For today's T21 tidbit, I'm reposting the image of Erin's actual chromsomes. It is called a karyotype image and it shows a picture of the chromosomes found in one of Erin's cells. I never thought I'd be looking at my child's chromosomes, but now that we have the image, I find it pretty cool! If you click on the image, you'll see that the pairs of chromosomes are numbered. On the bottom, you'll see the smallest chromosomes, number 21, with three copies.
There are actually three types of Down syndrome, and
karyotyping, is used to determine which type your child has. The most common of the three types of Down syndrome is called Trisomy 21. With this type, the extra 21st chromosome is found in every cell in the body. Translocation Down syndrome is the second most common type. In this type of Down syndrome, a part of chromosome number 21 breaks off and attaches itself to another chromosome, often chromosome number 14. This causes all cells in the body to have the extra piece of the 21st chromosome. When a child is born with this type of Down syndrome it could mean that one of the parents is carrying chromosomal material that is unusually arranged. The third type of Down syndrome, and the least common, is called Mosaic Down Syndrome. In this type of Down syndrome the separation of the 21st chromosome occurs in one of the first few cell divisions AFTER fertilization. This causes the baby to have some cells with 46 chromosomes and some with 47. Because of the fact that not all cells contain the extra chromosome 21, the range of Down syndrome features will depend on the ratio of cells with 46 chromosomes to those with 47 chromosomes.
We assume that Erin has Trisomy 21. Four of her cells were tested after birth, and all four had 47 chromosomes. We know for sure that she does not have Translocation Ds. Since her birth, the protocol to rule out Mosaic Ds is starting to change. Many doctors are now requesting that more cells be looked at - up to 100-200. They say this many are necessary to rule out Mosaic Ds. And the cells should come from different parts of the body (skin, tissue, blood). Because most labs, in the past, have only tested a few cells, some theorize that Mosaic Ds is actually more common that previously thought.
Many parents really don't care which type of Ds their child has...but I find it all so fascinating :) We sure love our girl with designer genes....designed by God.
Be sure to ask a question if you have any, about Ds or Erin, during Ds Awarness month. I'd be more than happy to put my teacher hat on :)
