattern of normal and abnormal cells in the body. This happens due to abnormal cell division after fertilization.

Translocation Down Syndrome
This is another type of Down syndrome, where the chromosome 21 is attached to another chromosome (translocated). This translocation occurs before or during conception. These children with Down syndrome have two copies of chromosome 21, but also have an additional copy of chromosome 21 attached to the translocated chromosome. This type of abnormality is very, very rare.

Is Down Syndrome Hereditary?
Many people often wonder if Down syndrome can be inherited. The main causes of Down syndrome during pregnancy is the abnormalities occurring during cell division. Trisomy 21 as well as mosaic Down syndrome cannot be inherited. Only 4 percent of children with Down syndrome may get the condition from either of the parents. This occurs only in case of translocation Down syndrome. The mother or the father has some kind of rearranged genetic material that is passed on to the unborn baby. If the father is the carrier of this rearranged genetic material there are about 3% chances of transferring it to the children. In case of mothers, there are 12% chances that the unborn baby will inherit translocation Down syndrome.

There are no behavioral or environment causes of Down syndrome. This is a purely genetic disorder that occurs due to error in cell division. Hope the above paragraphs on what causes Down syndrome has helped you understand the reason behind this genetic disorder.