Down syndrome is the most common (but rare) genetic condition in which an individual has an extra copy of the 21st chromosome. A typical person has 46 chromosomes. People with Down syndrome have 47.
How does it happen? Here it comes, Biology 101 on Down syndrome.
All cells reproduce, either by mitosis, or meiosis.
Mitosis basically means the cell copies all of its contents (including it's 46 chromosomes) and then divides to produce 2 daughter cells.
Meiosis is the process in which reproductive cells divide. The egg and the sperm do not copy themselves, instead, they "split" in half, resulting in an egg having 23 chromosomes, and sperm having 23 chromosomes, to make a total of 46 when they come together.
In the case of Down syndrome, the 21st chromosome (typically in the egg) fails to "split," resulting in Trisomy 21 (three 21 chromosomes) when it is united with the sperm.
What causes Down syndrome? Why does an egg fail to disjunction on the 21st chromosome?
We don't know. There are only speculations. It is believed that maternal age is a factor (since women have ALL their eggs present even BEFORE they are born, and therefore, the older the women, the older the eggs).
I was 25 years old when I conceived Nichole. At that point, according to science, my chances were 1/2500.
Now, the following is MY OPINION. Please do not take it at face value.
I believe that the reason they think maternal age is a factor is because women 35 years and older have all the pre-natal tests done. Women 35 and younger, many many times chose not to have these tests. It makes sense that you will see ANY condition more often in a population that is routinely getting tested, as opposed to the population that selectively chooses to do so.
Eighty percent of babies with Down syndrome are born to women 35 and younger!
There are three different "types" of Down syndrome.
1) Non-disjunction Trisomy 21. The most common. 92% of people with Down syndrome have this type. It is basic meiosis where the 21st chromosome did not disjunction. (As I explained before)
2) Translocation Down syndrome. This is where one of the 21st chromosomes (either from sperm, or cell) is "broken." When it gets "broken" it "splits" in two, therefore, resulting in an extra 21st chromosome. This condition is believed to be hereditary. It is believed that 6% of individuals with Down syndrome have Translocation Ds.
3) Mosaic Down syndrome. Both the cell and the sperm are "typical." The non-disjunction occurs somewhere down the line of cell division resulting in an individual that has some "normal" cells, and some "Trisomy" cells. It does not matter how many "normal" cells there are, what matters is where those normal cells would be. For example, if the cells that form the eyes are not affected, an individual would sadly not display the beautiful almond shaped eyes characteristic of Down syndrome. Only 2% of individuals with Down syndrome have Mosaic Ds.
Some people believe this might also be hereditary. There is little to no difference in development of individuals with Mosaic Down syndrome as opposed to the other two types, UNLESS, it happened at the LAST STAGES of cell division. In some cases it is even possible for a person to have Mosaic Down syndrome and not know it.
What does Nichole have? Plain Non-disjunction Trisomy 21.
Are there different "levels" of Down syndrome? Or is there such a thing as a "low case" or "severe" case?
No, Down syndrome is Down syndrome. Development is directly linked to health issues.
Nichole would be considered "high functioning" (I know, she is a baby!) but she has had no serious health problems. Other babies that have serious health problems have a harder time "catching up."
Can doctors predict how well Nichole will do?
No. Nobody can. Nichole is Nichole. Most often doctors and other professionals talk about things that babies or individuals with Down syndrome can or cannot do. But, nobody can tell me what Nichole can or cannot do, she will show us what she is capable of, and she is doing amazing! She is her own person, and she will develop in her own rate, at her own time.
Is there any way to prevent Down syndrome?
Yes, there is a way that will guarantee that you will never have a child with Down syndrome. Do not have children :) Other than that, there is nothing that you can do or not do to prevent Down syndrome, or to cause Down syndrome for that matter. It is a God thing, it is a gift, and very few are fortunate and blessed to know this beautiful and amazing road.
God chose only a few of us to have these precious babies with a little extra something :) Even though I like to think it is because we are "special," I know for me it is because I needed much changing. It is a heart and life altering miracle. I am humbled and honored God chose me to be Nichole's mom.
Is Down syndrome a burden? ABSOLUTELY NOT! It is the greatest blessing our family has ever known. And Nichole continues to touch lives and hearts of those around her. There is nothing "less than perfect" about that.
For you created my inmost being,
you knit me together in my mother's womb,
I praise you because I am fearfully and wonderfully made
your works are wonderful,
I know that full well
God does not make mistakes, especially, when there is an extra 21st chromosome :)