[tri-med] Re: Fw: anyone do this

> ----- Original Message -----
> From: "gina L Anderson"
> > i was wounding if anyone did this or not , test there other children ,
for
> trisomy's Gina because i've heard of thishappening before where a lady had
a
> child and it was trisomy 8 m and she was tested for it to and was told she
> had it. I thing is she was in good health and her IQ was average, and
> did'nthave any of the things that trisomy's have ,

In part I agree with your geneticist. If it had happened as this lady is
describing it would be medical history and it would turn the medical
profession on their heads!!!!!

This may be complicated but I will try and explain simply.

Of all the different forms of trisomy, mosaicism is the least likely to be
hereditary. In mosaicism it is thought that the baby started out with normal
chromosomes and then an error occurred very early on when the cells were
dividing so that some cells gained an extra chromosome. (there is another
theory but this is the most accepted theory)

Because the error occurred after conception there is no way that it could be
hereditary. If it was a problem inherited from either parent the problem
would be in every cell, not some as in mosaicism.

However if a person who has mosaic trisomy has children of their own then
they have a much higher risk (between 25 - 100%) of having a child with
"full" trisomy 18. They will NOT have a child with mosaicism - their
children will either have the normal complement of chromosomes or they will
have a "full" trisomy depending on whether the egg or sperm is trisomic or
not.

Most cases of "full" trisomy are random events, that is they are not
hereditary at all. The problem which causes the trisomy is actually thought
to be an inborn problem with the egg or the sperm that is present before
conception. As a result doctors do not normally recommend testing the parent
or siblings.

However, there is ONE case reported in the literature where one family had a
number of children with trisomy 18. The parents were tested and one of the
parents was found to have mosaic T-18. Obviously the parent did not know.
But the outcome was as I described earlier. They had children who either had
a completely "normal" chromosome arrangement or they had children with
"full" trisomy.

Obviously this is very rare, but it has happened.......... recently there
have been two other cases in the literature of children with a mosaic
trisomy having children, one had a pre-implantation biopsy and the other
used donor sperm.

If a child has a partial trisomy, then there is a much higher chance that
one of the parents has a balanced translocation. Testing of the parents is
normally recommended and if the parents are found to be carriers then the
siblings are usually tested as well.

However having said that if it would make you feel better then by all means
you can have your chromosomes tested. I did :-) Because the risk of it being
hereditary however are so minimal it would probably not be covered by your
insurance. The geneticist however will probably not test your other children
unless there is a reason to think that they may be effected (i.e. if your
chromosomes came back with a problem) as its considered an invasion of their
right to privacy. Similarly the geneticist declined to do gonadal testing on
Alex (checking to see if his sperm had trisomic cells or not) until he is of
an age where he can consent to the testing himself..........

The bottom line is that those of us who have children with a mosaic
diagnosis can rest easiest of all that it did not come from us, but then we
have the other worry that our children will have children with a "full"
trisomy. It breaks my heart to think that Alex will have to go through this
"again".........

After the game the king and the pawn go in the same box.
-Italian proverb

Keep Looking for Rainbows!!!
Karen, Mum to Alex (6, T-18 mosaic)
Sydney, Australia
http://members.optushome.com.au/karens
http://www.trisomyonline.org

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

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