[tri-med] Genetics 102 - Environmental Effects

This is a straight cut and paste of a previous post I have made.

>>Firstly - environmental effects.
At this point in time there is no known correllation between environmental
effects and Trisomy. And in the case of "full" trisomy this is not likely to
be an issue - why?
Because in full trisomy it is thought that the error in the egg or sperm
that causes the trisomy is present before the conception of the child.
Research also shows that
the majority (but by no means all) of the extra chromosomes come from the
mother. So lets look first at the case where the extra chromosome is present
in the egg.
The mothers eggs are all formed during the neonatal period, that is in
utero. So if an environmental factor was to be implicated it would have to
have been what your mother was exposed to whilst she was pregnant not you
yourself.
The fathers sperm however are "generated" every three months so it is
possible that environmental factors could effect chromosomes in the sperm -
however nature, God or whoever is in control has also created its own
"control" - remember there are zillions (OK millions but you get my drift)
of those little tadpoles created every time, even though it only takes one
to make a baby :-). But each of those tadpoles has a heck of a journey to
make it to the egg - and only the fittest survive.

In the case of mosaicism you have a different scenario because the error
(they think!!) happens after conception, within the first few hours.
With mosaicism there is an error in the way the cell divides. Whether this
happens at the stage of one cell splitting into two, two cells splitting
into 4 etc is unknown. In fact there is some speculation that everyone has a
few "trisomy" cells floating around in them but the mosaicism is such low
frequency that you would have to test a heck of a lot of cells to find them.
So again unless you made a baby and then went straight out and microwaved a
coffee from a microwave that leaked or sat on a nuclear power plant its
unlikely to have been caused by
that :-))

The other possibility for mosaicism is that the baby started out as "full"
trisomy and then by the natural process of "fixing" things somehow the extra
chromosome was "gotten rid of" in some cells. In which case we go back to
the full trisomy scenario.

Now the other thing is that if environmental issues were implicated in
Trisomy we would see an increase in Trisomy births after environmental
"accidents" and to date this hasn't been observed. Now it is hard to pick
when statistics aren't collected and that is why I have looked so hard at
Australian statistics. Over here every case of chromosomal abnormality that
is diagnosed in a cytogenetic lab is reported to the National Department of
perinatal statistics. and in the 20 years that they have been collecting
these statistics the incidence rate has stayed the same.
I specifically looked closely at the stats after the French nuclear testing
and also regional areas (looking for things like pesticides etc in farming
areas) and truly the figures have been very even and constant. But yes there
was an increase in other conditions such as thyroid cancer in children after
the nuclear testing etc.
If the "environmental accident" were in our parents generation we would see
"clusters" of babies born to a generation and again that isn't borne out by
the statistics. Trisomy is really quite evenly distributed over the age
range on what we expect.

I believe that as of next year the US is also starting to collect national
figures on diagnosed chromosomal abnormalities. This will give us a better
picture because you have a larger population - but its going to take time to
get that picture.

Now this doesn't rule anything out by any means but at this point thats the
understanding of the "professionals" and it sort of makes sense (if any of
this makes sense)>>


                  Building ___ooOOoo__ Rainbows
                       www.trisomyonline.org
                  Families Helping Families On-line

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