Day 3...Types of Down syndrome.

There are 3 types of Down syndrome. I'm just going to give a simple explaination as to what they are and how they occur because if I had to use all the scientific terms I would have to do some research for the correct words for cell division such as meiosis and mitosis.

The most common type is called Nondisjuntion in which about 95% of those with Ds have. This occurs because of an incorrect cell division in either the egg or the sperm right when conception occurs or even before the two even unite. One will have 24 chromosomes instead of the usual 23. So when the egg and sperm unite and one has 23 chromosomes and the other has 24 there is an extra chromosome there and if it happens to be an extra 21st chromosome then Down syndrome will occur. The cells will continue to do their cell division thing over and over again and each and every time this happens that extra 21st chromosome is copied and transmitted to each new cell. Nondisjuction is where EVERY single cell in the body has the extra copy of that chromosome.

3-4% of those with Ds have Translocation Trisomy 21. This happens when the extra 21st chromosome is attached to another chromosome, usually number 14 or another 21st. About 1/4 of Translocations happen during fertilization. The other 3/4 are inherited from a parent. This is the only type of Down syndrome that can result from a condition in a parent's genes.

Lastly, about 1% of those with Ds have Mosaicism. This happens when an incorrect cell division occurs in one of the earliest (but not the first) cell divisions AFTER fertilization. Since it was not the first cell division and there were already some normal divisions that contain the normal amount of chromosomes then not all cells will contain an extra copy of the 21st chromosome. So not EVERY cell in their bodies have the extra copy like the other two types.

The only way to determine what type someone has is to do a Karyotype, which are pictures made from blood samples. The blood samples are cultured, allowed to grow in a petri dish. Then the chromosomes are isolated by a microscope and then grouped into pairs and numbered according to size. There is a picture of one on my Day 1 Challenge.

Joey has the Nondisjunction type...every cell in his body has an extra 21st chromosome. There was some debate between some people as to whether Joey had Ds or not so we had a Karyotype done. I'm assuming Isaiah has the same type also.