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Thu 18 May, 2006 09:08 pm
Why exactly is it that older parents have an increased risk of producing a downs syndrome child?
If, for any reason, the woman's ovary was still in top health, would this mean the risk of DS didn't increase?
I suspect, but do not know, that it has to do with the age of the egg, not the ovary per se.
Um..
But new eggs are produced all the time.. right?
Not to my recollection. But again, I'm harking back to high school biology from the Stone Age so I could be wrong. I thought however that a woman is born with a finite number of ova.
Hm, just found an internet site which says it is to do with the fact a younger woman's immune system is better, and it is more likely to detect and abort a DS baby then an older woman
A baby girl has all of the eggs she will ever have (barring implantation) when she is born. They're released all the time (well, once a month or so), but it's that original store of 'em that is released one at a time.
That would make a certain amount of sense. Without knowing anything about the subject, I'd guess it is a combination of several factors.
God, I so love it when I'm right! It means dementia has yet to set in.
Check out a site for support/info on Down's. I can dig one up if ya want.
After 40, and the older one becomes, the risk increases slightly. It's not much, but it does increase.
There are other factors to consider as well.
Tests can be run and looking at family history if one is concerned.
And here's more rightness:
Quote:
Clues to Why Old Eggs Fail
Release Date:
April 16, 2004
Contact:
Bernice Wuethrich, NIGMS
Older women are more likely to give birth to children with Down syndrome, a form of mental retardation. The condition is caused by the presence of three copies, rather than the standard two copies, of chromosome 21 in human cells. This problem in chromosome distribution, called meiotic nondisjunction, occurs in the course of the cell division that gives rise to eggs (as well as to sperm). But no one knows how or why meiotic nondisjunction increases as eggs age. The question has been difficult to answer because scientists were unable to develop an animal model in which to study the condition.
Now, Sharon Bickel, Ph.D., a molecular biologist at Dartmouth College in Hanover, New Hampshire, has developed a method that uses fruit flies to gain insight into this puzzle of human biology. Fruit flies continuously produce eggs, but Bickel manipulated the diet of the flies in a way that suspended the maturation of their eggs, allowing them to "age." This mimicked the aging of human eggs.
Studying the "aged" fruit fly eggs, Bickel found that the incidence of meiotic nondisjunction jumped just as it does in older women. Her work also indicated that a back-up genetic system that normally helps to ensure proper chromosome separation and distribution deteriorates as fruit fly eggs age. No one yet knows if the same back-up system exists in humans, or if identical mistakes account for the increased risk of Down syndrome in the children of older mothers. But the fruit fly model system will allow Bickel and others to investigate these important questions.
http://www.nigms.nih.gov/News/Briefs/brief_bickel.htm
Will it keep you from making awful puns for a while?
(Kidding, I like 'em.)
In that case, not egg-zactly!
flushd, I was surprised that when I went to a bunch of Down Syndrome sites they contained info about the fact of increased risk with age, but not WHY. (Not that I found, anyway.)
Yer yolking.
This isn't conclusive, but closer:
Quote:Why us?
Chromosomal abnormalities happen by chance. You did not cause this by anything you did or did not do during pregnancy. A woman is born with a certain number of eggs and does not produce new ones during her life. The longer an egg lives, like any tissue, the more likely something will go wrong. Why this happens in sperm is more of a mystery. New sperm cells are continuously being made. There is no such thing as an "old sperm." For some unknown reason the risk of nondisjunction occurring in sperm increases in men over fifty.
http://www.askdrsears.com/html/10/T107400.asp
Close enough for guv'mint work, as my grandpa used to say.
You know I crack you up.
I don't think anyone knows 'why' except the eggs are older and so....
they have the aging problems. lol.
my take.
Not the brighest crayon in the box (me,that is)
So,the theory about the immune system is wrong? It actually is to do with the age of the eggs? So if a woman had young, implanted eggs.. that would take away the risk?
Thanks for everyone's help
As I said earlier, I think what's most likely is that there is a combination of factors. I think the age of the egg is one factor, and maybe the biggest factor, but I doubt it is the only factor.
While I haven't found anything about this in relation to Down Syndrome, I know that the fetal environment is also extremely important to development -- the stuff you already said about spontaneous abortion of disabled fetuses (though I think it might not be about the immune system per se -- I'll see what I can find about that) but also stuff like the amount and type of hormones, nutrition, etc.
Additionally, as shown in the quote above, the father's sperm has something to do with the risk, too -- it's not just about the mom/ eggs.
And 75-80% of kids with Down Syndrome are born to young moms (under 35, I think), so it's not like there is no risk even if everything else is covered, though I know you're talking about reducing risk.
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