[tri-med] Genetics 104 - Testing

A re-post of another post that I have made

>>Why do the geneticists say that most of us don't need to be tested??

Generally when a baby is tested for a trisomy the cytogenetics people have a
fair idea of whether the trisomy is caused by a translocation or is just the
"freak" occurrence thing. They get this idea by how the extra chromosome
presents itself.

In most cases of "full" trisomy the extra chromosome is a whole extra
chromosome. That is there are three 18 chromosomes (or three 13, 12, 11 etc
etc)

Now as we know a translocation can produce that extra chromosome and you
will have a child with "full" trisomy whatever but usually in the case of a
translocation the extra chromosome is not normally in one whole piece but
rather the extra chromosome is normally in 2 or more pieces. When the lab
folk see this extra chromosome in "pieces" (even though there is a whole
extra chromsome there in all) they will suspect that one of the parents is
the "carrier" of a balanced translocation and hence recommend testing
because the risk of recurrence increases significantly. Now that doesn't
mean that a translocation can't produce the "whole" extra chromosome or that
when a chromosome is in "pieces" that its always a balanced translocation
its just that those situations are "less" likely.

When Alex was tested the extra chromosome was a whole extra chromosome and
so they told me that I did not need testing, the chances of it recurring or
being the result of a translocation were minute (ie the less than 1%)

Being the reader and researcher I am though it didn't take me long to find
one single literature reference to a parent have sub-clinical T-18 mosaicism
(that is no obvious charecteristics of T-18) but having the mosaicism
diagnosed after repeated infertility and miscarriage problems. That was
enough for me to worry about it for my girls (I know that I wont be having
more children - not physically possible, though they said that about me
having Alex LOL) So Alex's dad and I both had the tests done - they were
"normal".

Now in all the hundreds of articles out there on Trisomy I have only ever
found two cases of undetected mosaicism "causing" problems so given those
odds the doctors are probably right that in the majority of cases it wont
show anything - however I agree that for peace of mind, that is if its
worrying you, why not be tested??
As far as cost is concerned I think that thats a crazy excuse - I mean its
going to cost a heck of a lot more for an amnio (and most pregnant mothers
are going to have one these days whether or not there were problems before)
so why balk at part of that cost to give you piece of mind BEFORE you fall
pregnant!!!

Paula in your situation with dual citizenship can you have the test done in
the UK under the national health system so that you don't have to pay??? I
guess thats one of the real benefits here. Alex has had a number of tests
(because of the unusualness of the mosaicism) and the doctors don't mind
ordering them because the government is picking up the tab (and it keeps my
questions down LOL). Its me that draws the line on him being a guinea pig,
but if they are taking blood for some other reason I don't mind them having
an extra few mls - I just one subject him to more skin biopsies ( he has
enough scars and been through enough pain!!!)

Another way of course folks is to get a lab interested in the research
side - whether the extra chromosome is from the mother or the father and be
a part of the chromosomal testing that would involve???

I hope that helps some........


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

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