The causes of Down Syndrome

Next, I will talk about factors having Down syndrome babies. First of all, Down syndrome is caused by something is not right from the cell division that produce extra copy of chromosome 21.  The type of error that we can find is non disjunction. When one cell divides in two, pairs of chromosomes are split so that one of the pair goes to one cell and other pair goes to the other cell. Most of the time, the error occurs at random during the formation of an egg or sperm. This is when the non behavioural activity of the parents or environmental factor is known to cause Down syndrome. I really believe that reasons that cause down syndrome actually come from parents maybe the lifestyle and maybe it is sent by God to test human being whether they could handle this kind of children or not . After research has done by the researches on this cell division error they have found that more than 90% of cases, the extra copy of chromosomes 21 come from the mother in the egg. About 4% of the cases, the father provides the extra copy of chromosome 21 through the sperm. In the remaining cases, the error occurs after fertilization as the embryo grows. This has shown that researches trying to prove that both men and women are just the same that producing this kind of error. Having Down syndrome children is not that bad, it is just some kind of error that happens in fertilization.

            There are various types of Down syndrome is complete trisomy 21. Like I have describe about an error during the formation of the egg or the sperm results in wither one having an extra chromosome. So after the egg and sperm unite, the resulting cells will also have three copies of chromosome 21. The complete extra copy of chromosome 21 is in all of the person's cells—or a complete trisomy. Second types is mosaic trisomy 21. Not every cell in the body is exactly the same. In about 1% of Down syndrome cases, most of the cells in the body have the extra chromosome, but some of them don't. This is called "mosaicism." Mosaic trisomy 21 can occur when the error in cell division takes place early in development but after a normal egg and sperm unite. It can also occur early in development when some cells lose an extra chromosome 21 that was present at conception. The symptoms of someone with mosaic trisomy 21 may vary from those of someone with complete trisomy 21 or translocation trisomy 21, depending on how many cells have the extra chromosome. Lastly is translocation trisomy 21 where the chromosomal change, only part of an extra copy of chromosome 21 is in the cells. The extra part of the chromosome gets "stuck" to another chromosome and gets transmitted into other cells as the cells divide. This type of change causes about 4% of Down syndrome cases. There are no distinct cognitive or medical differences between people with translocation trisomy 21 and those with complete trisomy 21.(National Institute of Child Health and Human Development,2015)

The photo above describe about the causes of Down's Syndrome

Sometimes, a parent who does not have Down syndrome may carry a translocation in chromosome 21 that can be passed on to children and cause Down syndrome. Studying the parents’ chromosomes can reveal whether this is the cause of the syndrome. A genetic counselor can assist families affected by translocation trisomy 21 in understanding the risk of Down syndrome in future pregnancies.